qsm554 acond lecture

8/8/2019 QSM554 ACond Lecture

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QSM554

AIR CONDITIONINGAIR CONDITIONING

SITI NORAZNIZA AHMAD SEKAKSITI NORAZNIZA AHMAD SEKAK



AIRAIR--CONDITIONING SYSTEMCONDITIONING SYSTEM

FULLFULL AIRAIR--CONDITIONINGCONDITIONING

² DEF : Air-conditioning is the process of

treating air to control temperature,

humidity, cleanliness and distribution

² REASON : The increasing scale of public

and commercial buildings demanded

effective ways of cooling the interior.



AIRAIR--CONDITIONING SYSTEMCONDITIONING SYSTEM


4 controlled elements :

1. Temperature

2. Humidity

3. Air quality

4. Air distribution velocity



AI AIRR--CONDITIONING SYSTEMCONDITIONING SYSTEM

The diagram below shows some typical heat gains in a roomThe diagram below shows some typical heat gains in a room



AIR AIR--CONDITIONING SYSTEMCONDITIONING SYSTEM

Factors to be considered in the building

distribution are:

1.Economy

By achieving minimum duct layout

2.Retain

capability of serving the different spacesaccording to the differing requirements

3.Balance

Fan pressure, duct & grills size to the

different part of the building, get balance

share of supply



MECHANICAL COMPONENTSMECHANICAL COMPONENTS

i) A compressor ii) A fan

iii) A condenser coiliv) An evaporator coilv) A chemical refrigerant



AIRAIR--CONDITIONINGCONDITIONING


1.1. TemperatureTemperature

TheThe refrigerationrefrigeration componentcomponent ofofthethe systemsystem removesremoves heatheat fromfrom

thethe incomingincoming air air toto 2020oo ² ²2525oo viaviarefrigerationrefrigeration cyclecycle..



AIRAIR--CONDITIONINGCONDITIONINGFULL AIR-CONDITIONING

2. Humidity

AA personperson feelsfeels aa coolingcooling effecteffect dueduetoto thethe evaporationevaporation ofof hishis sweatsweat..

TheThe lower lower thethe humidityhumidity thethe faster faster raterate ofof evaporation,evaporation, thethe cooler cooler aapersonperson feelsfeels..

TheThe relativerelative humidityhumidity isis aroundaround 4040%%-- 6060%%..

ThisThis isis thethe levellevel ofof humidityhumidity thatthat isis

mostmost comfortablecomfortable for for aa personperson




FULL AIR-CONDITIONING2. Humidity

Humidification(+)

A process of increasing the relativehumidity of the air .

The incoming air pass wetted strips, pans ofwater or water spray so that the air willabsorb the moisture and become morehumidified.




2. Humidity

Dehumidification(-)

A process of reducing the relative humidity.

Condensation can cause dehumidification. In condensation, the air temperature is

brought to below point causing the requiredamount of air moisture to condense.

Then the air is brought up to the desiredtemperature by using heating.




2. Humidity

In the Malaysian hot and humid

climate, the air has to be madeless humid

In trying to make the air less

humid, most large air-conditioning systems willdehumidify then humidify the air.




2. Humidity

This is done by exposing theThis is done by exposing the

incoming air to the condenser incoming air to the condenser coilcoil

The air is now less humid but isThe air is now less humid but is

too dry for human comforttoo dry for human comfort




FULL AIR-CONDITIONING

2. Humidity

The next step is bringing up the humidity

of the air to a level which is comfortablefor humans.

This is done by first slightly heating the air

and then passing the humidified lesscontrol air through a water spray.

This increases the humidity to a levelcomfortable for humans.




3. Air quality

In ventilated air-conditioning systems,air is brought into a building to replace

used air. Most air-conditioning systems are

actually sophisticated ways ofmechanical ventilation.

Air quality is associated with air purity.There are 2 aspects associated with air purity which are cleanliness andoxygen contents.





4.4. Air Air distributiondistribution velocityvelocity

The conditioned air needs to be movedThe conditioned air needs to be movedand distributed to the required spacesand distributed to the required spaces

in the building.in the building.

A fan is used to move the air throughA fan is used to move the air throughthe air delivery system.the air delivery system.

The delivery system consists ofThe delivery system consists of



FULLFULL AIRAIR--CONDITIONINGCONDITIONINGThe delivery system consists of:The delivery system consists of:

a.a.supply & return air ductssupply & return air ducts -- the pipe /the pipe /passageway in which the air movespassageway in which the air moves

b.b.control damperscontrol dampers ³ ³ to change theto change thedirection of the movement of air sodirection of the movement of air sothat some of the air can be directedthat some of the air can be directed

to duct branchesto duct branchesc.c.duct insulationduct insulation -- to insulate heat fromto insulate heat from

heating the cooler air and insulateheating the cooler air and insulatefrom any sound of the moving air from any sound of the moving air

AIR AIR--CONDITIONINGCONDITIONING





d. sound dampers - to stop sound frombeing produced by moving air

e. fire dampers - to prevent the spreadof fire through ducts

f. supply air grilles (s.a.g) and return air

grilles (r.a.g) - used to diffused the airso that the air is evenly distributed asit enters the room space.



Components:Components:

FanFan FiltersFilters

DuctworkDuctwork

Fire DampersFire Dampers

DiffusersDiffusers

FanFan

Filter Filter

DuctworkDuctwork

Fire Damper Fire Damper

Diffuser Diffuser



AIR-CONDITIONINGFACTOR O

FCHOSING AIR-CONDITIONING:

Weather analysis / Climate: outdoor design

temperature

Construction / building scale : location,

orientation, type of buildingBuilding analysis: the scale effect ofincreased volume and thermal impacts

Activities: inside activities, internalcomfort criteriaQuality and prestige: higher expectation

of comfort




AIR-CONDITIONING CATEGORIES:

1. Heating air-conditioning

To treat the air so that a comfortable warm

environment is produced for the building interior.

2. Refrigeration air-conditioning (Cooling air-conditioning)

To treat the air so that a comfortable cool

environment is produced for the building interior.

Note:

For the purpose of this subject, we will study

more about Refrigeration-conditioning as it is more

applicable in this country.

AIR-CONDITIONING



REFRIGERATIONREFRIGERATION AIRAIR--CONDITIONINGCONDITIONINGAIRAIR--CONDITIONINGCONDITIONING CATEGORIESCATEGORIES::




REFRIGERATION AIR-CONDITIONING

The vapour compression refrigeration cycle is asfollows:

1. Compression:

the compressor compresses the low-pressure gas so that the gas becomeshotter and has high pressure.

Because of the high pressure, the boiling

point of the refrigerant is increased. Thus the gas refrigerant is carrying excess

heat but could not release it due to theinsulated pipe.




2. Condensation: the hot high pressure gas passes

through the condenser (condenser coils).

The condenser is a coiled pipeexposed to the outside air.

Excess heat and latent heat istransferred to the cooler outside air and the gas changes into high-pressure liquid at room temperature.




3. Expansion:3. Expansion: the pressure of the liquid is loweredthe pressure of the liquid is lowered

after passing through the expansionafter passing through the expansionvalve.valve.

This causes the liquid refrigerant toThis causes the liquid refrigerant tohave a lower boiling point and make ithave a lower boiling point and make ita cold liquid under low pressure.a cold liquid under low pressure.




44.. EvaporationEvaporation::

thethe coldcold liquidliquid refrigerantrefrigerant under under lowlowpressurepressure absorbsabsorbs heatheat fromfrom thethe air air

cyclecycle thusthus coolingcooling thethe air air..

TheThe refrigerantrefrigerant turnsturns intointo aa lowlow--

pressurepressure gasgas duedue toto thethe absorbedabsorbed

heatheat..

It goes back to Step No. 1 to continueIt goes back to Step No. 1 to continuethe cyclethe cycle



AIRAIR--CONDITIONINGCONDITIONINGAIRAIR--CONDITIONINGCONDITIONING PLANTPLANT

In the fully air-conditionedbuilding, thewindows are fixedshut. The air indoorsis enclosed and

separate from theair outdoors, and itstemperature andhumidity arecontrolled to closelimits by circulatingit through specialplant.



AIRAIR--CONDITIONINGCONDITIONING PLANTPLANT




TYPES OF AIRTYPES OF AIR--CONDITIONINGCONDITIONING

SYSTEMSSYSTEMSAir conditioning systems fall into three (3) mainAir conditioning systems fall into three (3) maincategoriescategories ::

i)i) Central plantCentral plant systemssystems

one centralone central source of conditioned air distribute asource of conditioned air distribute aductwork networkingductwork networking

ii)ii) Room air conditioning unitsRoom air conditioning units

selfself--contained packagecontained package units which can beunits which can be

positioned in each roompositioned in each roomiii)iii) Fan coil unitsFan coil units

are room units and incorporateare room units and incorporate heat exchangersheat exchangerspiped withpiped with chilled water chilled water and a fan to provideand a fan to providecool air.cool air.



CENTRAL PLANTCENTRAL PLANT

SYSTEMSSYSTEMS



Central plantCentral plant systemssystems

- +

Exhaust air Return air

Fresh airSupply air

Recirculated air

Supply fan

Cooling coil Heater

SCHEMATIC DIAGRAM OF CENTRAL PLANT

AIR CONDITIONING SYSTEM




Has central refrigeration plant Has central refrigeration plant

CustomisedCustomised design include ventilation duct,design include ventilation duct,terminal unit, AHU and distribution pipes.terminal unit, AHU and distribution pipes.

Have to provide a room for its equipment.Have to provide a room for its equipment.

Installed during building construction.Installed during building construction.

Thus, the system has to be integrated with theThus, the system has to be integrated with the

building plan.building plan. DampersDampers are used to control the amount of air inare used to control the amount of air in

each duct. It is common to have 20% fresh aireach duct. It is common to have 20% fresh airand 80% recirculated air to buildings.and 80% recirculated air to buildings.



Central plant systems

Filters are required to remove particles of dustand general outdoor pollution. Air filters serve as

cleaning mechanisms. They are used in home

cooling systems and heating ducts as well as

vacuum cleaners and breathing masks. Bytrapping large particles of dust, lint, mold spores

and even hair, filters help residential systems

process the polluted air and produce cleaner,

healthier air.

This translates to a lower incidence of pneumonia,

influenza and asthma, all conditions that are

exacerbated by breathing polluted air



FiltersFilters Classification:Classification:

DryDry

Viscous Viscous

ElectrostaticElectrostatic

Activated Carbon Activated Carbon



Central plant systems

The secondary filter, after the mix point, isused to remove fine dust particles or other

contaminant picked up in the rooms and

recirculated back into the plant. A removable bag filter is generally used

for this where a series of woven fibre bags

are secured to a framework which can be

slid out of the ductwork or air handling unit

(A.H.U.) for replacement.



Central plantCentral plant systemssystemsAir Handling Units (AHU)Air Handling Units (AHU)



AHU OPERATION AHU OPERATION -- schematicschematic



Air Handling Units ( AHU)1) Fresh air is usually drawn from the top of the building through

a louvered intake (fresh air inlet).

2) Recirculated air and fresh air are then mixed in the mixingbox

3) The mixed air is then filtered

4) A preheater coil will provide initial heat energy in the air andraised its temperature.

5) A water spray washer will humidifies and clean the air

6) A Final or reheater establishes the supply air temperature &humidity.

7) The Inlet fan or centrifugal type will generate sufficient

pressure thru a ductwork.8) At the Inlet duct the air will flow thru it.

9) Exhaust duct will release some of the air to outside.

10) Recirculating duct will use some of the air from the room tobe used again.




Air handling units ( Air handling units ( A.H.U A.H.U.) are widely used.) are widely usedas a package unit which incorporates allas a package unit which incorporates allthe main plant items as shownthe main plant items as shown

Pipework, ductwork and electricalPipework, ductwork and electricalconnections are made after the unit is set connections are made after the unit is set in place on site.in place on site.

Since air conditioning plant rooms tend toSince air conditioning plant rooms tend tobe at roof level, the largerbe at roof level, the larger A.H.U's A.H.U's arearelifted into place by crane before the roof islifted into place by crane before the roof isfixed.fixed.




The photograph below shows a typicalThe photograph below shows a typicalair handling unit with handles on theair handling unit with handles on thedoors for access to equipment.doors for access to equipment.




Air Handling Units (AHU)Air Handling Units (AHU)Suitability:Suitability:

This system is suited for large multi roomThis system is suited for large multi roombuildings and halls where it is uneconomicalbuildings and halls where it is uneconomicalto install separate AC units to each room.to install separate AC units to each room.

Higher cost operation.Higher cost operation.



Room air conditioning unitsRoom air conditioning units

These units use refrigerant to transferThese units use refrigerant to transfercooling effect into rooms.cooling effect into rooms.

Standard designStandard design

Room air conditioning units fall into twoRoom air conditioning units fall into twomain categories:main categories:

1.1. Split typeSplit type

2.2. Window/wall unitsWindow/wall units



Room air conditioning unitsRoom air conditioning unitsSplit typeSplit type

outdoor unitoutdoor unit : generates the cold refrigerant : generates the cold refrigerant gasgas

indoor unitindoor unit :uses this cold refrigerant to cool:uses this cold refrigerant to cool

the air in a space.the air in a space. TheThe outdoor unit outdoor unit uses auses a compressorcompressor and airand air

cooledcooled condensercondenser to provide cold refrigerant to provide cold refrigerant to ato a cooling coilcooling coil in thein the indoor unit indoor unit

A fan then blows air across the cooling coil A fan then blows air across the cooling coiland into the room.and into the room.

The indoor unit can either be ceiling mountedThe indoor unit can either be ceiling mounted

(cassette unit(cassette unit) or floor mounted.) or floor mounted.




Split typeSplit type

The drawing below shows a ceiling mounted (cassette unit)The drawing below shows a ceiling mounted (cassette unit)



Room air conditioning unitsRoom air conditioning unitsSplit typeSplit type

The photographs below show a ceilingThe photographs below show a ceilingmounted cassette and an outdoor unit.mounted cassette and an outdoor unit.



Central Plant SystemsCentral Plant Systems

Advantages:Advantages:1.1. Noise in rooms is usually reduced if plant Noise in rooms is usually reduced if plant

room is away from occupied spaces.room is away from occupied spaces.

2.2. The whole building can be controlled fromThe whole building can be controlled froma central control station.a central control station.

-- optimum start and stop can be usedoptimum start and stop can be used

-- time clocks can bring air conditioning ontime clocks can bring air conditioning onand off at appropriate times.and off at appropriate times.

3.3. Maintenance is centralised in the plant Maintenance is centralised in the plant

room. Plant is easier to access.room. Plant is easier to access.



Central Plant SystemsCentral Plant Systems

Disadvantages:Disadvantages:

1.1. Expensive to install a complete fullExpensive to install a complete fullcomfort aircomfort air--conditioning systemconditioning system

throughout a building.throughout a building.2.2. Space is required for plant and to runSpace is required for plant and to run

ductwork both vertically in shafts andductwork both vertically in shafts and

horizontally in ceiling spaces.horizontally in ceiling spaces.3.3. Individual room control is difficult withIndividual room control is difficult with

central plant.central plant.



ROOM AIR CONDITIONINGROOM AIR CONDITIONING

UNITSUNITS

WINDOW / WALL UNITSWINDOW / WALL UNITS

i i i i ii i i i i



Room air conditioning unitsRoom air conditioning unitsWindow / Wall UnitsWindow / Wall Units

moremore compactcompact than split units since all thethan split units since all theplant items contained inplant items contained in oneone box.box.

Window unitsWindow units are installed into anare installed into an

appropriate hole in the window andappropriate hole in the window andsupported with a metal frame.supported with a metal frame.

Wall unitsWall units are built into an external wallare built into an external wall

and contain all the necessary items of and contain all the necessary items of equipment to provide cool air.equipment to provide cool air.




Window / Wall UnitsWindow / Wall Units




Window / Wall UnitsWindow / Wall Units A small A small hermetically sealed compressorhermetically sealed compressor

is to provide refrigerant gas at the pressureis to provide refrigerant gas at the pressure

required to operate the refrigeration cycle.required to operate the refrigeration cycle. The condenser is used to condense theThe condenser is used to condense the

refrigerant to a liquid which is then reducedrefrigerant to a liquid which is then reduced

in pressure and piped to the cooling coil.in pressure and piped to the cooling coil.




Window / Wall UnitsWindow / Wall Units




Suitability :Suitability :

Light duty AC systemLight duty AC system

Used for residential building and in smallUsed for residential building and in smallto medium sized buildingto medium sized building



Room Air Conditioning UnitsRoom Air Conditioning Units

Advantages:Advantages:

1.1. Cheaper to install.Cheaper to install.

2.2. Individual room control.Individual room control.

3.3. Works well where rooms haveWorks well where rooms haveindividual requirements.individual requirements.

4.4. No long runs of ductwork.No long runs of ductwork.

5.5. Can be used to heat as well as coolCan be used to heat as well as coolif a reversing valve is fittedif a reversing valve is fitted




Disadvantages:Disadvantages:

1.1.Sometimes the indoor unit fan becomesSometimes the indoor unit fan becomesnoisy.noisy.

2.Noisy compressor in outdoor unit.2.Noisy compressor in outdoor unit.3.Each unit or group of units has a filter,3.Each unit or group of units has a filter,

compressor and refrigeration pipeworkcompressor and refrigeration pipework

that needs periodic maintenance andthat needs periodic maintenance andpossible repossible re--charging.charging.




Disadvantages:Disadvantages:5.Not at robust as central plant.

6.The majority of room air conditioners just

recirculate air in a room- no fresh air supply although most

manufacturers make units with fresh

air capability.



F

AN COIL

UNITS



These are room air conditioners but useThese are room air conditioners but usechilled water instead of refrigerant.chilled water instead of refrigerant.

Units can be floor or ceiling mounted.Units can be floor or ceiling mounted.

The chilled water is piped to a finned heat The chilled water is piped to a finned heat exchanger as in a fan convector.exchanger as in a fan convector.

A fan blows room air across the heat A fan blows room air across the heat

exchanger and cool air is emitted into theexchanger and cool air is emitted into theroom, as shown.room, as shown.

Fan coil unit (FCU)Fan coil unit (FCU)



Fan coil unitsFan coil units

FAN COIL UNIT

(refrigeration plant)

Room Air

Cool Air

Chilled water pipes

Drip tray and condensate drain

T

Centrifugal fans

Cabinet

Thermostat

Dust filter

Outlet louvre

Finned pipe heat exchanger



Fan coil units (FCU)xFan coil units (FCU)x

A multi room system use central refrigeration A multi room system use central refrigerationplant plant

The plant is used to chill water that is pipedThe plant is used to chill water that is piped

to individual rooms.to individual rooms. A separate network of ventilation ducts A separate network of ventilation ducts

supplies fresh air to each room.supplies fresh air to each room.

The chill water is used to cool the free airThe chill water is used to cool the free airbefore it enters the room.before it enters the room.

Thus, each room has individual control overThus, each room has individual control overthe conditioned air.the conditioned air.



Fan coil units (FCU)Fan coil units (FCU)

Suitability :Suitability :

for conditioning a large number of for conditioning a large number of

small,small, individually controlledindividually controlled, and, and

variably occupied rooms, e.g.variably occupied rooms, e.g.

hotels, motels, hospitals, campuseshotels, motels, hospitals, campuses

Highly popular forHighly popular for multimulti--storeystorey

office buildingoffice building in Malaysiain Malaysia



Fan Coil UnitsFan Coil Units

Advantages Advantages

1.1. Cheaper to install than all airCheaper to install than all air

central plant system.central plant system.2.2. Individual room control.Individual room control.

3.3. Works well where rooms haveWorks well where rooms have

individual requirements.individual requirements.

Fan Coil UnitsFan Coil Units



Fan Coil UnitsFan Coil UnitsDisadvantages:Disadvantages:

1.1. Sometimes the indoor unit fan becomesSometimes the indoor unit fan becomesnoisy,noisy,

2.2. Each unit requires maintenance.Each unit requires maintenance.

3.3. Long runs of pipework are required.Long runs of pipework are required.4.4. A chiller is still required to produce chilled A chiller is still required to produce chilled

water therefore they do not save as muchwater therefore they do not save as much

in plant and plant room space as room airin plant and plant room space as room airconditioners.conditioners.

5. Fresh air facility may not be installed.5. Fresh air facility may not be installed.



Choosing an A/C SystemChoosing an A/C System

Generally central plant systems are usedGenerally central plant systems are usedin largein large prestigious buildingsprestigious buildings where awhere ahigh quality environment is to behigh quality environment is to beachieved.achieved.

Cassette units and other split systems canCassette units and other split systems canbe used together with central plant be used together with central plant systems to provide a moresystems to provide a more flexibleflexible

design.design.

Each system has its own advantages andEach system has its own advantages andthe following is a summary of some of thethe following is a summary of some of the

main advantages and disadvantages.main advantages and disadvantages.



ENDEND

qsm554 acond lecture

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