08 industrial application

8/11/2019 08 Industrial Application

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International MSc Programme Sustainable Energy EngineeringInternational MSc Programme Sustainable Energy Engineering

THERMAL COMFORT AND INDOOR CLIMATE

Lecture:

- HVAC SYSTEMS IN INDUSTRIAL APPLICATIONS

Assist. Prof. Igor BALEN


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Industrial applications

- many industrial buildings require large quantities of energy, both in

manufacturing and maintaining building environmental conditions.

- energy can be saved by proper use of insulation and ventilation, and by

recovery of waste heat.

- HVAC systems should control temperature and humidity, cleanliness,

have low noise levels, control health-threatening fumes, and provide spot

cooling to prevent heat stress.

- air-conditioned environment allows a worker to perform assigned duties

without fatigue from the effects of temperature and humidity results in

better continuous performance. It may also improve morale and reduce

absenteeism.


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Production requirements

- air temperature and cleanliness affect quality in manufacturing precision

instruments, lenses, and tools. When manufacturing tolerances are within

5 m, close temperature control prevents expansion and contraction of the

material; high-efficiency particulate air (HEPA) or ultralow - penetration air

(ULPA) filter may be required.

- manufacturing pharmaceutical tablets requires close control of humidity

for optimum tablet formation.

- air temperature and relative humidity influence production rate and

product mass, strength, appearance, and quality in manufacturing or

processing hygroscopic materials such as textiles, paper, wood, leather,

and tobacco.


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- fermentation requires both temperature and humidity control to regulate

the rate of biochemical reactions. Designing such spaces should take into

account gases and other by-products generated by fermentation (CO2 in

brewing).

- in manufacturing metal products, temperature and relative humidity need

to be kept sufficiently low to prevent hands from sweating, thus protecting

the finished article from fingerprints and/or etching.

- application must be evaluated to determine the filtration needed to

counter the adverse effects on the product or process of dust particles,

airborne bacteria, smoke, spores, pollen, and radioactive particles.

- humidity can reduce static electricity in processing light materials such as

textile fibers and paper and where potentially explosive atmospheres or

materials are present. Static electricity is often detrimental to processing

and extremely dangerous in explosive atmospheres. Static electric charges

are minimized when relative humidity is above 35%.


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Employee requirements

- industrial plants are usually designed for an internal temperature of 16 to

32C and a maximum of 60% rh. Tighter controls are often dictated by the

specific operations and processes located in the building.

- nearly sedentary workers prefer a winter temperature of 22C and a

summer temperature of 26C at a maximum of 60% rh. Workers at a high

rate of activity prefer 18C; they are less sensitive to temperature changes

and can be cooled by increasing the air velocity.

- air-conditioning and ventilation systems must minimize exposure to toxic

and/or hazardous materials.

- concentrations of gaseous flammable substances must also be keptbelow explosive limits. Acceptable concentrations of these substances are

a maximum of 25% of the lower explosive limit.


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Design considerations

- design criteria include the space-by-space environment in the facilities,

process heat loads and exhaust requirements, heat and cooling energy

recovery, load factors and equipment diversity, lighting, cleanliness, etc.

- consideration should be given to the method of separating dirty

processes from areas that require progressively cleaner air.

- air-conditioning and structural envelope must prevent unwanted

condensation and ensure a high-quality product. Condensation can beprevented by eliminating thermal short circuits, installing proper insulation,

and using vapor barriers.

- HVAC systems can be located on the roof of the building. Air intakes

should not be located too close to loading docks or other sources of

contamination. System installation must be coordinated with other systems

and equipment that compete for space at the top of the building, such as

fire sprinklers, lighting, cranes, structural elements, etc.


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HVAC system and equiment selection

- basic system types:

Heating-only in cool climates, where ventilation air provides comfort forworkers.

Air washer systems, where high humidities are desired and where the

climate requires cooling.

Heating and evaporative cooling, where the climate is dry.

Heating and mechanical cooling, where temperature and humidity control

are required and other means of cooling are insufficient.

All systems include air filtration appropriate to the contaminant controlrequired.


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- Floor heating. Floor heating is often desirable in industrial buildings,

particularly in large, high-bay buildings, garages, and assembly areas

where workers must be near the floor, or where large or fluctuating outside

air loads make maintaining ambient temperature difficult. Floors may betempered to 18 to 21C by embedded hydronic systems or electrical

resistance cables.


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- Infrared heaters. High-intensity gas, oil, or electric infrared heaters

transfer heat directly to the occupants, equipment, and floor in the space

without appreciably warming the air, though some air heating occurs by

convection from objects heated by the infrared heaters. Heaters areusually mounted 3 to 9 m above the floor, along outside walls, and tilted to

direct maximum radiation to the floor. If the building is poorly insulated, the

controlling thermostat should be shielded to avoid influence from the

radiant effect of the walls.


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- Refrigerated cooling systems. Most commonly used are roof-mounted

direct-expansion packaged units. Larger systems may use chilled water

distributed to air-handling units. Equipment commonly uses positive

displacement (reciprocating, scroll, or screw) compressors with air-cooledcondensers. For processes that require dew points below 10C (e.g.,

pharmaceutical processing), desiccant-based systems should be

considered.


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- Evaporative cooling systems. Direct or indirect evaporative coolers or

air washers. Water atomized in the air stream evaporates, cooling the air.

Refrigerated water simultaneously cools and dehumidifies the air.

Evaporative cooling conserves energy, particularly in mild weather.Temperature and humidity of the exit air stream may be controlled by

varying the temperature of the chilled water and reheat coil and by varying

the quantity of air passing through the heat coil with a dew point

thermostat. It may be necessary to filter air entering the evaporative cooler.

Chemical treatment of the water may be necessary to prevent mineral

build-up or biological growth on the pads or in the pans.


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-Air filtration systems. Remove contaminants from the building supply or

exhaust air stream. Supply air filtration at the equipment intake removes

particulate contamination that may foul heat exchange surfaces,

contaminant products, or present a health hazard to people, animals, orplants. Exhaust systems remove air from spaces or capture aerosols, heat,

or gases at specific locations in a room and transport them so they can be

collected, inactivated, and safely discharged to the atmosphere.


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Industrial applications- Heat recovery. Process industry presents unique opportunities to

recover heat from the exhaust air stream for use in preconditioning

makeup air. Extreme care must be taken to ensure compatibility of heat

exchanger components and materials with contaminants often found inexhaust streams.


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Industrial applications- Maintenance. All designs should allow ample room to clean, service, and

replace any component quickly so that design conditions are affected as

little as possible. Maintenance of refrigeration and heat rejection

equipment is essential for proper performance without energy waste.Maintenance includes changing system filters periodically. Fan and motor

bearings require lubrication, and fan belts need periodic inspection. Direct-

and indirect-fired heaters should be inspected annually. Steam and hot-

water heaters have fewer maintenance requirements than comparable

equipment with gas or oil burners. For system compatibility, water

treatment is essential. Air washers and cooling towers should not be

operated unless the water is properly treated.


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Ventilation of the industrial environment

- localized ventilation systems:

- conditioned air is supplied

toward the breathing zone of the

occupants to create comfortableconditions and/or to reduce the

concentration of pollutants.

These zones may have air 5 to

10 times cleaner than the

surrounding air.


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Laboratories


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Laboratories

- primary objective in the design of HVAC systems for laboratories is

providing a safe environment for all personnel.

- labs frequently use 100% outside air, which broadens the range of

conditions to which the systems must respond.

- systems seldom operate at maximum design conditions attention to

partial load operations that are continually changing due to variations in

loads and requirements.

- modifications at some time are possible must consider to what extent

laboratory systems should be adaptable for other needs.

- nature and quantity of the contaminant, types of operations, and degree

of hazard dictate the types of sytems and local exhaust devices.


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Laboratories


- internal heat gains of 50 to 270 W/m2 or more are common for

laboratories with high concentrations of equipment.

- often stringent requirements for the control of temperature, humidity,

relative static pressure, and background particle count require

architectural features to allow the HVAC systems to perform properly.

- equipment rooms and their air intakes and exhaust stacks must belocated to avoid intake of fumes into the building. As with other buildings,

air intake locations must be chosen to minimize fumes from loading docks,

cooling tower discharge, vehicular traffic, etc.


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Laboratories

Laboratory fume hood

- ventilated enclosed work space intended to capture, contain, and exhaust

fumes, vapors, and particulate matter generated inside the enclosure.

- work opening has operable glass sash

for observation and shielding.

- different types: with constant or variable

air flow, constant or variable face velocity,with or without auxiliary air

- example with bypass for approximately

constant air flow and face velocity:


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Laboratories

Biological safety cabinet

- also called a laminar flow cabinet, categorized into 3 classes and 6

groups

- example of some cabinet types:

- important for the HVAC design are the proper placement of the biological

safety cabinet in the laboratory and the rooms air distribution.


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Laboratories

Biological safety cabinet

- Rake (1978):

A general rule of thumb should be that, if the cross draft or other disruptive

room airflow exceeds the velocity of the air curtain at the units face, thenproblems do exist. Unfortunately, in most laboratories such disruptive room

airflows are present to various extents. Drafts from open windows and

doors are the most hazardous sources because they can be far in excess

of 1 m/s and accompanied by substantial turbulence. Heating and air-conditioning vents perhaps pose the greatest threat to the safety cabinet

because they are much less obvious and therefore seldom considered... It

is imperative then that all room airflow sources and patterns be considered

before laboratory installation of a safety cabinet.

- should be located away from drafts, active walkways, and doors.

- exhaust systems for biological safety cabinets must be designed with

consideration of varying static pressure resistance requirements for

different groups.


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Laboratories

Ventilation

- total airflow rate for a laboratory is dictated by one of the following:

Total amount of exhaust from containment and exhaust devices Cooling required to offset internal heat gains

Minimum ventilation rate requirements

- minimum airflow rates are generally in the range of 6 to 10 air changes

per hour when the space is occupied by people; 15 air changes per hourfor animal housing and treatment areas.

- can be arranged for either constant-volume or variable-volume airflow

that incorporate either single-duct reheat or dual-duct configurations.

- labs in which chemicals and compressed gases are used generallyrequire nonrecirculating or 100% outside air supply systems.

- filtration for the air supply depends on the requirements of the laboratory

(from fine filters to HEPA).


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Laboratories

Control

- temperature in laboratories with a constant-volume air supply is generally

regulated with a thermostat that controls the position of a control valve on

a reheat coil in the supply air.

- for the laboratory to act as a secondary containment barrier, the air

pressure in the laboratory must be maintained slightly negative with

respect to adjoining areas. Exceptions are sterile facilities or clean spaces

that may need to be maintained at a positive pressure with respect toadjoining spaces.

- criteria for fume hood control differ depending on the type of hood. The

exhaust volumetric flow is kept constant for standard, auxiliary air, and air-

bypass fume hoods. In variable-volume fume hoods, the exhaust flow isvaried to maintain a constant face velocity.


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Clean spaces


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Clean spaces

- following major industries use clean spaces for their products:

Pharmaceuticals/Biotechnology; Microelectronics/Semiconductor (most

newer semiconductor clean rooms being ISO 14644-1 Class 5 or cleaner);

Aerospace (large-volume spaces with cleanliness levels of ISO 14644-1Class 8 or cleaner); Aseptic food processing and packaging; Automotive

paint booths; Crystal; Laser/optic industries;...


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Clean spaces

Particle control

- airborne particles vary from 0.001 m to several hundred micrometers.

Particles larger than 5 m tend to settle by gravity. In many manufacturing

processes, these airborne particles are viewed as a source ofcontamination.

- external particle sources are controlled primarily by air filtration, room

pressurization, and sealing space penetrations.

- people, clean room surface shedding, process equipment, and the

manufacturing process itself generate particles in the clean space. Internal

particle generation may not be controlled completely, but designer may

anticipate internal sources and design control mechanisms and airflow

patterns to limit their effect on the product.

- proper air filtration prevents most externally generated particles from

entering the clean room (using high-efficiency particulate air (HEPA) filters

and ultralow - penetration air (ULPA) filters).


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Clean spaces

Airflow patterns

- two general categories:

- Nonunidirectional aiflow. Has either multiple-pass circulatingcharacteristics or nonparallel flow. May provide satisfactory contamination

control for cleanliness levels of ISO 14644-1 Classes 6 through 8.

Presupposes that the major space contamination is from makeup air and

that contamination is removed in air-handler or ductwork filter housings or

through HEPA filter supply devices.

- Unidirectional aiflow. Not truly laminar, it is characterized as air flowing

in a single pass in a single direction through a clean room with generally

parallel streamlines. Removes contamination generated in the space and

minimizes cross-contamination perpendicular to the airflow. Air is typicallyintroduced through the ceiling HEPA or ULPA filters.


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Clean spaces


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Clean spaces

Design parameters

- unidirectional airflow with average air velocities from 0.3 to 0.45 m/s,

typically at 0.45 m/s, is widely used.

- clean-room temperatures are controlled from 20 to 22C with tolerancesof 0.06C, 0.1C, 0.3C, and 0.5C. In spaces with cleanliness levels

of ISO 14644-1 Class 7 and 8 tolerances are 1C.

- humidity should be maintained at 40 to 45 % with a tolerance of 5 %.

- to reduce the pressure drop across coils, the most effective method is toreduce their face velocities to 1.5 to 2 m/s. Result is a larger AHU.

- clean rooms and clean spaces always maintain a higher pressure than

the surrounding less clean space for 12 to 15 Pa to minimize the infiltration

of air contaminants.

- energy use of fans, chillers, and pumps in a clean-room system for a FS209 class 1 may be around 540 W/m2 of floor area (5 to 10 times higher

than that of an air-conditioning system for a commercial building).


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Clean spaces

- example semiconductor manufacturing plant:


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Clean spaces

- example ISO 14644-1 Class 4 clean room:


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Clean spaces

- example ISO 14644-1 Class 4 clean room air-conditioning process in

psychrometric chart:


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Computer rooms


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Computer rooms

Design criteria

- before it is introduced into the computer room, outside air should be

treated and preconditioned to remove dust, salts, and corrosive gases.

- system should maintain the room under positive pressure relative tosurrounding spaces. The need for positive pressure to keep contaminants

out of the room is usually a controlling design criterion.

- outside air quantity of 6 to 8 air changes per day usually satisfies

contaminant dilution requirements.- HVAC equipment for computer spaces should be served by electrically

isolated power sources to prevent electrical noise from adversely affecting

computer operation and reliability.


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Computer rooms

Air-conditioning systems

- computer rooms can be conditioned with a wide variety of systems,

including packaged precision air-conditioning units and central station air-

handling systems.

- precision units are available with chilled-water or multiple-refrigerant

compressors with separate refrigeration circuits, air filters, humidifiers,

reheat, and integrated control systems with remote monitoring panels and

interfaces. Self-contained air conditioners are usually located within thecomputer room but may also be remotely located and ducted to the

conditioned space.

- central stations have a larger capacity than precision air-conditioning

units and offer significantly greater opportunities for energy conservation.Systems that use direct evaporative humidification with mechanical cooling

and VAV control allow the use of outside air for free cooling without a

humidification energy penalty.


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Computer rooms

Air-conditioning systems

- example of packaged precision air-conditioning unit with underfloor air

supply


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Computer rooms

Energy conservation and heat recovery

- where secondary uses for recovered heat do not exist or justify heat

recovery, central station air-conditioning systems using outside air for free

cooling, variable-volume ventilation, and evaporative cooling/humidificationstrategies offer significant opportunities for reducing energy use and

improving air quality over precision air-conditioning systems.

- if a use for recovered energy exists, computer rooms are good

candidates for heat recovery because of their large year-round loads. Heatrejected during condensing can be used for space heating, domestic water

heating, or other process heat.


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General considerations

- central exhaust systems are usually designed for specific operations in

which the wood dust is captured at the machines and conveyed through an

overhead duct system to a collector.- metal ductwork should be used and grounded to prevent a buildup of

static electricity. Hoods should be made of spark-free, noncombustible

material. A pneumatic conveying system should be furnished to reduce the

accumulation of wood dust in the collecting duct system. The airflow rateand velocity should be capable of maintaining the air-dust mixture below

the minimum explosive concentration level. Dust collectors should be

located outside of the building.

- fans should be placed downstream of the dust collector and air-cleaning

equipment, and should be interlocked with the wood-processingequipment. When the fan stops, the wood process should stop

immediately and forward a signal to the alarm system.

Wood product facilities


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- temperature and humidity requirements in wood product process areas

vary according to product, manufacturer, and governing code.

- i.e. minimum number of air changes in wood industry recommended in

Canada is 2 ACH.

Wood product facilities

Paper product facilities

- in paper industry temperature inside an enclosed hood ranges from 50 to

60C at the operating floor to 80 to 95C in the hood exhaust plenum at 70

to 90% rh, with an exhaust rate generally ranging from 140 to 190 m3/s.

- most papers are produced with less than 10% moisture by mass. Dry

paper and pulp are hygroscopic and begin to swell noticeably and deform

permanently when stored where the relative humidity exceeds 38%.

-ventilation in paper machine buildings in the US ranges from 10 to 25

ACH in northern mills to 20 to 50 in southern mills.


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- air flow direction is controlled to feed from the tending to the drive side,

and from the dry end to the wet end. Main extract taking place above the

wet end, full advantage being made of the hot surfaces producing a

thermal uplift. A balance is made between the quantity of supply and

extract air. Large volumes of air (240 to 380 m3/s) are required to balance

the paper machines exhaust with the building air balance.



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- values which can be achieved and represent a good level system in

paper industry:



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- flow of heat energy in a modern paper mill. Primary energy for the

process is steam from the boiler, with full use being made of heat recovery:



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- example of the air curtain system for winding of tissue paper:



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Paint spraying facilities


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- different spray systems are more or less efficient at transferring paint onto

surfaces but all create what is called 'overspray'. This consists of relatively

large and visible paint droplets which land nearby but not on the objectbeing sprayed, and also fine paint particles (mist) which mix with and

remain suspended in air.

- fine particle paint aerosols will fill the volume of the booth or spray space

and will remain airborne for prolonged periods. How long will depend onthe particle size and the effectiveness of the ventilation.

- spray booths are ventilated enclosures providing a positive movement of

air in the spraying area to protect the health of those outside the booth to

give some protection to the health of the operator and to provide anatmosphere free from the risk of fire or explosion. Basic aim is to draw

clean air past the breathing zone of the operator as effectively as possible

before exhausting it after suitable filtration.


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- the air flow should be uniform over the whole working area and in a

direction such that the operator avoids breathing air contaminated at

dangerous levels by the liquid being sprayed. Airflow through a booth

should be as linear as possible i.e. in a down-draught booth for example

the air should literally move in a downward direction.

-mechanical ventilation of the booth must be maintained after spraying

ceases until the work area is free of all residual spray mist (purge time).

- most down-draught booths are run under positive pressure as thisprevents the inward leakage of dusty air. About 10% more air is supplied

than is extracted. The excess air leaks out through gaps under doors for

example and will carry some overspray/vapour out of the booth. This mode

of working is not recommended for highly toxic finishes such as

isocyanate-containing paints where vapour mist and droplets should be

contained within the booth.


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- airflow velocity values which should be achieved are a mean of not less

than 0.4 m/s and a minimum measured value of 0.3 m/s.

- inlet filters provide two advantages: they remove particulates which

might otherwise deposit on the painted surfaces and reduce the effects ofcross-draughts and disturbances which are external to the booth. 2-stage

filtration system with a prefilter and a final/ ceiling filter stage will usually

suffice.


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Kitchen ventilation


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Kitchen ventilation


- two purposes:

(1) provide a comfortable environment in the kitchen

(2) enhance the safety of personnel working in the kitchen and of otherbuilding occupants

- centerpiece of any kitchen ventilation system is an exhaust hood, used

primarily to remove effluent from kitchens.

- exhaust ductwork conveys exhaust air from the hood to the outside,

along with any grease, smoke, VOCs, and odors that are not extracted

from the air stream along the way. NFPA Standard 96 have set minimum

air velocity for exhaust ducts at 7.5 m/s. Maximum velocities are limited by

pressure drop and noise and typically do not exceed 12.5 m/s.

- exhaust fans for kitchen ventilation must be capable of handling hot,

grease-laden air. The fan should be designed to keep the motor out of the

air stream.


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Kitchen ventilation

- commercial kitchen exhaust hoods:


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Kitchen ventilation


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Kitchen ventilation

- common type of exhaust fans is roof ventilator (upblast fan) for mounting

at the exhaust stack outlet. Discharge is upward or outward from the roof

or building. Aluminum upblast fans must be listed for the service.


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Kitchen ventilation


- properly designed kitchen ventilation system leaves a little negative

pressure (up to 5 Pa) preventing kitchen odors migrating to adjacent

building spaces, and maintaining a comfortable building environment.

- kitchens require minimum outdoor air ventilation of 25 m3/h per person

based on 22 persons per 100 m2. These requirements may be increased

or decreased in certain areas.

- terminal velocities at the leading edge of the hood should be kept to a

minimum of 0.25 m/s. Ceiling diffuser should be located so that the jet

velocity at the lip of the hood does not exceed 0.25 m/s.

- use of short circuit hoods has to be considered carefully. They introduce

unconditioned air into the hood, which reduces the supply air flow rate.

But, the problem is that the more short-circuited air is exhausted, the less

exhaust capacity is left to get rid of the kitchen effluent.


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Kitchen ventilation

Heat recovery

- heated exhaust air may be suitable for heat recovery; however, smoke

and grease in the exhaust air will, with time, cover any heat transfer

surface. Under these conditions, the heat exchangers require constantmaintenance (e.g., automatic washdown) to maintain acceptable heat

recovery.

- exhaust hood equipped with heat recovery is more likely to be cost

effective where food service facilities with large amounts of cookingequipment are used and/or the climate is extreme.

08 industrial application

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