hvac design checklist

66
Design considerations Design data Calculations Systems & equipment 66 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS 28 RADIATORS Project title .............................................................. Project No. ...................................... Design stage ............... Engineer ................................................................... Revision No .................................... Date ................................. Checked by.............................................................. Approved by .................................. Date ................................. Design inputs Notes / Design file cross-reference Zone heating loads Design flow and return temperatures Internal design condition Limiting pressure loss/m Limiting surface temperature Design outputs Notes / Design file cross-reference Schedule of radiators with water and surface temperature, connection and valve requirements stated, giving sufficient data for manufacturer selection Control requirements Statement of commissioning strategy Relevant specification clauses Key design checks Notes / Design file cross-reference Check that radiator will physically fit space available allowing for connection and installation space Check radiator surface temperature is safe for expected space usage Check radiator manufacturer’s design pressure is within system operating pressure Project specific checks & notes Notes / Design file cross-reference

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Page 1: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

66 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

28 RADIATORS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating loads

• Design flow and return temperatures

• Internal design condition

• Limiting pressure loss/m

• Limiting surface temperature

Design outputs

Notes / Design file cross-reference

• Schedule of radiators with water and surface temperature, connection and valve requirements stated, giving sufficient data for manufacturer selection

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that radiator will physically fit space available allowing for connection and installation space

• Check radiator surface temperature is safe for expected space usage

• Check radiator manufacturer’s design pressure is within system operating pressure

Project specific checks & notes

Notes / Design file cross-reference

Page 2: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 67

28 RADIATORS

Design inputs • Zone heating loads • Design flow and return temperatures • Internal design condition • Limiting pressure loss/m • Limiting surface temperature

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of partitions, glazing, doors etc

• Details of structural frame • Sill heights • Occupancy details • Space usage • Details of electrical outlet positions • Client control criteria • Constant temperature or variable temperature circuit See also: Sensor locations, Commissioning – piped systems, Pipework, Pumps

Design outputs • Schedule of radiators with water and surface temperature,

connection and valve requirements stated, giving sufficient data for manufacturer selection

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that radiator will physically fit space available allowing for

connection and installation space • Check radiator surface

temperature is safe for expected space usage

• Check radiator manufacturer’s design pressure is within system operating pressure

DESIGN WATCHPOINTS

Sizing & selection

1. Check approval by client of radiator type/make. 2. Check that heat loss calculations are based on a radiator system, ie

using correct proportion of radiant to convective output. 3. Check that manufacturer’s data is applicable to the conditions at which

the radiators will be operating and apply any relevant corrections for space temperature, flow and return temperatures etc. Note manufacturer’s outputs are based on particular water and space temperatures which may differ from the operating conditions.

4. It may be preferable to quote the minimum output required at design conditions than to quote a manufacturer’s type and model.

5. Review application to check whether low surface temperature radiators are required.

6. Check radiator manufacturer’s design pressure is within system operating pressure at an early design stage.

7. Check that return water temperatures will meet requirements of system if condensing boilers are used.

8. Allow for the effect on emission of any paint or special finishes or architectural enclosures.

9. Allow for obstructions and consider space layout and partitioning, coordinating positions of radiators with the anticipated furniture positions and electrical outlet positions.

10. Check aesthetics of radiator selection, eg common heights within one space, not excessively small etc.

11. Consider whether flexibility is needed in layout to allow for future reconfiguration of office space.

12. Allow for localised effects in large spaces, eg corner positions. 13. Radiator type ie single panel, double panel, finned etc can make

significant output differences. 14. Consider most suitable pipework circuit, eg F&R, reverse return, self

balancing, single pipe etc. 15. The piping layout should be as unobtrusive and simple as possible. 16. Design circuits to be self-balancing where possible.

Installation, operation and control

17. Position radiators, where possible, to minimise downdraughts 18. Connection position, eg TBOE/BOE, makes a difference to output.

19. Consider control options carefully, eg TRVs, zonal etc when planning layout and check compatibility with space usage and future needs.

20. Capacity control is usually by variable temperature constant volume to maintain adequate flow through emitters, eg using a weather compensated VT circuit, trimmed by TRVs if required.

21. TRVs need to be able to close against available system pressure. Provide effective differential pressure control on circulating systems.

22. Make provision to maintain some flow through system when large numbers of TRVs close to avoid damage to pump motors. Check pump minimum flowrate.

23. TRVs should be placed on the flow, not return, unless bi-directional valves are utilised. Flow directions are marked on the valves.

24. TRVs should be appropriately positioned to sense temperature. When installed on the flow the thermostat is best positioned on the horizontal to prevent heat from pipework/valve body affecting thermostat operation.

25. Check that sensors are positioned to adequately reflect zone conditions and not adversely affected by localised conditions such as solar gains or office equipment.

26. Consider the requirements for circuit balancing, location and correct selection of commissioning sets for flow rates. Individual emitters and small circuits are often commissioned on a temperature basis rather than flow.

27. Large temperature differentials, eg 20K, can result in small water flows and difficulties in flow measurement.

Access & maintenance

28. Allow adequate access for maintenance. 29. Consider the use of “swivel” pipe connections for rear radiator access for

decorating purposes, rather than radiator removal. 30. Air vents should be provided for each radiator. 31. Sufficient isolation and drain points should be provided to avoid the need

to isolate and drain part of system to access a single radiator.

Economics

32. Consider whole life cost of system compared to other choices. 33. Consider impact of choice of system design temperature drop on emitter

size and pump size/power.

Page 3: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

68 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

29 NATURAL CONVECTORS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating loads

• Design flow and return temperatures

• Internal design condition

Design outputs

Notes / Design file cross-reference

• Schedule of convectors with water temperature, connection and valve requirements stated giving sufficient information for manufacturer selection

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check approval by client of convector type/make

• Check that convector will physically fit space available allowing for connection and installation space

Project specific checks & notes

Notes / Design file cross-reference

Page 4: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 69

29 NATURAL CONVECTORS

Design inputs • Zone heating loads • Design flow and return temperatures • Internal design condition

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of partitions, glazing, doors etc

• Details of structural frame • Sill heights • Occupancy details • Space usage • Details of electrical outlet positions • Client control criteria • Floor depth (if floor trench model considered) See also: Sensor locations, Commissioning – piped systems, Pipework, Pumps

Design outputs • Schedule of convectors with water temperature, connection and

valve requirements stated giving sufficient information for manufacturer selection

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check approval by client of convector type/make • Check that convector will physically fit space available allowing

for connection and installation space

DESIGN WATCHPOINTS

Sizing & selection

1. Check approval by client of convector type/make. 2. Check that heat loss calculations are based on a convector system, ie

using correct proportion of radiant to convective output. 3. Consider at an early stage whether natural or forced (fan) convectors are

the most appropriate. Natural convectors are always preferable to fan convectors, unless more heat output is required.

4. Check that manufacturer’s data is applicable to the conditions at which the convectors will be operating and apply any relevant corrections for space temperature, flow and return temperatures etc. Note manufacturer’s outputs are based on turbulent flow in fixed size piping, and on specific configurations.

5. Very low flow rates should be avoided as turbulent flow is required – check manufacturer’s recommendations.

6. Check that return water temperatures will meet requirements of system if condensing boilers are used.

7. Check that surface temperature is appropriate for location. 8. Check convector manufacturer’s design pressure is within system

operating pressure at an early design stage. 9. Consider room air diffusion patterns. Consider impact on convector

output of accelerated air flow, eg from downdraughts or mechanical ventilation systems.

10. Allow for obstructions. Horizontal convector grilles can easily be used as an extra shelf or standing area. Consider the use of angled grilles if necessary.

11. Allow for localised effects in large spaces, eg corner positions. 12. Consider whether flexibility is needed in layout to allow for future

reconfiguration of office space. 13. Allow for the effect on emission of any paint or special finishes or

architectural enclosures. 14. Clear air flow through the convector is required for rated output. Check

the air inlet and outlet is not restricted and is within manufacturers recommendations.

Installation, operation & control

15. If continuous perimeter convectors are being considered keep finned sections to a reasonable length to allow transportation and installation, and to permit adequate control.

16. Consider control options carefully, eg TRVs, zonal etc when planning layout and check compatibility with space usage and future needs.

17. Capacity control is usually by variable temperature constant volume to maintain adequate flow through emitters, eg using a weather compensated VT circuit, trimmed by TRVs if required.

18. TRVs need to be able to close against available system pressure. Provide effective differential pressure control on circulating systems.

19. Make provision to maintain some flow through system when large numbers of TRVs are close to avoid damage to pump motors. Check pump minimum flowrate.

20. Check that sensors are positioned to adequately reflect zone conditions and not adversely affected by localised conditions such as solar gains or office equipment.

21. Consider the requirements for circuit balancing, location of commissioning sets, correct selection of commissioning sets for flow rates. Individual emitters and small circuits are often commissioned on a temperature basis rather than flow.

22. Large temperature differentials, eg 20K, can result in small water flows and difficulties in flow measurement.

Access & maintenance

23. Allow adequate access for maintenance. 24. Provide an air vent for each convector which is fed from below. 25. Sufficient isolation and drain points should be provided to avoid the need

to isolate and drain part of a system just to access a single convector.

Economics

26. Consider whole life cost of system compared to other choices.

Page 5: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

70 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

30 RADIANT PANELS/RADIANT SYSTEMS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating loads

• Design flow and return temperatures (if water system)

• Internal design condition

• Infiltration rate

• Ventilation rates

Design outputs

Notes / Design file cross-reference

• Schedule of panels with connection and valve requirements stated/schedule of radiant heaters, giving sufficient information for manufacturer selection

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that heat loss calculations are based on the use of radiant panels/heaters

• Check predicted occupant comfort in the space

• Check irradiance levels are acceptable

• Check mounting height compatible with space usage

Project specific checks & notes

Notes / Design file cross-reference

Page 6: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 71

30 RADIANT PANELS/RADIANT SYSTEMS

Design inputs • Zone heating loads • Design flow and return temperatures (if water system) • Internal design condition • Infiltration rate • Ventilation rates

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of partitions, glazing, doors etc

• Details of structural frame • Occupancy details • Space usage • Client control criteria • Details of any high level obstruction, eg cranes, light fittings • Details of materials and equipment likely to be kept in space See also: Sensor locations, Commissioning – piped systems, Pipework, Pumps

Design outputs • Schedule of panels with connection and valve requirements

stated/schedule of radiant heaters, giving sufficient information for manufacturer selection

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that heat loss calculations are based on the use of radiant

panels/heaters • Check predicted occupant comfort in the space • Check irradiance levels are acceptable • Check mounting height compatible with space usage

DESIGN WATCHPOINTS

Sizing & selection

1. Check that heat loss calculations are based on the use of radiant panels/radiant heaters, ie using correct proportion of radiant to convective output.

2. Check predicted occupant comfort in the space as the difference between air and radiant temperatures can give rise to feelings of discomfort. Also check irradiance levels are within comfort limits.

3. Check that manufacturer’s data is applicable to the conditions at which the panels will be operating and apply any relevant corrections for space temperature, flow and return temperatures etc.

4. It may be preferable to quote the minimum output required at design conditions than to quote a manufacturer’s type and model.

5. Check manufacturer’s design pressure is within system operating pressure for water systems.

6. Confirm finish and colour. 7. Decide whether spot or total heating is required. 8. The number and arrangement of radiant panels/heaters should be

designed to minimise both the variation in mean radiant temperature and radiant asymmetry throughout the heated space.

9. For spot heating applications occupants should receive heat from two opposing directions to minimise discomfort due to radiant asymmetry.

10. Check that any materials close to the heaters will be unaffected by high temperatures. Allow adequate clearance between radiant heaters and surrounding materials that could be affected.

11. Check what products will be stored and processes carried out in the space. Radiant systems may be contraindicated if some gases are used, eg solvents, paint spraying etc. (Risk of fire and of some gases breaking down into toxic constituents if they came into contact with hot surfaces, eg vapours containing chlorine can form hydrochloric acid when they meet certain materials.)

12. Check whether flexibility is needed in layout to allow for future reconfiguration of space.

13. Check whether noise levels are critical as some radiant systems with combustion fans generate noise.

14. Check there is sufficient capacity for type of system, eg sufficient gas capacity for gas system etc.

15. Consider combustion air and flue requirements for direct fired units.

16. Consider and allow for the effect of thermal expansion of the panel on ceilings and pipe connections.

17. Check that the piping system has sufficient flexibility to allow for differential heating, ie the fact that radiant heaters do not all heat up at the same time.

18. Avoid high points in the pipework where air pockets can form.

Installation, operation & control

19. Provide warning notices to ensure materials are not stored in proximity to heaters.

20. Consider method of control - zonal etc when planning layout. Check this is compatible with planned usage of space and any planned or future partitioning.

21. Check that sensors are positioned to adequately reflect zone conditions and not adversely affected by localised conditions.

22. Sensors need to be positioned so they “see” the heated space and are not hidden by machinery or partitions.

23. Radiant systems give an offset between air and resultant temperatures - often of more than 3K. When air sensors are used to control radiant heating they will tend to underestimate the resultant temperature and do not respond to the rise in radiant temperature at system start leading to overheating and wasted fuel.

24. Black bulb sensors can be used in conjunction with air sensors, with the black bulb sensor used to provide the basic control function and the air sensor used to initiate a boost function if there is a drop in air temperature.

25. Consider whether frost protection is required to protect building and contents.

Access & maintenance

26. Allow adequate access for maintenance. Maintenance costs can be reduced by allowing access for mobile access equipment, eg cherry pickers rather than having to use scaffolding.

27. Provide air vents for water system radiant heaters.

Economics 28. Consider whole life cost of radiant panels system compared to other

system choices.

Page 7: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

72 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

31 UNDERFLOOR HEATING

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating loads

• Design flow and return temperatures

• Internal design condition

Design outputs

Notes / Design file cross-reference

• Schedule of zones giving heat output requirements, flow rates (for wet system), maximum floor temperatures and connection and valve requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that floor surface temperature is satisfactory for use of space

• Check that the depth of floor screed is sufficient to accommodate pipes

• Check that pump duty is adequate

Project specific checks & notes

Notes / Design file cross-reference

Page 8: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 73

31 UNDERFLOOR HEATING

Design inputs • Zone heating loads • Design flow and return temperatures • Internal design condition

Design information • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, glazing, doors etc

• Details of structural frame • Occupancy details • Space usage • Details of floor finish, construction and expansion joints • Client control criteria See also: Sensor locations, Commissioning – piped systems, Pipework, Pumps

Design outputs • Schedule of zones giving heat output requirements, flow rates (for

wet system), maximum floor temperatures and connection and valve requirements

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that floor surface temperature is satisfactory for use of

space • Check that the depth of floor screed is sufficient to accommodate

pipes • Check that pump duty is adequate

DESIGN WATCHPOINTS

Sizing & selection 1. Check that heat loss calculations are based on an underfloor system, ie

using correct proportion of radiant to convective output. 2. Check whether return water temperatures will meet requirements of

system if condensing boilers are used. 3. Check that the design water temperatures are achievable. Thermostatic

mixing valves are usually needed to control water temperatures between 45 - 55°C depending on application.

4. Check that pump duty is adequate. Due to the long circuit lengths system pressure losses may be higher than for other system types.

5. Check that the floor temperature is satisfactory for both comfort and required heat output. Typical maximum surface temperatures are 25°C in occupied and 28°C in transient areas.

6. Specify adequate insulation under entire system to reduce casual heat loss to floor below.

7. Specify an insulating edging strip around the perimeter of concrete floors to reduce the effect of cold bridging.

8. Check that the depth of floor screed is sufficient to accommodate pipes. Typically 50-75 mm screed needed depending on manufacturers requirements. Reinforcing may be necessary if screed depth is reduced.

9. Check that pipe materials are not affected by concrete - eg plastic or multi-layer.

10. Check that selected floor coverings are suitable for under-floor heating, eg carpets typically with less than 0·15 m2 K/W, adhesives suitable for temperatures up to 40°C, timber with moisture content below 10%.

11. Check that loop lengths do not exceed recommended lengths - typically around 100 m depending on supplier.

12. Pipe circuits should go to coldest areas first. Since the water will cool as it progresses, coldest areas should be close to the beginning of each pipe loop.

13. Piping should be joint free within the screed to reduce the risk of leakage. 14. Electric systems should use self-regulating cables to prevent floor

overheating. 15. Check that high limit protection is provided. High floor temperatures can

cause comfort problems and damage to, eg timber floors.

16. Consider and allow for expansion. Most plastic piping materials take up expansion within the pipe so no further allowance is needed.

17. Consider the consequences of system leakage for water systems. 18. Avoid the use of ferrous materials where gas diffusion through plastic

pipe walls cannot be eliminated. Plastic pipe is porous to oxygen, which can cause corrosion of other materials.

Installation, operation & control

19. Consider provision of protection against freezing for floor coils after pressure testing, whilst building construction is incomplete.

20. The sequencing of installation should consider the effect of coil laying/screeding on follow-on trades.

21. Check that the warm up time for the system is acceptable, particularly if there is intermittent occupation.

22. Check that controls system takes into account longer pre-heat /decay times due to thermal inertia, ie allow for slow warm up and cool down time.

23. Check that temperature swings in the space are acceptable. 24. Check the heated area is properly zoned, eg different flow temperatures

are required for concrete floors and timber floors. Two port valves, mixing valves and room thermostats will be required to deal with these zones.

25. Check that sensors are positioned to adequately reflect zone conditions and not adversely affected by localised conditions such as solar gains or office equipment.

Access & maintenance

26. Pipework terminations/manifolds should be clearly labelled and easily accessible.

27. Check that planned water treatment regime is suitable for entire system.

Economics

28. Consider whole life costs of underfloor heating compared to other choices.

Page 9: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

74 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

32 PERIMETER FAN COILS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Fresh air requirements

• Fresh air supply condition

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• Schedule of fan coils giving sufficient data for manufacturer selection

• Fan coil electrical and control requirements

• Condensate flow rates for drainage sizing

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check throw from grille.

• Check noise level from fan coils

• Fall in condensate pipe work (if applicable)

• Airside or waterside control

• Check system pressure and control valve choice

Project specific checks & notes

Notes / Design file cross-reference

Page 10: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 75

32 PERIMETER FAN COILS

Design inputs • Zone heating and cooling loads • Internal design conditions • Fresh air requirements • Fresh air supply condition • Noise rating for each zone

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of structural frame • Occupancy details • Space usage • Position of drainage pipes that can be used for condensate run off • Client control criteria See also: Future needs, Ventilation requirements, Sensor locations, Pipework, Ductwork, Pumps

Design outputs • Schedule of fan coils giving sufficient data for manufacturer

selection • Fan coil electrical and control requirements • Condensate flow rates for drainage sizing • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check throw from grille • Check noise level from fan coils • Fall in condensate pipe work (if applicable) • Airside or waterside control • Check system pressure and control

valve choice

DESIGN WATCHPOINTS

Sizing & selection

1. Consider room air diffusion patterns. Consider impact on output of accelerated air flow, eg from downdraughts or mechanical ventilation systems.

2. Check that manufacturer’s data is applicable to the conditions at which the fan coils will be operating and apply any relevant corrections for space temperature, flow and return temperatures etc. Note manufacturer’s outputs are based on particular chilled water and space temperatures which may differ substantially from the required operating conditions.

3. Check performance is acceptable for both sensible and latent cooling requirements. The proportion of latent and sensible cooling will vary with chilled water temperature. (See pt 2.)

4. Changes in fan speed make a significant difference to cooling output and noise. Manufacturers often state cooling/ heating performance at highest fan speed setting. (See pt 6.)

5. Check manufacturer’s stated outputs for both thermal and acoustic performance are verified by certified independent laboratory tests.

6. Check the noise level is acceptable for the usage of the space. High fan speed settings can create noise problems and where ever possible fan coil units should be sized using a low to medium fan speed setting. Supplementary attenuation may be required.

7. Check the throw is adequate under both heating and cooling, and will not cause dumping or short circuiting.

8. Allow for obstructions. Horizontal convector grilles can easily be used as an extra shelf or standing area. Consider the use of angled grilles if necessary.

9. Allow for localised effects in large spaces, eg corner positions. 10. Check correct selection of index run for both pipe and duct work. 11. Fan coils with direct fresh air provision (ie direct connection to outside)

often only offer fairly crude control of fresh air quantity by adjustable damper. Poor shut off can create problems if building is to be pressure tested or needs to be shut down.

12. Consider whether a bespoke architectural enclosure will be required for the fan coils. If so allow sufficient space for fresh air intake and discharge and adequate access to the fan coil units and controls.

13. Consider any known future needs or flexibility requirements when positioning fan coils so they are away from potential partition lines.

14. Check that return air path to units is adequate.

Installation, operation & control

15. A boxed riser may be necessary to route pipework between floors and should be integrated with the space layout to be as unobtrusive as possible.

16. The low air pressure developed by fan coil units necessitates relatively short secondary ductwork, especially when flexible ductwork is used.

17. Check that control positions are compatible with partitioning. If sensing return air check that air sensed is from area served.

18. Consider both waterside and airside control options and select accordingly.

19. Temperature control sensors should be located in room or, if in the return air path, away from the incoming fresh air stream.

20. Four-port control valves should be provided with both local and main branch strainers upstream to prevent blockage.

21. Check that control valves can operate correctly against system pressure as they may not close against high system pressures, eg four-port valves may not be able to close against system pressure at part load which can lead to simultaneous heating and cooling.

22. Heating duties of four-pipe fan coil units are often so low for commissioning purposes that flow is laminar and flow rates and pressure drops unmeasurable. Consider suitable remedies, eg reducing flow temperature.

Access & maintenance

23. Allow for adequate access to fan coil units for cleaning and maintenance, eg filter changes etc. Check that any architecturally designed casings are removable for maintenance.

24. Provide air vents for each unit and local drain points. 25. Gravity fed condensate drainage systems require sufficient fall in the pipe

work to ensure adequate run off. Check whether access to the ceiling void of floor below is possible (may belong to another tenant). Alternatively, a pumped condensate system may be required.

26. Fan coils have low grade filters and the maintenance of these needs consideration particularly for fan coils with direct fresh air provision.

Economics

27. Consider expected life of equipment. 28. Consider whole life cost of fan coil system compared to other choices.

Page 11: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

76 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

33 OVERHEAD FAN COILS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Fresh air requirements

• Fresh air supply condition

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• Schedule of fan coils giving sufficient data for manufacturer selection

• Schedule of supply air diffusers giving sufficient data for manufacturer selection

• Fan coil electrical and control requirements

• Statement of commissioning strategy

• Relevant specification clauses

• Condensate flow rates for drainage sizing

Key design checks

Notes / Design file cross-reference

• Check noise level from diffusers and fan coils

• Airside or waterside control

• Fall in condensate pipe work (if applicable)

• Check throw from diffuser

Project specific checks & notes

Notes / Design file cross-reference

Page 12: HVAC Design checklist

Design considerations Design data Calculations Systems & equipment

© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 77

33 OVERHEAD FAN COILS

Design inputs • Zone heating and cooling loads • Internal design conditions • Fresh air requirements • Fresh air supply condition • Noise rating for each zone

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of structural frame • Occupancy details • Space usage • Ceiling type and grid size • Lighting system and position of luminaires • Position of drainage pipes that can be used for condensate run off • Client control criteria See also: Future needs, Ventilation requirements, Sensor locations, Pipework, Ductwork, Diffusers

Design outputs • Schedule of fan coils giving sufficient data for manufacturer

selection • Schedule of supply air diffusers giving sufficient data for

manufacturer selection • Fan coil electrical and control requirements • Statement of commissioning strategy • Relevant specification clauses • Condensate flow rates for drainage sizing

Key design checks • Check noise level from diffusers and fan coils • Airside or waterside control • Fall in condensate pipe work (if applicable) • Check throw from diffuser

DESIGN WATCHPOINTS

Sizing & selection 1. Check that manufacturer’s thermal and acoustic data is applicable to the

conditions at which the fan coils will be operating and apply any relevant corrections for space temperature, flow and return temperatures etc. Note manufacturer’s outputs are based on chilled water and space temperatures, and room dimensions which may differ substantially from the required operating conditions.

2. Check performance is acceptable for both sensible and latent cooling requirements. The proportion of latent and sensible cooling will vary with chilled water temperature. (See pt 1.) Fan coil output is usually selected on sensible duty and chilled water pipework sized on total duty.

3. Changes in fan speed make a significant difference to cooling output and noise. Manufacturers often state cooling/ heating performance at highest fan speed setting. (See pt 5.)

4. Check manufacturer’s stated outputs for both thermal and acoustic performance are verified by certified independent laboratory tests.

5. Check noise level is acceptable for the usage of the space. High fan speed settings can create noise problems and wherever possible fan coil units should be sized using a low to medium fan speed setting.

6. Check supply air temperature off fan coil under both cooling and heating. Too low a temperature gives dumping and draughts, too high a temperature gives stratification and discomfort at foot level.

7. Check that throw from diffusers is satisfactory under both heating and cooling and whether the throw of any two diffusers cross each other as this can cause cold air to dump.

8. Check the index run has been correctly selected for the duct work as secondary ductwork can be of significant length.

9. Check that the pressure drop across the secondary ductwork and diffuser is within the capability of the fan coil.

10. Consider return air path, eg via air handling light fittings, dedicated grilles, shadow ceiling gaps etc.

11. Check whether the ceiling is sealed. 12. Check whether fresh air is supplied direct to FCU or to plenum. 13. Consider balance between size of plenum and size of fan coil. 14. Consider any known future needs or flexibility requirements when

positioning fan coils so they are away from potential partition lines and will supply all planned spaces.

Installation, operation & control 15. Check for downdraughts at windows if no other heating source and

arrange perimeter diffusers to compensate. 16. Check that control positions are compatible with any partitioning. If

sensing return air check that air sensed is from area served. 17. Check whether airside or waterside control will be used, with return air

sensor or remote wall-mounted sensor. 18. Check that control valves can operate correctly against system pressure

as they may not close against high system pressures. 19. Consider control criteria ie individual control, control in groups of two of

three, group from single BMS outstation etc. 20. Fire barriers which are breached by, eg condensate pipes should be

adequately sealed. 21. Check whether fresh air makeup is humidified by direct steam injection.

This can lead to limescale build up which needs removal. 22. The low air pressure developed by fan coil units necessitates relatively

short secondary ductwork, especially when flexible ductwork is used. A guideline is a max. 1m for flexible duct. If a longer length is needed check the effect on pressure drop.

23. Where possible, select all supply diffusers served by fan coil units with low pressure drop and maintain same pressure drop at all diffusers for ease of commissioning.

24. Gravity fed condensate drainage systems require sufficient fall in the pipework for adequate run off. Shallow ceiling voids may not permit long drainage pipe runs and a pumped condensate system may be required. (NB: pumps can be unreliable.)

Access & maintenance 25. Flexible hoses need to comply with relevant HEVAC Standard and be

suitable for continuous water temperature changes. 26. Provide air vents for each unit and local drain points. Check units can be

isolated and by-passed during flushing and chemical cleaning. 27. Allow adequate access to fan coil units for cleaning, filter replacement,

general maintenance etc. If possible, also allow for removal of complete unit for bench maintenance or replacement.

Economics 28. Consider whole life cost of fan coil system against other choices.

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78 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

34 NATURAL VENTILATION

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Required fresh air quantities and summer and winter air change rates

• Zone and building heat losses and heat gains

Design outputs

Notes / Design file cross-reference

• Ventilation strategy and specification including ventilation type, eg cross ventilation, single sided etc; schedule of window types, actuators, method of control; schedule of transfer grilles if used etc.

• Analysis of predicted ventilation performance

• Requirements for solar shading, where appropriate

• Layout plan drawings showing air flow paths

• Control philosophy to be applied, where appropriate

Key design checks

Notes / Design file cross-reference

• Check that air change rate is sufficient to provide satisfactory fresh air and temperatures for occupants

• Check room air distribution patterns and air velocities in the occupied zone for both summer and winter

• Cross check design performance under still air conditions

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 79

34 NATURAL VENTILATION

Design inputs • Required fresh air quantities and summer and winter air change

rates • Zone and building heat losses and heat gains

Design information

• Planned ventilation strategy • Building type, orientation and usage • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details, grilles etc

• Occupancy details incl. estimated max. occupancy • Geography, landscape, surrounding buildings • External levels of noise and pollutants, local wind conditions • Planning and fire regulations • Any internal noise transmittance constraints See also: Ventilation requirements, Infiltration, Glazing, Mixed mode ventilation systems

Design outputs • Ventilation strategy and specification including ventilation type,

eg cross ventilation, single sided etc; schedule of window types, actuators, method of control; schedule of transfer grilles if used etc

• Analysis of predicted ventilation performance • Requirements for solar shading, where appropriate • Layout plan drawings showing air flow paths • Control philosophy to be applied, where appropriate

Key design checks • Check that air change rate is sufficient to provide satisfactory fresh

air and temperatures for occupants • Check room air distribution patterns and air velocities in the

occupied zone for both summer and winter • Cross check design performance under still air conditions

DESIGN WATCHPOINTS

Sizing & selection

1. Be realistic about system performance and achievable internal conditions with the client. A naturally ventilated open plan office cannot be controlled in summer to similar temperatures to an air conditioned space.

2. Check external noise and pollution levels to assess whether natural ventilation is feasible as part of initial ventilation strategy.

3. Assess the security arrangements and risks associated with opening windows as part of initial ventilation strategy.

4. Natural ventilation is intrinsically variable – always check performance under worst case scenario, eg on a warm day with no wind, as part of design assessment.

5. Wind speeds will be less in summer than winter. 6. Take the prevailing wind direction into account when positioning the inlet

and outlet points for natural ventilation schemes. 7. Over a building depth of 15 m the ventilation strategy can be very

complex with 6 m depth often the limit for single sided ventilation. 8. The effective depth for natural ventilation systems varies from 2 x floor to

ceiling height for single sided single opening to 5 x floor to ceiling height for cross flow or stack ventilation. The use of an atria can allow greater depth depending on design. (See CIBSE AM10.)

9. Driving pressures for natural ventilation are very low, often less than 10 Pa. As a result natural ventilation will not be efficient where there are obstructions to the flow path or resistance to air flow, eg partitions, furnishing, changes of direction etc.

10. Single sided ventilation is more effective with a double opening, ie tall windows with a top and bottom opening to allow local stack effect circulation. This can be used where cross ventilation of some spaces may not be possible due to structural partitioning.

11. Cross ventilation is most effective with an open plan. Any partitions should be kept low, preferably under 1·2 m in height. Tall furniture should be placed perpendicular to the perimeter wall to present the least resistance to air flow in the room.

12. For cross ventilation with full height partitions, ie central corridor and perimeter rooms, windows in the internal wall or transfer grilles in walls or doors can be used although the resistance of these to air flow must be considered.

13. Transfer grilles to aid cross ventilation can be expensive and pose a possible fire risk. Grilles with fire dampers may be a solution.

14. Tall windows, or windows with top openings can promote cross ventilation at high level without inducing draughts at desk heights.

15. Passive stack ventilation can be used when cross ventilation and single sided ventilation cannot provide a sufficient air change rate.

16. Consider the use of trickle ventilators for permanent background ventilation in winter.

17. Heat gains from lighting, office equipment and people that may lead to overheating should be taken into account.

18. Natural ventilation is unlikely to cope with heat gains exceeding 40 W/m2. Reduce heat gains where possible or consider the use of exposed concrete ceiling slabs and/ or night ventilation/cooling or mixed mode strategies.

Installation, operation & control

19. Check that occupant fresh air requirements can be met at all times. 20. Check that the air change rate in summer is sufficient to remove heat

gains from the space and maintain adequate thermal comfort. 21. Check room air distribution patterns and likely air velocities in the

occupied zone for both summer and winter to ensure even distribution and avoid stagnant zones and occupant discomfort. Summer ventilation rates can be substantially greater than those in winter and the effect of this should be considered.

22. For comfort and to avoid draughts mean local air velocities should be below 0·15 m/s in winter and 0·25 m/s in summer. Higher air speeds in summer may be tolerated, but nuisance draughts, eg those that disturb papers should be avoided (ie over 0·5 m/s).

23. Local desk fans can create nuisance draughts for other occupants. 24. Provide occupant training to ensure they understand planned system

operation and can adapt conditions to changes in weather. 25. Consider noise attenuation strategies.

Access & maintenance

26. Check that openable windows are easily accessible. 27. Motorised window actuators will require maintenance.

Economics

28. Consider application of lighting controls to reduce summer heat gain. 29. Consider relocation and grouping of high heat gain equipment so heat

can be removed by separate system.

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80 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

35 MIXED MODE VENTILATION SYSTEMS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Infiltration rates

• Fresh air requirements

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• Mixed mode ventilation strategy document for use during design, commissioning and operation

• Detailed layouts and services drawings

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses and equipment schedules

Key design checks

Notes / Design file cross-reference

• Agree acceptable design conditions with client, including any relaxation or tolerance in internal temperatures

• Check the integration of control between mechanically and naturally ventilated areas

• Provide adequate instruction to ensure the building occupants understand how to operate the systems effectively

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 81

35 MIXED MODE VENTILATION SYSTEMS

Design inputs • Zone heating and cooling loads • Internal design conditions • Infiltration rates • Fresh air requirements • Noise rating for each zone

Design information

• Planned ventilation strategy • Building type, orientation and usage • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Occupancy details and internal heat sources • External levels of noise and pollutants • Planning and fire regulations • Ceiling type and grid size, distribution space available • Details of extract systems, eg toilet or kitchen extract • Details of any zoning and pressurisation requirements • Locations of fire compartmentation/separation See also: Ventilation requirements, Zoning, Glazing, Natural ventilation, Constant air volume A/C systems

Design outputs • Mixed mode ventilation strategy document for use during design,

commissioning and operation • Detailed layouts and services drawings • Control requirements • Statement of commissioning strategy • Relevant specification clauses and equipment schedules

Key design checks • Agree acceptable design conditions with client, including any

relaxation or tolerance in internal temperatures • Check the integration of control between mechanically and

naturally ventilated areas • Provide adequate instruction to ensure the building occupants

understand how to operate the systems effectively

DESIGN WATCHPOINTS

Sizing & selection

1. Be realistic about system performance and achievable internal conditions with the client. An open plan office with a mixed mode ventilation ie a combination of natural and mechanical ventilation cannot be controlled in summer to similar temperatures to a fully air conditioned space.

2. Check that the type of system is suitable for the area it serves. Be realistic where natural ventilation can be applied, and where some form of mechanical ventilation or cooling will be needed. Relocating or rationalising heat generating equipment can sometimes make some form of natural ventilation viable.

3. Check that systems work equally well under both summer and winter operations. Poor design can lead to draughts in winter.

4. Too many opening windows may undermine the mechanical ventilation system. The naturally ventilated and mechanically ventilated or cooled areas need to be zoned very carefully to enable each to operate and be controlled effectively.

5. Check that indoor air quality can be maintained. Avoid having natural ventilation in areas adjacent to external noise or pollution sources, eg railways, heavy traffic, industrial facilities, areas where vehicles could be off loading or mechanical ventilation discharge points. These spaces may need sealed windows and mechanical ventilation.

6. Examine air flow patterns carefully to check there is no adverse interaction between the different systems. Poorly placed supply or extract grilles can disrupt the performance of natural ventilation measures, resulting in poor environmental conditions.

7. Design measures to deal with high heat gain sources locally where possible before they get distributed throughout the space, eg local split cooling units operating in re-circulation mode placed close to large photocopiers, printers etc may still permit the use of natural ventilation as the air volume dealt with by the unit is balanced.

8. When designing stack effect ventilation systems, consider issues such as fire separation. Due to the need for zoning, fire dampers may have to be added to ventilation shafts in case of fire to stop flames spreading between zones.

9. Take the prevailing wind direction into account when positioning the inlet and outlet points for natural ventilation schemes.

10. Single sided ventilation can be suitable for spaces with a room depth of up to 6 metres. Cross ventilation can ventilate a deeper floor plate at approximately five times the floor to ceiling height.

11. Open plan is essential for cross ventilation. Any partitions should be kept low, and perimeter offices avoided.

12. Driving pressures for natural ventilation are very low, often less than 10 Pa. As a result natural ventilation will not be efficient where there are partitions, obstructed air flow paths, changes of direction, etc. that will create resistance to the air flow.

13. Natural ventilation can typically deal with space heat gains of up to 40 W/m2. If loads are higher and cannot be reduced by relocating heat producing sources then mechanical cooling may be required.

Installation, operation & control

14. The integration of control between mechanically and naturally ventilated areas can be difficult. Examine all the systems, natural and mechanical, in each operating mode or period to see how they interact.

15. Where a mixed mode strategy is employed, it is essential that the building occupants understand how to operate the systems effectively, eg to use cross ventilation in naturally ventilated areas by opening windows in opposing walls.

16. Provide local controls wherever practical so that occupants can control their own surroundings.

Access & maintenance

17. Consider maintenance access requirements for high level window actuators.

18. Consider and provide access to all installed system components, including any fire and volume control dampers as well as plant.

Economics

19. Where the requirement for mechanical cooling is local, consider using a unitary rather than central solution. Small unitary air conditioning systems may be more energy and space efficient than central system options as well as having lower capital costs.

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82 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

36 CONSTANT AIR VOLUME AIR CONDITIONING SYSTEMS (CAV)

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Infiltration rates

• Fresh air requirements

• Fresh air supply condition

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• Supply & extract air flow rates

• System design drawings

• Schedule of relevant plant and equipment giving sufficient information for manufacturer selection

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check air system is balanced, and that other intermittent systems do not interact adversely

• Check whether use of free cooling is possible

• Check whether heat recovery is possible

• Check system velocity is acceptable

• Check fresh air percentages

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 83

36 CONSTANT AIR VOLUME AIR CONDITIONING SYSTEMS (CAV)

Design inputs • Zone heating and cooling loads • Internal design conditions • Infiltration rates • Fresh air requirements • Fresh air supply condition • Noise rating for each zone

Design information

• Planned ventilation strategy • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Space usage, occupancy and details of heat sources • Ceiling type and grid size, locations of luminaires • Distribution space available • Details of extract systems, eg toilet or kitchen extract • External levels of noise and pollutants • Planning and fire regulations • Details of any zoning and pressurisation requirements • Locations of fire compartmentation/separation See also: Ventilation requirements, Fan & duct sizing, Ductwork, Diffusers, Fans, Air handling units

Design outputs • Supply & extract air flow rates • System design drawings • Schedule of relevant plant and equipment giving sufficient

information for manufacturer selection • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that the air system is balanced, and that other intermittent

systems do not interact adversely • Check whether the use of free cooling is possible • Check whether heat recovery is possible • Check system velocity is acceptable • Check fresh air percentages

DESIGN WATCHPOINTS

Sizing & selection

1. Check the variation between zone loads and review whether CAV, ie all-air air conditioning system with constant air flow rate and variable supply air temperature, is the most appropriate and energy efficient system choice.

2. Check that adequate fresh air is provided for each zone under all operating conditions. Some zones will require a higher percentage of fresh air than others, base on the worst case if necessary.

3. Check minimum and maximum acceptable supply temperatures to space. 4. Check that the air system is balanced, and that other intermittent systems

do not interact adversely, eg toilet extract system. 5. Check for any simultaneous heating and cooling requirements, and zone

the system accordingly. With a north/south or east/west building, it may be advantageous to provide two separate distribution zones and control them individually. However, this may increase installation costs.

6. Check system velocities are appropriate to application (see Fan & duct sizing) considering both noise and energy efficiency.

Installation, operation & control

7. Check the available space within the ceiling void to house the distribution system. Aspect ratios of ductwork may need to be altered to overcome local obstructions, and the depth or height required for diffusers and their plenum boxes can be considerable.

8. Insulate supply ductwork where passing through warm areas to avoid the risk of condensation. This applies particularly to ceiling spaces being used as return plenums, risers, plant rooms, etc. Fresh air intake ductwork that passes through warm areas should also be insulated.

9. Where fire dampers are to be used in fire separation curtains above ceilings or below floors, make sure that the correct frame type is selected, and is installed properly to maintain integrity. Install to the manufacturer’s instructions.

10. Avoid locating supply and extract/return diffusers too closely as it may result in short circuiting and the system under-performing.

11. Choose a suitable control strategy for the system. As the same volume of air will be provided all the time, the emphasis should be placed on a suitable dead band between heating and cooling.

12. To save energy, consider the use of CO2 sensors in the return air ductwork to modulate the proportion of fresh air to suit occupancy.

13. Consider the use of variable or 2-speed fans with local override controls to enable the system to operated at reduced volume during periods of low occupancy or heat gain, to save energy.

Access & maintenance 14. Provide access to all system components once installed. As well as the

usual plant items such as fans, coils and filters, all fire and volume control dampers must be accessible for checking and resetting during the life of the installation.

Economics 15. Check whether free cooling can be used to save energy. This can act as

a useful buffer between heating and cooling, particularly in recirculating systems, and saves energy.

16. Consider the use of heat recovery devices wherever possible, but check the penalty of additional system resistance and the resulting increased fan power requirements.

17. Consider dedicated air-handling plant and system for high load areas. Alternatively, where overcooling may occur in some zones when the system is in full cooling mode, consider the use of re-heat batteries in the distribution ductwork, eg for a north facing zone in a system where the southern elevation cooling loads dictate the supply temperature. Although this is an expensive and energy wasting solution as the air that has been cooled is heated up again, for small zones this may be the most cost effective capital solution, or may be employed where the cost of installing separate distribution ductwork to each zone would be prohibitively expensive.

18. Check that specific fan power does not exceed Building Regulation requirements (Part L). Select fans for high operating efficiency. Additional capital costs are generally recovered very quickly by energy savings in operation.

++

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84 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

37 DISPLACEMENT VENTILATION

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Fresh air requirements

• Zone heating and cooling loads

• Infiltration to space

• Heat gains and losses for all space surfaces

• Internal design conditions including air quality

Design outputs

Notes / Design file cross-reference

• Displacement ventilation strategy document for use during design, commissioning and operation

• Supply and extract volume flow rates with design temperature and humidity

• Schedule of supply diffusers and extract grilles giving sufficient data for manufacturer selection

• Layout drawings of diffuser locations

Key design checks

Notes / Design file cross-reference

• Check maximum air flow summed over all air terminals

• Check that mean air speed is within comfort limits

• Check vertical temperature gradient is within comfort limits

• Check near zone around each terminal

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 85

37 DISPLACEMENT VENTILATION

Design inputs • Fresh air requirements • Zone heating and cooling loads • Infiltration to space • Heat gains and losses for all space surfaces • Internal design conditions including air quality

Design information

• Planned ventilation strategy • Occupancy details and space usage • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of distribution space available • Lighting system and position of luminaires incl. height • Details of heat sources and any contaminant sources • Whether the system will be used in conjunction with static cooling

devices • Possible positions or facilities for exhaust air See also: Ventilation requirements, Natural ventilation

Design outputs • Displacement ventilation strategy document for use during design,

commissioning and operation • Supply and extract volume flow rates with design temperature and

humidity • Schedule of supply diffusers and extract grilles giving sufficient

data for manufacturer selection • Layout drawings of diffuser locations

Key design checks • Check maximum air flow summed over all air terminals • Check that mean air speed is within comfort limits • Check vertical temperature gradient is within comfort limits • Check near zone around each terminal

DESIGN WATCHPOINTS

Sizing & selection

1. Check an appropriate method of calculation is used, eg BSRIA COP 17/99.

2. Heat gains and losses at all space surfaces are needed, particularly at interface with exterior to enable prediction and analysis of surface temperatures and subsequent convection flows.

3. Analysis of whole space air diffusion is essential including localised convection at all encompassing surfaces (cool and warm), and from internal heat sources, incl. occupants. Details and positions of heat and contaminant sources and extracts are required for full analysis.

4. Check fresh air requirements are met under all operating conditions. 5. Check that the fresh air “lake” (providing fresh cool air for occupants) is

maintained at acceptable air quality. Vitiated air that has risen to high level should not re-enter the occupied zone.

6. Check height of boundary layer (between fresh air lake and warm room air) is acceptable. Note this layer is easily disturbed, eg by people entering room.

7. Limit temperature differentials between supply and ambient air to avoid draughts. Check air velocities in the occupied zone.

8. Check that the vertical temperature gradient is acceptable for comfort, eg not more than 2 K/m over the occupied zone.

9. Check DV terminals do not cause draughts, particularly at ankle level, and keep the “near zone” (discomfort zone near terminal face) as small as possible. Keep velocities low – a rule of thumb is to check maximum air flow is 6ach-1 or less, summed over all terminals.

10. Check supply terminals taller than 600 mm for entrainment of contaminated room air, as well as draughts.

11. Check entrainment of supply if supply air temp. is less than 19oC. 12. If DV is used in conjunction with systems that provide high level cool

surfaces, eg chilled beams or chilled ceilings, take particular care that vitiated air does not drop back into the occupied zone.

13. DV can be used with static chilled beams but not fan assisted as these can create draught and contaminant mixing problems.

14. DV should not be used in the presence of gaseous pollutants colder or denser than ambient air.

15. DV should not be used if there are strong possible disturbances to room air flow or if room heights are less than 2·3m.

16. DV should not be used if the room is to be heated by the ventilation system unless the heat load is suitably low.

17. The higher the space the more effective DV can be. 18. Check heat gains into floor from both above and below as these are often

substantial. 19. Plenum chambers used with DV floor terminals can have a number of

problems : • If these are also used for IT cabling and ballasts from lights in

ceiling below this can add substantially to the heat gain which must be allowed for. Alternatively terminals can be ducted with insulated ducts (expensive).

• Consider air distribution in the plenum chamber. Non-uniform air distribution can give backflow through terminals and over pressurisation at other terminals leading to supply problems and discomfort. Need to achieve uniformity of pressure in the plenum, eg consider use of textile socks at the inlet to chamber and/or increasing supply duct numbers.

• Leakage can be a considerable problem with plenum chambers and add substantially to energy usage. Access points, eg floor tiles can be a problem. Leakage should be minimised by good sealing and leakages to untreated spaces should be eliminated.

Installation, operation & control 20. Check distribution space available and whether raised floor possible. 21. Downdraughts can interfere with effective DV. Check the impact of

windows/rooflights. 22. If used with chilled beams or ceilings control of both systems needs

careful consideration and scheduling. Static cooling is more efficient and should be used to meet the main cooling load. In this case check that the ventilation requirement is still met adequately.

Access & maintenance 23. Check adequate access to system is available.

Economics 24. DV is primarily a ventilation system and does not normally have a large

cooling capacity. Consider the use of passive measures to reduce heat gains especially solar gain.

25. Consider the provision of heat recovery, preferably enthalpy recovery, as high efficiencies are achievable.

26. For detailed operating energy prediction daily patterns of occupancy use are required for the year.

27. Consider whole life cost of system compared to other choices.

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86 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

38 CHILLED BEAMS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Fresh air requirements

• Infiltration to space

• Perimeter heat gains and losses

• Internal design conditions

• Chilled water flow and return temperatures

Design outputs

Notes / Design file cross-reference

• Schedule of chilled beams with rated output at room conditions, required chilled water temperatures and control requirements

• Layout drawings showing beam dimensions and positions, and pipework connections

• Clear identification of return air pathways

• Input to co-ordinated ceiling layout including lighting

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check ceiling space available

• Check beam type

• Check condensation will not form on beams

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 87

38 CHILLED BEAMS

Design inputs • Zone heating and cooling loads • Fresh air requirements • Infiltration to space • Perimeter heat gains and losses • Internal design conditions • Chilled water flow and return temperatures

Design information

• Planned ventilation strategy • Occupancy details and space usage • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of distribution space available • Lighting system and position of luminaires • Details of heat sources • Client future need requirements See also: Future needs, Ventilation requirements, Chillers

Design outputs • Schedule of chilled beams with rated output at room conditions,

required chilled water temperatures and control requirements • Layout drawings showing beam dimensions and positions, and

pipework connections • Clear identification of return air pathways • Input to co-ordinated ceiling layout including lighting • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check ceiling space available • Check beam type • Check condensation will not form on beams

DESIGN WATCHPOINTS

Sizing & selection

1. Check that selection data meets design requirements ie that manufacturer’s stated outputs are applicable to the required design operating conditions, eg space temp, chilled water temps etc.

2. Decide whether passive or active beams will be used (ie with/without ducted air supply which induces additional flow through beam).

3. Check space available - some passive chilled beams require a clear space of some 300 mm above the beam for adequate air circulation. This can give a total required ceiling depth in excess of 600 mm depending on manufacturer.

4. Open chilled beams can give stronger downward convection currents than closed beams resulting in higher air velocities and lower air temperature in the occupied zone and hence localised discomfort. Restriction of operating temperatures and cooling outputs may be needed to overcome this.

5. Review pyschrometric calculations to check that condensation will not form on the beams. Check chilled water temperatures - there should be a sufficient safety margin between the lowest beam temperature and the highest potential dew point temperature in the space. Consider providing condensation control for chilled beams (to prevent chilled water temp. falling below room dew point temp.).

6. Full details of internal heat sources are required, eg position and output details including height and surface temperatures.

7. Heat gains from lighting can be discounted if closed (capped) chilled beams are used as heat will go into the exhaust air.

8. Check lighting heat gains are included when open (uncapped) chilled beams are used, unless air extract is via luminaires.

9. When open beams are used with extract from ceiling void the rate of extract can affect beam output.

10. Restrict amount of cooling at a given position. Rule of thumb -except at outer perimeter restrict output of chilled beams to no more than 100 W/m run. At the extreme perimeter the amount can be increased to up to 300 W/m run to cope with solar gains. In this case the perimeter control zone must be separately controlled.

11. Consider return air pathways. 12. Check that any ceiling extract system is evenly distributed to provide

even removal of vitiated air and avoid room lateral air displacement.

Installation, operation & control

13. If open chilled beams are used, particular care is needed to prevent these being overwhelmed by perimeter solar driven updraughts.

14. Allowance should be made for changes in the future partitioning of the space when number and position of beams and control grouping is selected.

15. If used in conjunction with displacement ventilation control of both systems needs careful consideration and scheduling. Displacement ventilation is primarily used for ventilation but can provide some cooling. Static cooling is more efficient and should be used to meet the main cooling load. In this case check that the ventilation requirement is still met adequately.

16. Timed on/off control methods are usually best due to large effect of reduced water flow on heat exchange at the close approach conditions.

17. Thermal imaging can be used to check for adequate flow in the chilled beams.

Access & maintenance

18. Pipework requires adequate venting and access to vent positions. 19. Allow adequate access for maintenance/replacement. 20. Common access points may be needed for other ceiling systems such as

electrical distribution, lighting etc. Careful layout co-ordination is required.

Economics

21. Consider whole life cost of system compared to other air conditioning systems.

22. Check different types of chilled beams to select the most cost effective option.

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39 CHILLED CEILINGS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Fresh air requirements

• Infiltration to space

• Perimeter heat gains and losses

• Internal design conditions

• Chilled water flow and return temperatures

Design outputs

Notes / Design file cross-reference

• Schedule of chilled ceiling requirements with rated output at room conditions, required chilled water temperatures and control requirements

• Layout drawings showing any panel dimensions and positions, and pipework connections

• Clear identification of return air pathways

• Input to co-ordinated ceiling layout including lighting

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check client/architect approval of ceiling

• Check condensation will not form on ceiling

• Check net area of chilled ceiling for output

Project specific checks & notes

Notes / Design file cross-reference

Page 24: HVAC Design checklist

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39 CHILLED CEILINGS

Design inputs • Zone heating and cooling loads • Fresh air requirements • Infiltration to space • Perimeter heat gains and losses • Internal design conditions • Chilled water flow and return temperatures

Design information

• Planned ventilation strategy • Occupancy details and space usage • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of distribution space available • Lighting system and location of luminaires • Details of heat sources • Client future need requirements See also: Future needs, Ventilation requirements, Chillers

Design outputs • Schedule of chilled ceiling requirements with rated output at room

conditions, required chilled water temperatures and control requirements

• Layout drawings showing any panel dimensions and positions, and pipework connections

• Clear identification of return air pathways • Input to co-ordinated ceiling layout including lighting • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check client/architect approval of ceiling • Check condensation will not form on ceiling • Check net area of chilled

ceiling for output

DESIGN WATCHPOINTS

Sizing & selection

1. Check that selection data meets design requirements, ie that manufacturer’s stated outputs are applicable to the required design operating conditions, eg space temp, chilled water temps etc. Check net area of chilled ceiling for output.

2. Check client/architect approval of ceiling. Consider ceiling appearance - different batches of same panel can appear different and large panels can produce a dimple effect on the ceiling if not sufficiently strong/supported.

3. A rule of thumb best practice design basis is: optimum soffit surface temperature of 17oC, ie water flow and return temps of 16/18oC.

4. Check the panel design selected has an acceptable balance between acoustic performance and thermal performance (perforated backing or tin backing).

5. Review pyschrometric calculations to check that condensation will not form on the ceiling. Check chilled water temperatures - there should be a sufficient safety margin between the lowest ceiling temperature and the highest potential dew point temperature in the space. Consider providing condensation control for the chilled ceiling (to prevent chilled water temp. falling below room dew point temp.).

6. Full details of internal heat sources are required, eg position and output details including height and surface temperatures.

7. Chilled ceilings are best when a separate fresh air supply system, eg low level supply or displacement ventilation is provided. Combined system and control operation needs careful consideration.

8. Check that the temperature gradient along long panel runs gives an acceptable horizontal space temperature gradient (ie not too great).

9. Allowance should be made for the higher radiant cooling that will be achieved at the perimeter as warm surfaces will give a higher temperature difference and thus a higher total cooling effect.

Installation, operation & control 10. Careful layout co-ordination with other trades is required. 11. Consider whether panel manufacturer will do design, installation and

commissioning or whether three separate companies involved. 12. On-site assembly of chilled ceiling panels can lead to damage and

contamination of panel surface. Pre-assembled cassettes provide a better option.

13. Check requirements re earth bonding.

14. Flexible connections can be easily damaged on site or by installation of other services. Check that a good quality connection is specified.

15. Allowance should be made for changes in the future partitioning of the space when number and position of panels and control grouping is selected.

16. Heating of perimeter outer zone on shade side of building is often required at the same time as chilled ceilings will be required for adjacent inner zones. Control therefore needs careful consideration.

17. Perimeter outer zones will require separate control and possibly the use of chilled beams where heat gains and losses are markedly disproportionate to adjacent inner zones.

18. Timed on/off control methods are often best. 19. If used in conjunction with natural ventilation then suitable control must

be provided to preclude condensation problems. (See pt 5.) 20. Chilled ceilings have relatively low cooling power. Pre-conditioning or

post-conditioning may be necessary at peak periods. 21. If used in conjunction with displacement ventilation control of both

systems needs careful consideration and scheduling. Displacement ventilation is primarily used for ventilation but can provide some cooling. Static cooling is often used to meet the main cooling load. In this case check the ventilation requirement is still met adequately.

22. Thermal imaging can be used to check for adequate flow in the chilled ceiling, contact to ceiling tiles and proper response to control.

23. Insulation is required for top surface of panel and should be adequately fixed to remain in position on hinged panels.

Access & maintenance 24. Pipework requires adequate venting and access to vent positions. 25. Hinged ceiling access panels work well but require that good flexible

connections are used for the pipework. 26. Check that individual legs or tiles can be isolated if required (in case of

damage/ replacement). 27. Common access points may be needed for other ceiling systems such as

electrical distribution, lighting etc.

Economics 28. Consider whole life cost of system compared to other air conditioning

systems. 29. Check different types of chilled ceilings to select most cost effective

option.

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40 VARIABLE AIR VOLUME SYSTEMS (VAV)

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Fresh air requirements for each zone

• Fresh air supply condition

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• Schedule of VAV unit sizes with rated output at room conditions, minimum fresh air requirement, turn down ratios, minimum & maximum inlet pressure at VAV box, control requirements etc. giving sufficient information for manufacturer selection

• System layout drawings showing unit positions and connections

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that the fresh air requirements for every zone are met under maximum turndown

• Check that room air diffusion patterns are acceptable at low volume flows

• Check that the noise output is acceptable at high volume flows

Project specific checks & notes

Notes / Design file cross-reference

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40 VARIABLE AIR VOLUME SYSTEMS (VAV)

Design inputs • Zone heating and cooling loads • Internal design conditions • Fresh air requirements for each zone • Fresh air supply condition • Noise rating for each zone

Design information

• Planned ventilation strategy • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Space usage, occupancy and details of heat sources • Ceiling type and grid size • Lighting system and locations of luminaires • Distribution space available • Details of extract systems, eg toilet or kitchen extract • External levels of noise and pollutants • Planning and fire regulations • Details of any zoning and pressurisation requirements • Locations of fire compartmentation/separation See also: Ventilation requirements, Fan & duct sizing, Ductwork, Diffusers, Fans, Air handling units

Design outputs • Schedule of VAV unit sizes with rated output at room conditions,

minimum fresh air requirement, turn down ratios, minimum & maximum inlet pressure at VAV box, control requirements etc. giving sufficient information for manufacturer selection

• System layout drawings showing unit positions and connections • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that the fresh air requirements for every zone are met under

maximum turndown • Check that room air diffusion patterns are acceptable at low

volume flows • Check that the noise output is acceptable at high volume flows

DESIGN WATCHPOINTS

Sizing & selection

1. Consider choice of VAV system type with respect to system requirements and energy efficiency, eg fan assisted terminals (FAT), terminal reheat, induction VAV etc.

2. Fresh air quantities cannot be controlled to individual areas therefore check that the fresh air requirements for all zones are met under all possible operating conditions including when the supply system is on maximum turndown.

3. Check that room air diffusion patterns are acceptable at low volume flows, with no stagnant areas in the occupied zone.

4. Check that the turndown ratio is acceptable (generally limited to 3:1) to avoid problems with throw and air stagnation.

5. If the turndown ratio is over 60%, instability may occur and fan sequencing will be required to maintain airflow in the stable range.

6. Reheat coils can be needed on internal zones and other areas with low relative heat gains, to prevent over-cooling on minimum turndown.

7. Check that humidity levels do not rise to unacceptable levels on turndown.

8. The use of variable geometry diffusers should be considered to maintain design throws at turndown.

9. Check that the noise output is acceptable at high volume flows, secondary and tertiary attenuators may be required.

10. VAV systems can induce negative building pressure if used in conjunction with fixed extract systems such as toilet extract because of the effects of the turndown ratio. This can result in inadequate fresh air, negative pressure in occupied areas leading to difficulty in opening doors and contamination from toilet odours.

11. Size riser ductwork on peak simultaneous loads per floor. 12. Consider any known future needs or flexibility requirements when

positioning VAV units so they are away from potential partition lines and will supply all planned spaces.

Installation, operation & control

13. VAV control needs very careful consideration to ensure that fresh air requirements, heating and cooling requirements and adequate room air diffusion can be achieved.

14. Consider location of room temperature sensors with respect to air streams.

15. Consider types of terminal box required and methods of air volume control, eg static pressure, velocity grid etc.

16. Check minimum static pressures are available at inlet to index terminal box.

17. The need for reheating should be minimised. The controls should include features to maximise supply air temperature and minimise reheat, eg supply temperature compensation - lifting the supply temperature in cooler months.

18. VAV systems can have difficulties with simple damper control of fresh air quantities as negative pressure in the mixed air plenum will vary with supply volume which can lead to inadequate fresh air at low supply rates. A control system that actively controls outdoor air is needed to ensure that minimum fresh air rates are maintained under all conditions.

19. Consider the use of CO2 sensors in return air ductwork to increase or reduce the proportion of outside air to suit occupancy.

20. Consider sensor locations carefully and the selection of slave units as future flexibility can become restricted.

21. VAV systems do not provide close humidity control. 22. Extract fan control should be linked to supply air volume flow rate to

balance volume flows as supply volume varies. Directly linking supply and extract fan control can cause problems as they may have different characteristics.

Access & maintenance 23. Allow adequate access to VAV units for maintenance etc.

Economics 24. Consider the option of full fresh air VAV with heat recovery. 25. Fan assisted terminal (FAT) VAV systems can be more energy efficient

as turndown of the primary plant can be greater without risk of dumping and primary air supply temperatures can be lower meaning less air is distributed and fan power is reduced.

26. Consider the use of free cooling to reduce energy use. 27. Consider whole life cost of VAV system compared to other choices.

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41 VARIABLE REFRIGERANT FLOW SYSTEMS (VRF)

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Internal design conditions

• Type of VRF system required - cooling only, heating and cooling or simultaneous heating and cooling (heat recovery systems)

• Required capacity of units in heating and cooling modes

• Airflow of units

Design outputs

Notes / Design file cross-reference

• Schedule of unit sizes, output capacity, airflow, noise levels, weight, dimensions, electricity supply

• Plan layout drawings showing position of indoor and outdoor units, routing of refrigerant pipework

• Schedule of control devices required for individual control

Key design checks

Notes / Design file cross-reference

• Check that refrigerant used complies with the latest protocols

• Check noise levels are acceptable at high outputs

• Check indoor unit control requirements, ie room sensors or return air sensor controls

Project specific checks & notes

Notes / Design file cross-reference

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41 VARIABLE REFRIGERANT FLOW SYSTEMS (VRF)

Design inputs • Zone heating and cooling loads • Internal design conditions • Type of VRF system required- cooling only, heating and cooling

or simultaneous heating and cooling (heat recovery systems) • Required capacity of units in heating and cooling modes • Airflow of units

Design information

• Planned ventilation strategy • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Details of structural frame • Space usage and occupancy details • Noise rating for each zone • Ceiling type and grid size, distribution space available • Lighting system and position of luminaires • Planning and fire regulations • Electrical supply, phase and current required • Client control criteria See also: Heat pumps

Design outputs • Schedule of unit sizes, output capacity, airflow, noise levels,

weight, dimensions, electricity supply • Plan layout drawings showing position of indoor and outdoor

units, routing of refrigerant pipework • Schedule of control devices required for individual control

Key design checks • Check that refrigerant used complies with the latest protocols • Check noise levels are acceptable at high outputs • Check indoor unit control requirements, ie room sensors or return

air sensor controls

DESIGN WATCHPOINTS

Sizing & selection

1. Variable refrigerant flow systems are sometimes referred to as variable refrigerant volume (VRV).

2. Consider choice of VRF system type with respect to system requirements and energy efficiency, eg cooling only, heating and cooling or simultaneous heating and cooling (heat recovery systems).

3. Check that refrigerant to be used complies with latest protocols. 4. Check planned ventilation strategy and consider how fresh air

requirements will be met for spaces served by VRF systems. 5. Consider best position for indoor units ie above ceiling, ceiling

suspended, wall or floor installation. 6. Check noise levels are acceptable at high outputs, secondary and tertiary

attenuators may be required. 7. If attenuators are installed check carefully that the pressure drop through

them can be overcome by the fan in ducted indoor units. 8. Check that external units do not recirculate or exhaust to other units. If

located in enclosures check that adequate air flow is available for peak duty.

9. Check that the outdoor units can be positioned in acceptable locations. 10. Consider refrigerant pipe work routes carefully to minimise runs through

occupied spaces. 11. Check maximum permissible vertical and total refrigerant pipe work runs.

Minimise both horizontal and vertical pipe runs and the number of joints and bends required. Distribution losses in complex refrigerant pipe work can account for up to 12% reduction in performance. Apply correction factors for long pipe runs as given by manufacturers.

12. Do not assume that the pipe work distances between the indoor and outdoor units will be similar between manufacturers for similar capacity equipment.

Installation, operation & control

13. Specify that the installation should be carried out by competent and trained refrigeration technicians and close attention paid to the manufacturer’s recommended procedures (eg purging with nitrogen whilst brazing, system flushing, pressure testing, evacuation, adding additional refrigerant and electrical commissioning checks).

14. High quality control should be exercised during installation, and a rigorous pipework proving scheme carried out before the system is accepted and signed off.

15. Indoor unit control requirements should be established, eg room sensors or return air sensor controls.

Access & maintenance

16. Check that there is adequate access for general maintenance to both units and distribution pipework.

17. Check that any maintenance or service agreement includes regular and thorough leak testing.

18. Final documentation for pressure testing certification and electrical safety checks must be supplied to be kept by the owner.

Economics

19. To maximise the efficiency potential of VRF simultaneous heating and cooling systems, the building in which they are to be installed should have a consistent year round cooling load, typically 12 to 15 kW for a 10 HP system.

20. Consider whole life cost of VRF system compared to other choices.

Phase controller

VRF indoor unit Compressors

Heat exchangers

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42 TOILET EXTRACT

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Required ventilation rates/ airchange rates

• Details of toilet provision and layout – number of WCs, washbasins, showers etc

Design outputs

Notes / Design file cross-reference

• Required extract air flow rates

• Layout drawings showing toilet extract systems

• Schedule of required fans and motor drives, with fan duties and requirements for standby, giving sufficient information for manufacturer selection

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Cross check extract rates as air changes per hour

• Check that statutory requirements are met, eg for minimum ventilation rates

Project specific checks & notes

Notes / Design file cross-reference

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42 TOILET EXTRACT

Design inputs • Required ventilation rates/ airchange rates, if specified in client

brief • Details of toilet provision and layout – number of WCs,

washbasins, showers etc

Design information

• Planned ventilation strategy • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors etc showing toilet positions

• Ceiling type and grid size • Distribution space available • Information on other services within the ceiling voids • Details of any zoning and pressurisation requirements • Planning and fire regulations • Locations of fire compartmentation/separation • Building Regulations See also: Ventilation requirements, Intake and discharge locations, Pressurised zones, Commissioning – ducted systems, Ductwork, Fans

Design outputs • Required extract air flow rates • Layout drawings showing toilet extract systems • Schedule of required fans and motor drives, with fan duties and

requirements for standby, giving sufficient information for manufacturer selection

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Cross check extract rates as air changes per hour • Check that statutory requirements are met, eg for minimum

ventilation rates

DESIGN WATCHPOINTS

Sizing & selection

1. Check that Building Regulations and any other statutory requirements are met.

2. Natural ventilation should only be employed where there is direct access to the outdoor air. The ventilation opening(s) should have an area of at least 1/20th of the floor area of the room or 0·1 m2, whichever is greater and part of the opening must be at high level, ie at least 1·75 m above floor level.

3. For mechanical ventilation, ensure absolute minimum extract rate of 3 air changes per hour or 6 litres/s per WC pan or washbasin, whichever is greater. (See Building Regulations.)

4. For public lavatories it is good practice to increase the extract rate to within 5 to 10 air changes per hour.

5. Toilet areas should be kept at negative pressure, relative to adjacent occupied areas, in order to impede the leakage of smells into those adjacent occupied areas. This is typically achieved by extracting 20% more from the toilets than is mechanically supplied.

6. Replacement air for lavatories in public buildings should be introduced at or close to comfort temperature and at a velocity not exceeding 1·5 m/s.

7. For small systems make up air can be supplied via door transfer grilles from circulation or lobby areas. Architects sometimes prefer not to have grilles in doors in which case the door can be undercut – this has the added advantage of allowing any water leaks to be visible.

8. If transfer grilles are used they may require acoustic baffles or sound attenuation for privacy.

9. Grilles in fire doors should have an appropriate fire rating and, eg a fire damper or intumescent core.

10. For public lavatories supply air is often provided to the lobby area with a transfer grilles between lobby and toilet areas, but for large public lavatories supply to the toilet/wash area may be needed to avoid excessive velocities through the transfer grilles(s).

11. Check that the proposed exhaust fan location is suitable, eg does not cause noise problems and is positioned away from supply air intakes to avoid any risk of short-circuiting.

Installation, operation & control

12. Check there is adequate distribution space for planned routing of extract ductwork.

13. Toilet extract systems should be completely independent and not connected to other extract systems.

14. Toilet extract systems usually operate intermittently. It is important to check that this does not interact adversely with other ventilation systems in the building.

15. With extract systems that operate intermittently ensure that the system will continue to operate 15 to 20 minutes after use of the space stops. This can be done by linking fan operation to the light switch for an internal toilet or by using movement detectors.

16. Duplicate fans with automatic changeover are commonly used for toilet extract. Alarms for the run fan linked to control box or BMS system are usually provided to give failure alert.

17. Check that fire dampers have been specified where ductwork passes through fire barriers.

18. Check provision has been made for system commissioning. (See Commissioning – ducted systems.)

Access & maintenance

19. Provide access to all system components once installed. 20. Consider fan operation and control for run and standby fans to keep

standby fans maintained in good running order, eg by use of manual changeover between run and standby.

Economics

21. Consider the use of heat recovery from the exhaust air from continuously operating systems. The heat recovery system should be one that does not transfer any contaminants, eg run-around coil.

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43 KITCHEN EXTRACT

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Details of cooking equipment to be installed, size, power consumption, fuel etc

• Volume of exhaust air required (if specified for specialist applications)

Design outputs

Notes / Design file cross-reference

• Required extract (and supply) air flow rates

• Layout drawings /schematic of kitchen ventilation scheme with extract flow rates, showing position of canopies, ductwork, dampers, etc

• Schedule of required extract and supply fans and motor drives, giving sufficient information for manufacturer selection

• Schedule of canopy dimensions, materials and other components

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Cross check extract rates as air changes per hour

• Check that local authority and Building Regulations relating to kitchens, fire etc, are met

• Check that all components are fire rated

• Check that fresh air ventilation rates are sufficient to meet COSHH and WHO guidelines for CO exposure levels

Project specific checks & notes

Notes / Design file cross-reference

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43 KITCHEN EXTRACT

Design inputs • Details of cooking equipment to be installed, size, power

consumption, fuel etc • Volume of exhaust air required (if specified for specialist

applications)

Design information

• Architect drawings showing kitchen layout, including equipment positions, ceiling depths, etc

• Occupancy details • Fuel source and type ie gas, oil, electricity, solid fuels • Details of other heat sources in space • Whether ventilation is to be provided by means of a canopy or

ventilated ceiling • Type of filtration required • Allowable exhaust temperatures • Building and kitchen access details • Materials to be used for the fabrication of the canopies, ceilings

and ductwork • Planning and fire regulations See also: Ventilation requirements, Intake and discharge locations, Pressurised zones, Commissioning – ducted systems, Ductwork, Fans

Design outputs • Required extract (and supply) air flow rates • Layout drawings /schematic of kitchen ventilation scheme

showing position of canopies, extract flow rates, make up air, spigot connections, ductwork, dampers, fire suppression, ventilated ceilings etc

• Schedule of required extract and supply fans and motor drives, with fan duties and any requirements for drive adjustment, speed control and standby, giving sufficient information for manufacturer selection

• Schedule of canopy dimensions, materials and other components • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Cross check extract rates as air changes per hour • Check that local authority and Building Regulations relating to

kitchens, fire etc, are met • Check that all components are fire rated • Check that fresh air ventilation rates are sufficient to meet

COSHH and WHO guidelines for CO exposure levels

DESIGN WATCHPOINTS

Sizing & selection

1. Check that the local authority and Building Regulations relating to fire, basement kitchens, contaminants and odours are met.

2. Check that any HSE or statutory requirements for safe working conditions are met, eg check that fresh air ventilation rates are sufficient that CO exposure levels to which kitchen staff are subjected do not exceed COSHH limits of 300 ppm for 10 minutes, or WHO guidelines of 10 ppm as an average over 8 hours.

3. Check whether canopies or a ventilated ceiling will be used. 4. Design should be based on details of cooking equipment. 5. All components of the kitchen supply and extract systems, fans, ductwork

etc, should be fire rated. 6. Where canopy sizes are given use a minimum velocity of 0·35 m/s

through the canopy opening. 7. As a guide the extract rate should not be less than 17·5 l/s per m2 of floor

area, nor less than 20 to 30 air changes per hour. 8. Separate preparation and wash up facilities, stores etc for large kitchens

require a minimum of 10 air changes per hour. 9. Extract hoods must be placed directly above all kitchen cooking

appliances. 10. Check whether lighting is required within the canopy or ceiling and the

type of lighting required ie fluorescent tubes, bulkhead lights. 11. Check the type of filtration required, eg mesh filters, baffles filters,

cartridges, water wash or cold water mist. 12. Check that the extract fan and supply fans (if provided) are able to

overcome the system losses and deliver the required flow rates. Although filters should be regularly cleaned consider effect of dirty filter.

13. The high temperatures and grease content of the air encountered make it desirable to select bifurcated extract fans, ie fans with the motor out of the air stream.

14. Check that extract fans are selected with appropriate construction and materials ie able to withstand very high temperatures.

15. Extract fans should be sited carefully to direct hot air away from the rooftop.

16. Check that the discharge position does not create a noise or odour nuisance and is sited to avoid short-circuiting across to supply inlets.

Installation, operation & control

17. Consider carefully how make-up air is to be provided – from adjoining areas or via a designated supply system. For high extract rates it may be necessary to supply air adjacent to hoods to avoid excessive velocities in the occupied zone.

18. Where make up air is drawn from occupied spaces check this does not caused any noise and draught nuisance.

19. Where the kitchen forms part of a properly ventilated restaurant, the majority of replacement air may be drawn in from the dining area.

20. Velocities through serving hatches should not exceed 0·25 m/s. Where the serving hatches are small and replacement air is drawn from adjoining restaurants, permanent grilles sized to 1·0 to 1·5 m/s through the free area should be provided.

21. In serveries care must be taken to avoid premature cooling of food caused by excess air movement.

22. Where the kitchen is in an enclosed area, eg basement, a separate kitchen supply system should be provided.

23. Kitchens should be kept under negative pressure to avoid transfer of cooking odours etc. For sealed areas this is typically achieved by extracting 15% more air than is provided by mechanical supply.

24. Not all equipment will be operating all the time. Consider the impact on kitchen conditions and on ventilation for surrounding areas.

25. Check access requirements for installation of hoods/canopies to determine number of sections required for fabrication.

Access & maintenance

26. Check there is adequate access for cleaning and inspection of the whole kitchen extract system.

27. Avoid bends or dips which might collect residues. 28. Check that a residue trap is installed at the base of any vertical riser.

Economics

29. Consider the use of heat recovery from the exhaust air.

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44 PIPEWORK

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Details of fluid, eg water, glycol solution etc

• Design flow and return temperatures

• System mass flow rates

• Ambient conditions

Design outputs

Notes / Design file cross-reference

• Schematic of pipework layout and associated plant showing required flow rates

• Schedule of pipe sizes and lengths, materials, fittings, pumps, control valves etc

• Valve and flow measurement device schedule with design flow rates and pressure signals

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that both flow velocities and pressure drops are within acceptable limits

• Check that specified pipework, jointing methods and fittings are pressure rated above the maximum working pressure of the system and that they are suitable for the operating temperatures and resistant to chemical water treatment

Project specific checks & notes

Notes / Design file cross-reference

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© BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS DESIGN CHECKS FOR HVAC 99

44 PIPEWORK

Design inputs • Details of fluid, eg water, glycol solution etc • Design flow and return temperatures • System mass flow rates • Ambient conditions

Design information • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of plant rooms etc • Details of structural frame • Details of distribution space available • Pipe materials and insulation details • Limiting velocity and pressure loss/metre • Details and resistance coefficients for fittings etc • Appropriate system water temperature range • Maximum allowable system working pressure See also: Spatial co-ordination, Commissioning – piped systems, Flushing & chemical cleaning, Pump & pipe sizing, Pumps

Design outputs • Schematic of pipework layout and associated plant showing

required flow rates • Schedule of pipe sizes and lengths, materials, fittings, pumps,

control valves etc • Valve and flow measurement device schedule with design flow

rates and pressure signals • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that both flow velocities and pressure drops are within

acceptable limits • Check that specified pipework, jointing methods and fittings are

pressure rated above the maximum working pressure of the system and that they are suitable for the operating temperatures and resistant to chemical water treatment

DESIGN WATCHPOINTS

Sizing & selection (see also: Pump & pipe sizing)

1. Heating systems: decide appropriate system water temperature range for application, eg 70-95oC for LTHW, 100-120oC for MTHW and over 120oC for HTHW etc.

2. Chilled water systems: decide appropriate system water temperature range for application, eg 6-12oC for primary pipework and 10-15oC for secondary pipework for comfort cooling systems. Note that water temperatures should be higher (typically 11°C flow and 17°C return) in data hall cooling systems etc.

3. Design should minimise pipe and valve noise, erosion, installation and operating costs. Check that both flow velocities and pressure drops are within acceptable limits. (See Pump & pipe sizing.)

4. Check that the specified pipework, jointing methods and fittings are pressure rated above the maximum working pressure of the system, and that they are suitable for the operating temperatures and resistant to chemical water treatment.

5. Allow for future expansion of the pipework distribution system when required by provision of valved, plugged or capped tee connections.

6. Design closed circuit pipework using reverse return arrangements to facilitate commissioning, if cost and space allow.

Installation, operation & control

7. Check whether structural beams can be altered, drilled or cut when considering pipework routes.

8. Check that safety devices, ie pressure relief valves are fitted for sealed heating systems.

9. Hydronic systems should be designed with air vents to minimise the amount of entrained air in the piping circuit. Air vents should be placed on horizontal branches and tops of risers.

10. Double regulating valves and flow measurement devices should be provided at branches, sub-branches and terminal devices ie where there may be a pressure imbalance.

11. Flow measurement devices should be sited in locations giving manufacturer’s required straight pipe clear dimensions upstream and downstream.

12. Size double regulating valves such that they can take out residual pressures without having to be closed to a position less than 25% open.

13. Size flow measurement devices such that a pressure drop signal greater than 1kPA is achieved at the design flowrate to facilitate measurement.

14. The spacings between pipework supports should be adequate to prevent deflection of pipework. (Guidance is given in CIBSE B16.)

15. Design to allow for thermal expansion in pipework that is subjected to temperature changes. Bends, loops and various proprietary devices can be designed in to the system to absorb expansion.

16. Requirements for anchoring, expansion loops and slide points should be specified.

17. The pipework distribution system should be designed to allow distribution flow rate balancing for initial commissioning and rebalancing for future changes in operational requirements.

18. Provide test points across plant items for measurement of temperatures and pressures.

19. Check that pressure ratings of pipes, components and joints exceed maximum system operating pressures. Values available from British Standards and manufacturers of pipes or jointing materials.

20. Check that temperature ratings of pipes, components and joints exceed maximum system operating temperatures. Values available from pipe and component manufacturers.

21. Check that provision has been made for system commissioning. (See Commissioning – piped systems.)

Access & maintenance

22. Isolation valves should be provided to allow adequate maintenance of the system, eg to allow individual circuits to be maintained and equipment items to be replaced without full system shutdown.

23. Provide sufficient flushing and chemical cleaning supply points and drains. (See BSRIA AG 1/2001 Pre-commission cleaning of pipework systems.)

24. Drain points should be installed at all low points.

Economics

25. Design should minimise installation and operating costs.

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100 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

45 DUCTWORK

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Air volume flow rates in all main and branch ducts

• Supply air condition

• Supply and extract terminal positions and air flow rates

Design outputs

Notes / Design file cross-reference

• Total system resistance for use in leakage test assessments

• Schematic of ductwork layout and associated plant showing required flow rates

• Schedule of duct sizes, lengths, dampers, fittings etc

• Ductwork specification clauses providing information on materials, flow test points etc

• Statement of commissioning strategy

Key design checks

Notes / Design file cross-reference

• Check duct velocities are within acceptable limits to comply with noise criteria

• Check an appropriate duct construction standard has been specified

• Check there is sufficient space in any false ceilings, allowing for duct insulation and fixings

Project specific checks & notes

Notes / Design file cross-reference

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45 DUCTWORK

Design inputs • Air volume flow rates in all main and branch ducts • Supply air condition • Supply and extract terminal positions and air flow rates

Design information

• Architectural drawings for all zones including space plan and layout, floor to ceiling heights, position of plant rooms etc

• Details of structural frame • Details of distribution space available • Ceiling type and grid size • Information on other services within the ceiling void or service

risers • Information on fire standards and which walls and floors are fire

barriers See also: Spatial co-ordination, Pressurisation, Commissioning – ducted systems, Fan & duct sizing, Diffusers, Fans

Design outputs • Total system resistance for use in leakage test assessments • Schematic of ductwork layout and associated plant showing

required flow rates • Schedule of duct sizes, lengths, dampers, fittings etc • Ductwork specification clauses providing information on

materials, flow test points etc • Statement of commissioning strategy

Key design checks • Check duct velocities are within acceptable limits to comply with

noise criteria • Check an

appropriate duct construction standard has been specified

• Check there is sufficient space in any false ceilings, allowing for duct insulation and fixings

DESIGN WATCHPOINTS

Sizing & selection (see also: Fan & duct sizing)

1. Check an appropriate duct construction standard has been specified. HVCA DW144 Specification for Sheet Metal Ductwork is the most commonly specified in the UK (NB this replaces DW142). American SMACNA equivalents are available.

2. Check that correct ductwork pressure standards are specified for expected positive and negative pressures. HVCA DW144 provides static pressure ranges for low, medium and high pressure ducts. Construction standards will vary for each of these categories.

3. Check ductwork air leakage standards have been specified. 4. Specialised extract systems, eg industrial, laboratory etc will require

specialist input. 5. Ductwork layouts should be carefully considered to:

be as short as possible • account for physical constraints such as lift shafts and structural

columns and beams • minimise tight bends • reduce the need for builder’s work • be as self-balancing as possible to reduce damper pressure

drops. 6. Check that the air velocity at all points within the ductwork system is

within design limits and complies with relevant noise criteria. 7. Consider breakout noise and cross-talk and take appropriate measures if

necessary. Check layout makes best use of inherent (passive) attenuation.

8. Low frequency noise generation should be avoided. 9. Check that duct velocities are suitable for duct mounted accessories such

as attenuators, heater batteries, filters etc. 10. Check the temperatures of areas that the ductwork passes through to

see if insulation is required. 11. Check that ductwork insulation requirements have been adequately

specified. 12. Check crowded areas to avoid potential clashes with other services

distribution. 13. Check that the aspect ratio limit has not been exceeded at any point. 14. Use round ductwork wherever possible, eg for terminal branches, to

reduce costs, but ensure attenuation is not compromised. 15. Check that flexible ductwork requirements and locations are specified.

Flexible ductwork lengths should be kept as short and straight as possible and must comply with the specification limits. Flexible ductwork lengths should not be used for forming bends.

16. Check whether an overall positive building pressure is required and size the extract system accordingly.

17. Kitchen extract and smoke pressurisation systems should use fire rated ductwork.

18. Check whether any specialist protective finishes are required.

Installation, operation & control

19. Check the available space within the ceiling void to house the distribution system. Aspect ratios of ductwork may need to be altered to overcome local obstructions, and the depth or height required for diffusers and their plenum boxes can be considerable.

20. Check whether structural beams can be altered, drilled or cut when considering ductwork routes.

21. Check that all the ductwork dimensions have been included on the drawings.

22. Check that the ductwork can be supported in accordance with the specification ie that the structure is compatible to allow attachment of supports and that space allowance is sufficient.

23. Damper positions should be clearly identified. 24. Check that balancing dampers are in the optimum locations. 25. Check that fire/smoke dampers have been specified where ductwork

passes through fire barriers. 26. Check provision has been made for system commissioning. (See

Commissioning – ducted systems.)

Access & maintenance 27. Access hatches should be provided for all equipment within the ductwork

system such as filters, heater and cooling batteries and humidifiers. 28. Access hatches should be provided for all dampers - control, balancing

and fire. 29. Adequate provision should be made for future internal cleaning of the

ductwork system. 30. Check that access to all measuring points is provided to facilitate system

commissioning.

Economics 31. Design should minimise installation and operating costs. 32. Consider balance between higher velocity ductwork with consequent

space saving in relation to the need for greater attenuation and greater energy use.

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46 DIFFUSERS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Supply air volume flow rate for each space/zone

• Internal design conditions

• Supply air condition

• Noise rating for each zone

Design outputs

Notes / Design file cross-reference

• System design drawings showing diffuser positions, required supply air flow rates, throw and throw directions

• Diffuser schedule including pressure drop, air volume flow rates, NR rating, details of plenum box, neck size/nominal face size, method of support and finish etc

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check diffuser is compatible with the ceiling system

• Check diffuser performance in both heating and cooling modes

• Check coverage and throw

• Check the air velocity in occupied zone is acceptable

Project specific checks & notes

Notes / Design file cross-reference

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46 DIFFUSERS

Design inputs • Supply air volume flow rate for each space/zone • Internal design conditions • Supply air condition • Noise rating for each zone

Design information

• Planned ventilation strategy • Architectural drawings for all zones including space plan and

layout, floor to ceiling heights, position of partitions, doors, glazing and shading details etc

• Space usage, occupancy and details of heat sources • Ceiling type and grid size • Details of ceiling void depths • Lighting system and locations of luminaires • Details of any contaminant sources • Limiting velocity in occupied zone See also: Spatial co-ordination, Ductwork

Design outputs • System design drawings showing diffuser positions, required

supply air flow rates, throw and throw directions • Diffuser schedule including pressure drop, air volume flow rates,

NR rating, details of plenum box, neck size/nominal face size, method of support and finish etc

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check diffuser is compatible with the ceiling system • Check diffuser performance in both heating and cooling modes • Check coverage and throw • Check the air velocity in occupied zone is acceptable

DESIGN WATCHPOINTS

Sizing & selection

1. Select the diffusers carefully to avoid excessive noise generation and check that noise levels are acceptable for application. The noise levels resulting from a number of diffusers will be greater than that from a single one.

2. Check type of diffuser is appropriate for application, eg fixed geometry, adjustable, slot etc.

3. The ductwork connection onto the diffuser should be adequately sized to provide the correct velocity onto the unit as specified by the manufacturer.

4. Outlet velocity is critical to the correct performance of the diffuser. Excessive velocity will result in excessive noise and nuisance from draughts, whereas too low a velocity will result in short throws and poor air distribution.

5. Room dimensions must be assessed accurately in order to determine the throw required. This should be accurately matched with the throw available from diffuser options.

6. Check coverage and throw to ensure that no areas of excessive velocity or stagnation are created in occupied areas.

7. Consider carefully the required throw directions when considering diffuser type and positions, eg radial discharge, linear discharge or 1, 2 or 3 or 4-way throw.

8. Take into account diffusers at angles to each other as the throws can be affected.

9. When selecting diffusers, check the performance in both heating and cooling modes as the air flow is generally lower when heating and the throw may not be sufficient.

10. Check that diffusers selected for use with a VAV systems are suitable as the air volume through the diffuser may vary from 100% in full cooling down to 30%.

11. Avoid locating supply and extract/return diffusers too closely as it may result in short circuiting and the system under-performing.

12. Diffusers should be located to suit the occupancy and usage of the space. Supply diffusers should be located to avoid causing draughts and general nuisance.

13. Locate diffusers over glazing to deal with solar gains and cold draughts at the point of entry into the space.

14. Where possible locate supply and extract grilles/diffusers to deal with heat gains/contaminants at source.

Installation, operation & control

15. Check that the diffuser is compatible with the ceiling system. Select diffusers wherever possible that match the ceiling grid and layout.

16. Carefully check the available space within the ceiling void to house the diffuser as the height of the plenum box may be considerable.

17. Integrate the diffuser assembly with the constraints of the structure. The exact location of the diffusers may be dictated by ring beams or columns, etc.

18. Consider the arrangements for commissioning and adjusting the diffusers as this can be problematic once installed.

19. Flexible ductwork to diffusers should be kept as short as possible and should comply with specification limits, eg a maximum of 1m.

20. Provide details of plenum box requirements if required including whether it is top or side entry.

Access & maintenance

21. Access to ceiling systems should be considered and access hatches provided.

Economics

22. Selection of constant size diffusers for appearance can lead to oversized diffusers and “dumping” effects in some instances.

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47 PUMPS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Details of fluid, eg water, glycol solution, oil etc

• Design flow and return temperatures

• System mass flow rates

• System pressure drops

• Ambient conditions including surrounding air temperature

Design outputs

Notes / Design file cross-reference

• Schematic of pump layout installation, mounting, pipework connections etc

• Schedule of pump types, flow rates, pressures and efficiencies including motor requirements, drive type and adjustment, speed control and stand by provision

• Media details: water/refrigerant, temperature etc

• Schedule of electricity supply requirements

Key design checks

Notes / Design file cross-reference

• Check whether high efficiency or variable speed pumps would be appropriate

• Check pump is suitable for media to be pumped

• Check the minimum required net positive suction head (NPSH)

• Consider any need for duty and standby pump provision

• Check the pump orientation is correct

Project specific checks & notes

Notes / Design file cross-reference

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47 PUMPS

Design inputs • Details of fluid, eg water, glycol solution, oil etc • Design flow and return temperatures • System mass flow rates • System pressure drops • Ambient conditions including surrounding air temperature

Design information

• Details of pipework system layout including pipe lengths and fittings, materials and insulation details

• Details of possible locations, eg plant room location and layout, space available for installation of pumps and drives, permissible weights

• Criticality of system served • Electrical supply – 1 or 3 phase • Pump type – centrifugal – end suction, in line, immersed rotor,

displacement – helical or rotary • Drive type – belt or direct • Noise criteria See also: Commissioning – piped systems, Pump & pipe sizing, Pipework

Design outputs • Schematic of pump layout installation, mounting, pipework

connections etc • Schedule of pump types, flow rates, pressures and efficiencies

including motor requirements, drive type and adjustment, speed control and stand by provision

• Media details – water/refrigerant, temperature etc • Schedule of electricity supply requirements

Key design checks • Check whether high efficiency or variable speed pumps would be

appropriate • Check pump is suitable for the media to be pumped • Check the minimum required net positive suction head (NPSH) • Consider any need for duty and standby pump provision • Check the pump orientation is correct

DESIGN WATCHPOINTS

Sizing & selection (see also: Pump & pipe sizing)

1. Select pump characteristic curve(s) to avoid unstable operation over design range ie avoid flat region of curve.

2. Oversized pumps in terms of excess pressure can waste energy. Absorbing excess pressure/flow by throttling is very energy inefficient. Consider the use of pumps that allow impeller or belt drive change or consider the use of variable speed pumps.

3. Variable speed pumps and motors should always be first choice for variable flow systems as this enables the varying system requirements to be met effectively. Check that the variable flow pump does not have to go below minimum turndown - check manufacturer’s data.

4. For variable speed pumping consider performance at two operating points ie at full load and the worst case part load flow rate and pressure requirement.

5. For variable speed pumping check that the combined pump curve is steep and within anticipated range of system curves.

6. Most variable speed pumps come with integrated motors and control. Where this is not the case for variable speed pumping the method of control (ie inverters etc) should be carefully matched to pump motors.

7. Where possible choose ‘high efficiency’ pumps and ensure that the operating efficiency of the pump is maximised at the most frequent operating condition.

8. Where possible select ‘high efficiency’ motor drives. 9. Check that there will be positive pressure in the pump by checking the

net positive suction head (NPSH) available against the minimum NPSH required - check pump manufacturer information. Negative pressure can cause cavitation to occur which can cause considerable damage to the impeller.

10. Check NPSH and NRVs (non return valves) for open circuit pumps, eg cooling towers.

11. Check the pump is suitable for the media to be pumped ie water or refrigerant (some pumps will not pump ethylene glycol for example).

12. Check all pump components and materials are suitable for application and media, including bearings, glands etc.

Installation, operation & control

13. Consider the need for duty and standby pump provision. Auto changeover is commonly used with pump failure alarms linked to control box or BMS system. (See also point 19.)

14. Check the pump orientation is correct. 15. Provide isolating valves at both suction and discharge sides to allow

pump to be isolated/removed/replaced. Allow adequate access for pump removal.

16. Check the correct glands are used and that the glands are suitable for use during any system chemical cleaning process.

17. Consider whether flexible or solid connections are most appropriate. 18. Consider noise levels. Adequate provision should be made to reduce

vibration and noise generation, including anti-vibration mountings and/or inertia bases where appropriate.

Access & maintenance

19. Consider pump operation and control for duty and standby pumps to keep both maintained in good running order, eg by use of autoshare.

20. Check that pumps are not installed at the lowest point of the system and are protected by a strainer to prevent ingress of dirt.

21. Pumps should be raised above ground level to facilitate draining and a drain point and vent provided.

22. Pressure gauges should be fitted at the suction and discharge points of the pump.

23. Ensure correct IP (Ingress Protection) rating for water tightness and dust-tightness is specified for electrical connections.

24. Check that local electrical isolation is possible. 25. Safety guards and an emergency stop facility should be provided for

pump and motor moving parts.

Economics

26. Check that the most efficient pump is selected (see pts 2 & 3). 27. Consider relative whole life costs and merits of different pump types ie

belt driven, direct coupled etc.

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48 FANS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Design air volume flow rate

• Supply air condition

• System pressure drop

• Ambient conditions, including barometric pressure

• Noise criteria

Design outputs

Notes / Design file cross-reference

• Schematic of fan layout installation, mounting, connection to ductwork, discharge direction, drive arrangement etc

• Schedule of fan types, flow rates and system pressures including motor requirements, drive type and adjustment, speed control, standby provision etc

• Schedule of fan ancillary items including fan bearings, drive guards, variable inlet guide vanes or outlet dampers, anti-vibration mounts, suction and discharge connections etc

• Schedule of electricity supply requirements

Key design checks

Notes / Design file cross-reference

• Check that fan performance matches actual system pressure/volume characteristics

• Check that the proposed fan location is suitable

• Check that the condition of entering air is acceptable

• Check suitable allowance has been made for possible changes in system characteristics

Project specific checks & notes

Notes / Design file cross-reference

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48 FANS

Design inputs • Design air volume flow rate • Supply air condition • System pressure drop • Ambient conditions, including barometric pressure • Noise criteria

Design information • Details of ductwork system layout including duct lengths and

fittings, materials and insulation details • Details of possible locations, eg, plant room location and layout,

space available for installation of fan and drives, permissible weights

• Criticality of system served • Electrical supply – 1 or 3 phase • Fan selection criteria • Application, eg fan coil unit, air conditioning unit, mechanical

ventilation for boiler plant room, mechanical draught for boilers, cooling towers, etc

See also: Ventilation requirements, Pressurised zones, Intake and discharge locations, Commissioning – ducted systems, Fan & duct sizing, Ductwork, Air handling units

Design outputs • Schematic of fan layout installation, mounting, connection to

ductwork, discharge direction, drive arrangement etc • Schedule of fan types, flow rates and system pressures including

motor requirements, drive type and adjustment, speed control and standby provision

• Schedule of fan ancillary items including fan bearings, drive guards, variable inlet guide vanes or outlet dampers, anti-vibration mounts, suction and discharge connections etc

• Schedule of electricity supply requirements

Key design checks • Check that fan performance matches actual system

pressure/volume characteristics • Check that the proposed fan location is

suitable • Check that the condition of entering air is

acceptable • Check suitable allowance has been made

for possible changes in system characteristics

DESIGN WATCHPOINTS

Sizing & selection (see also: Fan & duct sizing)

1. Review Building Regulations requirements. 2. Check that fan performance matches actual system pressure/volume

characteristics. 3. Allow for the pressure drop through the fan connections on both suction

and discharge sides including intake grilles etc. Flexible connections can have relatively high pressure drops.

4. Check that fan location is suitable, ie does not cause noise problems, provides acceptable quality of intake air for a supply fan and does not cause pollution or cross-circuiting from an exhaust fan outlet.

5. Consider fan location carefully to check there is adequate space for connections on both suction and discharge without sharp bends or obstructions that could affect fan performance.

6. Check that both the quality and condition of entering air is acceptable ie free from dirt, corrosive fumes or inflammable gases and acceptable dry bulb temperature, moisture content, air density.

7. Select fan type to suit application. Consider fan efficiency, noise level, pressure developed, power characteristic, size etc and any need for variable flow, eg for comfort applications centrifugal fans have a wide range of quiet efficient operations at relatively high pressures and air flow can be varied by simple drive adjustments.

8. For non comfort applications, select a fan suitable for the application and working environment, eg high temperature rated for smoke extract, bifurcated for battery rooms/fume extract etc.

9. Centrifugal fans with forward curved blades will run at relatively low speed in comparison with other types for the same duty.

Installation, operation & control

10. Check suitable allowance has been made for possible changes in system characteristics, eg for variable volume units or dirty filters.

11. Consider any need for duty and standby fan provision, eg toilet extract, critical systems etc. Auto-changeover is commonly used with fan failure alarms linked to control box or BMS system.

12. Consider noise levels. Adequate provision should be made to reduce vibration and noise generation, including anti-vibration mountings and/or inertia bases where appropriate.

13. Fans within plenums and cabinets or in the immediate vicinity of a wall should be located so that air flow into the fan inlet is unobstructed. Fan performance will be reduced significantly if the space between fan inlet and enclosure is too restrictive.

14. For in line fans air should enter the fan uniformly in an axial direction without spin. Take care with the position of fittings, eg an elbow downstream in close proximity to the fan inlet will result in turbulence, uneven flow and reduced fan performance.

15. Check that the system connections on fan outlet do not obstruct air flow or cause turbulence. Poor outlet connections will reduce fan performance.

16. If a plenum chamber is to be used with an axial flow fan, use a bellmouth inlet to reduce the losses.

17. Check that anti-vibration mountings for fans are equally loaded. 18. Silencers should not be coupled to the fan directly especially if there are

splitter silencers.

Access & maintenance

19. Check adequate space is allowed for maintenance and replacement. 20. Check that local electrical isolation is possible. 21. Safety guards and an emergency stop facility should be provided for fan

and motor moving parts.

Economics

22. High velocity systems result in greater system resistance, higher losses and larger fans. Low velocity systems result in lower losses, smaller fans and a more effective design.

23. Consider most efficient way to match fan performance to system requirements and provide volume control. Varying blade pitch (axial fans), varying fan speed or using inlet guide vanes are more energy efficient than dampers.

24. Check that specific fan power does not exceed Building Regulation requirements (Part L).

25. Select fans for high operating efficiency. Additional capital costs are generally recovered very quickly by energy savings in operation. A good practice guideline for fan power for offices is less than 2W/ls-1.

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49 BOILERS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Heat loads

• DHWS requirement

• Required flow and return temperatures & whether LTHW, MTHW, HTHW or steam

• System operating pressure

• Minimum flow rate

• Static head at boiler

• Test pressure ratings

Design outputs

Notes / Design file cross-reference

• Schematic of boiler layout installation, pipework connections etc

• Schedule of boiler types, sizes, rated output, flow rates, pressures, temperatures, burner type, turndown required and stand by provision

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check boiler thermal efficiency at full & part load

• Check boiler combustion efficiency at full & part load

• Check that Nox levels are acceptable

• Check that there is adequate combustion air make-up

Project specific checks & notes

Notes / Design file cross-reference

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49 BOILERS

Design inputs • Heat loads • DHWS requirement • Required flow and return temperatures & whether LTHW,

MTHW, HTHW or steam • System operating pressure • Minimum flow rate • Static head at boiler • Test pressure ratings

Design information

• Details of plant room location and layout, space available, permissible weights, access

• Fuel type, availability and any storage required (eg oil) • Building usage: continuous /intermittent. • Electrical supply - 1 or 3-phase • Ratio of summer to winter load ie DHWS load to total • Client requirements for standby provision • Noise criteria See also: Plant space allowance, Pumps, Oil storage tanks, HVAC control systems

Design outputs • Schematic of boiler layout installation, pipework connections etc • Schedule of boiler types, sizes, rated output, flow rates, pressures

and temperatures, including burner type, turndown required and stand by provision

• Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check boiler thermal efficiency at full and part load • Check boiler combustion efficiency at full and part load • Check that Nox levels are acceptable • Check that there is adequate combustion air make-up

DESIGN WATCHPOINTS

Sizing & selection 1. Comply with relevant regulations, eg Building Regulations, CDM, Means

of Escape, Health & Safety at Work etc. 2. Consider fuel requirements and check fuel source, availability and

storage requirements, eg whether bulk fuel storage is needed. 3. If gas fired boilers are used check whether gas pressure is adequate or

whether a gas booster is needed. 4. Consider ventilation requirements. Check whether air flow into the boiler

room is sufficient for combustion and boiler room ventilation or whether a mechanical ventilation system will be required. Check there is adequate provision for combustion air make-up.

5. Check that pre-heat requirements have been considered and that the boiler(s) are sized to take account of the pre-heat period.

6. Consider part load operation when selecting boiler / no. of modules etc to optimise performance and maximise part load efficiency.

7. Check turndown requirements, eg on/off, high/low, fully modulating. 8. Check system operating pressure is suitable, ie with no risk of flash

steam formation. 9. Check flue is an appropriate size and type for the selected boiler(s). 10. Check whether draught diverters are needed. 11. Check that the flue gas temperature is acceptable and will not cause

condensation/corrosion problems. 12. Check whether back end corrosion protection is necessary, eg bypass or

shunt pump at start up. 13. For condensing boilers :

• consider and provide for drainage of condensate • avoid positioning flue where surrounding equipment or fabric can

be damaged by condensate • check that radiators and pipework have been sized on lower

temperatures and higher differentials • maximise the length of time that the return water temperature

allows condensing of boiler exhaust gases. 14. For condensing boilers a system to allow condensing at all times would

result in larger emitters with low flows which may not be cost effective and could cause commissioning problems.

15. To improve the efficiency of condensing boilers connect the condensing coil to a low temperature application, eg underfloor heating, fresh air preheat etc.

Installation, operation & control 16. Check that the floor loadings are acceptable. 17. A three way cock should be fitted on the boiler return connection. This

means it is impossible to trap water inside the boiler as the boiler can only be isolated by opening the three-way cock to drain.

18. Each boiler, or group of boilers in a modular system, should be fitted with safety valve, pressure and temperature gauges and drain valve.

19. MTHW/HTHW system drain valve discharges should be taken to a safe discharge location.

20. The boiler safety pressure relief valve should be fitted in an appropriate location where it cannot be isolated from the boiler. Safety valves for MTHW/HTHW systems should be vented to atmosphere in safe locations.

21. Check that each boiler in a multi or modular boiler installation can be isolated from the others by isolating valves and by switches in the electrical and fuel lines.

22. Consider control requirements for modular and multi-boiler installations at an early stage and check that the system matches the control design.

23. Consider the required fire alarm interface and safety shutdown features and procedures.

24. Check that adequate controls/BMS interface provided. 25. Boilers can be noisy – check that sound levels are acceptable,

particularly for sensitive locations, eg hotels.

Access & maintenance 26. Check the access requirements for getting the boiler(s) into the plant

room and for removal for replacement. 27. Consider optimum layout of boilers, pumps and pressurisation units. 28. Allow sufficient access to the boiler(s) for maintenance, eg allow

sufficient space for burner door swing.

Economics 29. Review life expectancy. Lightweight, low water content boilers generally

have much shorter life but have lower initial cost. 30. Consider whole life costs when selecting boilers or modules. 31. Review client requirement for standby and ensure boiler selection

achieves optimum performance and most cost effective standby.

Flue headerFlue header

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50 AIR HANDLING UNITS (AHUS)

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone heating and cooling loads

• Fresh air requirements

• Fresh air supply condition

• Design air supply condition

• Fan gains

Design outputs

Notes / Design file cross-reference

• Schematic of AHU layout installation, pipework & ductwork connections etc

• Schedule of AHU types, sizes, rated output, flow rates, heating and cooling duties etc

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check specified filtration standards are sufficient

• Check attenuation requirements and whether special acoustic measures are required

• Allow for heat gain across fan

• Check energy use targets are met

Project specific checks & notes

Notes / Design file cross-reference

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50 AIR HANDLING UNITS (AHUS)

Design inputs

• Zone heating and cooling loads • Fresh air requirements • Fresh air supply condition • Design air supply condition • Fan gains

Design information

• Details of plant room location and layout, space available, permissible weights, access

• Type of heat recovery device if any • Position of fresh air intake/discharge louvre • Air leakage class of casing - as Eurovent • Noise criteria See also: Plant space allowance, Intake & discharge locations, Fans, Humidifiers, Heat recovery systems, HVAC control systems

Design outputs • Schematic of AHU layout installation, pipework & ductwork

connections etc • Schedule of AHU types, sizes, rated output, flow rates, heating

and cooling duties etc • Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check specified filtration standards are sufficient • Check attenuation requirements and whether special acoustic

measures are required • Allow for heat gain across fan • Check energy use targets are met

DESIGN WATCHPOINTS

Sizing & selection 1. Check any planning restrictions on roof mounted plant. 2. Check that the coil contact factors correspond with the heating and

cooling supply calculations. 3. Allow for heat gains across the fan/ductwork. 4. Check that pressure drops used for design allow for the actual duct

configuration of inlet and discharge duct connections as selected. 5. Check velocity and pressure drop through the AHU is not excessive. 6. Check whether heat/cooling recovery can be included. Check that any

heat recovery system is appropriate for the system (eg enthalpy recovery for full fresh air systems) and efficient.

7. Consider whether ran and standby fans/motors are required. 8. For efficient operation use high efficiency fans and motor drives and

include a fully variable output facility. 9. Check requirements for humidification/dehumidification. High space

humidity levels can occur if cooling is used without de-humidification, consider face and by-pass control on cooling coils to assist this.

10. Check that specified filtration standards are sufficient and that the location of the filters, eg, before or after fan, are suitable to avoid leakage into system of unfiltered air.

11. Check the AHU intake is in an appropriate position, eg remote from the exhaust and away from any sources of fumes etc.

12. The intake duct and connection should be of an adequate size to allow full fresh air under free cooling conditions.

13. The recirculation duct connection should be of an adequate size to allow full recirculation under start up.

14. If multiple heating or cooling coils are used check whether a common connection is required.

15. Assess the need for moisture eliminators when using humidifiers. 16. Check sound attenuator requirements. Selected fan noise spectrum and

specified attenuator noise spectrum should both be given. 17. Check noise levels are acceptable both in terms of system noise and

noise breakout to plantroom. 18. Check whether the AHU construction details prevent the risk of

condensation on the frame of the AHU. 19. Consider the use of ‘flat pack’ type units if space is limited.

Installation, operation & control 20. For externally located AHUs check the appropriate specification been

selected with regard to weather resistant materials. 21. Check floor loadings are acceptable for roofs and intermediate floors. 22. Condensate drains should be provided for any heat recovery units.

23. Check that condensate from cooling coils can be adequately collected/run to drain, eg by the use of drain pans.

24. Check that condensate traps are suitable for operating pressures, eg have sufficient depth available to avoid being sucked dry by the fan.

25. Provide vents and drains for the tubes of hot water heater and cooler batteries.

26. Provide air breaks on drains to avoid contamination of supply air. 27. Provide a high temperature cut out for electric heater batteries. 28. Electric heater battery control should be interlocked with the fan and a

flow proving switch so it cannot operate if the fan is not running. 29. Gas heater batteries burners should be interlocked with the fan and a

flow proving switch so they cannot operate if the fan is not running. 30. Check it is clear whether control dampers on incoming/outgoing & mixing

dampers are provided by AHU supplier or ductwork supplier. 31. When supplying fresh air through an AHU, provide measures to protect

unit in winter at low ambient conditions and avoid filter or coil damage through freezing. Where frost coils are used as pre-heaters prior to the air entering other AHU components, the controls must be configured to protect the frost coil if water filled. This can be done with two stage protection ie the circulating pump is brought on when the ambient temperature drops to, eg 50C, and the boiler plant brought on if the ambient continues to drop to, eg 20C.

Access & maintenance 32. Check access requirements for getting the AHU into the plant room or on

the roof etc and consider access needs for replacement. 33. Allow sufficient access to the AHU for maintenance including the removal

of fans, cooling/heating coils, filters etc. (a rule of thumb is AHU width plus 150mm).

34. Check if a bulkhead light is required. 35. Check whether vision panels are required for the AHU. 36. Check that local electrical isolation is possible. 37. Safety guards and an emergency stop facility should be provided for fan

and motor moving parts. 38. Provide safety interlock on access door for gas fired heater batteries.

Economics 39. Consider the additional cost of improved AHU acoustics versus reduced

downstream attenuation to arrive at the optimum solution. 40. Cooling is expensive therefore any measures that can be taken to reduce

loads ie reduce heat gains, should be considered and the client advised accordingly.

41. Dehumidification and humidification are expensive and tight humidity control can add substantially to system cost. (See Humidifiers.)

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51 HUMIDIFIERS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Internal design conditions - temperature and humidity

• Design air supply condition

• Fresh air supply condition

• Local external design conditions - temperature and humidity

• Percentage outdoor air in the ventilation system

• Total air flow rate

• Infiltration rate to the conditioned space

Design outputs

Notes / Design file cross-reference

• Schematic of humidifier layout installation and water supply services

• Schedule of humidifier sizes and duties

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check design complies with legionella legislation and guidance

• Check humidity load takes into account humidity sources in conditioned space and any losses

• Check control requirements and energy usage

• Check that the humidifier type selected is appropriate for the application

Project specific checks & notes

Notes / Design file cross-reference

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51 HUMIDIFIERS

Design inputs • Internal design conditions - temperature and humidity • Design air supply condition • Fresh air supply condition • Local external design conditions - temperature and humidity. • Percentage outdoor air in the ventilation system • Total air flow rate • Infiltration rate to the conditioned space

Design information

• Details of plant room location and layout, space available, permissible weights, access

• Analysis of humidification requirements and occurrence • Building and space usage • Annual hours of operation • Humidity sources in the conditioned space, eg occupancy,

manufacturing or processing activities • Details of any dehumidification in conditioned space, eg by air

conditioning systems, dehumidifiers etc • Details of available water supply and quality • Required control precision See also: Internal design criteria, Air handling units, HVAC control systems

Design outputs • Schematic of humidifier layout installation and water supply

services • Schedule of humidifier sizes and duties • Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check design complies with legionella legislation and guidance • Check that humidity load takes into account humidity sources in

the conditioned space and any losses • Check control requirements and energy usage • Check that the humidifier type selected is appropriate for the

application

DESIGN WATCHPOINTS

Sizing & selection

1. Ensure installation complies with relevant legionella legislation and that design follows good practice guidelines on reduction/avoidance of legionellosis. A good practice guideline to reduce risk is to specify humidifiers that do not create a spray, eg steam or evaporative humidifiers.

2. Check requirements for humidification for both summer and winter and the control precision required.

3. Consider usage of space to assess any additional sources of humidity, eg sinks, coffee machines, microwaves.

4. Check that the humidity load for the building takes into account additional humidity sources in the conditioned space and any losses from the space including infiltration (ie humidifier load = sources + losses).

5. Check that the humidifier type selected is appropriate for the application, eg steam, ultrasonic etc.

6. Check whether humidification occurs predominantly while the space is being heated or cooled as this influences the choice of humidifier.

7. Design should avoid excess misting or low air supply air temperatures that can result in incomplete evaporation and puddling in the ductwork. Consider the installation of eliminator plates or sizing the chamber generously.

8. In ducted systems the air velocity at the position of moisture absorption should not exceed 5 m/s to minimise carry-over.

9. Check face velocity required for humidifier. Baffles or expansions can be used to ensure ideal air velocities.

10. With ultrasonic humidifiers condensation will result if the supply air upstream of the humidifier is too cold.

11. Ultrasonic humidifiers absorb energy from the supply air as it evaporates and provides a secondary cooling effect. This can be beneficial where simultaneous humidification and air conditioning are required, but detrimental when heating and humidifying.

Installation, operation & control

12. Ultrasonic humidifiers require a supply of mineral-free, deionised water. 13. Ultrasonic humidifiers in air supply ducts should be installed at least 3-4

metres upstream of any turns or obstructions in the ductwork to allow the mist time to evaporate. Installations close to bends or obstructions will result in condensation on the duct wall.

14. Steam humidifiers do not need to absorb heat from the supply air to evaporate a cool mist and can therefore be installed within 1 metre of unobstructed ductwork.

15. A non-corrosive condensate drip pan should be installed to prevent corrosion.

Access & maintenance

16. Allow adequate access to humidifier for maintenance. 17. Check that local electrical isolation is possible.

Economics

18. Electrically powered steam humidifiers have significant energy consumption.

19. Dehumidification and humidification are expensive and tight humidity control can therefore add substantially to system cost as dehumidification requires increased cooling coil sizing and re-heat facilities, and humidification requires additional plant, energy and water supplies to generate the moisture. Consider what level of humidity control is appropriate to the application.

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52 CHILLERS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Total cooling load

• Required chilled water on/off conditions

• Type of refrigerant

• Ambient design conditions and extremes

Design outputs

Notes / Design file cross-reference

• Schematic of chiller layout installation, pipework connections etc

• Schedule of chiller types, sizes, refrigerant, rated output, design chilled water flow (outlet) and return (inlet) temperatures and flow rates, pressure drop and stand by provision

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check part load performance

• Check refrigerant type meets client approval

• Check electric cables are sized for maximum possible loading

Project specific checks & notes

Notes / Design file cross-reference

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52 CHILLERS

Design inputs • Total cooling load • Required chilled water on/off conditions • Type of refrigerant • Ambient design conditions and extremes

Design information

• Details of plant room location and layout, space available, permissible weights, access

• Building usage: continuous /intermittent. • Building load profile • Number of hours run per year • Size of water buffer for system • Type of cooling application - equipment or comfort • Criticality of cooling • Client requirements for standby and future needs • Noise criteria • Electrical supply – 1 or 3-phase • Maximum water pressure See also : Plant space allowance, Air handling units, Cooling towers, HVAC control systems

Design outputs • Schematic of chiller layout installation, pipework connections etc • Schedule of chiller types, sizes, refrigerant, rated output, design

chilled water flow (outlet) and return (inlet) temperatures and flow rates, pressure drop and stand by provision

• Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check part load performance • Check refrigerant type meets client approval • Check electric cables are sized for maximum possible loading

DESIGN WATCHPOINTS

Sizing & selection

1. Check at an early stage that refrigerant type meets client approval. 2. When selecting chiller consider product availability, reliability, past

performance and spares availability. 3. Check that the chiller type selected is appropriate for the application,

location and space available, eg screw, centrifugal, absorption, reciprocal, packaged, etc. Consider method of heat rejection - air cooled, with cooling tower etc.

4. Check that the design flow rate through chiller(s) matches chilled water system design flow rate, and check that on and off temperatures for the chiller are the same as required for the system the chiller is serving.

5. Check design takes into account ambient and extreme conditions at design location, eg temperatures at roof level may be higher than ambient design temperatures.

6. Check that the design noise levels from the chiller(s) are acceptable taking into account any locally occupied areas. Check vibration levels acceptable.

7. Check whether night set back is required for noise reasons. 8. Consider part load operation when selecting chiller(s) to optimise

performance and maximise part load efficiency. 9. Check that heat can be properly rejected. 10. Check commonality of design information if using remote air cooled

condensers from a different supplier to the chiller. 11. Check reduction in capacity if using glycol mixtures. 12. Provide adequate filtration of chilled water - particularly if plate heat

exchangers are used. 13. For coastal sites, check appropriate coatings and materials are specified

for externally located packaged chillers (salty atmosphere can rapidly corrode air cooled condensers).

14. Check frost protection requirements. 15. External air cooled condensers should be corrosion resistant and have

weather proof motors. 16. Fan motors of induced draught condensers should have a suitable

protective treatment if mounted in the air stream.

Installation, operation & control

17. Check that the floor loadings are acceptable for both roof and intermediate floor locations.

18. Check there is adequate space around air cooled condensers to permit unimpeded air flow, particularly with multiple chiller installations.

19. Check piping configuration & control for multiple chillers to achieve an acceptable off condition and avoid temperature dilution, ie avoid mixing chilled water with return water circulating through not-in-use chillers to prevent an unacceptable mixed condition.

20. Check that the system capacity is adequate to ensure start/stop and cylinder switching frequencies are kept within the limits of chiller design. If inadequate then a buffer vessel will be required.

21. Check that a suitable control/BMS interface is fitted if appropriate. 22. Stop valves and refrigerant pressure gauges should be fitted on

compressor refrigerant suction and discharge connections. 23. Suitable safety and control devices should be fitted to each chiller, eg low

chilled water flow rate safety device, chilled water low temperature thermostat etc.

24. Check requirement for refrigerant leakage alarm system. 25. Consider required electrical provision - information will be needed on

maximum start currents, run currents, starts per hour etc. 26. Check whether HV or LV starters are required. 27. Provide a permanent separate electric supply for crankcase heater.

Access & maintenance

28. Provide adequate maintenance access, including tube withdrawal. 29. Provide adequate access for installation and replacement. Consider

whether plant will be broken down into components and taken down in lift or whether crane access will be needed.

30. Check that local electrical isolation is possible and provide adequate entry access for electric cable.

Economics

31. Consider whole life costs when selecting chillers to determine optimum choice.

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53 COOLING TOWERS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Overall heat rejection load - this requires details of the building cooling load and chiller performance data

• Water condition on/off chiller

• Ambient conditions including wet bulb temperature

Design outputs

Notes / Design file cross-reference

• Schematic of cooling tower layout installation, pipework connections etc

• Schedule of cooling tower types, sizes, rated output, condenser water flow (outlet) and return (inlet) temperatures and flow rates, pressure drop, required heat rejection performance etc

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

• Method of chemical/biocide dosing

Key design checks

Notes / Design file cross-reference

• Check that installation complies with legionella legislation and follows good design practice guidelines

• Check that suitable water treatment provision has been made

Project specific checks & notes

Notes / Design file cross-reference

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53 COOLING TOWERS

Design inputs • Overall heat rejection load - this requires details of the building

cooling load and chiller performance data • Water condition on/off chiller • Ambient conditions including wet bulb temperature

Design information

• Details of possible locations, eg plant room location and layout, space available, permissible weights, access

• Information from chiller manufacturer on chiller performance and COP

• Weather data for site particularly information on prevailing wind direction and strength

• Client future cooling need requirements See also : Plant space allowance, Pumps, Air handling units, Chillers, Heat recovery systems, Waterside free cooling

Design outputs • Schematic of cooling tower layout installation, pipework

connections etc • Schedule of cooling tower types, sizes, rated output, condenser

water flow (outlet) and return (inlet) temperatures and flow rates, pressure drop, required heat rejection performance etc

• Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses • Method of chemical/biocide dosing

Key design checks • Check that installation complies with

legionella legislation and follows good design practice guidelines

• Check that suitable water treatment provision has been made

DESIGN WATCHPOINTS

Sizing & selection

1. Ensure installation complies with relevant legionella legislation and that design follows good practice guidelines on reduction/avoidance of legionellosis.

2. Ensure specific and reportable facilities are provided to ensure safety against legionella at all times regardless of condition of maintenance, ie a fail safe design.

3. Select appropriate type of cooling tower for the application, eg forced/induced draught, open/closed circuit etc.

4. Select location carefully so that the air discharge, which could be contaminated, is not carried into air intakes, or into openable windows or across public access routes.

5. Check whether any local industry creates significant amounts of dust or fumes (air borne dust will be rapidly washed from the air and can collect in the cooling tower, eg cement dust from a cement works.) This may make the use of cooling towers non-viable.

6. Cooling towers should be sited away from fresh air intakes and flue outlets.

7. Check that adequate space is available to prevent recirculation of intake air.

8. Check location of tower in relation to pumps to ensure flooded suction. 9. Check that the design noise levels from the cooling tower(s) are

acceptable for the proposed location taking into account any locally occupied areas.

10. Check water supply quality and check that a suitable filtration system is selected to suit chiller condenser.

Installation, operation & control

11. Check wintertime safety for the installation. Consider any frost protection requirements.

12. Check power supply and control interlocks with chillers are satisfactory. 13. Check operating efficiency and water consumption.

14. A water meter should be installed to measure make up water and be suitable for BMS interface.

15. Consider the use of plate heat exchangers to hydraulically isolate chillers from cooling towers, to prevent dirty water from cooling tower fouling the condenser circuit. Alternatively consider the use of an indirect cooling tower.

Access & maintenance 16. Consider and specify water treatment requirements and check that

construction of tower is suitable for planned regime. 17. Provide adequate access for maintenance - check the cooling tower

housing offers full and easy access. 18. Provide adequate access for installation and replacement. Consider

whether roof top plant will be broken down into components and taken down in lift or whether crane access will be needed.

19. Check there is adequate access to the plate heat exchanger, if used, for cleaning and other maintenance.

20. Consider including a strainer in the cooling tower circuit. 21. Any part of the system open to atmosphere should be fitted with a leaf or

rubbish protection grid. 22. Check the cooling tower fill pack is easily removable and easy to clean. 23. Provide sufficient space for removal of fan shaft. 24. Check that local electrical isolation is possible. 25. Safety guards and an emergency stop facility should be provided for

pump, fan and motor moving parts.

Economics 26. Consider whether provision for free cooling using the cooling towers can

be made. 27. Consider specifying inverters for the cooling tower fans (these can make

worthwhile energy savings). 28. Consider whole life costs and relative merits of different cooling tower

types, eg closed cell versus open cooling towers to determine optimum choice.

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54 HEAT RECOVERY SYSTEMS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Zone & building heating and cooling loads

• Internal design conditions

• Fresh air supply condition

• Supply air condition

• Exhaust air condition

• Supply and exhaust flow rates and velocities

Design outputs

Notes / Design file cross-reference

• Heat recovery strategy document

• Schematic of heat recovery system installation, showing position and connections to HVAC system

• Schedule of heat recovery equipment types and sizes with performance data, eg heat recovery efficiency, face velocity etc, and operating conditions, eg supply and return conditions

• Electrical requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that the additional resistance of the heat exchange devices within the air stream has been included for pump and fan selection

• Check whether latent heat recovery is required

Project specific checks & notes

Notes / Design file cross-reference

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54 HEAT RECOVERY SYSTEMS

Design inputs • Zone & building heating and cooling loads • Internal design conditions • Fresh air supply condition • Supply air condition • Exhaust air condition • Supply and exhaust flow rates and velocities

Design information

• Details of possible locations, eg plant room location and layout, space available, permissible weights, access

• Details of planned HVAC system • Ceiling type and grid size • Noise criteria See also: Pumps, Fans, Air handling units

Design outputs • Heat recovery strategy document • Schematic of heat recovery system installation, showing position

and connections to HVAC system • Schedule of heat recovery equipment types and sizes with

performance data, eg heat recovery efficiency, face velocity etc, and operating conditions, eg supply and return conditions

• Electrical requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that the additional

resistance of the heat exchange devices within the air stream has been included for pump and fan selection

• Check whether latent heat recovery is required

DESIGN WATCHPOINTS

Sizing & selection

1. Heat recovery should be considered at an early design stage as system layouts will need to take into account heat recovery requirements, eg proximity of supply and exhaust air streams.

2. Temperature conditions across the whole season should be taken into account when assessing viability.

3. Infiltration has a significant impact on the viability of air to air heat recovery.

4. Check that the desired temperature and humidity is maintained without adding or removing more heat than necessary.

5. Consider application, space available and required air quality when selecting heat recovery systems, eg run-around coil, thermal wheel, plate heat exchanger, heat pipes, heat pump, regenerator.

6. When selecting a suitable heat recovery system consider the quality and condition of the exhaust air to assess likely contaminant load and composition, moisture content etc.

7. Consider whether latent heat transfer is required as well as sensible. 8. Consider whether cross-contamination between air streams is acceptable

or not for the application. Assess the risk of cross contamination between exhaust and supply air streams by both carryover and leakage when considering heat recovery system options.

9. Allow for the additional resistance of heat exchange devices within the air stream when sizing fans (and pumps for a wet heat recovery system), as this can be substantial. The extra fan power required should be taken into account when assessing system economics.

10. The efficiency (effectiveness) of the heat recovery device can be used as a measure of the heat recovered, eg typical efficiencies are: • Run around coils - 45-65% (depending on number and spacing of

coil rows and temperatures)

• Thermal wheels - 65-85% (depending on media construction in the thermal wheel)

• Recuperators/Plate heat exchangers - 50-80%

11. In applications involving thermal wheels there will be possible cross-contamination from exhaust air stream to supply air stream.

12. Supply and extract ducts need to be adjacent to incorporate a thermal wheel.

13. There will be a risk of cross-contamination if mechanical damage occurs with a plate heat exchanger.

14. Consider the option of preheating incoming air via atria, conservatories and open roof spaces or by using waste heat from air-cooled condensers from, eg industrial refrigeration and computer rooms.

Installation, operation & control

15. Provide condensate drains where required. 16. Frost protection should be provided for run-around coils. 17. Provide modulation control – to prevent overheating in warm weather.

Access & maintenance

18. Filters should be provided for both supply and exhaust air streams to reduce risk of fouling.

19. Allow sufficient access for installation and maintenance. 20. Check that local electrical isolation is possible. 21. Safety guards and an emergency stop facility should be provided for

pump and motor moving parts.

Economics

22. Consider whole life costs and relative merits of heat recovery system different cooling tower types.

23. Check that when integrating heat recovery systems into the design of air conditioning and ventilation systems there is sufficient energy being rejected to justify the added complications and running costs when installing heat recovery devices.

Thermal w

heel

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120 DESIGN CHECKS FOR HVAC © BSRIA AG 1/2002 - LICENSED TO OVE ARUP & PARTNERS & PARTNERS

55 HEAT PUMPS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Building heating and cooling loads

• Grade of heat available from primary energy source

• Building heat loss as a function of outdoor temperature

• Supply air volume

Design outputs

Notes / Design file cross-reference

• Layout drawings showing installation of heat pump in the required application, position of indoor and outdoor units, routing of refrigerant pipework

• Schedule of heat pump, performance data, associated components, refrigerant pipework sizes etc

• Electrical requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check appropriate unit is used for the application

• Check that the energy required for defrost is taken into account when estimating the overall power consumption

• Check the heat pump can satisfy the heat requirement over the full range of operating conditions

• Check noise levels are acceptable

Project specific checks & notes

Notes / Design file cross-reference

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55 HEAT PUMPS

Design inputs • Building heating and cooling loads • Grade of heat available from primary energy source • Building heat loss as a function of outdoor temperature • Supply air volume

Design information

• Information from different heat pump manufacturers on performance data for comparison, eg variation of heat pump capacity with outdoor temperature (for air source heat pumps), performance of heat pump (COP and power consumption) under full and part load conditions

• Details of possible locations for indoor and outdoor units, eg plant room location and layout, space available, permissible weights, access

• Building layout details to allow routing of refrigerant lines • Building orientation – solar radiation, wind effects • Details of planned HVAC systems including distribution layouts • Acceptable refrigerant type • Electrical supply – 1 or 3-phase • Noise criteria See also: Chillers, Heat recovery systems

Design outputs • Layout drawings showing installation of heat pump in the required

application, position of indoor and outdoor units, routing of refrigerant pipework

• Schedule of heat pump, performance data, associated components, refrigerant pipework sizes etc

• Electrical requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check appropriate unit is used for the application • Check that the energy required for defrost is taken into account

when estimating the overall power consumption • Check the heat pump can satisfy the heat requirement over the full

range of operating conditions • Check noise levels are acceptable

DESIGN WATCHPOINTS

Sizing & selection

1. Check at an early stage that refrigerant type meets client approval. 2. When selecting heat pump consider product availability, reliability, past

performance and spares availability. 3. Consider whether the heat pump will be used for a heating application,

cooling application or both. Reversible cycle heat pump types include air to air, air to water, water to water, water to air, ground to air, ground to water, air to ground, dehumidifiers.

4. Do not extrapolate performance curves beyond the manufacturer’s published data.

5. Check design takes into account ambient and extreme conditions at design location, eg temperatures at roof level may be higher than ambient design temperatures.

6. Problems such as coil freezing can arise if standard units are supplied for high sensible load applications.

7. The frequency and duration of defrosting and the energy required to achieve defrost should be considered. Check that the energy required for defrost is taken into account when estimating the overall power consumption.

8. The potential noise problems arising from the use of heat pumps need to be considered early in the design process.

9. Check that at low temperature the heat pump can satisfy the heat requirement ie examine the full range of operating conditions, not only the characteristics at the design temperatures.

10. Consider part load operation when selecting heat pump to optimise performance and maximise part load efficiency.

11. Refrigerant piping should be kept as short and simple as possible between the indoor and outdoor units.

12. Check that the diameter and length of the refrigerant lines meets the manufacturer’s recommendations for the particular unit being installed.

13. The vapour line on the heat pump unit should be fully insulated. Check the insulation is capable of withstanding the high temperatures of the discharge vapour.

Installation, operation & control

14. Check the air discharge from any outdoor units does not compromise the performance of adjacent units.

15. Heat pump protection should include high and low refrigerant pressure cut outs, compressor delay starter timer, high temperature cut out, systems flow switches and defrost mechanism in air source units.

16. A condensate drain must be fitted to units that will be operating at temperatures below the dew point.

17. All tubing connections should be tested for leakage before starting the unit to check that there are no refrigerant leaks.

18. Check that the control systems include a means of matching the space loads efficiently and without excessive cycling.

Access & maintenance

19. Check there is sufficient clearance around the unit for proper airflow and service access.

20. Inbuilt condensate pumps are susceptible to malfunction and must be cleaned and maintained regularly.

21. Check that local electrical isolation is possible. 22. Safety guards and an emergency stop facility should be provided for

pump and motor moving parts.

Economics

23. Oversizing of heat pumps will cause excessive cycling, reduced performance and reduced life.

24. Avoid the inefficient use of supplementary heating. It is the most common problem in heat pump application, giving rise to running costs in excess of predictions.

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56 WATER SIDE FREE COOLING - DIRECT

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Building load profile for whole year

• Weather data for year

• Ambient conditions including wet bulb temperature

Design outputs

Notes / Design file cross-reference

• Schematic of free cooling system and HVAC systems, etc

• Schedule of appropriate free cooling equipment and performance data, supply conditions, ie temperature and humidity, required heat rejection performance etc

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

• Method of chemical/biocide dosing

Key design checks

Notes / Design file cross-reference

• Check whether load profile indicates sufficient demand for cooling during months when free cooling is possible

• Check highest chilled water temperature that can be used by the chilled water systems and equipment

• Check that suitable water treatment provision has been made

• Check that the design considers and reduces the risk of fouling

Project specific checks & notes

Notes / Design file cross-reference

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56 WATER SIDE FREE COOLING - DIRECT

Design inputs • Building load profile for whole year • Weather data for year • Ambient conditions including wet bulb temperature

Design information

• Details of possible locations, eg plant room location and layout, space available, permissible weights, access

• Details of proposed comfort cooling systems • Details of any process cooling systems • Client future cooling need requirements See also: Cooling towers, Water side free cooling – indirect

Design outputs • Schematic of free cooling system and HVAC systems, etc • Schedule of appropriate free cooling equipment and performance

data, supply conditions, ie temperature and humidity, required heat rejection performance etc

• Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses • Method of chemical/biocide dosing

Key design checks • Check whether load profile indicates sufficient demand for cooling

during months when free cooling is possible • Check highest chilled water temperature that can be used by the

chilled water systems and equipment • Check that suitable water treatment provision has been made • Check that the design considers and reduces the risk of fouling

DESIGN WATCHPOINTS

Sizing & selection

1. Direct free cooling systems interconnect chilled water and condenser circuits during free cooling allowing heat to be directly rejected by the cooling tower.

2. Sizing should be carried out at winter free cooling conditions. Cooling towers sized for summer peak loads may not be big enough to take full advantage of the full free cooling potential.

3. Check whether any local industry creates significant amounts of dust or fumes. Cooling towers are very effective at removing dust/pollution from the air, but when configured for direct free cooling, maintenance levels in areas of high airborne pollution may be prohibitively high to ensure filters are kept clean and the chilled water circuit is protected from erosion and sediment.

4. Consider designing chilled water systems and selecting plant and equipment to operate at higher chilled water temperatures to maximise free cooling potential. Operation at relatively high chilled water temperatures will enable free cooling for a greater portion of the weather year.

5. The overall approach temperature between the chilled water supply and the ambient wet bulb temperature should be kept as low as practicable to maximise the number of hours each year that free cooling is possible. (For direct systems the overall approach temperature is simply the approach across the cooling towers.)

6. Design to avoid fouling of chilled water circuit, eg by water treatment regime, use of strainers , filters etc.

Installation, operation & control

7. A self-cleaning, full flow filtration system should be specified for direct free cooling that can remove particles down to approx. 120 microns. Side-stream filtration is inadequate for direct free cooling as it is unlikely to provide adequate protection.

8. Check that the water consumption required for the cleaning cycle is not excessive.

9. Consider the impact of both salt (in coastal locations) and pollen as potential contamination sources.

10. Care should be taken in the system design to prevent water hammer This will occur whenever the chilled water flow undergoes rapid deceleration, eg if control valves are modulated too quickly.

11. Non-ferrous components should be used wherever possible. The thorough mixing of air and water in open circuit cooling towers results in a significant amount of air becoming entrained and held in solution. At points of low static pressure in the chilled water circuit, oxygen can come out of solution and combine with metal to form oxides which can lead to corrosion problems.

Access & maintenance 12. Consider and specify water treatment requirements. A strict water

treatment regime is needed to protect the chilled water system. Corrosion coupons can be used to monitor the effectiveness of corrosion inhibitors.

13. Provide adequate access for installation, maintenance and component replacement - check the cooling tower housing offers full and easy access.

14. Check that local electrical isolation is possible. 15. Safety guards and an emergency stop facility should be provided for

pump, fan and motor moving parts. 16. Check who will be responsible for maintenance and the water treatment

regime. 17. The building user/operator needs to understand the basic principle of

operation of the free cooling system and the importance of regular maintenance. Poor maintenance can have a detrimental effect on the whole chilled water system and lead to the free cooling system being taken off-line indefinitely.

18. Operation & Maintenance manuals should be clear on the importance of adequate regular system maintenance.

Economics 19. As part of system feasibility investigation check whether the load profile

indicates sufficient demand for cooling during the months when free cooling is possible.

20. The effectiveness of water side free cooling systems is determined by the number of hours it can operate annually. System design should aim to maximise the number of hours each year that free cooling is possible. (See points 4 & 5.)

21. Consider the use of ‘overcooling’ outside normal hours to cool the building structure and reduce loads.

22. Consider the balance between the installation costs of larger plant to handle the increased flow rates for higher temperatures against the energy saving and payback period.

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57 WATER SIDE FREE COOLING - INDIRECT

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Building load profile for whole year

• Weather data for year

• Ambient conditions including wet bulb temperature

Design outputs

Notes / Design file cross-reference

• Schematic of free cooling system and HVAC systems, etc

• Schedule of appropriate free cooling equipment and performance data, supply conditions ie temperature and humidity, required heat rejection performance etc

• Schedule of electricity supply requirements

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

• Method of chemical/biocide dosing

Key design checks

Notes / Design file cross-reference

• Check whether load profile indicates sufficient demand for cooling during months when free cooling is possible

• Check the highest chilled water temperature that can be used by the chilled water systems and equipment

• Check that the design considers and reduces the risk of fouling

• Check that suitable water treatment provision has been made

Project specific checks & notes

Notes / Design file cross-reference

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57 WATER SIDE FREE COOLING - INDIRECT

Design inputs • Building load profile for whole year • Weather data for year • Ambient conditions including wet bulb temperature

Design information

• Details of possible locations, eg plant room location and layout, space available, permissible weights, access

• Space available and maximum ground loading for plate heat exchanger (PHE) location

• Pressure limits for the PHE (consult supplier) • Potential to add plates to PHE at later date • Details of proposed comfort cooling systems • Details of any process cooling systems • Client future cooling need requirements See also: Cooling towers, Water side free cooling – direct

Design outputs • Schematic of free cooling system and HVAC systems, etc • Schedule of appropriate free cooling equipment and performance

data, supply conditions ie temperature and humidity, required heat rejection performance etc

• Schedule of electricity supply requirements • Control requirements • Statement of commissioning strategy • Relevant specification clauses • Method of chemical/biocide dosing

Key design checks • Check whether load profile indicates sufficient demand for cooling

during months when free cooling is possible • Check the highest chilled water temperature that can be used by

the chilled water systems and equipment • Check that the design considers and reduces the risk of fouling • Check that suitable water treatment provision has been made

DESIGN WATCHPOINTS

Sizing & selection

1. Indirect free cooling keeps the chilled water circuit as a closed circuit, rejecting heat through a heat exchanger between cooling tower and chilled water circuit or using a closed circuit cooling tower.

2. Consider including an over-sizing margin to offset the effects of fouling when sizing a plate heat exchanger (PHE) for indirect free cooling (see pt 8).

3. Check the potential to add plates to plate heat exchangers at a later date, ie check whether the PHE frame is able to take more plates or already at its limit for the given system.

4. Consider designing chilled water systems and selecting plant and equipment to operate at higher chilled water temperatures to maximise free cooling potential. Operation at relatively high chilled water temperatures will enable free cooling for a greater portion of the weather year.

5. The overall approach temperature between the chilled water supply and the ambient wet bulb temperature should be kept as low as practicable to maximise the number of hours each year that free cooling is possible. (For indirect systems this will be the sum of the approach across the cooling towers and the PHE, or if indirect cooling towers are used, the overall approach temperature will simply be that of the tower.) (See point 6.)

6. Plate heat exchangers should be sized to achieve a minimal approach temperature, in the order of 1·5K - 2K. However, in achieving this, it is also important that the flow through the PHE remains as turbulent as possible to reduce fouling.

7. Allow for the additional resistance of plate heat exchangers when sizing pumps, as this can be substantial. The additional pumping costs incurred should be considered against potential free cooling when assessing system economics.

8. Design to compensate for the effects of fouling. Cooling tower water can cause fouling in plate heat exchangers due to a combination of crystallisation, sedimentation and organic material growth. Fouling resistance is dependent on water quality, temperature, turbulence, velocity, flow patterns, plate material and surface finish. Methods to overcome this include water treatment and possibly oversizing, eg in many cases an over-sizing margin of 20% (or less depending on water quality) will compensate for the effects of fouling.

Installation, operation & control

9. Overall efficiency of the chilled water system can be improved by operating the plate heat exchanger only when the system is in free cooling mode and isolating it during conventional chiller operation. However some environments may require the condenser to be permanently isolated from the relatively dirty cooling tower water, keeping the PHE in use when chillers are running. This will reduce system efficiency as the overall approach temperature between the condenser and the ambient wet bulb temperature will be increased.

Access & maintenance

10. Consider and specify water treatment requirements. 11. Provide adequate access for installation, maintenance and component

replacement. 12. Check there is adequate access to the plate heat exchanger, for cleaning

and other maintenance. 13. Check that local electrical isolation is possible. 14. Safety guards and an emergency stop facility should be provided for

pump, fan and motor moving parts. 15. Check who will be responsible for maintenance and the water treatment

regime. 16. The building user/operator needs to understand the basic principle of

operation of the free cooling system and the importance of regular maintenance.

17. Operation & Maintenance manuals should be clear on the importance of adequate regular system maintenance.

Economics

18. As part of system feasibility investigation check whether the load profile indicates sufficient demand for cooling during the months when free cooling is possible.

19. The effectiveness of water side free cooling systems is determined by the number of hours it can operate annually. System design should aim to maximise the number of hours each year that free cooling is possible. (See points 4 & 5.)

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58 OIL STORAGE TANKS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Details of application, eg domestic, commercial or industrial boiler plant, generator etc

• Details of system demand, eg heating system size and output, generator capacity etc

• Details of boiler/generator installation – burners, controls etc

• Details of fuel type, ie oil grade and availability

• Installation position, eg indoors, outdoors or roof top installations

Design outputs

Notes / Design file cross-reference

• Schematic of oil storage tank installation and connection of pipe work to services, eg boiler plant, generator set etc

• Schedule of oil storage tank sizes, capacity, weight at brimful capacity, fill point and venting details, whether oil heating required etc

• Schedule of ancillary equipment, eg dispensing pumps, contents gauge, anti-spillage device

• Control requirements

• Statement of commissioning strategy

• Relevant specification clauses

Key design checks

Notes / Design file cross-reference

• Check that the oil storage tank system is adequately bunded

• Check that oil supply and return pipework used in the installation is adequately sized to the requirements of the service that the oil is being provided to

Project specific checks & notes

Notes / Design file cross-reference

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58 OIL STORAGE TANKS

Design inputs • Details of application, eg domestic, commercial or industrial boiler

plant, generator etc • Details of system demand, eg heating system size and output,

generator capacity etc • Details of boiler/generator installation – burners, controls etc • Details of fuel type, ie oil grade and availability • Installation position, eg indoors, outdoors or roof top installations

Design information

• Details of possible locations, eg plant room location and layout, space available, permissible weights, access

• Details of building structural frame • Space requirements for installation • Schematic of plant room layout and routing of oil supply and

return pipes from oil tank to plant (boilers or generators) See also: Plant space allowance, Boilers

Design outputs • Schematic of oil storage tank installation and connection of pipe

work to services, eg boiler plant, generator set etc • Schedule of oil storage tank sizes, capacity, weight at brimful

capacity, fill point and venting details, whether oil heating required etc

• Schedule of ancillary equipment, eg dispensing pumps, contents gauge, anti-spillage device

• Control requirements • Statement of commissioning strategy • Relevant specification clauses

Key design checks • Check that the oil storage tank

system is adequately bunded • Check that oil supply and return

pipework used in the installation is adequately sized to the requirements of the service that the oil is being provided to

DESIGN WATCHPOINTS

Sizing & selection

1. Where tanks are sited within, on, or over a building the requirements within BS5410 Parts 1 and 2 governing fire-resisting tank chambers and ventilation must be strictly adhered to.

2. Check that the proposed location is suitable, considering access, weight limits, safety, environmental protection etc.

3. Oil storage tank systems should not be sited within 50 m of a spring or borehole or within 10 m of a watercourse or drain (either surface water or foul sewer), which oil could drain into in the event of spillage.

4. The oil storage regulations 2000 require that all oil storage tank systems should be provided with some form of bunding. This can be a masonry or concrete bund or a prefabricated bund which forms an integral part of the tank.

5. The oil storage tank system must be adequately bunded. The bund capacity should be sized to contain a minimum of 110% of the brimful capacity of the primary tank.

6. Consider using an enclosed bund in preference to an open one as it offers more protection.

7. Where there are two or more tanks installed within a bund, the bund capacity should be at least 110% of the brimful capacity of the largest tank or 25% of the combined capacity of all tanks whichever is greater.

8. A prefabricated bund should have sufficient strength and thickness to withstand the hydrostatic forces arising from the containment of 110% of the primary tank’s contents. It should be adequately supported, should not distort and be capable of protecting the primary tank, connecting pipework and ancillary equipment from impact damage, vandalism and weathering where possible.

9. Check that oil supply and return pipework used in the installation is adequately sized to the requirements of the service that the oil is being provided to.

10. Anti-vandal security cabinets should be fitted in order to reduce the risk of vandalism.

11. Oil storage tank systems and ancillary equipment that are at risk from impact damage should be protected with kerbs, bollards or other forms of barriers.

Installation, operation & control

12. Where tanks are to be sited within the basement of a building, check that there is sufficient space to allow for installation.

13. All fill pipes should preferably pass through the top of the tank and be located within the confines of the bund.

14. For multiple storage tank installations, separate fill points should be provided for each tank.

15. All oil storage tank systems should be fitted with either a reliable overfill cut out (anti-spillage) valve or a fail-safe high level alarm.

16. Prefabricated enclosed bunds and primary tanks must be vented to atmosphere.

17. Extended vent pipes should be provided with an overpressure relief device.

18. The use of low level draw off connections from the primary tank that terminate outside the bund is not recommended as it presents a high level risk to the environment as any leaks can result in the uncontained loss of the entire contents of the tank.

19. Low level tank drains should not be fitted to oil storage tank systems unless they are absolutely necessary.

20. Bund drains, if required, must not discharge directly into the mains sewerage system.

21. All oil storage tanks should be fitted with a reliable form of contents gauge.

22. The oil care sticker should be placed on the oil storage tank system. This gives general guidance on the safe use of oil storage tank systems, actions to be taken in the event of an oil spill and the Environment Agency’s emergency hot line telephone number.

Access & maintenance 23. All pipework to the services should be sited above ground where possible

to facilitate inspection and repair. 24. Check that there is adequate access to the oil storage tank system for oil

delivery tankers and the emergency services.

Economics

25. Safety and security should be prime design considerations.

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59 HVAC CONTROL SYSTEMS

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Information on systems to be controlled, to include: − schematic drawings of systems to be

controlled − description and required sequence of

operation of plant − zoning details if required − details of devices to be controlled − interfaces with other equipment & between

systems

• Control set points and permitted tolerances

Design outputs

Notes / Design file cross-reference

• System control strategy and description

• Control strategy flow charts

• Schematics and descriptions of building services plant and systems to be controlled and monitored

• Required functional capability of control systems

• Standby plant: rotation requirements and operating routines

• Control system specification

• Schedule of control system components, sensors, thermostats, other input/output devices

• Metering requirements

Key design checks

Notes / Design file cross-reference

• Check controls satisfy any required fail-safe criteria

• Check that the required safety and emergency operation and overrides are defined

• Check requirements for interface with fire systems

• Check type & availability of connections in other systems that require an interface

• Identify requirements for operator interfaces

Project specific checks & notes

Notes / Design file cross-reference

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59 HVAC CONTROL SYSTEMS

Design inputs • Information on systems to be controlled, eg heating, cooling,

ventilation, humidification/dehumidification, lighting etc, to include: − schematic drawings of systems to be controlled − description and required sequence of operation of plant − zoning details if required − details of devices to be controlled, eg pumps, valves,

fans, dampers, drive motors, electrical, electronic and pneumatic actuators etc

− interfaces with other equipment & between systems • Control set points and permitted tolerances

Design information

• Details of building use and architectural drawings for all zones including space plan and layout

• Building Regulations • Manufacturers performance data for the appropriate control

equipment. • Accuracy and range of sensors for temperature, pressure, humidity

and velocity measurements • Available power supply - volts, frequency and phase • Client/user operational requirements and future needs See also: Sensor locations, Internal design criteria, Building management systems

Design outputs • System control strategy and description • Control strategy flow charts • Schematics and descriptions of building services plant and systems

to be controlled and monitored • Required functional capability of control systems, ie automatic

on/off switching of plant, optimisation of plant operation and services, monitoring of plant status and environmental conditions, provision of energy management information etc

• Standby plant: rotation requirements and operating routines • Control system specification • Schedule of control system components, sensors, thermostats and

other input/output devices • Metering requirements

Key design checks • Check controls satisfy any required fail-safe criteria • Check that the required safety and emergency operation and

overrides are defined • Check requirements for interface with fire systems • Check type & availability of connections in other systems that

require an interface • Identify requirements for operator interfaces

DESIGN WATCHPOINTS

Sizing & selection

1. Check compliance with relevant regulations and codes including Building Regulations part L.

2. Define type of controls to be used, ie stand alone or BMS. 3. Check with client whether local or central occupant control required. 4. Check that local and central user interfaces are easy to understand. 5. Check whether the building to be occupied by the owner, a single tenant,

or multi-tenanted. 6. Identify each control element as input and/or output and schedule all

physical inputs and all physical outputs to control devices. 7. Check and specify the interaction of the HVAC system with other building

services, eg lighting, lifts, fire alarms, standby generators and consider the required control interfaces.

8. Specify method of sending control signals from controllers to controlled device, eg electrical, electronic, pneumatic, radio control.

9. Provide automatic systems with simple overrides. 10. Check that the system will provide the specified control conditions within

the limits. 11. Control systems should be robust and capable of re-configuration. 12. Define default values of setpoints and other parameters which the user

can change as required. 13. Define the accuracy or maximum acceptable tolerances of variable to be

controlled, eg temperature, humidity, velocity, pressure etc.

Installation, operation & control

14. Be aware of the limits of control accuracy, eg a typical water temperature sensor may only be accurate to ±1°C, and in a CHW s ystem where the flow and return temperatures are 6°C and 12°C it is possible the controls could register the respective temperatures as 7°C a nd 11°C (an error of 33%).

15. User interactive controls should be placed in obvious places, not where they will be obscured or difficult to reach.

16. Set control dead bands wide enough to avoid hunting without promoting larger variance across control limits.

17. Control systems should be designed such that the effect of control on one zone does not affect another zone, eg multi-zone control central air-handling systems.

18. Control systems should be designed such that the effect of control on one system does not affect another system, eg check that the cooling system is not affected by a perimeter heating system such as slot diffusers over trench heating with TRVs.

19. State how design conditions are to be validated without suitable environmental conditions at time of commissioning, eg if heating is commissioned during summer or cooling during winter.

20. Check requirements for interface with fire systems/fire officer requirements. Check that the required safety and emergency operation and overrides are defined, eg life safety issues re motorised fire and smoke dampers in air handling systems.

21. Check that the controls satisfy any required fail-safe criteria, eg primary control valves on LPHW system to close in the event of plant shut down or power failure; or hard wired safety interlocks for frost protection, to prevent overheating (particularly with electric heater elements).

22. Consider commissioning requirements. Testing and commissioning should be recorded and comply with CIBSE commissioning codes and other necessary standard tests and procedures.

Access & maintenance

23. Configure controls to detect problems & initiate appropriate alarms. 24. Consider requirements for maintenance.

Economics

25. The default state should be low energy state so that systems go off when there is no further need for them.

26. Do not select equipment that is capable of producing more precise control than the application requires.

27. Do not specify controls with a degree of accuracy to which the plant or building is unable to respond, eg close control of humidity in office with openable windows or specifying ± 1°C where the plan t is DX control with only 1 or 2 steps.

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60 BUILDING MANAGEMENT SYSTEMS (BMS)

Project title ...............................................................Project No. ...................................... Design stage ...............

Engineer ....................................................................Revision No .................................... Date.................................

Checked by...............................................................Approved by .................................. Date .................................

Design inputs

Notes / Design file cross-reference

• Information on systems and plant to be controlled as listed under HVAC control systems

• Control set points and permitted tolerances

Design outputs

Notes / Design file cross-reference

• Recommended system control strategy

• Schematics and descriptions of building services plant and systems to be controlled and monitored

• Required functional capability of control system given by HVAC control systems and operational schedules

• BMS points schedule

• BMS full specification, incl. schedule of control system components

• Plans and drawings of plant and sensor locations, cable/trunking layouts/routes

Key design checks

Notes / Design file cross-reference

• Check that the installation complies with relevant standards and regulations

• Check if there is a requirement to integrate with other control systems or other equipment

• Check with client the level of occupant control required

• Check complexity of design is appropriate to application

Project specific checks & notes

Notes / Design file cross-reference

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60 BUILDING MANAGEMENT SYSTEMS (BMS)

Design inputs • Information on systems and plant to be controlled as listed under

HVAC control systems • Control set points and permitted tolerances

Design information

• Details of building use and architect drawings/floor plans showing layout

• General BMS requirements, eg the location of the central station, control facilities required at outstations, the extent of any user programming of control algorithms, likely future extensions of BMS

• Required interfaces to other data networks, computers and software

• Availability and type of interface provided for plant items to be controlled by BMS.

• Availability of power supply for outstations/central station • User operational requirements and skill levels See also: Sensor locations, HVAC control systems

Design outputs • Recommended system control strategy • Schematics and descriptions of building services plant and systems

to be controlled and monitored • Required functional capability of control system given by HVAC

control systems and operational schedules • BMS points schedule – describes parameters to be monitored or

controlled, eg, pressure, temperature, damper position, status etc, to enable provision of appropriate sensor or actuator and outstation

• BMS full specification, incl. schedule of control system components with number of operator facilities and their equipment, outstation details, sensors, control flow charts, graphics schedules, maintenance schedules

• Plans and drawings of plant and sensor locations, cable/trunking layouts/routes

Key design checks • Check that the installation complies with relevant standards and

regulations • Check if there is a requirement to integrate with other control

systems or other equipment • Check with client the level of occupant control required • Check complexity of design is appropriate to application

DESIGN WATCHPOINTS

Sizing & selection

1. Check compliance with relevant British Standards, BS Codes of Practice and Building Regulations etc.

2. Check whether the building is to be occupied by the owner, a single tenant, or multi-tenanted.

3. Check with client the level of occupant control required. 4. Check that the BMS specification details the exact requirements and

provides the control and monitoring required. 5. Consider what is the main function of the BMS when selecting an

appropriate system, eg improved environmental control, improved building management, better plant monitoring etc.

6. Check if there is a requirement to integrate with other control systems and consider whether integration with other systems such as fire, access, security control and lighting would be beneficial.

7. Consider integration of cabling in large BMS installations with IT networks.

8. Check whether remote monitoring of plant via BMS is required and design system accordingly.

9. Check that all BMS products adhere to all relevant manufacturing standards, regulations and statutes, eg CE, EMC etc.

10. Check that outstations operate from the installed power supply and are able to preserve existing software and data for a period of not less than 72 hours in the event of electrical power failure.

11. Check that the equipment is protected against the effects of conducted and radiated electrical interference and moisture, dust and dirt to relevant standards.

12. Power supplies for data distribution equipment connected to the public switched network should comply with relevant standards, eg BSEN 41003:1993.

13. Modems for connecting BMS equipment to public telephone networks should conform to relevant standards, eg BS6320:1992.

14. Check if primary and secondary plant already have DDC controllers. 15. Consider appropriate control protocols, eg LONWORKS, EIB, CAN,

BACnet etc. 16. Consider power supply provision for failure modes & the use of UPS.

17. Consider which communication networks to use between hardware and BMS, eg hardwire connection, wireless systems.

18. Check routing of cables between plant controls and BMS.

Installation, operation & control 19. Operational schedules describe the way in which the buildings and plant

are to be controlled to enable determination of monitoring and control routines essential to the BMS.

20. Check the complexity of the specified design to ensure it matches the user skill levels and cost plan allowances.

21. Check that heating and cooling systems do not conflict in any controlled zone.

22. Check that control panels are provided with the option for manual operation of plant in the event of failure of programmed automatic control or for test purposes, eg hand/off/auto switches.

23. Check that the software includes routines that confirm that specific items of plant, ie pumps, fans etc are functioning correctly, and are also capable of starting and stopping plant.

24. Check that the software includes weather compensation routines to control heating and cooling systems in relation to the external weather conditions.

25. Check that the software includes frost protection routines to protect the building and the building services systems from frost damage.

26. Check with client the alarms required, the threshold level and whether alarms are to be registered as “critical” or merely “warning”.

27. Consider requirements for commissioning. Follow good practice approach, eg CIBSE commissioning codes.

Access & maintenance 28. Consider requirements for maintenance. 29. Consider use with monitoring and targeting software and maintenance

management software.

Economics 30. As part of the value engineering exercise check the number of control

and sensor channels required.