HVAC Design Principles written by: HARISH ASHRAF,LIJO JOHN
Whether you're upgrading an existing system or building a new one, good knowledge of the principles of heating and air conditioning, and typical designs, will allow you to make wise decisions when the time comes. These principles, along with descriptions of typical components, are referenced here. •
HVA stands for Heating, Ventilation, and Air onditioning. This is the building system that regulates the inside temperature of the building and, in some systems, the air !uality as well. The principles of HVA design include the basic theory of system operation and the factors that determine the si"e and capacity of the e!uipment installed in the system. #nce you ha$e an understanding of the basics, you%ll be gi$en information information concerning the di&erent types of air conditioning systems. The next step is to learn about the $arious components that make up an HVA system. or example, the air conditioning portion of an HVA system re!uires refrigerant to cool the air inside the building, so the $arious refrigerants that can be found in air conditioning systems are fully discussed. inally, you%ll learn about the details of HVA system installation, including the placement of compressor and condenser units, as well as heat exchangers, "ones, and controls.
Basic Principles of HVAC System Design, Operation and Determining Capacity Requirements (eferenced here are informational resources regarding the basics of HVA design and operation. When upgrading a current HVA system or getting ready to build a new system in a residential or commercial building, one of the most important design considerations
is correctly correctly calculating the heating and cooling loads that the system will support. These calculations are described in complete detail in the articles below and sample calculations are gi$en to help you achie$e the fullest understanding of how to make the calculations properly possible. After reading through this section, you will ha$e the knowledge and tools re!uired to make good HAV system design decisions. d ecisions.
Dierent et!ods for Remo"ing Heat in HVAC Systems Air conditioners are not the only systems a$ailable in HVA for the remo$al of heat from a building%s en$ironment. en$ironment. A heat pump is similar to an air conditioning system, but has some signi)cant di&erences, and ad$antages. These di&erences are discussed in detail so you will be able to make a decision between the two, and *ust so you ha$e an understanding understanding of what what these two types of systems are. A nice $ariety of types of air conditioning systems can be used in o$erall HVA system design. +ystem types such as direct expansion, expansion, chilled water, split, and window air conditioners are described in detail in the resources referenced below. After reading through this section, you will ha$e a more complete understanding of the di&erent types of cooling systems a$ailable for HVA systems. Heat Remo"al et!ods
Components of an HVAC System There are two main components of a heating, $entilation, and air conditioning system. These two parts are the air handler, heating and cooling system, and the heat exchanger. n most cases, the heat source is some type of furnace. n an air conditioning system, the cooling system is composed of a number of uni!ue subcomponents. n the articles referenced below, the $arious components in an HVA system are described and explained. -ou%ll also )nd a description of the components in a split air conditioning system. Refrigerants #$plained ost air conditioners operate on the principle of gas compression and expansion. This gas is known in the air conditioning and refrigeration industry as a refrigerant. When this refrigerant is compressed, it becomes !uite cold. This refrigerant is then sprayed into the heat exchanger using some sort of expansion $al$e. There ha$e been four main refrigerants used in air conditioners o$er the years. The refrigerant in primary use has been (/ 01, although this is being slowly phased out for (/23a. All of the di&erent refrigerants are explained in detail, with special treatment for (/01, as the fa$ored refrigerant for a number of years, being gi$en. Air Conditioner System %nstallation An HVA system with components that are incorrectly installed or installed in ways that are disad$antageous is one that is poorly designed. aximi"ing air4ow across the heat exchanger unit ensures maximum heat transfer and maximum system e5ciency. A heating, $entilation, and air conditioning system that is improperly installed will also detract from system e5ciency. 6lacing the
thermostat too near an air outlet or return, for example, will also cause e5ciency to su&er. How installation a&ects HVA system design will be discussed below in some detail. +afety and longe$ity concerns are also brie4y discussed.
Basics of HVAC HVA stands for Heating, Ventilation and Air onditioning. The ob*ecti$e of HVA is to control the temperature of air along with control of moisture, )ltration of air, etc. n this article we discuss HVA for beginners and the essentials of comfort "one engineering along with psychometric chart.
Basic &eed for HVAC The ob*ecti$e of HVA are to control the temperature of air inside the designated 7Air onditioned8 space along with control of moisture, )ltration of air and containment of air borne particles, supply of outside fresh air for control of oxygen and carbon dioxide le$els in the air conditioned space, and )nally control of the mo$ement of air or draught. All these factors comprise of a successful HVA system. Air conditioning has changed o$er the years from *ust cooling of a space to the e&ecti$e control of all the abo$e parameters. HVA has its history in 09:0 when ;r. + patent for a refrigerating machine. Though refrigeration in that period was concerned with the preser$ation of fro"en meat for transport and making of ice, gradually the concept of cooling for comfort arose. n 0?@1, the ew -ork +tock Bxchange was one of the )rst air conditioned buildings.
Air conditioning ranges from simple air conditioning by use of window A and split A where cooling, and minor )ltration and dehumidifying, is done to complicated air conditioning systems used in process plants, ships, museums, and centrally air conditioned buildings.
Processes of HVAC The processes by which e&ecti$e control of parameters in an air conditioned space is maintained are as followsC •
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HeatingC To increase the temperature by adding thermal energy to a space. oolingC To decrease the temperature by remo$ing thermal energy from a space. HumidifyingC The process of increasing the relati$e humidity of a space by addition of water $apor or steam. ;ehumidifyingC The process of remo$ing the water $apor or humidity of a space. leaningC The process of remo$ing dust, pollens, smoke and contaminants from air inside the space. VentilatingC The process of adding external air to freshen up the air and maintaining gas ratio. Air mo$ementC To control the mo$ement of the supplied air so that the inhabitants of the space do not feel discomfort.
Psyc!ometric C!art and Comfort Air #ngineering A psychrometric chart is a chart drawn between temperature, relati$e humidity, enthalpy, wet bulb temperature, etc. As in the air conditioning process, the
air is undergoing many changes like in temperature, change in energy, and change in humidity, etc. t is $ery easy to understand and calculate the changes on the basis of a psychrometric chart. The design of the psychrometric chart is based on two simple factsC that the indoor air is a mixture of air as well as water $apor and it contains energy that keeps on changing due to $arious interactions. A+H(AB%s standard ::/1@@3 describes thermal comfort as the state of mind which expresses satisfaction with the thermal en$ironment and is assessed by a sub*ecti$e e$aluation. Howe$er state of mind cannot be measured and therefore based on sur$eys a comfort "one or rectangle is drawn in the psychometric chart at which most of the people will feel comfortable. The le$el of comfort of a person is $ery sub*ecti$e and depends on the following factorsC age, physical acti$ity, health, and clothing. t is further dependent on other factors like air temperature, air $elocity, humidity, and radiant temperature. This means that e$en if the air temperature is 13 deg DE: deg F, but the humidity is high at ?@G a person will not feel comfortable or $ice $ersa. B$en if the humidity is at ?@ G but the air temperature is 09 deg D3 deg F, an indi$idual may feel comfortable. Howe$er, if both the temperature and humidity are comfortable but the speed of the air is high, a person may feel draught e&ects and wind chill factor comes in e&ect. +imilarly all the other parameters may be normal, but the sub*ect is sitting in front of an un/ tinted window and may feel radiant heat that may make him uncomfortable. Thus all parameters ha$e to be taken into consideration, and the comfort "one is dependent on the extremities of the points from which you feel comfortable to uncomfortable. Thus within a comfort "one
most of the people will feel comfortable if all these points are addressed.
%mportance of HVAC Design The HVA system selected hapha"ardly for your home or o5ce can turn out to be insu5cient or highly expensi$e. or achie$ing comfortable conditions at optimum costs, HVA design for your home or o5ce is important. •
When you are planning to install a new HVA system in your home or o5ce, it is important to select the air/conditioner of proper tonnage and speci)cations. 6eople tend to select the air/conditioner hapha"ardly without considering the $arious sources of heat generation in their rooms or o5ces. There are three possibilities if you select your heating or cooling system without following the basic designing principlesC 0F 'irst, if you ha$e selected too small air/conditioner it won%t gi$e you the desired cooling e&ect, hence your in$estment on the machine will be wasted along with your precious time and e&orts. 1F Second possibility is that you ha$e chosen an excessi$ely bigger machine. ow this will not only increase you initial cost of the machine but also its
running cost. Iarger compressors will consume large amounts of power and bring highly una&ordable electric bills. n place of a small air/conditioner, which could ha$e easily been su5cient for you, you ha$e purchased a big machine. 2F (!ird possibility depends on your luck. The hapha"ardly selected air/conditioner turns out to be appropriate for you in terms of su5cient cooling e&ect, low initial cost and minimum running cost. While installing the HVA system in home or o5ce, don%t select the machine hapha"ardly and don%t depend on the luck. Ask your $endor or engineer to consider the $arious sources of heat generation in your home or o5ce and design HVA system of proper tonnage and air/4ow rate. The professional HVA designers ha$e a heat load calculation chart and ensure that the HVA system of proper speci)cations is selected for your home or o5ce. They will measure $arious dimensions of your space which is to be cooled, including that of walls and roofs, and )nd out the heat gained by them. They will also consider the number of windows, type of windows, blinds and their exposure to sun and accordingly decide on the heat gained by them. The heat emitted by lights and other electrical appliances is also considered. #ne of the most important parameters to consider is the number of people that will occupy the room or the o5ce. After measuring the total amount of heat generated in the home or o5ce per hour, the HVA designer will suggest you the HVA system of proper tonnage so that you will feel comfortable in your room or o5ce without
excessi$e burden of electricity bills. ;esigning the HVA system for your house or o5ce is as crucial as designing the complete house or o5ce. ;on%t ignore this important factor. omfort at reasonable cost is ensured. Factors Affecting HVAC Designing and Heat Load Calculations
Heat is generated inside the room from $arious sources. +ome of these include heat gained by the walls, heat entering from the windows, heat generated by the people, electrical e!uipments etc. •
The heat is generated in the air/conditioned space from $arious sources. To maintain the comfort conditions inside the room the total heat generated inside the room per hour should be remo$ed completely. Here are $arious sources of heat that a&ect HVA designing and heat load calculations, these areC 0F Heat gained )y t!e *alls C The walls of the room gain heat from the sun by way of conduction. The amount of heat depends on the wall material and its alignment with respect to sun. f the wall of the room is exposed to the west direction, it will gain maximum heat between 1 to : pm. The southern wall will gain maximum heat in the mid/day between 01 to 1 pm. The heat gained by the wall facing north direction is the least. The heat gained by the walls in day/time gets stored in them, and it is released into the rooms at the night time thus causing excessi$e heating of the room. f the walls of the room are insulated the amount of heat gained by them reduces drastically. 1F
Heat gained )y t!e roof and partitions C f the roof is exposed directly to the sun, it absorbs maximum heat. f there is other room abo$e the air/conditioned room, then the amount of heat gained by the roof reduces. The heat gained by the partitions of the room depends upon the type of partition. 2F Heat gained )y t!e *indo*s C Windows of the room are exposed directly to the surrounding and the heat from the sun enters the room by radiation. As in the case of the walls, the heat gained by the rooms through windows depends on their alignment. f there are su5cient curtains on the windows and the external awning the amount of heat gained by radiation reduces. The type of glass doors on the windows also a&ects the amount of heat gained through the windows by radiation. 3F Heat generated )y t!e people C The people inside the room generate lots of heat. The heat dissipated by working people is more than from sitting people. :F Heat generated )y t!e electrical appliances C Heat is generated by electrical appliances like lights, motors, co&eemakers, electronic e!uipments, etc. should also be considered for heat load calculations, which is also called cooling load calculations. F Heat gain from outside air C #utside air is normally at a greater temperature than the room temperature. When this air comes inside the room, it brings certain amount of heat along with it. A good HVA designer will thoroughly consider all the sources of heat inside the room and )nd out the total
amount of heat generated inside the room per hour. These days it has become easier for engineers to design HVA as $arious softwares are a$ailable which can also be integrated with AutoA;. Jased on these heat load calculations, they will suggest you the air/conditioning system of proper capacity for your room. How Heating and Ventilation Loads are Assessed
Jefore selecting the appropriate HVA system, builders )rst need to determine the heating and $entilating loads. Ioads are determined by some en$ironmental factors and design calculations. Iearn more about why its so important. •
The most important element in the design and selection of a heating and $entilating system is the determination of the heating and $entilation loads in the building where the system is to be installed. Accurate assessment of these loads will facilitate the correct selection of the system for the re!uired building. A perfect system will function constantly with $ariable producti$ity, which is commensurate with the heat load of the building as the climate changes. +uch a system can be attained with accurate design analysis of the heating load of the building and the selection of a proper heating system.
'actors of Heating and Ventilating +oads The following factors should be taken into consideration while determining the heating and $entilating loads of a structureC
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Amount of heat distributed through the area exposed to locations which are not heated. Amount of heat necessary for the air to become hot, which penetrates from the cracks ad*acent to the windows and doors, and also from the entrance, when persons come in or go out of the building. Heat which is necessary to make the air that has come mechanically into the building as $entilation air hot. A $ariety of other loads.
Design Calculations The basis for determining the heating load are the constant a"erage temperature for *inter nig!ts and any continuous supply of !eat present at all times. The !uantity of heat accumulated by the building must be taken into consideration as well as the energy of any cooling e!uipment. et!od for #stimating Heating +oad The normal process for estimation of heat load is as followsC •
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arry out an assessment of the weather conditions pre$ailing outside the building, including humidity, temperature, path of wind and speed. ;etermine the desirable inside air temperature to be maintained. Assess the temperature in ad*oining locations which are not heated. hoose the coe5cient of heat transmission. Bstablish the outside areas by which heat is dissipated.
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Bstimate the losses by heat transference from glass, bricks, and base in the building. alculate the heat loss from the underground area.
Structure Of Building ;esign calculations, and the selection of heating system, are largely based on the structure of the building and its use, including the exposure of building to wind, the direction of the sun, periods of occupancy and part of day when the building will be used, and the expected )nancial impact of the e!uipment and fuel. All these factors should be considered while assessing the heating and $entilating loads of a building. Sur"ey of t!e Residential Building for Heat +oad Calculations #nce you ha$e understood the $arious sources of heat in the residential building, we ha$e to now carry out the sur$ey of the building for heat load calculations.
Sur"ey of t!e Building or Room #nce you ha$e understood the $arious sources of heat in the residential building, we ha$e to now carry out the sur$ey of the building for heat load calculations. The sur$ey of the building in$ol$es measuring $arious dimensions of the building, orientation of the building, and applying $arious factors to calculate the heat load calculations. With the help of sur$ey one can also decide the best air conditioning system suitable for the building and also the methods to install it.
or the sur$ey of the building the accompanying heat load calculation form has to be used. To carry out the heat load calculations you ha$e to determine all the parameters mentioned in the form, )ll them in the form and carry out $arious calculations, which will e$entually help you )nd the total heat load of a single room. Iet us see the $arious parameters of the building to be sur$eyed as mentioned in the heat load calculations form. The discussions that follow will explain you all the parts of the form, the sur$ey to be carried out and how to )ll the form. or each of the rooms separate heat load calculations form has to be )lled. or your con$enience the heat load calculations has been attached below, please refer it for all further reading and calculations.
Heat +oad Calculations 'orm
(opmost Portion of t!e Heat +oad Calculations 'orm n topmost part of the heat load calculations form you ha$e to )ll the basic details like name of the customer, their address, the person who buys the air conditioning system, the person who will install the air conditioning system, estimate number, heat load estimated by, and date. After carrying our heat load calculations you can also )ll the details of proposed e!uipment manufacturer, model, and si"e of the machine. After the sur$ey of the building you will also be able to )ll the details of the direction of the house or room, total 4oor area for which
the heat load calculations are done, and the inside $olume of the space that has been sur$eyed. After these basic details, you ha$e to )ll the design conditions for the room. These are $ery important and will ha$e a ma*or impact on the total tonnage of the air conditioning system re!uired for the room. n the design conditions space you must note down the outside and desired inside dry bulb and wet bulb temperatures. The di&erence between the two, as mentioned in the form, has also to be noted.
Orientation of t!e Room and Various Dimensions ow you can come to the lower part of the heat load calculations form and start the sur$ey of the room. or this you should ha$e with you two instrumentsC the magnetic compass and the measuring tape. The magnetic compass will help you determine the orientation of the room including the directions of the all the walls and the windows. The measuring tape will help you determine all the dimensions of the all the walls, partitions, windows, 4oor, roof, ceiling etc. f you are ready with these instruments let us carry out the following measurementsC •
n topmost part of the heat load calculations form you ha$e to )ll the basic details like name of the customer, their address, the person who buys the air conditioning system, the person who will install the air conditioning system, estimate number, heat load estimated by, and date. After carrying our heat load calculations you can also )ll the details of proposed e!uipment manufacturer, model, and si"e of the machine. After the sur$ey of the building you will also be able to )ll
the details of the direction of the house or room, total 4oor area for which the heat load calculations are done, and the inside $olume of the space that has been sur$eyed.
- Solar Heat .ained )y t!e /indo*s 6lease refer the heat load calculations form abo$e. irstly, )nd the direction of all the windows using magnetic compass. n the accompanying heat load calculations form, you will notice six directions of the windowsC northeast, east, southeast etc. +eparate north direction has not been mentioned since it is assumed that heat absorbed by the windows in north direction is $ery small. or all the windows in all the directions measure the dimension of windows and )ll the details in appropriate column. or instance, if there is a window of 13 s! ft in north east direction, )ll the details for orth Bast in the 7tem8 column the area of 13 in the 7Area8 column. +imilarly, )ll the areas for all the windows located in all the directions. ext, select the proper factor for each of the windows from 7actor8 column and round the appropriate factor. or example, for the northeast direction window if there is external awning round o& the factor 1@ associated with outside awning. (educe this factor by appropriate margin for glass block windows, storm windows or windows with double glass and )nd corrected factor. n a similar manner, round o& the associated factors for all the windows in all the directions and apply correction factor where$er necessary. ext, multiply the area of each window with the corrected factor associated with it. These details are )lled in the 7Area x actor8 column. The maximum $alue of this
column has to be )lled in the last column of JT>KH( that indicates the solar heat gained by the windows. ext, you ha$e to )nd out the solar heat gained by the windows due to designed dry bulb temperature di&erence between outside and inside. or this )rstly, )nd the total area of all the windows and )ll them in the area column. ind out if the windows are of single glass or double glass and )ll the details in the appropriate areas column. ow, round o& the proper factor for the designed dry bulb temperature di&erence. or example, if the desired dry bulb temperature di&erence between the atmosphere and the room is 0E the associated factor would be 11 for single glass window and 0@ for double glass window. ultiply the total area of the window by this rounded factor and )ll the result in the last column that indicates the total JT>KH( gained by the windows.
Solar Heat .ained )y t!e /alls To )nd the heat gained by the wall )nd the total area of all the walls of the room Dexcluding partitionsF. ind out if walls are non/insulated or insulated and the thickness of insulation if any. Accordingly, )ll the details in the areas column for the appropriate type of wall. ow round o& the associated factor with it for the designed dry bulb temperature di&erence. ultiply the total area of the wall with this factor and )ll the result in the last column of JT>KH( that indicates the total heat gained by the walls per hour. •
To the subtotal of heat gained by the room add additional 2@G of the subtotal to account for the latent heat inside the room. This will gi$e the total heat load inside the room. The air conditioner of suitable tonnage that can remo$e all the total heat gained by the room should be selected. The suitable manufacturer and
best possible model of the air conditioner can also be recommended to the customer. This ends the total process of heat load calculations using the ready/made form.
Heat .ained )y t!e Partitions n a similar manner, )nd the total area of the partitions, round o& the factor associated with it, multiply the two and )ll the result in the last column to )nd the total JT> absorbed by the partition per hour. #nly the partitions that are connected to the non/air conditioned rooms are to be considered. Solar Heat .ained )y t!e Roof To )nd the total heat gained by the roof, )nd out the total area of the roof and check if it is insulated or non/ insulated. ind the thickness of insulation if it is insulated. ow round o& the associated factor. ultiply the total area with this factor and )ll the result in the last column to )nd the total JT> of heat gained by roof per hour. Heat .ained )y t!e Ceiling and 'loor Jy the same procedure as explained for the roof, )nd the heat gained by the ceiling and the 4oor. Heat .ained )y t!e Room Air from t!e Outside Air or %n0ltrated Air The total outside air or in)ltrated air that enters the room has been linked with the total 4oor area of the room. ind the total 4oor area of the room and multiply it with the associated factor that gi$es the total JT> gained by room from the outside air. Heat .ained )y Room Air from t!e People
To take into account the total heat gained by the room air form the people inside the room, )nd the a$erage number of people that will stay in the room most of the time. ultiply it by 1@@ as mentioned in the form and put the result in the last column for total heat gained from the people per hour.
Su)total of Heat .ained )y t!e Room Air The subtotal gi$es the total heat gained by the room air from the windows, walls, partitions, roofs, ceiling, 4oor, outside air and people inside the room. (otal Heat +oad %nside t!e Room and (otal (onnage of AC Required To the subtotal of heat gained by the room add additional 2@G of the subtotal to account for the latent heat inside the room. This will gi$e the total heat load inside the room. The air conditioner of suitable tonnage that can remo$e all the total heat gained by the room should be selected. The suitable manufacturer and best possible model of the air conditioner can also be recommended to the customer. This ends the total process of heat load calculations using the ready/made form. Residential Heat +oad #stimate 'orm1 Heat +oad Calculations ade #asy This article describes the procedure for heat load calculations using a readily a$ailable form. Here the )rst column of the form comprising of $arious sources of heat ha$e been discussed.
Heat +oad Calculations ade #asy )y Popular Demands any readers ha$e been re!uesting for the actual method of heat load calculations using which they can carry out the heat load calculations $ery easily without going into more details. As such the heat load calculations is a long and complicated process. To make the life easier for the readers and those who want to do heat load calculations in professional manner, ha$e discussed the method using the heat load calculation form. This is a $ery easy method that can be used to perform the calculations manually or you can put the data simply in the Bxcel sheet and get the heat load calculations done immediately. n the attached form herewith you will see $arious sources of heat and some factors associated to them. irst of all let us try to understand the $arious sources of heat mentioned in the 7tem8 column of the form. -ou can print this form and use it for all the heat residential load calculations. There is a separate form for the heat calculations of the commercial building, which will be shared in the next series of articles. Jy the way, the form attached here has all the terms in JT>, will soon try to get the one in + units as well, howe$er the description gi$en below remains the same for both.
Heat +oad Calculations 'orm
Sources of Heat inside t!e Residential Room The application of air conditioning is re!uired because heat is generated inside the room from $arious sources. The main purpose of the air conditioning systems is to remo$e this heat and create comfort conditions. The temperature and humidity re!uired for the human comfort are 1: degree and :@G respecti$ely. ;ue to $arious heat sources the temperature inside the room becomes $ery high so all the heat generated inside the room has to be remo$ed. Jefore actually starting the heat load calculations let us try to see the $arious sources of heat inside the room mentioned in the items list of the heat load calculations form Dplease refer the attached form abo$eF.
Solar Heat .ain )y t!e /indo*s
- Solar Heat .ain from t!e /indo*s The solar heat is one of the prominent sources of heat inside the room. t enters the rooms $ia windows, walls and the roof. The solar heat entering the room $ia
windows produces the heating e&ect immediately. The amount of heat entering the room $ia windows depends on following factorsC
a- (!e si2e of t!e *indo*1 Iarger the si"e of the window more is the heat gained from it. )- Orientation of t!e *indo*1 This is the direction of the window in the room. As per the $arious positions of the sun throughout the day, it has been found that in the morning the maximum amount of heat is absorbed by the windows in the eastern direction Dsee the images belowF. This means the windows in east direction absorb maximum heat in the morning when sun rises. n the afternoon the sun reaches o$erhead position so the windows in south absorb maximum heat in the afternoon. Jut this intensity of heat is lesser than that absorbed from east and west. n the late afternoon sun reaches western side and its temperature becomes maximum around 3pm. Thus the windows in west absorb maximum heat in the late afternoon. The amount of heat absorbed by the windows in east and west directions is maximum, it's lesser for the windows in south direction and least for the windows in north direction since sun does not mo$e to north. c- (!e glass used for t!e *indo*s1 The double glass used for the windows helps reducing the solar heat gained from the windows. +imilarly, if the glass is co$ered with black or other color shades the amount of solar heat absorbed by it reduces. d- (!e a*nings used for t!e *indo*s1 The awnings built outside the windows help reduce the amount of direct heat absorbed by the window. e- (!e curtains used for t!e *indo*s1 The curtains also play important role in absorption of heat by the windows. The curtains can be thick or thin, inside the
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room or outside the room or on both sides, the color of the curtains can be dark or light. All the curtains help reduce the amount of heat absorbed by the windows. The dark shades, thick curtains and curtains on both the sides are more e&ecti$e. The solar heat is one of the prominent sources of heat inside the room. t enters the rooms $ia windows, walls and the roof. The solar heat entering the room $ia windows produces the heating e&ect immediately.
3- Solar Heat .ained )y t!e /alls
5- Heat .ained )y t!e Partitions1 There can be partitions inside the room with air conditioned room or non/air conditioned room. The amount of heat absorbed by the partitions with non/air conditioned rooms is higher. 6- Solar Heat .ained )y t!e Roof of t!e Room
The outside air is at higher temperature than the room air. When it comes inside the room it raises the room temperature. The outside air can come inside the room due to opening of the door or it can leak inside through $arious openings in doors and windows, this air is also called as in)ltrated air.
:- Heat .ained from t!e People The people inside the room release lots of latent heat and the sensible heat. ore the number of people inside the room more is the heat released inside it. Once all t!e sources of !eat descri)ed in t!e items list of t!e !eat load calculations !a"e )een understood, *e are no* ready to perform t!e !eat load calculations for t!e residential room; (!e 0rst and t!e foremost step in !eat calculations is carryout t!e sur"ey of t!e room or )uilding; %n t!e ne$t article *e s!all see "arious factors of t!e )uilding to )e sur"eyed;
/!at is a Psyc!rometric C!art< O"er"ie* of Components A 6sychrometric hart is an important tool for HVA engineers to carry out heat load or cooling load calculations and )nd solutions to $arious air condition
related problems. (ead an o$er$iew of the components included in a psychrometric chart. •
The series of articles on properties of air discussed important properties of air like relati$e humidity, dry bulb temperature, wet bulb temperature, dew point temperature, sensible heat and latent heat. We shall now see how the air beha$es when it is sub*ected to changes in temperature and humidity to suit the $arious applications for which the air conditioning is meant. The beha$ior of the air can be studied $ery con$eniently and accurately by using a psychrometric chart.
/!at is Psyc!rometric C!art< 6sychrometric charts are graphic representations of the psychrometric properties of air. Jy using psychrometric charts HVA engineers can graphically analy"e di&erent types of psychrometric processes and )nd solution to many practical problems without ha$ing to carry out long and tedious mathematical calculations. The psychrometric chart looks complicated with $ast numbers of lines and cur$es in it, but is $ery easy to understand if you know the basic properties of air. -ou will also understand its worth when you actually use it considering the fact that you won%t ha$e to use any formulae to )nd the properties of air in di&erent conditions, all you will ha$e to know is two parameters of air and the rest are easily found on the chart. Various +ines and Cur"es in t!e Psyc!rometric C!art All the properties of air indicated in the psychrometric chart are calculated at the standard atmospheric pressure. or other pressures rele$ant corrections ha$e to
be applied. The psychrometric chart looks like a shoe. The $arious lines shown in the chart are as follows Dplease refer the )gs belowFC
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- Dry Bul) =DB- (emperature +ines1 The dry bulb temperature scale is shown along the base of the shoe shaped psychrometric chart forming the sole. The ;J temperature increases from the left to the right. The $ertical lines shown in the chart are the constant ;J temperature lines and all the points located along a particular $ertical line ha$e same ;J temperature. 3- oisture Content1 oisture content is the water $apor present in the air and is measured in gram per kg of dry air DgmKkg of dry airF. The moisture present within the air is indicated by the $ertical scale located towards the extreme right. The hori"ontal lines starting from this $ertical scale are constant moisture lines. 5- /et Bul) =/B- (emperature +ines1 The outermost cur$e along the left side indicates the Wet Julb DWJF temperature scale. The constant WJ temperature lines are the diagonal lines extending from WJ temperature cur$ed scale downwards towards the right hand side of the chart. All the points located along the constant WJ temperature line ha$e the same temperature.
6- De* Point =DP- (emperature +ines1 +ince the dew point temperature of the air depends on the moisture content of the air, constant moisture lines are also constant ;6 temperature lines. The scale of the ;6 and WJ temperature is the same, howe$er, while the constant WJ temperature lines are diagonal lines extending downwards, the constant ;6 temperature lines are hori"ontal lines. Thus the constant ;6 and WJ temperature lines are di&erent.
Psychrometric Processes: Sensible Cooling and Sensible Heating of Air
+ensible cooling and sensible heating are basic psychrometric processes used for $arious applications. Iet us see what these processes are and how they are represented on the psychrometric chart.
Psyc!rometric Processes n the domestic and industrial air conditioning applications some psychrometric processes ha$e to be performed on the air to change the psychrometric properties of air so as to obtain certain $alues of temperature and humidity of air within the enclosed space. +ome of the common psychrometric processes carried out on air areC sensible heating and cooling of air, humidi)cation and dehumidi)cation of air, mixing of $arious streams of air, or there may be combinations of the $arious processes.
llustrating and analy"ing the psychrometric properties and psychrometric processes by using the psychrometric chart is $ery easy, con$enient and time sa$ing. n the next few paragraphs we shall see some of the most commonly employed psychrometric processes in the )eld of HVA and how they are represented on the psychrometric chart.
Sensi)le Cooling of t!e Air ooling of the air is one of the most common psychrometric processes in the air conditioning systems. The basic function of the air/conditioners is to cool the air absorbed from the room or the atmosphere, which is at higher temperatures. The sensible cooling of air is the process in which only the sensible heat of the air is remo$ed so as to reduce its temperature, and there is no change in the moisture content DkgKkg of dry airF of the air. ;uring sensible cooling process the dry bulb D;JF temperature and wet bulb DWJF temperature of the air reduces, while the latent heat of the air, and the dew point D;6F temperature of the air remains constant. There is o$erall reduction in the enthalpy of the air. n the ordinary window or the split air conditioner the cooling of air is carried out by passing it o$er the e$aporator coil, also called as the cooling coil. The room air or the atmospheric air passes o$er this coil carrying the refrigerant at extremely low temperatures, and gets cooled and passes to the space which is to be maintained at the comfort conditions. n general the sensible cooling process is carried out by passing the air o$er the coil. n the unitary air conditioners these coils are cooled by the refrigerant passing through them and are called also called e$aporator coils. n central air conditioners these coils are
cooled by the chilled water, which is chilled by its passage through the e$aporator of the large air conditioning system. n certain cases the coil is also cooled by the some gas passing inside it. The sensible cooling process is represented by a straight hori"ontal line on the psychrometric chart. The line starts from the initial ;J temperature of the air and ends at the )nal ;J temperature of the air extending towards the left side from high temperature to the low temperature Dsee the )gure belowF. The sensible cooling line is also the constant ;6 temperature line since the moisture content of the air remains constant. The initial and )nal points on the psychrometric chart gi$e all the properties of the air.
Sensi)le Heating of t!e Air +ensible heating process is opposite to sensible cooling process. n sensible heating process the temperature of air is increased without changing its moisture content. ;uring this process the sensible heat, ;J and WJ temperature of the air increases while latent of air, and the ;6 point temperature of the air remains constant. +ensible heating of the air is important when the air conditioner is used as the heat pump to heat the air. n the heat pump the air is heated by passing it o$er the condenser coil or the heating coil that carry the high temperature refrigerant. n some cases the heating of air is also done to suit di&erent industrial and comfort air/
conditioning applications where large air conditioning systems are used. n general the sensible heating process is carried out by passing the air o$er the heating coil. This coil may be heated by passing the refrigerant, the hot water, the steam or by electric resistance heating coil. The hot water and steam are used for the industrial applications. Iike the sensible cooling, the sensible heating process is also represented by a straight hori"ontal line on the psychrometric chart. The line starts from the initial ;J temperature of air and ends at the )nal temperature extending towards the right Dsee the )gureF. The sensible heating line is also the constant ;6 temperature line. How to Use a Psychrometric Chart written by: Haresh Khemani • edited by: Lamar Stonecypher • pdated: !"#!"$%!#
>sing a psychrometric chart is !uite easy if you know the properties of air. This article describes $arious lines and cur$es in a psychrometric chart and how to use the them.
Various +ines and Cur"es in t!e Psyc!rometric C!art All the properties of air indicated in the psychrometric chart are calculated at standard atmospheric pressure. or other pressures, rele$ant corrections ha$e to be applied. The psychrometric chart looks like a shoe. The $arious lines shown in the chart are as follows Dplease refer the )gF. n the )rst part of this series we saw representation of ;J, WJ, ;6 temperature and moisture content on the pschrometric chart. ow we'll explore some more parameters.
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7- Relati"e Humidity =RH- +ines1 The (H lines are the cur$es extending from the lower left to the upper right part of the psychrometric chart. The di&erent cur$es of (H indicate di&erent $alues of humidity measured in percentage. The $alue of (H reduces from left towards right. The extreme left cur$e along the shoe indicates (H of 0@@G and is also called the saturation cur$e because the condition of air along this line is fully saturated no matter what the ;J and WJ temperatures are. Along the saturation cur$e all the three temperatures, the ;J, WJ and ;6 are same. 8- (otal #nt!alpy of t!e Air1 The total enthalpy of the air comprises of the sensible heat and the latent heat. The enthalpy scale in the psychrometric chart is located outside the main body. The constant enthalpy lines extend from the enthalpy scale down toward the right side of the chart. To )nd the $alue of the enthalpy of the any gi$en air, one should know its WJ temperature. The constant enthalpy line passing through the gi$en $alue of the WJ temperature indicates the enthalpy of the air. 9- Speci0c Volume of t!e Air1 The speci)c $olume of air is an important parameter since one has to consider the amount of air to be handled by the cooling coil, cooling fan, etc and accordingly the rating of cooling coil and fan has to be found out. rom
the psychrometric chart we can )nd out the speci)c $olume of the re!uired air and )nd the total $olume of the re!uired air by multiplying it with the total weight of the air re!uired. The constant speci)c lines start from the saturation cur$e and drop down with the slight angle to the $ertical lines. They indicate the $alue in either m 2Kkg or ft2Klb. f any of the two $alues from ;J, WJ, ;6 temperature and the relati$e humidity are known, all other $alues can be easily found from the psychrometric chart, without ha$ing to carry out any calculations.
#$ample S!o*ing Ho* to >se Psyc!rometric C!art onsider an example of air where the gi$en $alues of ;J and WJ temperature are E9 degrees and : degrees respecti$ely. We will )nd out $arious $alues from these gi$en $alues of ;J and WJ temperatures. 0F #n the psychrometric chart locate $alue E9 o on the ;J temperature scale located at the bottom of the chart. 1F Iocate WJ temperature of : o on the saturation cur$e scale. 2F Bxtend the $ertical line Dconstant ;J temperature lineF from E9o and the diagonal line Dconstant WJ temperature lineF from :o and get the point of intersection of the two lines, which indicates the condition of the gi$en air. 3F ind out the $alues of $arious parameters at this point. The relati$e humidity line passing though this point indicates (H of :@G. The hori"ontal line passing though this point and meeting the saturation cur$e indicates ;6 temperature of :9o. The speci)c $olume of this air is 02.E ft2Klb and the enthalpy of air is 2@ JtuKlb.
Ad"antages of t!e C!art 0F f all the $alues are calculated manually using the formulae, it takes lots of time, but with a psychrometric chart these $alues can be found within seconds or minutes. 1F With a psychrometric chart we can easily )nd out the present and the )nal condition of the air. +ay if the air is cooled from 0@@ o to E:o, all we ha$e to do is draw the hori"ontal line to locate the initial and )nal condition of the air. 2F A psychrometric chart is $ery useful in carrying out heat load or cooling load calculations.
AutoCAD HVAC Design and Heat +oad Calculations Soft*are written by: Haresh Khemani • edited by: Lamar Stonecypher • pdated: !$"!%"$%%& A number of software programs ha$e come on the market that make complex HVA design and heat load calculations $ery simple. Here one such product named AutoA; HVA ;esign software is described. •
f you are a HVA professional you are sure to need a HVA and heat load calculations software. n this software all you ha$e to do is put data of $arious dimensions of walls, roof, partitions, window, electrical
loads, and the number of people inside the room. t automatically calculates the heat load and recommends the tonnage for your air/conditioning system. -ou can also draw all the drawings necessary for you. ;esign master o&ers AutoA; HVA software for designing and drafting. ;esign aster performs heat load calculations as per the standards of A+H(AB handbook. urther, it can make the calculations directly from your AutoA; pro*ectL hence you don%t ha$e to put in the data manually. -ou can get the output either on the screen or to a printer. Here are some of the other features of ;esign aster AutoA; HVA design softwareC 0F %ntegrated *all information1 The walls of the rooms are made of $arious materials and si"es. The ;esign master HVA and heat load calculations software has wide $ariety of walls prede)ned in it. The options of the wall as a partition are also included. The dimensions of the wall are calculated directly from AutoA; software drawing. 1F Pro?ect %nformation C The HVA designers can put in the pro*ect information which is common throughout the building. The default conditions set for the rooms can be easily o$erridden. 2F Heat gained inside t!e room C Jased on the dimensions and area of the room taken from AutoA;, the heat gained by walls and windows is calculated automatically. The other loads of number of people,
electrical e!uipments and outside can also be calculated by putting the rele$ant information. 3F Duct Si2ingC Jased on the total heat load calculations the HVA design engineer can calculate the of air re!uired inside the room and )x the duct si"ing. n ;esign aster%s AutoA; HVA software, the designers can si"e the ducts by three popular methodsC constant $elocity, constant pressure drop, or static regain. There is also a facility of including $arious types of duct )ttings within duct design. The layout of the duct drawings can be easily printed. :F a4ing 3D and 5D dra*ingsC With ;esign aster%s HVA design software you can easily make 1; drawings and con$ert them into 2; models by *ust a click of a button and print them. F Calculating t!e C'C The HVA designer can easily calculate the air 4ow rates 4owing through $arious ducts in . The integration of ;esign aster%s HVA software with AutoA; o&ers se$eral ad$antages. n fact it is a creati$e concept that has made HVA designing faster than e$er before.
Types of Air Conditioning Systems
An HVA designer will recommend di&erent types of air conditioning systems for di&erent applications. The most commonly used are described in this article. •
The choice of which air conditioner system to use depends upon a number of factors including how large the area is to be cooled, the total heat generated inside the enclosed area, etc. An HVA designer would consider all the related parameters and suggest the system most suitable for your space.
/indo* Air Conditioner /indo* air conditioner is the most commonly used air conditioner for single rooms. n this air conditioner all the components, namely the compressor, condenser, expansion $al$e or coil, e$aporator and cooling coil are enclosed in a single box. This unit is )tted in a slot made in the wall of the room, or more commonly a window sill.
Parts of t!e /indo* Air Conditioners Windows air conditioners are one of the most widely used types of air conditioners because they are the simplest form of the air conditioning systems. Window air conditioner comprises of the rigid base on which all the parts of the window air conditioner are assembled. The base is assembled inside the casing which is )tted into
the wall or the window of the room in which the air conditioner is )tted. The whole assembly of the window air conditioner can be di$ided into two compartmentsC the room side, which is also the cooling side and the outdoor side from where the heat absorbed by the room air is liberated to the atmosphere. The room side and outdoor side are separated from each other by an insulated partition enclosed inside the window air conditioner assembly Drefer )g 0 belowF. n the front of the window air conditioner on the room side there is beautifully decorated front panel on which the supply and return air grills are )tted Dthe whole front panel itself is commonly called as front grillF. The lou$ers )tted in the supply air grills are ad*ustable so as to supply the air in desired direction. There is also one opening in the grill that allows access to the control panel or operating panel in front of the window air conditioner. The $arious parts of the window air conditioner can be di$ided into following categoriesC the refrigeration system, air circulation system, $entilation system, control system, and the electrical protection system. All these ha$e been discussed in details below along with the front panel and other parts.
/indo* Air Conditioner
(!e Refrigeration System of t!e /indo* Air Conditioner The refrigeration system of the window air conditioner comprises of all the important parts of the refrigeration cycle. These include the compressor, condenser, expansion $al$e and the e$aporator. All these components ha$e been shown in )g 2 abo$e. The refrigerant used in most of the window air conditioners is (11. The compressor used in the window air conditioners is hermetically sealed type, which is portable one. This compressor has long life and it carries long warranty periods. n case of the maintenance problems it can be replaced easily from the company. The condenser is made up of copper tubing and it is cooled by the atmospheric air. The condenser is co$ered with the )ns to enable faster heat transfer rate from it. The capillary tubing made up of $arious rounds of the copper coil is used as the expansion $al$e in the window air conditioners.
)lter that )lters the refrigerant and also remo$es the moisture particles, if present in the refrigerant. Iike condenser, the e$aporator is also made up of copper tubing of number of turns and is co$ered with the )ns. The e$aporator is also called as the cooling coil since the rooms air passes o$er it and gets cooled.
Air Circulation System of t!e /indo* Air Conditioner The air circulation system of the window air conditioner comprises of the following parts Dplease refer )g 3 M :F. - Blo*er1 This is the small blower that is )tted behind the e$aporator or cooling coil inside the assembly of the window air conditioner system. The blower sucks the air from the room which )rst passes o$er the air )lter and gets )ltered. The air then passes o$er the cooling coil and gets chilled. The blower then blows this )ltered and chilled air, which passes through the supply air compartment inside the window air conditioner assembly. This air is then deli$ered into the room from the supply air grill of the front panel. 3- Propeller fan or t!e condenser fan1 The condenser fan is the forced draft type of propeller fan that sucks the atmospheric air and blows it o$er the condenser. The hot
refrigerant inside the condenser gi$es up the heat to the atmospheric air and its temperature reduces. 5- 'an motor1 The motor inside the window air conditioner assembly is located between the condenser and the e$aporator coil. t has double shaft on one side of which the blower is )tted and on the other side the condenser fan is )tted. This makes the whole assembly of the blower, the condenser fan and the motor highly compact.
Split Air Conditioner +plit Air onditioner The split air conditioner comprises of two partsC the outdoor unit and the indoor unit. The outdoor unit, )tted outside the room, houses components like the compressor, condenser and expansion $al$e. The indoor unit comprises the e$aporator or cooling coil and the cooling fan. or this unit you don%t ha$e to make any slot in the wall of the room. urther, present day split units ha$e aesthetic appeal and do not take up as much space as a window unit. A split air conditioner can be used to cool one or two rooms. N
Parts of the Split Air Conditioner: Wall Mounted Indoor nit The indoor unit of the split air conditioner is a box type housing in which all the important parts of the air conditioner are enclosed. The most common type of the indoor unit is the wall mounted type though other types like ceiling mounted and 4oor mounted are also used.
Split Air Conditioner *it! /all ounted %ndoor >nit
/all ounted %ndoor >nit t is the indoor unit that produces the cooling e&ect inside the room. The indoor unit of the split air conditioner is a box type housing in which all the important parts of the air conditioner are enclosed. The most common type of the indoor unit is the wall mounted type though other types like ceiling mounted and 4oor mounted are also used. We shall discuss all these types in separate articles, here we shall discuss the wall mounted type of the indoor unit. These days the companies gi$e utmost importance to the looks and aesthetics of the indoor unit. n the last couple few years the purpose of the indoor unit has changed from being a mere cooling e&ect producing de$ise to a beautiful looking cooling de$ise adding to the o$erall aesthetics of the room. This is one of the ma*or reasons that the popularity of the split units has increased tremendously in the last few years. Iet us see the $arious parts enclosed inside the indoor unit of the split air conditionerC
- #"aporator Coil or t!e Cooling Coil1 The cooling coil is a copper coil made of number turns of the copper tubing with one or more rows depending on the capacity of the air conditioning system. The cooling coil is co$ered with the aluminum )ns 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 $ery low temperature and $ery low pressure enters the cooling coil. The blower absorbs the hot room air or the atmospheric air and in doing so the air passes o$er the cooling coil which leads to the cooling of the air. This air is then blown to the room where the cooling e&ect has to be produced. The air, after producing the cooling e&ect 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 4ows 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 co$ered with the insulation tape.
3- Air 'ilter1 The air )lter is $ery important part of the indoor unit. t remo$es all the dirt particles from the room air and helps supplying clean air to the room. The air )lter in the wall mounted type of the indoor unit is placed *ust before the cooling coil. When the blower sucks the hot room air, it is )rst passed through the air )lter and then though the cooling coil. Thus the clean air at low temperature is supplied into the room by the blower. •
#ne of the most popular types split air conditioners is the wall mounted type of split A. n these As the indoor unit is mounted on wall inside the room or the o5ce.
5- Cooling 'an or Blo*er1 nside the indoor unit there is also a long blower that sucks the room air or the atmospheric air. t is an induced type of blower and while is sucks the room air it is passed
o$er the cooling coil and the )lter due to which the temperature of the air reduces and all the dirt from it is remo$ed. The blower sucks the hot and unclean air from the room and supplies cool and clean air back. The shaft of the blower rotates inside the bushes and it is connected to a small multiple speed motor, thus the speed of the blower can be changed. When the fan speed is changed with the remote it is the speed of the blower that changes.
6- Drain Pipe1 ;ue to the low temperature refrigerant inside the cooling coil, its temperature is $ery low, usually much below the dew point temperature of the room air. When the room air is passed o$er the cooling due the suction force of the blower, the temperature of the air becomes $ery low and reaches le$els below its dew point temperature. ;ue to this the water $apor present in the air gets condensed and dew or water drops are formed on the surface of the cooling coil. These water drops fall o& the cooling coil and are collected in a small space inside the indoor unit. To remo$e the water from this space the drain pipe is connected from this space extending to the some external place outside the room where water can be disposed o&. Thus the drain pipe helps remo$ing dew water collected inside the indoor unit. To remo$e the water e5ciently the indoor unit has to be a tilted by a $ery small angle of about 1 to 2 degrees so that the water can be collected in the space easily and drained out. f this angle is in opposite direction, all the water will get drained inside the room. Also, the if the tilt angle is too high, the indoor unit will shabby inside the room.
7- +ou"ers or 'ins1 The cool air supplied by the blower is passed into the room through lou$ers. The lou$ers help changing the angle or direction in which the air needs to be supplied into the room as per the re!uirements. With lou$ers one easily change the direction in which the maximum amount of the cooled air has to be passed. There are two types of lou$ersC hori"ontal and $ertical. The hori"ontal lou$ers are connected to a small motor and there position can set by the remote control. #nce can set a )xed position for the hori"ontal lou$ers so that chilled air is passed in a particular direction only or one can keep it in rotation mode so that the fresh air is supplied throughout the room. The $ertical lou$ers are operated manually and one can easily change their position as per the re!uirements. The hori"ontal lou$ers control 4ow of air in upper and downward directions of the room, while $ertical lou$ers control mo$ement of air in left and right directions. Installation of the Split Air Conditioners: !eciding the "ocation of Indoor and #utdoor nits
The installation of the split air conditioners is the most important and crucial part. f it is done properly your air conditioner will gi$e you optimum performance, but if it is not done properly you won't get the desired cooling e&ect and there may be fre!uent maintenance problems.
%ntroduction Jy now we ha$e seen the di&erent parts of the split air conditioners, now let us the installation of these Acs. The
installation of the split air conditioners is the most important and crucial part. f it is done properly your air conditioner will gi$e you optimum performance, but if it is not done properly you won't get the desired cooling e&ect and there may be fre!uent maintenance problems of which the most prominent can be the gas or refrigerant leakage. The installation of the split air conditioner should be done by an expert air conditioning technician and the task should not be left to a no$ice person who is experimenting with your A. t re!uires lots of practice to become an expert split A installation and erection technician. Various factors ha$e to considered during the installation of any split air conditioner, here we are going to consider how to do the installation of wall mounted split air conditioner. n other articles we would consider installation of other types of split air conditioners also.
+ocation of %ndoor and Outdoor >nits
+ocation of t!e %ndoor and t!e Outdoor >nits The )rst step in the installation of split A is deciding the location of the indoor and the outdoor units, only then the next important steps of the installation can be initiated. Iet us the see the factors to be considered when deciding the location of these unit Dsee the images belowFC - %ndoor >nit1
Here are the important suggestions when deciding the location of indoor unit inside the roomC aF The indoor unit is located inside the room at the location from where the air can be distributed e$enly throughout the room. bF As far as possible the indoor should be installed abo$e the bed so that the maximum cooling e&ect can be obtained. t should be located directly abo$e the bed. f one has to a$oid the direct 4ow of chilled air on the body, one can always change the direction of the lou$ers. The indoor unit can also be installed on wall towards your feet though it can be installed on other side walls also. cF The wall mounted indoor unit should be located at the height of about 9 to 0@ feet from the 4oor so that that most of the chilled air is used for cooling the room and not merely for cooling the hot roof. dF The indoor unit should be accessible easily so that one can con$eniently clean the )lter e$ery fortnight and the whole unit and also that one can manually change the position of the lou$ers easily. eF f the indoor unit is installed abo$e certain window, make sure that it is in symmetry with the window, else the unit will look shabby. The indoor unit is meant to add to the aesthetics of the room and not destroy it.
3- Outdoor >nit1 Here are some points to consider when deciding the location of the outdoor unitC aF The outdoor unit should be located in the open space preferably on the terrace so that the air can 4ow freely o$er the compressor and the condenser. f the terrace is not a$ailable it can be kept on the awning abo$e the wall
or it can be hanged on the external wall supported by the angles. bF 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 de$ices. The installation and gas charging also should be con$enient. cF There should not be any hindrances in front of the outdoor that would block the passage of fan air from passing to the open space. Any blockages will seriously a&ect the performance of the A and can also lead to the burning of hermetically sealed compressor coil. dF The surface on which the outdoor unit is to be installed should be rigid enough to a$oid its $ibration. The $ibration of the outdoor unit will raise excessi$e noise and also lead to the breaking of the copper tubing and leakage of the refrigerant. t is always ad$isable to keep the outdoor unit at the height abo$e the indoor unit. f the outdoor unit is kept at le$el below the indoor, some of the compressor power is used in pumping the refrigerant against the gra$ity, thus reducing the o$erall performance of the compressor. ost of the outdoor units are !uite silent so one does not ha$e to worry about their noise. The internal parts of the outdoor unit are shielded against the rain and sun rays, so one can rest assured about their safety in di&erent climatic conditions. The refrigerant at $ery low temperature 4ows inside the tubing between indoor and the outdoor unit, and there is always some loss of refrigerant e&ect to the atmosphere from these tubing, hence the distance between the indoor and the outdoor unit should be kept as minimum as possible to reduce the loss of the cooling e&ect. The
maximum distance between the indoor and the outdoor units can be about 0: meters. 'ac(a)ed Air *onditioner
An H+A* desi)ner wi s))est this type o- air conditioner i- yo want to coo more than two rooms or a ar)er space at yor home or o--ice. /here are two possibe arran)ements with the pac(a)e nit. In the -irst one, a the components, namey the compressor, condenser 0which can be air cooed or water cooed1, e2pansion 3a3e and e3aporator are hosed in a sin)e bo2. /he cooed air is thrown by the hi)h capacity bower, and it -ows thro)h the dcts aid thro)h 3arios rooms. In the second arran)ement, the compressor and condenser are hosed in one casin). /he compressed )as passes thro)h indi3ida nits, comprised o- the e2pansion 3a3e and cooin) coi, ocated in 3arios rooms.
Pac4aged Air Conditioners @ (ypes of Pac4aged AC This article describes what the package air conditioner is and the types of packaged air conditioners.
Pac4aged Air Conditioners The window and split air conditioners are usually used for the small air conditioning capacities up to : tons. The central air conditioning systems are used for where the cooling loads extend beyond 1@ tons. The packaged air conditioners are used for the cooling capacities in between these two extremes. The packaged air conditioners are a$ailable in the )xed rated capacities of 2, :, E, 0@ and 0: tons. These units are used commonly in
places like restaurants, telephone exchanges, homes, small halls, etc. As the name implies, in the packaged air conditioners all the important components of the air conditioners are enclosed in a single casing like window A. Thus the compressor, cooling coil, air handling unit and the air )lter are all housed in a single casing and assembled at the factory location. ;epending on the type of the cooling system used in these systems, the packaged air conditioners are di$ided into two typesC ones with water cooled condenser and the ones with air cooled condensers. Joth these systems ha$e been described belowC
Pac4aged Air Conditioners *it! /ater Cooled Condenser n these packaged air conditions the condenser is cooled by the water. The condenser is of shell and tube type, with refrigerant 4owing along the tube side and the cooling water 4owing along the shell side. The water has to be supplied continuously in these systems 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 single casing along with the compressor, expansion $al$e, and the air handling unit including the cooling coil or the e$aporator. This whole packaged air conditioning unit externally looks like a box with the control panel located externally. n the packaged units with the water cooled condenser, the compressor is located at the bottom along with the condenser Drefer the )gure belowF. Abo$e these components the e$aporator or the cooling coil is located. The air handling unit comprising of the centrifugal blower
and the air )lter is located abo$e the cooling coil. The centrifugal blower has the capacity to handle large $olume of air re!uired for cooling a number of rooms. rom the top of the package air conditioners the duct comes out that extends to the $arious rooms that are to be cooled. All the components of this package A are assembled at the factory site. The gas charging is also done at the factory thus one does not ha$e to perform the complicated operations of the laying the piping, e$acuation, gas charging, and leak testing at the site. The unit can be transported $ery easily to the site and is installed easily on the plane surface. +ince all the components are assembled at the factory, the high !uality of the packaged unit is ensured.
Pac4age AC *it! /ater Cooled Condenser
Pac4aged Air Conditioners *it! Air Cooled Condensers n this packaged air conditioners the condenser of the refrigeration system is cooled by the atmospheric air. There is an outdoor unit that comprises of the important components like the compressor, condenser and in some cases the expansion $al$e Drefer the )gure belowF. The outdoor unit can be kept on the terrace or any other open place where the free 4ow of the atmospheric air is
a$ailable. The fan located inside this unit sucks the outside air and blows it o$er the condenser coil cooling it in the process. The condenser coil is made up of se$eral turns of the copper tubing and it is )nned externally. The packaged As with the air cooled condensers are used more commonly than the ones with water cooled condensers since air is freely a$ailable it is di5cult maintain continuous 4ow of the water. The cooling unit comprising of the expansion $al$e, e$aporator, the air handling blower and the )lter are located on the 4oor or hanged to the ceiling. The ducts coming from the cooling unit are connected to the $arious rooms that are to be cooled.
Pac4age Air Conditioner Air Cooled Condenser
Compressors and Capacity Control System in the Pacaged Air Conditioners
This article describes the arrangement of compressors in the package air conditioners with multiple compressors. t also describes the capacity control system in these units.
Compressors and Control System in t!e Pac4aged Air Conditioners The packaged air conditioners are used for the low to medium tonnage of air conditioning load ranging from : to 1@ tons also higher. or smaller loads up to : tons single compressor is used. or the higher load of more than : tons two compressor are used in the package air conditioning system forming two independent refrigeration systems. Though the two systems are independent they are housed in the same supporting framework. The e$aporator systems of these two systems are entwined together. With the two compressors installed in the system there is facility for the capacity control of the air conditioning plant thus one can run the plant fully or partially as per the heating load or as per the number of rooms to be cooled. At full capacity both the compressors can be kept running, while at the partial load one of the compressors can be kept o&. The capacity control can also be done automatically by thermostat. The two compressors also ensure that the air conditioning plant won't stop completely when one of the compressor breaks down, for the system can still keep on running though on partial capacity. The water cooled condenser used with the two compressor system can be single shell but partitioned inside it for di&erent passages for the refrigerant from the two compressors. There can also be two di&erent water cooled condensers for two di&erent systems. f the condenser is of air cooled type, there would be two condensers either placed side/by/side or entwined together *ust like the e$aporator of the system.
(!ermostat Setting for (*o Compressor Systems or controlling the operation of the two compressor packaged air conditioning system, two di&erent thermostats can be connected to the two cooling systems. This will allow for the capacity control of both the compressors to ensure optimum running of the plant. n many cases the thermostat is connected to the compressor of one cooling system only. n this case one compressors keeps on running at full capacity and the other compressor remains shut or runs at partial or full capacity depending on the cooling load. To ensure that one compressor won't wear and tear at the fast rate, the compressor running at the full capacity is interchanged from time/to/time. The two compressor system is used for the cooling loads between : to tons 0: tons, for higher loads more than two units can be installed as per the re!uirements. There can be multiple air handling units in these systems sending the chilled air to di&erent parts of the building. The compressor and the condenser units are housed in the same location of the building thus there is one common place for the return air. f these units ha$e water cooled condenser, the hot water coming out from them is cooled in the single cooling tower. ;uring the full load all the compressors run at the full capacity, and when the load reduces one or more compressors are stopped manually or automatically, which makes the other compressors to run at the full load. When the compressor runs at full capacity it runs more e5ciently. Whether the packaged air conditioner consists of single compressor or the multiple
compressors, most of the components are assembled at the factory site, so the installation of the package A is !uite easy.
Central Air Conditioning Plants entral air conditioning plants are used for applications like big hotels, large buildings ha$ing multiple 4oors, hospitals, etc, where $ery high cooling loads are re!uired. The article describes $arious possible arrangements of 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 window and split air conditioners are used for single rooms or small o5ce spaces. f the whole building is to be cooled it is not economically $iable to put window or split air conditioner in each and e$ery room. urther, these small units cannot satisfactorily cool the large halls, auditoriums, receptions areas etc. n the central air conditioning systems there is a plant room where large compressor, condenser, thermostatic expansion $al$e and the e$aporator are kept in the large plant room. They perform all the functions as usual similar to a typical refrigeration system. Howe$er, all these parts are larger in si"e and ha$e higher capacities. The compressor is of open reciprocating type with multiple cylinders and is cooled by the water *ust like the 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 $al$e, in the central air conditioning systems thermostatic expansion $al$e is used. The chilled is passed $ia the ducts to all the rooms, halls and other spaces that are to be air conditioned. Thus in all the rooms there is only the duct passing the chilled air and there are no indi$idual cooling coils, and other parts of the refrigeration system in the rooms. What is we get in each room is the completely silent and highly e&ecti$e air conditions system in the room. urther, the amount of chilled air that is needed in the room can be controlled by the openings depending on the total heat load inside the room. The central air conditioning systems are highly sophisticated applications of the air conditioning systems and many a times they tend to be complicated. t is due to this reason that there are $ery few companies in the world that speciali"e in these systems. n the modern era of computeri"ation a number of additional electronic utilities ha$e been added to the central conditioning systems. There are two types of central air conditioning plants or systemsC 0F Direct e$pansion or D central air conditioning plantC n this system the huge compressor, and the condenser are housed in the plant room, while the expansion $al$e and the e$aporator or the cooling coil and the air handling unit are housed in separate room. The cooling coil is )xed in the air handling unit, which also has large blower housed in it. The blower sucks the hot return air from the room $ia ducts and blows it o$er
the cooling coil. The cooled air is then supplied through $arious ducts and into the spaces which are to be cooled. This type of system is useful for small buildings. 1F C!illed *ater central air conditioning plant1 This type of system is more useful for large buildings comprising of a number of 4oors. t has the plant room where all the important units like the compressor, condenser, throttling $al$e and the e$aporator are housed. The e$aporator is a shell and tube. #n the tube side the reon 4uid passes at extremely low temperature, while on the shell side the brine solution is passed. After passing through the e$aporator, the brine solution gets chilled and is pumped to the $arious air handling units installed at di&erent 4oors of the building. The air handling units comprise the cooling coil through which the chilled brine 4ows, and the blower. The blower sucks hot return air from the room $ia ducts and blows it o$er the cooling coil. The cool air is then supplied to the space to be cooled through the ducts. The brine solution which has absorbed the room heat comes back to the e$aporator, gets chilled and is again pumped back to the air handling unit. To operate and maintain central air conditioning systems you need to ha$e good operators, technicians and engineers. 6roper pre$entati$e and breakdown maintenance of these plants is $ital.
Direct #$pansion =D- (ype of Central Air Conditioning Plant or System
There are two types of central air conditioning systemsC ;irect Bxpansion D;OF type of central air condition plants and hilled Water type of the central air conditioning plants. This article describes the ;O central air conditioning system.
%ntroduction There are two types of central air conditioning systemsC ;irect Bxpansion D;OF type of central air condition plants and hilled Water type of the central air conditioning plants. n the ;O system the air used for cooling the room or space is directly passed o$er the cooling coil of the refrigeration plant. n case of the chilled water system the refrigeration system is used to )rst chill the water, which is then used to chill the air used for cooling the rooms or spaces. Joth these systems ha$e been discussed in detailsL this article discusses ;O system, while the next one describes chilled water system.
Direct #$pansion =D- (ype of Central Air Conditioning Plant n the direct expansion or ;O types of air central conditioning plants the air used for cooling space is directly chilled by the refrigerant in the cooling coil of the air handling unit. +ince the air is cooled directly by the refrigerant the cooling e5ciency of the ;O plants is higher. Howe$er, it is not always feasible to carry the refrigerant piping to the large distances hence, direct expansion or the ;O type of central air conditioning system is usually used for cooling the small buildings or the rooms on the single 4oor.
There are three main compartments of the ;O type of central conditioning systems Dplease refer the )g belowFC
D Central Air Conditioning Plant
- (!e Plant Room1 The plant room comprises of the important parts of the refrigeration system, the compressor and the condenser. The compressor can be either semi/hermetically sealed or open type. The semi/hermetically sealed compressors are cooled by the air, which is blown by the fan, while open type compressor is water cooled. The open compressor can be dri$en directly by motor shaft by coupling or by the belt $ia pulley arrangement. The condenser is of shell and tube type and is cooled by the water. The refrigerant 4ows along the tube side of the condenser and water along the shell side, which enables faster cooling of the refrigerant. The water used for cooling the compressor and the condenser is cooled in the cooling tower kept at the top of the plant room, though it can be kept at other con$enient location also.
3- (!e Air Handling >nit Room1 The refrigerant lea$ing the condenser in the plant room enters the thermostatic expansion $al$e and then the air handling unit, which is kept in the separate room. The air handling unit is a large box type of unit that comprises of the e$aporator or the cooling coil, air )lter and the large blower. After lea$ing the thermostatic expansion $al$e
the refrigerant enters the cooling coil where it cools the air that enters the room to be air conditioned. The e$aporator in the air handling unit of the ;O central air conditioning system is of coil type co$ered with the )ns to increasing the heat transfer e5ciency from the refrigerant to the air. There are two types of ducts connected to the air handling unitC for absorbing the hot return 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 that has absorbed the heat from the room $ia the ducts. This air is then passed through the )lters and then o$er the cooling coil. The blower then passes the chilled air through ducts to the rooms that are to be air conditioned. •
The ;O expansion system runs more e5ciently at higher loads. B$en in case of the breakdown of the plants, the other plants can be used for the cooling purpose. The ;O types of central air conditioner plants are less popular than the chilled water type of central conditioning plants.
5- Air Conditioned Room1 This is the space that is to be actually cooled. t can be residential room, room of the hotel, part of the o5ce 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 the grills or di&users that supply the chilled air to the room. The air absorbs the heat and gets heated and it passes through another set of the grill and into the return air duct that ends into the air handling unit room. This air is then re/circulated by the air handling unit.
Though the e5ciency of the ;O plants is higher, the air handling units and the refrigerant piping cannot be kept at $ery long distance since there will be lots of drop in pressure of the refrigerant along the way and there will also be cooling losses. urther, for the long piping, large amounts of refrigerant will be needed which makes the system $ery expensi$e and also prone to the ma instance problems like the leakage of the refrigerant. ;ue to these reasons the ;O type central air conditioning systems are used for small air conditioning systems of about : to 0: tons in small buildings or the number of rooms on a single 4oor. f there are large air conditioning loads, then multiple direct expansion systems can be installed. n 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 ;O expansion system runs more e5ciently at higher loads. B$en in case of the breakdown of the plants, the other plants can be used for the cooling purpose. The ;O types of central air conditioning plants are less popular than the chilled water type of central conditioning plants.
Chilled Water Central Air Conditioning Systems
n the pre$ious article we saw ;O type of central air conditioning plant, this article describes chilled water type of central air conditioner.
C!illed /ater 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 se$eral 4oors are to be air conditioned. While in the direct expansion type of central air conditioning plants, refrigerant is directly used to cool the room airL in the chilled water plants the refrigerant )rst chills the water, which in turn chills the room air. n chilled water plants, the ordinary water or brine solution is chilled to $ery low temperatures of about to 9 degree elsius by the refrigeration plant. This chilled water is pumped to $arious 4oors of the building and its di&erent parts. n each of these parts the air handling units are installed, which comprise of the cooling coil, blower and the ducts. The chilled water 4ows through the cooling coil. The blower absorbs return air from the air conditioned rooms that are to be cooled $ia the ducts. This air passes o$er the cooling coil and gets cooled and is then passed to the air conditioned space.
C!illed Central Air Conditioners
Various Parts of t!e C!illed /ater Air Conditioning Plant All the important parts of the chilled water air conditioning plant are shown in the abo$e )gure and described in detail belowC
- Central Air Conditioning Plant Room1 The plant room comprises of all the important components of the chilled water air conditioning plant. These include the compressor, condenser, thermostatic expansion $al$e and the e$aporator or the chiller. The compressor is of open type and can be dri$en by the motor directly or by the belt $ia pulley arrangement connected to the motor. t is cooled by the water *ust like the automoti$e engine. The condenser and the e$aporator are of shell and tube type. The condenser is cooled by the water, with water 4owing along the shell side and refrigerant along the tube side.The thermostatic expansion $al$e is operated automatically by the solenoid $al$e. The e$aporator is also called as the chiller, because it chills the water. f the water 4ows along the shell side and refrigerant on the tube side, it is called as the dry expansion type of chiller. f the water 4ows along tube side and the refrigerant along the shell side, it is called as the 4ooded chiller. The water chilled in the chiller is pumped to $arious parts of the building that are to be air conditioned. t enters the air handling unit, cools the air in cooling coil, absorbs the heat and returns back to the plant room to get chilled again. The amount of water passing into the chiller is controlled by the 4ow switch. n the central air conditioning plant room all the components, the compressor, condenser, thermostatic expansion $al$e, and the chiller are assembled in the structural steel framework making a complete compact refrigeration plant, known as the chiller package. 6iping re!uired to connect these parts is also enclosed in this unit making a highly compact central air conditioning plant.
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The air handling handling units are are installed in the $arious parts of the building that are to be air conditioned, in the place called air handling unit rooms. The air handling handling units comprise comprise of the cooling cooling coil, coil, air )lter, the blower and the supply and return air ducts. The chilled water 4ows through the cooling coil. The blower absorbs the return hot air from the air conditioned space and blows it o$er the cooling coil thus cooling the air. This cooled air passes o$er the air )lter and is passed by the t he supply air ducts into the space which is to be air conditioned. The air handling unit and the ducts passing through it are insulated to reduce the loss of the cooling e&ect.
3- Air Handling >nit Rooms1 The air handling handling units are are installed in the $arious parts of the building that are to be air conditioned, in the place called air handling unit rooms. The air handling units comprise of the cooling coil, air )lter, the blower and the supply and return air ducts. The chilled water 4ows through the cooling coil. The blower absorbs the return hot air from the air conditioned space and blows it o$er the cooling coil thus cooling the air. This cooled air passes o$er the air )lter and is passed by the supply air ducts into the space which is to be air conditioned. The air handling unit and the t he ducts passing through it are insulated to reduce the loss of the cooling e&ect. 5- Air Conditioned Rooms1 These are are the rooms rooms or spaces that are are to be air conditioned. These can be residential or hotel rooms, halls, shops, o5ces, complete theater, $arious parts of the airport etc. At the top of these rooms the supply and the return air ducts are laid. The supply air ducts supply the cool air to the room $ia one set of the di&users, while
the return air ducts absorbs the hot return air from the room by another set of the di&users. The hot return air enters the air handling unit, gets cooled and again enters the room $ia supply duct to produce air conditioning e&ect.
6- Cooling (o*er1 The cooling cooling tower is used used to cool the water that absorbs heat from the compressor and the condenser. When water 4ows through these components some water gets e$aporated, to make up this loss some water is also added in the cooling tower. The cooling tower is of e$aporati$e type. Here Here the water is cooled by the atmospheric air and is re/circulated through the compressor and the condenser.
Air Handling nits or $an Coil nits
As the name suggests air handling unit is the box type of unit that handles the room air. This article describes $arious parts of the air handling unit, its working and types.
/!at are Air Handling >nits or 'an Coil >nits< The air handling handling units are are $ery important important parts of the central air conditioning plants, packaged air conditioning plants and also the roof mounted mounted split air conditioning systems. As the name suggests air handling unit is the box type of unit that handles the room air. t comprises of
the cooling coil o$er which the hot return air from the room 4ows, gets cooled and 4ows back to the room to cool it. The circulation of the air is carried out by the blower. The )lter in the air handling unit enables cleaning of the air. The air handling units are also called as fan coil units in case of roof mounted split A units, since they comprise of the fan and the cooling coil. The air handling handling units are are installed at at the di&erent di&erent places in the building to be air conditioned. They are connected connected to the cool air supply and return air ducts which are laid in all the rooms to be cooled. n case of the central air conditioning plants the air handling units are installed on the 4oor, while in case of the split air conditioners, they are mounted on the roof inside the room abo$e the false ceiling. n case of packaged units they can be installed on the 4oor or the roof. The $arious $arious parts of the the air handling handling unit and their their working are discussed in details belowC
Air Handling >nits
- Bo$ #nclosure1 All the parts of the air handling unit are enclosed in the box type of enclosure. This ensures compactness of the unit and protection of all the components inside it. The whole box is insulated to pre$ent the loss of heat from the unit. 3- Cooling Coil1
The cooling is one of the most important parts of the air handling units. t is made up of copper tubing of se$eral turns and co$ered with the )ns to increase the heat transfer e5ciency of the cooling coil. n direct expansion D;OF type of the central air conditioning plants the refrigerant 4ows though the cooling coil, which also acts as the e$aporator of the plant. n case of the chilled water system the chilled water from the chiller 4ows through the cooling coil. n packaged and the split air conditioners also the refrigerant 4ows directly through the cooling coil, thus acting as the e$aporator of the system. The hot return air from the room 4ows o$er the cooling and gets cooled. This air is supplied to $arious rooms $ia the ducts. The 4ow of chilled water or the refrigerant to the cooling coil is controlled by the solenoid $al$e. •
The cooling is one of the most important parts of the air handling units. t is made up of copper tubing of se$eral turns and co$ered with the )ns to increase the heat transfer e5ciency of the cooling coil. n direct expansion D;OF type of the central air conditioning plants the refrigerant 4ows though the cooling coil, which also acts as the e$aporator of the plant. The air handling is connected to the supply air and return air ducts. The supply air duct supplies the cool air from the air handling unit to $arious rooms. The fan or the blower sucks the hot return air from the room and blows it o$er cooling coil, cools it and sends it to the room to be air conditioned. There are two possible arrangements of the fans in air handling unitsC draw though arrangement and blow through arrangement.
5- Ducts1 The air handling is connected to the supply air and return air ducts. The supply air duct supplies the cool air from
the air handling unit to $arious rooms, while the return air supplies hot return air from $arious rooms back to the air handling unit. There is one main supply duct that bifurcates into $arious small ducting that are laid in all the rooms that are to be cooled. The return ducts from all the rooms also end into one main duct. All the supply and return air ducts are co$ered with the insulation material to pre$ent the loss of the cooling e&ect. The ducts are designed and laid such that there is e$en distribution of the cooled air to the rooms as per their heat loads and there is least wastage of the cooling e&ect.
5- 'an or Blo*er1 The fan or the blower sucks the hot return air from the room and blows it o$er cooling coil, cools it and sends it to the room to be air conditioned. There are two possible arrangements of the fans in air handling unitsC draw though arrangement and blow through arrangement. n the draw through arrangement the fan sucks the return air through the )lter and the cooling coil. As the air passes o$er the cooling coil its gets chilled, it is then passed to the rooms to be cooled. n case of the blow through arrangement the fan absorbs the return air and blows it o$er the air )lter and the cooling coil. The air then 4ows to the rooms to be air conditioned. The draw through arrangement is used more commonly due to its compactness. The fans are of centrifugal types. The capacity of the air handling units is rated in terms of the amount of air that can be handled by its fan. The capacity of the fan can be 2@,@@@cfm Dcubic feet per minuteF with the static pressure of about E: to 0@@mm of water gauge.
Air Handling >nit 'an
6- Air 'ilter1 Air )lter is one the important parts of any air conditioning system. The air )lter remo$es dirt, dust, smoke and other impurities from the air and cleans. The air )lter is usually attached to the cooling air and before it. The air is )rst absorbed or pushed o$er the air )lter and then o$er the cooling coil.
Comparison of D and C!illed /ater Central Air Conditioning Plants The ;irect Bxpansion D;OF and hilled Water central air conditioning plants are both used at di&erent places depending on the applications and si"e of the place to be air conditioned. Iet us see the comparison of ;O and chilled water central air conditioning plants.
%ntroduction The ;irect Bxpansion D;OF and hilled Water central air conditioning plants are both used at di&erent places depending on the applications and si"e of the place to be air conditioned. Joth of them ha$e their own ad$antages and disad$antages. Iet us see the comparison of ;O and chilled water central air conditioning plants.
- D Central Air Conditioning Plants are more #cient n the ;O type of central air conditioning plants the air used for cooling the room is directly chilled by the refrigerant in the cooling coil of the air handling unit. ;ue to this heat transfer process is more e5cient, since there is no middle agency in$ol$ed for the heat transfer resulting in higher cooling e5ciency. n case of the chilled water system, the cooling e&ect from the refrigerant is )rst transferred to the chilled water, which is then used to chill the air used for cooling the room. There is some loss of the cooling e&ect when it is being transferred from the refrigerant to the chilled water and from there to the air due to which the chilled water systems ha$e lesser cooling e5ciency. The chilled water acts as the secondary medium for cooling the room air in air handling unit. urther, the chilled water has to 4ow long distance along the whole building. #n its way it tends to get heated due to friction of 4ow and also due to surrounding heat absorption. The chilled water also has to be pumped by the pump, which adds more heat to it. Thus as the chilled water 4ows from the chiller to the air handling unit and again back to the chiller, apart from the heat from air, it also absorbs lots of additional heat, which leads to high increase in its temperature. The chiller has to remo$e this additional heat from the water due to which its e5ciency decreases or rather additional power is re!uired to remo$e this additional heat. n the ;O type of central air conditioning plants the refrigerant tra$els only through the small distances and there is no pump in$ol$ed so the additional heat absorption is less, which makes the ;O plants e$en more e5cient.
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3- (!e C!illed /ater Plants can )e used for t!e +arge ulti Storey Buildings n the direct expansion types of the central air conditioning plant, the refrigerant like (11 4ows through the whole air conditioning system including the air handling unit. When the refrigerant 4ows in the refrigeration piping there is lots of drop in its pressure. ;ue to this the length of the refrigeration tubing and the distance between the condenser and the air handling unit should be kept minimum possible. f the air handling unit is kept at the height more than the condenser, the loss in pressure is pronounced since refrigerant tra$elling from the condenser to the air handling unit is in li!uid state. As the distance between the air handling unit and the condenser increases the loss in pressure also increases. At certain point the losses may be so high that the refrigerant may not be able to reach the air handling unit, leading to complete failure of the system. At the larger height di&erence there is also oil return problem from the refrigerant to the compressor. ;ue to these reasons, in direct expansion type of the central air conditioning plant there is limitation on the distance between the condenser and the air handling unit. The distance between the two cannot be too high. This limits the application of the direct expansion type of central air conditioning systems to the small buildings or a number of rooms on the single 4oor. n such cases the plant room and air handling room and the rooms to be cooled are located on the same 4oor. The height di&erence between the condenser and the air handling units has to be !uite reasonable so that they can function well.
#ne of the solutions to increase the capacity of the ;O systems can be to increase the number of air handling units on upper 4oors. Jut with this will be additional number of *oints in the refrigerant tubing from which there will be higher chances of leakage of highly expensi$e refrigerant. This leads to too many operational and maintenance problems. #ne may think that we can employ compressor of $ery high capacity to increase the refrigerant pressure, but this will lead to highly excessi$e capital and running costs of the plant. This is because we will ha$e to install the compressor of capacity much higher than needed. Thus the direct expansion types of the air conditioning plants can be used only for smaller buildings or $arious rooms on the same 4oor. There are no pressure loss problems in the chilled water system. n this system chilled water is pumped by the pump at $ery high pressure, which is good enough to carry it to $arious 4oors of the multi storey building. The losses in the pressure of water are accommodated by the su5cient capacity of the pump, which has low capital and running cost. urther, the water doesn%t carry any oil so there are no oil return problems. n case of the chilled water system the compressor, condenser, expansion $al$e and the chiller are all kept at the same le$el in the single plant room. There is no problem as such of the height di&erence between the condenser and the air handling unit since the refrigerant does not tra$els to the air handling unit. The 4ow of the refrigerant is limited to the chiller plant. The water chilled in the chilled 4ows to the $arious air handling units kept on di&erent 4oors of the building. The whole arrangement and the structure of the chilled water type of central air
conditioning plant makes it more suitable for cooling the large multi storey buildings and e$en for $ery long distances along the same 4oor le$el. This makes the chilled water central air conditioners more popular than the direct expansion type ones.
4hat are the di--erences between F*5, AH5 6 FAH57
F*5 is the abbre3iation sed -or FAN *OIL 5NI/ that are a3aiabe -or either 89 or chied water system that hoses re-ri)erant or chied water coi respecti3ey. eside the type o- coi sed, the other components are common sch as the bower -an 6 -iters. F*5s are say a3aiabe -rom%.;< to< /R -rom 3arios brands across the )obe.
AH5 is the abbre3iation sed -or AIR HAN8LIN= 5NI/> is an ada3nce type o- F*5 beyond< /R capacity. /hey are either a3aiabe in standard si?es or cstome si?e 6 body constrction. In addition to the standard components 0bower -an 6 -iter1, it has ad3ance -iters, 5+ i)ht, mi2in) chambers, etc. dependin) pon the re@irement 6 constrction.
FAH5 is the abbre3iation sed -or FRSH AIR HAN8LIN= 5NI/. /hese are say centrai?ed nits empoyed to indce -resh air
@antities to the con-ines spaces. /hey come into pictre where3er there are imitations to -resh air inta(e either directy or thro)h AH5s. FAH5s are either o- norma constrction ha3in)!%%B -resh air thro)h a bower -an or /reated FAH5 that empoys an additiona cooin) coi to indce treated air into the con-ined space withot deterioratin) the indoor conditions. It a depends pon the seection o- the desi)ner to pro3ide an optimm H+A* sotion.
$C Fan *oi 5nit, as the name s))ests the nit hoses the ower0Fan1, the e3aporator *oi 0-or 89 System1 " Heat 2chan)er *oi0 -or sytems other than 891, Fiter and sometimes Heater *oi0ectric1. 5say ta(es the hot air -rom room and coo it then spy to room. AH5 is the abbre3iation sed -or AIR HAN8LIN= 5NI/> is an ada3nce type o- F*5 and normay made as to cstomer demandDsch as heater,3 amps,carbon -iter,hepa -iter, pre -iter and ba) -iters are normay sin) in a AH5ES with retrn air dct some -resh air aso and spy the coo pri-ied air to the premises by sin) bower and motor rnnin) with or withot +F8. $AH : Fresh Air Handin) 5nit, same as a AH5 bt dosent ha3e air recircation option0!%%B Fresh Air is sed1. /he Retrn air is e2tracted to the atmosphere either sed Heat 4hee or cois i(e heat e2chan)er coi,pre cooin) coi and cooin) coi with pre -iter, ba) -iter,5+ amp,H'A -iter,*arbon -iter G where it is appicabe and -or some nits sin) ectronic -iter aso./hen
spy the pri-ied coo air to the rooms with bet dri3en motor or direct dri3e controed by +F8.
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D AH5 is the abbre3iation sed -or AIR HAN8LIN= 5NI/> is an ada3nce type o- F*5 and normay made as to cstomer demandD sch as heater,3 amps,carbon -iter,hepa -iter, pre -iter and ba) -iters are normay sin) in a AH5ES with retrn air dct some -resh air aso and spy the coo pri-ied air to the premises by sin) bower and motor rnnin) with or withot +F8. Fan *oi 5nit, as the name s))ests the nit hoses the ower0Fan1, the e3aporator *oi 0-or 89 System1 " Heat 2chan)er *oi0 -or sytems other than 891, Fiter and sometimes Heater *oi0ectric1. 5say ta(es the hot air -rom room and coo it then spy to room. FAH5 : Fresh Air Handin) 5nit, same as a AH5 bt dosent ha3e air recircation option0!%%B Fresh Air is sed1. /he Retrn air is e2tracted to the atmosphere either sed Heat 4hee or cois i(e heat e2chan)er coi,pre cooin) coi and cooin) coi with pre -iter, ba) -iter,5+ amp,H'A -iter,*arbon -iter G where it is appicabe and -or some nits sin) ectronic -iter aso./hen spy the pri-ied coo air to the rooms with bet dri3en motor or direct dri3e controed by +F8. AH5 : Air handin) nit F*5 : Fan coi nit FAH5 : Fresh Air handin) nit
!. AH5 is )eneray a bi))er system than F*5.$. AH5 is more compe2 than the F*5 and that AH5 are o-ten sed in bi))er estabishments or spaces.#. /he AH5 system say channes air thro)h dcts whereas the F*5 may ha3e or donEt ha3e any dctwor(s.. AH5 system treats otside air whie F*5s basicay recyce or reDcircates the air.<. AH5 ha3e sections -or reheatin) and hmidi-yin) whereas the F*5 may ha3e heaters bt no Hmdi-ication .. F*5 are o-ten obser3ed to be noisier than the AH5. < $C D Fan *oi 5nit, as the name s))ests the nit hoses the ower0Fan1, the e3aporator *oi 0-or 89 System1 " Heat 2chan)er *oi0 -or sytems other than 891, Fiter and sometimes Heater *oi0ectric1. 5say empoyed -or pto to
'ate type H91 is sed where the temperatre o- -resh air is trans-ered to the e2tract air.
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F*5 is -an coi nit which is intaed -or sam capacities and ha3e ess options than AH5 i(e no hmidity contro and no specia options -or heat reco3ery o- air -iters. AH5 means Air Handin) 5nits and are a3aiabe in nmber o3arities and tonna)es -rom sma pto ar)e capacities. /hay are a3aiabe with nmber o- modi-ications which are normy not a3aiabe in F*5s as mentioned abo3e. 4hen the AH5 is sed -or -resh air ony then it is (nown as FAH5 0Fresh Air Handin) 5nit1. means there is no retrn dct ony -resh air sppy to the area. Hope this wi wor(
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; F*5 is an indoor nit with sma tona)e capacities sed with centra air conditionin) systems sch as chiers system. AH5 is an indoor and aso can be sed as otdoor aso sed with centra air conditionin) systems sch as chiers system bt ha3e a wide ran)e o- capacities ha3in) a )reat static pressre o- -ans to dei3er the air thro)h air dcts to bi) cooin) ?one areas. FAH5 is same i(e AH5 with -resh air!%%B.
