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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Designing Either Chilled Beamor VAV Systems for High Performance
John Murphy, LEED® AP BD+C Applications EngineerTraneIngersoll RandLa Crosse, Wisconsin
“High-Performance” Systems
• Brief review of today’s technical session– Overview of chilled beam systems– Assess marketed advantages of chilled beams vs. VAV– Discuss challenges of applying chilled beam systems
• “High-performance” chilled beam systems• “High-performance” VAV systems
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Passive or Active Chilled Beamsprimary air
nozzles
ceiling
coils
induced airinduced air
+primary air
active chilled beam
3
perforatedmetal casing
coilwaterpipes
passive chilled beam
active chilled beam
active chilled beamsPrimary Air System
primaryair handlerOA
activechilled beamPA
RA RA RA
PA
EARA
4
Primary air must be sufficiently drier than space: • to offset space latent load, and • to keep space DP below chilled beam surface temp
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
active chilled beam systems compared to VAV systemsSummary of Today’s Technical SessionPotential advantages of ACB• Smaller ductwork and
smaller air handlers
Challenges of ACB• High installed cost• Need to prevent
– Primary airflow < supply airflow, but likely > outdoor airflow
• Low sound levels• Impact on overall system energy?
– Primary airflow < supply airflow, but constant airflow
– Warm water for beams,
Need to prevent condensation
• Risk of water leaks• No filtration of local
recirculated air• Limited heating capability
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but cold water primary AHU– Increased pumping energy– No DCV, limited airside
economizing
10,000,000
12,000,000
Use
, kB
tu/
yr
Pumps
Fans
Heating
Houston Los Angeles Philadelphia St. Louis
Example Energy Analysis
2,000,000
4,000,000
6,000,000
8,000,000
An
nu
al B
uild
ing
En
erg
y U Heating
Cooling
Plug Loads
Lighting
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
office buildingExample Energy Analysis• “Baseline” chilled-water VAV system
– ASHRAE 90.1-2007, Appendix G (55°F supply air)
• Active chilled beam systemActive chilled beam system– Four-pipe active chilled beams– Separate primary AHUs for perimeter and
interior areas (with SAT reset and economizers)– Separate water-cooled chiller plants
(low-flow plant supplying primary AHUs)
• “High-performance” chilled-water VAV system48°F l i (d t k t d i d)
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– 48°F supply air (ductwork not downsized)– Optimized VAV system controls
(ventilation optimization, SAT reset)– Parallel fan-powered VAV terminals– Low-flow, water-cooled chiller plant
“High-Performance” Systems
• Brief review of today’s technical session– Overview of chilled beam systems– Assess marketed advantages of chilled beams vs. VAV– Discuss challenges of applying chilled beam systems
• “High-performance” chilled beam systems• “High-performance” VAV systems
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5
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
“High Performance” Chilled Beam Systems
• How can active chilled beam systems be designeddifferently for “high performance”?
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ACB challengesHigh Installed Cost
• Limited cooling capacity = lots of ceiling space– Warmer water temperature requires
more coil surface area– Induction with low static pressures requires more
coil surface area to keep airside pressure drop low
i h (8) i hill d b
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Example: 1000-ft2 office space Example: 1000-ft2 classroom
four (4) active chilled beams,each 6-ft long x 2-ft wide
eight (8) active chilled beams,each 4-ft long x 2-ft wide
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
System design variable
Impact on installed cost of the chilled beams
Impact on performance of the overall system
2-pipe versus 4-pipe chilled beams
A 2-pipe beam provides more cooling capacity than a 4-pipe beam because more coil surface is available
Using 2-pipe beams requires a separate heating system, otherwise it can result in poorer comfort control because either cold water or warm water is delivered to all zones
Primary airflow rate (cfm)
Increasing the primary airflow rate through the nozzles results in more air being induced from the space which increased
Increasing the primary airflow rate increases primary AHU fan energy use, increases noise in the space and requires a larger primaryinduced from the space, which increased
the capacity of the chilled beam coilsin the space, and requires a larger primary AHU and larger ductwork
Inlet static pressure of the primary air
Increasing the static pressure at the inlet to the nozzles results in more air being induced from the space, which increased the capacity of the chilled beam coils
Increasing the inlet pressure increases primary AHU fan energy use, and increases noise in the space
Dry-bulb temperature of the primary air
Delivering the primary air at a colder temperature means that less of the space sensible cooling load needs to be offset by the chilled beams
Using a colder primary-air temperature may cause the space to overcool and low sensible cooling loads, thus requiring the chilled beam (or separate heating system) to add heat to
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the chilled beams (or separate heating system) to add heat to prevent overcooling space
Entering water temperature
Supplying colder water to the chilled beam increases the cooling capacity of the beam
Using a colder water temperature requires the space dew point to be lower to avoid condensation, which means the primary air needs to be dehumidified to a lower dew point
Water flow rate (gpm)
Increasing the water flow rate increases the cooling capacity of the beam
Increasing the water flow rate increases pump energy use and requires larger pipes and pumps
“High Performance” Chilled Beam Systems
• How can active chilled beam systems be designeddifferently for “high performance”?
U t i b h ibl– Use two-pipe beams as much as possibleUse primary air system for morning warm-upConsider using a separate heating system
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7
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
System design variable
Impact on installed cost of the chilled beams
Impact on performance of the overall system
2-pipe versus 4-pipe chilled beams
A 2-pipe beam provides more cooling capacity than a 4-pipe beam because more coil surface is available
Using 2-pipe beams requires a separate heating system, otherwise it can result in poorer comfort control because either cold water or warm water is delivered to all zones
Primary airflow rate (cfm)
Increasing the primary airflow rate through the nozzles results in more air being induced from the space which increased
Increasing the primary airflow rate increases primary AHU fan energy use, increases noise in the space and requires a larger primaryinduced from the space, which increased
the capacity of the chilled beam coilsin the space, and requires a larger primary AHU and larger ductwork
Inlet static pressure of the primary air
Increasing the static pressure at the inlet to the nozzles results in more air being induced from the space, which increased the capacity of the chilled beam coils
Increasing the inlet pressure increases primary AHU fan energy use, and increases noise in the space
Dry-bulb temperature of the primary air
Delivering the primary air at a colder temperature means that less of the space sensible cooling load needs to be offset by the chilled beams
Using a colder primary-air temperature may cause the space to overcool and low sensible cooling loads, thus requiring the chilled beam (or separate heating system) to add heat to
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the chilled beams (or separate heating system) to add heat to prevent overcooling space
Entering water temperature
Supplying colder water to the chilled beam increases the cooling capacity of the beam
Using a colder water temperature requires the space dew point to be lower to avoid condensation, which means the primary air needs to be dehumidified to a lower dew point
Water flow rate (gpm)
Increasing the water flow rate increases the cooling capacity of the beam
Increasing the water flow rate increases pump energy use and requires larger pipes and pumps
active chilled beamsDetermining Primary Airflow Rate
• Primary airflow (PA) is b d l t f
PAbased on largest of:– Minimum outdoor airflow
required (ASHRAE 62.1)– Airflow required to offset
space latent load (depends on dew point of PA)Airflow needed to induce
RA
SA SA
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– Airflow needed to induce sufficient room air (RA) to offset the space sensible cooling load
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
active chilled beamsDetermining Primary Airflow Rate
Minimum OA per ASHRAE 62.1(to achieve LEED IEQc2)
C
Example: office space0.085 cfm/ft2(0.085 × 1.3 = 0.11 cfm/ft2)
ACB systemAirflow required to offset space latent load
Airflow needed to induce sufficient room air to offset
ibl li l d
0.085 cfm/ft2 (DPTPA = 47°F)0.11 cfm/ft2 (DPTPA = 49°F)0.36 cfm/ft2 (DPTPA = 53°F)
0.36 cfm/ft2 (55°F primary air)(four, 6-ft long beams)
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space sensible cooling loadVAV systemAirflow needed to offset space sensible cooling load
0.90 cfm/ft2(55°F supply air)
example office spaceCold vs. Neutral Primary Air
“Cold” (55°F) primary-air temperature
• four (4) ACBs, each 6-ft long x 2-ft widePA
( ) , g• primary airflow at design conditions = 0.36 cfm/ft2
• total water flow = 6.0 gpmRA
0.36 cfm/ft2
55°F
PA
0 50 f /ft2
“Neutral” (70°F) primary-air temperature
• six (6) ACBs, each 6-ft long x 2-ft widei i fl t d i diti 0 50 f /ft2
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RA
0.50 cfm/ft2
70°F• primary airflow at design conditions = 0.50 cfm/ft2
• total water flow = 9.0 gpm
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
“High Performance” Chilled Beam Systems
• How can active chilled beam systems be designeddifferently for “high performance”?
U t i b h ibl– Use two-pipe beams as much as possibleUse primary air system for morning warm-upConsider using a separate heating system
– Minimize primary airflow requiredDeliver primary air at a cold (rather than neutral) temperatureUse multiple, smaller primary AHUs to allow SAT reset (maximize cooling benefit minimize need for reheat)
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(maximize cooling benefit, minimize need for reheat)
active chilled beamsDetermining Primary Airflow Rate
Minimum OA per ASHRAE 62.1(to achieve LEED IEQc2)
C
Example: K-12 classroom0.47 cfm/ft2(0.47 × 1.3 = 0.61 cfm/ft2)
ACB systemAirflow required to offset space latent load
Airflow needed to induce sufficient room air to offset
ibl li l d
0.47 cfm/ft2 (DPTPA = 44°F)0.61 cfm/ft2 (DPTPA = 47°F)1.20 cfm/ft2 (DPTPA = 51°F)
0.47 cfm/ft2 (55°F primary air)(eight, 4-ft long beams)
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space sensible cooling loadVAV systemAirflow needed to offset space sensible cooling load
1.20 cfm/ft2(55°F supply air)
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
ACB challengesNeed to Prevent Condensation
• Primary air system used to limit indoor dew point (t i ll b l 55°F)(typically below 55°F)
• Warm chilled-water temperatures delivered to beams (typically between 58°F and 60°F)
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primary80
180
160
140
hum
idity
space 75°F DB50% RH55°F DP65 gr/lb
45-53°F DPair (PA)
70
50
4030
60
120
100
80
60
40
20
ratio, g
rains/lb
of d
ry air
spacespace
PAPA
44-60 gr/lb
Qlatent,space = 0.69 × CFMPA × (Wspace – WPA)
20
11030 40 50 60 70 80 10090dry-bulb temperature, °F
Primary air must besufficiently drier than the space
latent,space PA ( space PA)
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
active chilled beamsPrimary Air System
primary air handlerwith series desiccant wheel
OA
EA
activechilled beamPA
RA RA RA
PA
EA
RA
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Primary AHU for ACB Systems
series desiccantdehumidification wheel
total-energywheel
preheatcoil
OA'
CA
OA
EA
MA'MA
22
coolingcoil
RA PA
12
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
180
160
hum
OA 95°F DB118 gr/lb
RA 75°F DB50% RH55°F DP
series desiccant requires:• less cooling tons• no reheat• warmer coil temperature
… than cool + reheat
OA' 81°F DB81 gr/lb
80
70
50
40
60
MA
MA 160
140
120
100
80
60
40
mid
ity ratio, g
rains/lb
of d
ry aRA
OA
OA'
CA
76°F DB68 gr/lb
MA' 72°F DB79 gr/lb
CA 51°F DB52 gr/lb
PA 55°F DB41 gr/lb43°F DP
MA'
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11030 40 50 60 70 80 10090dry-bulb temperature, °F
4030 CAreheat 20
ir
PA
primary AHU with series desiccant wheel
“High Performance” Chilled Beam Systems
• How can active chilled beam systems be designeddifferently for “high performance”?
U t i b h ibl– Use two-pipe beams as much as possibleUse primary air system for morning warm-upConsider using a separate heating system
– Minimize primary airflow requiredDeliver primary air at a cold (rather than neutral) temperatureUse multiple, smaller primary AHUs to allow SAT reset (maximize cooling benefit minimize need for reheat)
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(maximize cooling benefit, minimize need for reheat)Deliver primary air at a lower dew point(may even allow for the delivery of colder water to beams)
13
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
System design variable
Impact on installed cost of the chilled beams
Impact on performance of the overall system
2-pipe versus 4-pipe chilled beams
A 2-pipe beam provides more cooling capacity than a 4-pipe beam because more coil surface is available
Using 2-pipe beams requires a separate heating system, otherwise it can result in poorer comfort control because either cold water or warm water is delivered to all zones
Primary airflow rate (cfm)
Increasing the primary airflow rate through the nozzles results in more air being induced from the space which increased
Increasing the primary airflow rate increases primary AHU fan energy use, increases noise in the space and requires a larger primaryinduced from the space, which increased
the capacity of the chilled beam coilsin the space, and requires a larger primary AHU and larger ductwork
Inlet static pressure of the primary air
Increasing the static pressure at the inlet to the nozzles results in more air being induced from the space, which increased the capacity of the chilled beam coils
Increasing the inlet pressure increases primary AHU fan energy use, and increases noise in the space
Dry-bulb temperature of the primary air
Delivering the primary air at a colder temperature means that less of the space sensible cooling load needs to be offset by the chilled beams
Using a colder primary-air temperature may cause the space to overcool and low sensible cooling loads, thus requiring the chilled beam (or separate heating system) to add heat to
25
the chilled beams (or separate heating system) to add heat to prevent overcooling space
Entering water temperature
Supplying colder water to the chilled beam increases the cooling capacity of the beam
Using a colder water temperature requires the space dew point to be lower to avoid condensation, which means the primary air needs to be dehumidified to a lower dew point
Water flow rate (gpm)
Increasing the water flow rate increases the cooling capacity of the beam
Increasing the water flow rate increases pump energy use and requires larger pipes and pumps
Waterside Economizer
chillers
variable-flowpumps
bypass forminimum flow mixing
valveTT
variable-flowpump
42°F57°F
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primaryair handlers
chilled beamsfrom
cooling tower waterside economizerheat exchanger
42°F 58°F
63°F
54°F
14
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
42°F
i bl fl
water chillers
58°F
42°F
54°F
variable-flowpumps
bypass forminimum flow
mixingvalve
primaryAHU coils
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variable-flowpump
TT
58°F63°F
fromcooling tower
waterside economizerheat exchanger
activechilled beams
“High Performance” Chilled Beam Systems
• How can active chilled beam systems be designeddifferently for “high performance”?
U t i b h ibl– Use two-pipe beams as much as possibleUse primary air system for morning warm-upConsider using a separate heating system
– Minimize primary airflow requiredDeliver primary air at a cold (rather than neutral) temperatureUse multiple, smaller primary AHUs to allow SAT reset (maximize cooling benefit minimize need for reheat)
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(maximize cooling benefit, minimize need for reheat)Deliver primary air at a lower dew point
– Incorporate a waterside economizer, if possible
15
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
“High-Performance” Systems
• Brief review of today’s technical session– Overview of chilled beam systems– Assess marketed advantages of chilled beams vs. VAV– Discuss challenges of applying chilled beam systems
• “High-performance” chilled beam systems• “High-performance” VAV systems
29
“High Performance” VAV Systems
• How are VAV systems being designeddifferently today for “high performance”?
O ti i d VAV t t l– Optimized VAV system controls
30
16
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
staticpressure
Fan-Pressure Optimization
VAV terminalswith DDC controllers
pressuresensor
supplyfan P
VFDVFD
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system-level controller
Supply-Air Temperature Reset
system-level controller
TTT
T
T
T
32
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Ventilation Optimizationair-handling (or rooftop) unit with Traq™ dampers• Reset outdoor airflow
SA RA
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CO2 OCC
• Required ventilation (TOD, OCC, CO2)• Actual primary airflow (flow ring)• Calculate OA fraction
VAV controllers
CO2TOD TODOCC
system-level controller• New OA setpoint
…per ASHRAE 62
“High Performance” VAV Systems
• How are VAV systems being designeddifferently today for “high performance”?
O ti i d VAV t t l– Optimized VAV system controls– Cold air distribution
34
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Lower Supply-Air Temperature
• Reduces supply airflowLess supply fan energy– Less supply fan energyand less fan heat gain
– Smaller fans, air handlers,VAV terminals, and ductwork
• Can reduce HVAC installed cost• Can reduce building construction cost• Improves occupant comfort
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– Lowers indoor humidity levels– Lowers indoor sound levels
“High Performance” VAV Systems
• How are VAV systems being designeddifferently today for “high performance”?
O ti i d VAV t t l– Optimized VAV system controls– Cold air distribution– Parallel fan-powered VAV terminals
36
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Parallel Fan-Powered VAV
heating coil(second stage of heat)
cool primary air fromVAV air-handling unit
warm air recirculatedfrom ceiling plenum(first stage of heat)
(second stage of heat)
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(first stage of heat)
“High Performance” VAV Systems
• How are VAV systems being designeddifferently today for “high performance”?
O ti i d VAV t t l– Optimized VAV system controls– Cold air distribution– Parallel fan-powered VAV terminals– “High-performance” chilled-water system
38
20
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
“High-Performance” Chilled-Water System
• Low flow, low temperature• Ice storage• Variable primary flow• High-efficiency chillers• Optimized plant controls• Waterside heat recovery• Central geothermal
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• Central geothermal
Summary
• Chilled beam and VAV systems h h d t d d b keach have advantages and drawbacks
• We need to move toward designing “high-performance” systems… not just the way it’s always been done!
40
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© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Advanced Energy Design Guides
• Funded by U.S. Dept of Energy• Climate-specific recommendations
www.ashrae.org/freeaedg
pfor achieving 30% or 50% energy savings(envelope, lighting, HVAC, water heating)
• Based on building energy simulations
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Advanced Energy Design Guides
AEDG for Small or Medium Office Buildings• “High-performance rooftop VAV systems are included
as an option to achieve 50% energy savings
AEDG for K-12 Schools• Both rooftop VAV and chilled-water VAV systems are
included as options to achieve 30% energy savings
AEDG for Small Hospitals and Healthcare Facilities
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p• Both rooftop VAV and chilled-water VAV systems are
included as options to achieve 30% energy savings
22
© 2010 Trane, a business of Ingersoll-Rand
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Additional Resources
• “Understanding Chilled Beam Systems,” TraneEngineers Newsletter ADM-APN034-EN (2009),www.trane.com/engineersnewsletter
• Chilled-Water VAV Systems, Traneapplication manual SYS-APM008-EN (2009)
• Cold Air Distribution System Design Guide, ASHRAE (1996)
• Advanced Energy Design Guide series, ASHRAE, www.ashrae.org/freeaedg
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