Bldg. Utilities

7/28/2019 Bldg. Utilities

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Window Air Conditioner

Window air conditioneris the most commonly used air conditioner for single rooms. Inthis air conditioner all the components, namely the compressor, condenser, expansionvalve or coil, evaporator and cooling coil are enclosed in a single box. This unit is fitted

in a slot made in the wall of the room, or often a window sill.
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the refrigeration system, air circulation system, ventilation system, control system, andthe electrical protection system. All these have been discussed in details below alongwith the front panel and other parts.

The Refrigeration System of the Window Air ConditionerThe refrigeration system of the window air conditioner comprises of all the importantparts of the refrigeration cycle. These include the compressor, condenser, expansionvalve and the evaporator. All these components have been shown in fig 3 above. Therefrigerant used in most of the window air conditioners is R22.

The compressor used in the window air conditioners is hermetically sealed type, whichis portable one. This compressor has long life and it carries long warranty periods. Incase of the maintenance problems it can be replaced easily from the company. Thecondenser is made up of copper tubing and it is cooled by the atmospheric air. Thecondenser is covered with the fins to enable faster heat transfer rate from it.

The capillary tubing made up of various rounds of the copper coil is used as theexpansion valve in the window air conditioners. Just before the capillary there is drier


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filter that filters the refrigerant and also removes the moisture particles, if present in therefrigerant.Like condenser, the evaporator is also made up of copper tubing of number of turns andis covered with the fins. The evaporator is also called as the cooling coil since therooms air passes over it and gets cooled. Just in front of the evaporator there is air filter

fitted in the front panel or front grill. As the room air is absorbed, it is first passed overthe filter so that it gets filtered. The filtered air is then blown over the cooling coil and thechilled air is passed into the room.The refrigerant after leaving the cooling coil enters the accumulator where it isaccumulated and then it is again sucked by the compressor for recirculation over thewhole cycle.

Air Circulation System of the Window Air Conditioner

The air circulation system of the window air conditioner comprises of the following parts(please refer fig 4 & 5).

1) Blower: This is the small blower that is fitted behind the evaporator or cooling coilinside the assembly of the window air conditioner system. The blower sucks the air fromthe room which first passes over the air filter and gets filtered. The air then passes overthe cooling coil and gets chilled. The blower then blows this filtered and chilled air,which passes through the supply air compartment inside the window air conditionerassembly. This air is then delivered into the room from the supply air grill of the frontpanel.

2) Propeller fan or the condenser fan: The condenser fan is the forced draft type ofpropeller fan that sucks the atmospheric air and blows it over the condenser. The hot

refrigerant inside the condenser gives up the heat to the atmospheric air and itstemperature reduces.

3) Fan motor: The motor inside the window air conditioner assembly is locatedbetween the condenser and the evaporator coil. It has double shaft on one side of whichthe blower is fitted and on the other side the condenser fan is fitted. This makes thewhole assembly of the blower, the condenser fan and the motor highly compact.

Control System of the Window Air Conditioners

In front of the window air conditioner there is control panel or the operating panel that

carries various control buttons. This control panel can be easily accessed from the frontpanel of the window air conditioner. The three important parameters that are to becontrolled inside thewindow air conditionerare the room air temperature, the flow rate ofthe air and the direction of the air. All these controls are discussed below and alsoshown in figure 1.

1) Thermostat for controlling the room air temperature: For controlling thetemperature inside the room there is thermostat. The thermostat sensor is connected
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directly to the cooling coil to sense its temperature. The thermostat is also connected tothe switch in control panel and it has the knob for setting the temperature. The personinside the room can easily set the temperature required by rotating this knob. In themodern window air conditioners, there is printed circuit board (PCB) to which thethermostat is connected. This PCB has remote sensor so the setting of the thermostat

can be easily changed by the remote control.

2) Air flow rate inside the room: The motor connected to the blower is of multispeedtype, so one can change the speed of the motor. As the speed of the motor changes theamount of air sucked by it and blown by it also changes and so the amount of airdelivered in the room also changes. The speed of the motor can be changed by theknob provided in the control panel or by the remote control if the air conditioner hasPCB fitted into it.

3) Direction of the air flow inside the room: In front panel of the window airconditioner there are horizontal lovers. Additionally, in front of the air conditioner body

and attached to it are the vertical louvers. The chilled air from blown by the blowerpasses into the room through these louvers. The horizontal louvers in the front panelenable changing the vertical motion direction of the air inside the room. The position ofthese lovers can be changed manually.

The vertical louvers enable changing the horizontal motion of the air inside the room.These louvers are connected to the small motor. The vertical louvers can be keptmoving in the vertical direction so that the air flows throughout the room uniformly orthey can be kept in the fixed direction so that the air flows in particular desired directiononly. The operation of the motor of the vertical lovers can be controlled by the smallbutton on the control panel of the window air conditioner (refer the figure below

especially figure 5 & 6). In case of the automatic window air conditioner with PCB, themotion of the vertical lovers can be controlled by the remote. The horizontal louvers inthe front panel and the vertical louvers enable fine control of the distribution of air insidethe room.


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Front Panel of the Window Air Conditioner

The very front covering of the window air conditioner assembly that is visible to theperson is the front panel (many times called as the front grill). For novice people thefront panel itself is the whole air conditioner. These days lots of importance is beinggiven to the aesthetics of the front panel so thewindow air conditioneralso serves as thedecorative item inside the room. The front panel has two important compartments:return air and supply air compartments. These are described below (please refer thefigure above, especially figure 5 & 6).


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1) Return air compartment: The return air compartment of the front panel comprises ofthe return air grill and the air filter. When the blower sucks the air, it is first over thereturn air grill and then over the air filter. Since the return air from the room comesinside the air conditioner via this part of the front panel, it is called as return aircompartment of the grill.

2) Supply air compartment: The supply air compartment of the front panel comprisesof the horizontal louvers as described above. The horizontal louvers help changing thevertical direction of air inside the room and their position can be changed manually asper the requirement.There is another opening in the front panel that provides access to the control panel ofthe window air conditioner. The front panel of the window air conditioner can beremoved easily for carrying out the maintenance works. If you want to remove the filterfrom the front panel, one can easily slide it out from the side without removing the wholepanel.

Tips for Installing the Window Air ConditionerHere are some important tips to remember before installing window air conditioner:

1) Install the window air conditioner on the largest wall of the room that is exposed tothe external atmosphere. Doing this ensures uniform distribution of the chilled air insidethe room.2) The height of the window AC inside the room should be about 75 cm to 120 cm fromthe floor. This will allow the flow of the fresh chilled within the room such that themaximum cooling effect would be utilized by the occupants inside the room. If the heightof the window AC is too high, lots of cooling effect of the air will be used to cool theceiling of the room.3) Keep the high current point ready before the installation around the location wherethe window AC will be installed.4) You can install the window AC either in the wall of the room or the window. If you are

installing the unit in the window make sure that the window is large enough and strongenough to bear the weigh

Split Air ConditionerThesplit air conditionercomprises of two parts: the outdoor unit and the indoor unit.The outdoor unit, fitted outside the room, houses components like the compressor,condenser and expansion valve. The indoor unit comprises the evaporator or coolingcoil and the cooling fan. For this unit you dont have to make any slot in the wall of theroom. Further, the present day split units have aesthetic looks and add to the beauty of

the room. The split air conditioner can be used to cool one or two rooms.Wall Mounted Indoor UnitIt is the indoor unit that produces the cooling effect inside the room. The indoor unit ofthe split air conditioner is a box type housing in which all the important parts of the airconditioner are enclosed. The most common type of the indoor unit is the wall mountedtype though other types like ceiling mounted and floor mounted are also used. We shalldiscuss all these types in separate articles, here we shall discuss the wall mounted typeof the indoor unit.
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These days the companies give utmost importance to the looks and aesthetics of theindoor unit. In the last couple few years the purpose of the indoor unit has changed frombeing a mere cooling effect producing devise to a beautiful looking cooling deviseadding to the overall aesthetics of the room. This is one of the major reasons that thepopularity of the split units has increased tremendously in the last few years. Let us see

the various parts enclosed inside the indoor unit of the split air conditioner:

1) Evaporator Coil or the Cooling Coil:

The cooling coil is a copper coil made of number turns of the copper tubing with one or

more rows depending on the capacity of theair conditioningsystem. The cooling coil is

covered with the aluminum fins so that the maximum amount of heat can be transferred

from the coil to the air inside the room.

The refrigerant from the tubing at very low temperature and very low pressure enters

the cooling coil. The blower absorbs the hot room air or the atmospheric air and in doing

so the air passes over the cooling coil which leads to the cooling of the air. This air is

then blown to the room where the cooling effect has to be produced. The air, afterproducing the cooling effect is again sucked by the blower and the process of cooling

the room continues.

After absorbing the heat from the room air, the temperature of the refrigerant inside the

cooling coil becomes high and it flows back through the return copper tubing to the

compressor inside the outdoor unit. The refrigerant tubing supplying the refrigerant from

the outdoor unit to the indoor unit and that supplying the refrigerant from indoor unit to

the outdoor unit are both covered with the insulation tape.

2) Air Filter:The air filter is very important part of the indoor unit. It removes all the dirt particles fromthe room air and helps supplying clean air to the room. The air filter in the wall mountedtype of the indoor unit is placed just before the cooling coil. When the blower sucks thehot room air, it is first passed through the air filter and then though the cooling coil. Thusthe clean air at low temperature is supplied into the room by the blower.

3) CoolingFan or Blower:Inside the indoor unit there is also a long blower that sucks the room air or theatmospheric air. It is an induced type of blower and while is sucks the room air it ispassed over the cooling coil and the filter due to which the temperature of the airreduces and all the dirt from it is removed. The blower sucks the hot and unclean airfrom the room and supplies cool and clean air back. The shaft of the blower rotatesinside the bushes and it is connected to a small multiple speed motor, thus the speed ofthe blower can be changed. When the fan speed is changed with the remote it is thespeed of the blower that changes.

4) Drain Pipe:Due to the low temperature refrigerant inside the cooling coil, its temperature is verylow, usually much below the dew point temperature of the room air. When the room airis passed over the cooling due the suction force of the blower, the temperature of the air


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becomes very low and reaches levels below its dew point temperature. Due to this thewater vapor present in the air gets condensed and dew or water drops are formed onthe surface of the cooling coil. These water drops fall off the cooling coil and arecollected in a small space inside the indoor unit. To remove the water from this spacethe drain pipe is connected from this space extending to the some external place

outside the room where water can be disposed off. Thus the drain pipe helps removingdew water collected inside the indoor unit.To remove the water efficiently the indoor unit has to be a tilted by a very small angle ofabout 2 to 3 degrees so that the water can be collected in the space easily and drainedout. If this angle is in opposite direction, all the water will get drained inside the room.

Also, the if the tilt angle is too high, the indoor unit will shabby inside the room.

5) Louvers or Fins:The cool air supplied by the blower is passed into the room through louvers. Thelouvers help changing the angle or direction in which the air needs to be supplied intothe room as per the requirements. With louvers one easily change the direction in whichthe maximum amount of the cooled air has to be passed.

There are two types of louvers: horizontal and vertical. The horizontal louvers areconnected to a small motor and there position can set by the remote control. Once canset a fixed position for the horizontal louvers so that chilled air is passed in a particulardirection only or one can keep it in rotation mode so that the fresh air is suppliedthroughout the room. The vertical louvers are operated manually and one can easilychange their position as per the requirements. The horizontal louvers control flow of airin upper and downward directions of the room, while vertical louvers control movementof air in left and right direction.


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Location of the Indoor and the Outdoor Units

1) Indoor Unit:Here are the important suggestions when deciding the location of indoor unit inside theroom:a) The indoor unit is located inside the room at the location from where the air can bedistributed evenly throughout the room.b) As far as possible the indoor should be installed above the bed so that the maximumcooling effect can be obtained. It should be located directly above the bed. If one has toavoid the direct flow of chilled air on the body, one can always change the direction ofthe louvers. The indoor unit can also be installed on wall towards your feet though it canbe installed on other side walls also.


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c) The wall mounted indoor unit should be located at the height of about 8 to 10 feetfrom the floor so that that most of the chilled air is used for cooling the room and notmerely for cooling the hot roof.d) The indoor unit should be accessible easily so that one can conveniently clean thefilter every fortnight and the whole unit and also that one can manually change the

position of the louvers easily.e) If the indoor unit is installed above certain window, make sure that it is in symmetrywith the window, else the unit will look shabby. The indoor unit is meant to add to theaesthetics of the room and not destroy it.

2) Outdoor Unit:Here are some points to consider when deciding the location of the outdoor unit:a) The outdoor unit should be located in the open space preferably on the terrace sothat the air can flow freely over the compressor and the condenser. If the terrace is notavailable it can be kept on the awning above the wall or it can be hanged on theexternal wall supported by the angles.b) The location of outdoor unit should be such that it is easily accessible for carrying out

the maintenance works of the compressor, condenser, and other devices. Theinstallation and gas charging also should be convenient.c) There should not be any hindrances in front of the outdoor that would block thepassage of fan air from passing to the open space. Any blockages will seriously affectthe performance of the AC and can also lead to the burning of hermetically sealedcompressor coil.d) The surface on which the outdoor unit is to be installed should be rigid enough toavoid its vibration. The vibration of the outdoor unit will raise excessive noise and alsolead to the breaking of the copper tubing and leakage of the refrigerant.It is always advisable to keep the outdoor unit at the height above the indoor unit. If theoutdoor unit is kept at level below the indoor, some of the compressor power is used in

pumping the refrigerant against the gravity, thus reducing the overall performance of thecompressor. Most of the outdoor units are quite silent so one does not have to worryabout their noise. The internal parts of the outdoor unit are shielded against the rain andsun rays, so one can rest assured about their safety in different climatic conditions.The refrigerant at very low temperature flows inside the tubing between indoor and theoutdoor unit, and there is always some loss of refrigerant effect to the atmosphere fromthese tubing, hence the distance between the indoor and the outdoor unit should bekept as minimum as possible to reduce the loss of the cooling effect. The maximumdistance between the indoor and the outdoor units can be about 15 meters.

Packaged Air Conditioners

The window and split air conditioners are usually used for the small air conditioningcapacities up to 5 tons. The central air conditioning systems are used for where thecooling loads extend beyond 20 tons. The packaged air conditioners are used for thecooling capacities in between these two extremes. The packaged air conditioners areavailable in the fixed rated capacities of 3, 5, 7, 10 and 15 tons. These units are usedcommonly in places like restaurants, telephone exchanges, homes, small halls, etc.
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As the name implies, in the packaged air conditioners all the important components ofthe air conditioners are enclosed in a single casing like window AC. Thus thecompressor, cooling coil, air handling unit and the air filter are all housed in a singlecasing and assembled at the factory location.

Depending on the type of the cooling system used in these systems, the packaged airconditioners are divided into two types: ones with water cooled condenser and the oneswith air cooled condensers. Both these systems have been described below:

Packaged Air Conditioners with Water Cooled Condenser

In these packaged air conditions the condenser is cooled by the water. The condenseris of shell and tube type, with refrigerant flowing along the tube side and the coolingwater flowing along the shell side. The water has to be supplied continuously in thesesystems to maintain functioning of the air conditioning system.

The shell and tube type of condenser is compact in shape and it is enclosed in a singlecasing along with the compressor, expansion valve, and the air handling unit includingthe cooling coil or the evaporator. This whole packaged air conditioning unit externallylooks like a box with the control panel located externally.

In the packaged units with the water cooled condenser, the compressor is located at thebottom along with the condenser (refer the figure below). Above these components theevaporator or the cooling coil is located. The air handling unit comprising of thecentrifugal blower and the air filter is located above the cooling coil. The centrifugalblower has the capacity to handle large volume of air required for cooling a number ofrooms. From the top of the package air conditioners the duct comes out that extends to

the various rooms that are to be cooled.

All the components of this package AC are assembled at the factory site. The gascharging is also done at the factory thus one does not have to perform the complicatedoperations of the laying the piping, evacuation, gas charging, and leak testing at thesite. The unit can be transported very easily to the site and is installed easily on theplane surface. Since all the components are assembled at the factory, the high qualityof the packaged unit is ensured.

Package AC with Water Cooled Condenser


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Packaged Air Conditioners with Air Cooled Condensers

In this packaged air conditioners the condenser of the refrigeration system is cooled bythe atmospheric air. There is an outdoor unit that comprises of the importantcomponents like the compressor, condenser and in some cases the expansion valve(refer the figure below). The outdoor unit can be kept on the terrace or any other openplace where the free flow of the atmospheric air is available. The fan located inside thisunit sucks the outside air and blows it over the condenser coil cooling it in the process.The condenser coil is made up of several turns of the copper tubing and it is finned

externally. The packaged ACs with the air cooled condensers are used more commonlythan the ones with water cooled condensers since air is freely available it is difficultmaintain continuous flow of the water.

The cooling unit comprising of the expansion valve, evaporator, the air handling blowerand the filter are located on the floor or hanged to the ceiling. The ducts coming fromthe cooling unit are connected to the various rooms that are to be cooled.

CENTRAL AIR CONDITIONING PLANTS

The central air conditioning plants or the systems are used when large buildings, hotels,

theaters, airports, shopping malls etc are to be air conditioned completely. The windowand split air conditioners are used for single rooms or small office spaces. If the wholebuilding is to be cooled it is not economically viable to put window or split air conditionerin each and every room. Further, these small units cannot satisfactorily cool the largehalls, auditoriums, receptions areas etc.In the central air conditioning systems there is a plant room where large compressor,condenser, thermostatic expansion valve and the evaporator are kept in the large plantroom. They perform all the functions as usual similar to a typical refrigeration system.
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However, all these parts are larger in size and have higher capacities. The compressoris of open reciprocating type with multiple cylinders and is cooled by the water just likethe automobile engine. The compressor and the condenser are of shell and tube type.While in the small air conditioning system capillary is used as the expansion valve, inthe central air conditioning systems thermostatic expansion valve is used.

The chilled is passed via the ducts to all the rooms, halls and other spaces that are tobe air conditioned. Thus in all the rooms there is only the duct passing the chilled airand there are no individual cooling coils, and other parts of the refrigeration system inthe rooms. What is we get in each room is the completely silent and highly effective airconditions system in the room. Further, the amount of chilled air that is needed in theroom can be controlled by the openings depending on the total heat load inside theroom.The central air conditioning systems are highly sophisticated applications of the airconditioning systems and many a times they tend to be complicated. It is due to thisreason that there are very few companies in the world that specialize in these systems.In the modern era of computerization a number of additional electronic utilities have

been added to the central conditioning systems.

There are two types of central air conditioning plants or systems:

1) Direct expansion or DX central air conditioning plant: In this system the hugecompressor, and the condenser are housed in the plant room, while the expansionvalve and the evaporator or the cooling coil and the air handling unit are housed inseparate room. The cooling coil is fixed in the air handling unit, which also has largeblower housed in it. The blower sucks the hot return air from the room via ducts andblows it over the cooling coil. The cooled air is then supplied through various ducts andinto the spaces which are to be cooled. This type of system is useful for small buildings.

2) Chilled water central air conditioning plant:This type of system is more useful forlarge buildings comprising of a number of floors. It has the plant room where all theimportant units like the compressor, condenser, throttling valve and the evaporator arehoused. The evaporator is a shell and tube. On the tube side the Freon fluid passes atextremely low temperature, while on the shell side the brine solution is passed. Afterpassing through the evaporator, the brine solution gets chilled and is pumped to thevarious air handling units installed at different floors of the building. The air handlingunits comprise the cooling coil through which the chilled brine flows, and the blower.The blower sucks hot return air from the room via ducts and blows it over the coolingcoil. The cool air is then supplied to the space to be cooled through the ducts. The brinesolution which has absorbed the room heat comes back to the evaporator, gets chilledand is again pumped back to the air handling unit.
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Direct expansion or DX central air conditioning plant

1) The Plant Room:The plant room comprises of the important parts of the refrigeration system, thecompressor and the condenser. The compressor can be either semi-hermetically sealedor open type. The semi-hermetically sealed compressors are cooled by the air, which isblown by the fan, while open type compressor is water cooled. The open compressorcan be driven directly by motor shaft by coupling or by the belt via pulley arrangement.
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The condenser is of shell and tube type and is cooled by the water. The refrigerantflows along the tube side of the condenser and water along the shell side, whichenables faster cooling of the refrigerant. The water used for cooling the compressor andthe condenser is cooled in the cooling tower kept at the top of the plant room, though itcan be kept at other convenient location also.

2) The Air Handling Unit Room:The refrigerant leaving the condenser in the plant room enters the thermostaticexpansionvalveand then the air handling unit, which is kept in the separate room. Theair handling unit is a large box type of unit that comprises of the evaporator or thecooling coil, air filter and the large blower. After leaving the thermostatic expansionvalve the refrigerant enters the cooling coil where it cools the air that enters the room tobe air conditioned. The evaporator in the air handling unit of the DX central airconditioning system is of coil type covered with the fins to increasing the heat transferefficiency from the refrigerant to the air.There are two types of ducts connected to the air handling unit: for absorbing the hotreturn air from the rooms and for sending the chilled air to the rooms to be air

conditioned. The blower of the air handling unit enables absorbing the hot return air thathas absorbed the heat from the room via the ducts. This air is then passed through thefilters and then over the cooling coil. The blower then passes the chilled air throughducts to the rooms that are to be air conditioned.

3) Air Conditioned Room:This is the space that is to be actually cooled. It can be residential room, room of thehotel, part of the office or any other suitable application. The ducts from the air handlingroom are passed to all the rooms that are to be cooled. The ducts are connected to thegrills or diffusers that supply the chilled air to the room. The air absorbs the heat andgets heated and it passes through another set of the grill and into the return air duct thatends into the air handling unit room. This air is then re-circulated by the air handling

unit.Though the efficiency of the DX plants is higher, the air handling units and therefrigerant piping cannot be kept at very long distance since there will be lots of drop inpressure of the refrigerant along the way and there will also be cooling losses. Further,for the long piping, large amounts of refrigerant will be needed which makes the systemvery expensive and also prone to the ma instance problems like the leakage of therefrigerant.Due to these reasons the DX type centralair conditioningsystems are used for smallairconditioning systemsof about 5 to 15 tons in small buildings or the number of rooms on asingle floor. If there are large air conditioning loads, then multiple direct expansionsystems can be installed. In such cases, when there is lesser heat load one of the

plants can be shut down and the other can run at full load. The DX expansion systemruns more efficiently at higher loads. Even in case of the breakdown of the plants, theother plants can be used for the cooling purpose. The DX types of central airconditioning plants are less popular than the chilled water type of central conditioningplants.
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Chilled Water Central Air Conditioning Plants

The chilled water types of central air conditioning plants are installed in the place where

whole large buildings, shopping mall, airport, hotel, etc, comprising of several floors areto be air conditioned. While in the direct expansion type of central air conditioningplants, refrigerant is directly used to cool the room air; in the chilled water plants therefrigerant first chills the water, which in turn chills the room air.

In chilled water plants, the ordinary water or brine solution is chilled to very lowtemperatures of about 6 to 8 degree Celsius by the refrigeration plant. This chilled wateris pumped to various floors of the building and its different parts. In each of these partsthe air handling units are installed, which comprise of the cooling coil, blower and theducts. The chilled water flows through the cooling coil. The blower absorbs return airfrom the air conditioned rooms that are to be cooled via the ducts. This air passes over

the cooling coil and gets cooled and is then passed to the air conditioned space.

Chilled Central Air Conditioners

1) The Plant Room:The plant room comprises of the important parts of the refrigeration system, thecompressor and the condenser. The compressor can be either semi-hermetically sealedor open type. The semi-hermetically sealed compressors are cooled by the air, which isblown by the fan, while open type compressor is water cooled. The open compressorcan be driven directly by motor shaft by coupling or by the belt via pulley arrangement.The condenser is of shell and tube type and is cooled by the water. The refrigerantflows along the tube side of the condenser and water along the shell side, whichenables faster cooling of the refrigerant. The water used for cooling the compressor andthe condenser is cooled in the cooling tower kept at the top of the plant room, though itcan be kept at other convenient location also.

2) The Air Handling Unit Room:The refrigerant leaving the condenser in the plant room enters the thermostaticexpansionvalveand then the air handling unit, which is kept in the separate room. Theair handling unit is a large box type of unit that comprises of the evaporator or thecooling coil, air filter and the large blower. After leaving the thermostatic expansionvalve the refrigerant enters the cooling coil where it cools the air that enters the room tobe air conditioned. The evaporator in the air handling unit of the DX central airconditioning system is of coil type covered with the fins to increasing the heat transferefficiency from the refrigerant to the air.There are two types of ducts connected to the air handling unit: for absorbing the hotreturn air from the rooms and for sending the chilled air to the rooms to be airconditioned. The blower of the air handling unit enables absorbing the hot return air thathas absorbed the heat from the room via the ducts. This air is then passed through the
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filters and then over the cooling coil. The blower then passes the chilled air throughducts to the rooms that are to be air conditioned.

3) Air Conditioned Room:This is the space that is to be actually cooled. It can be residential room, room of thehotel, part of the office or any other suitable application. The ducts from the air handling

room are passed to all the rooms that are to be cooled. The ducts are connected to thegrills or diffusers that supply the chilled air to the room. The air absorbs the heat andgets heated and it passes through another set of the grill and into the return air duct thatends into the air handling unit room. This air is then re-circulated by the air handlingunit.Though the efficiency of the DX plants is higher, the air handling units and therefrigerant piping cannot be kept at very long distance since there will be lots of drop inpressure of the refrigerant along the way and there will also be cooling losses. Further,for the long piping, large amounts of refrigerant will be needed which makes the systemvery expensive and also prone to the ma instance problems like the leakage of therefrigerant.

Due to these reasons the DX type centralair conditioningsystems are used for smallairconditioning systemsof about 5 to 15 tons in small buildings or the number of rooms on asingle floor. If there are large air conditioning loads, then multiple direct expansionsystems can be installed. In such cases, when there is lesser heat load one of theplants can be shut down and the other can run at full load. The DX expansion systemruns more efficiently at higher loads. Even in case of the breakdown of the plants, theother plants can be used for the cooling purpose. The DX types of central airconditioning plants are less popular than the chilled water type of central conditioningplants.

Chilled Water Central Air Conditioning Plants

The chilled water types of central air conditioning plants are installed in the place wherewhole large buildings, shopping mall, airport, hotel, etc, comprising of several floors areto be air conditioned. While in the direct expansion type of central air conditioningplants, refrigerant is directly used to cool the room air; in the chilled water plants therefrigerant first chills the water, which in turn chills the room air.

In chilled water plants, the ordinary water or brine solution is chilled to very lowtemperatures of about 6 to 8 degree Celsius by the refrigeration plant. This chilled wateris pumped to various floors of the building and its different parts. In each of these parts

the air handling units are installed, which comprise of the cooling coil, blower and theducts. The chilled water flows through the cooling coil. The blower absorbs return airfrom the air conditioned rooms that are to be cooled via the ducts. This air passes overthe cooling coil and gets cooled and is then passed to the air conditioned space.

Chilled Central Air Conditioners
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