SEMESTER V – BUILDING SERVICES III - HVAC UNIT I : AIR CONDITIONING : BASIC REFRIGERATION PRINCIPLES
THERMODYNAMICS Thermodynamics Thermodynamics is that branch of science dealing with the mechanical action of heat. heat. Ther There e are are cert certai ain n fund fundam amen ental tal prin princi cipl ples es of natu naturre, ofte often n call called ed laws laws of thermodynamics, which govern our existence here on Earth, several of which are basic, in the study of refrigeration. The rst and most important of these laws is the fact energy can neither be created or destroyed, but can be converted from one type to another.
HEAT Heat is a form of energy, primarily created by the transformation of other types of energy into heat energy. For examples, mechanical energy turning a wheel causes friction which creates heat.
TEMPERATURE Temperatur Temperature e is the scale used to measure the intensity of heat, the indicator that that dete deterrmine mines s whic which h way way the the heat heat ener energy gy will will move move.. In the the nit nited ed stat states es,, temperature is normally measured in degrees Fahrenheit, but the !entigrade scale "sometimes termed termed !elsius# is widely used in other parts of the world. $oth scales use two points as reference, the free%ing point of water and the boiling point of water at sea level. &ater free%es at '()F or *)!., and water boils at sea level at (+()F. or +**)!. n the Fahrenhei ahrenheitt scale, scale, the temperatu temperature re di-erence di-erence between between these two points points is divided into +* e/ual increments or degrees F., while on the !entigrade scale the temper temperatu ature re di-er di-erenc ence e is divide divided d into into +* +** * e/ual e/ual incre incremen ments ts or degre degrees es !. The relation between Fahrenheit and !entigrade scales can always be established by the following formulas0 Fahrenheit 1 234 "!entigrade plus '()# Fahrenheit 1 432 "Fahrenheit plus '()#
LATENT LATENT HEAT OF FUSION: FUS ION: 5 change of substance from a solid to a li/uid or from a li/uid to a solid involves the latent heat of fusion. It might also be termed the latent heat of melting, or the latent heat of free%ing. free%ing.
LATENT HEAT OF EVAPORATION: 5 change of a substance from a li/uid to a vapour, or from a vapour bac6 to a li/uid involves the latent heat of evaporation. &hen one pound of water boils or evaporates, it absorbs 27* $tu8s at a constant temperatu temperature re of (+()F (+()F and to condense one pound of steam to water water 27* $tu8s must be extracted from it. The absorption of heat by changing a li/uid to vapour, and the discharge of that heat by condensing the vapour is the 6eystone to the whole mechanical refrigeration proc proces ess, s, and and the the move moveme ment nt of the the late latent nt heat heat invo involv lved ed is the the basi basic c mean means s of refrigeration.
SATURATION TEMPERATURE : 9aturated temperature0 Temperature of a li/uid, vapor, or a solid, where if any heat is added or removed, a change of state ta6es place.
PRESSURE TEMPERATURE RELATIONSHIP FOR LIQUID REFRIGERANTS : For any given pressure, refrigerants refrigerants have a saturation temperature. If the pressure is low, the saturation temperature temperature is low. low. If pressure pressure is high, saturation temperature is high. The temperature temperature at which li/uid refrigerant refrigerant boils is dependent on the pressure pressure exerted on it. The vapour pressure of the li/uid, which is the pressure being exerted by the tiny molecules see6ing to escape the li/uid and become vapour, increase with an increase in temperature until at the point where the vapour pressure e/uals the external external pressure, pressure, boiling occurs.
REFRIGERANTION CYCLE COMPONENTS : VAPOUR COMPRESSION CYCLE : The main components of a vapour compression type refrigeration cycle are0 a. !:;E=9E< c. E?;5=9I= @5A@E d. E@5;<5T< !:;
Reciprocatin compressor has one or more piston and cylinder combinations. In this type of compressor, the pistons are designed in similar fashion to those used in a car engine0 they slide inside a cylinder, drawing in and compressing the gas refrigerant. Each cylinder features a suction valve for the gas refrigerant and a delivery valve through which the gas refrigerant is sent to the condenser after having been compressed. Rotar! compressor uses a rotary impeller driving refrigerant through a curved chamber to compress the refrigerant. Scro"" compressor features two involute scrolls0 one stationary, and one orbiting around the rst. >ue to which the gas contained between the two elements reaches a very high pressure and discharged through a hole in the centre.
Scre# compressor consists of two helically grooved rotors, housing with suction and discharge ports and compresses the refrigerant between the rotating groves. Centri$%a" compressor raises the pressure of the refrigerant by a centrifugal force within a circular casing. CONDENSER: !ondensers remove the cooling load, and the heat of compression and condense the high pressure refrigerant gas into high pressure li/uid refrigerant. !ondensers may be water cooled or air cooled. &ater cooled condensers use cooling towers. @arious types of watercooled condensers are shell and tube, shell and coil, evaporative etc. 5ircooled condensers employ cooling coils and fans.
E&PANSION VALVE : 5n expansion valve is used to regulate the Bow of li/uid refrigerant into an evaporator depending on the load. It reduces the pressure of the li/uid refrigerant thus dividing the high and low side of the system
EVAPORATOR: Evaporator is a heat exchanger and transfers the heat from the substance to be cooled to the li/uid refrigerant and converts it to vapour.
ELECTRIC MOTORS 5n electrical motor is such an electromechanical device which converts electrical energy into a mechanical energy. 5lmost all the motors used in H@5! application is
Induction :otor. The name coming from the fact that the current in the moving part is induced, the moving component having no connection to the source of current. 5n 5! motor has two basic electrical parts0 a stator and a rotor as shown in Figure . The stator is in the stationary electrical component. It consists of a group of individual electromagnets arranged in such a way that they form a hollow cylinder, with one pole of each magnet facing toward the center of the group. The term, stator is derived from the word stationary. The stator then is the stationary part of the motor. The rotor is the rotating electrical component. It also consists of a group of electromagnets arranged around a cylinder, with the poles facing toward the stator poles. The rotor, obviously, is located inside the stator and is mounted on the motorGs shaft. The term rotor is derived from the word rotating. The rotor then is the rotating part of the motor. The obCective of these motor components is to ma6e the rotor rotate which in turn will rotate the motor shaft. This rotation will occur because of magnetic phenomenon that unli6e magnetic poles attract each other and li6e poles repel. If we progressively change the polarity of the stator poles in such a way that their combined magnetic eld rotates, then the rotor will follow and rotate with the magnetic eld of the stator.
SINGLE PHASE MOTOR: 5 single phase motor has only one running winding or phase. They cannot form a rotating eld hence they are not self starting. In order to provide starting tor/ue a second winding called a starting winding is provided. These two windings wor6 together to start the motor. 5 relay is used to remove the starting winding once the motor reaches the rated seed. 9ingle phase motors are limited to maximum ' H;.
THREE PHASE MOTORS : This type of motor does not re/uire any starting device hence they are self starting induction motor. Three phase motors are wound with ' separate windings or phase. Each of the winding is +(* >eg out of phase with other windings. This results in a rotating magnetic eld and the motor does not re/uire separate starting mechanism.
Basic electrical components of an AC motor.
The rotating magnetic eld of an AC motor.
AIR HANDLING UNIT - AHU 5n 5irHandling nit "5H#, is a device used to condition and circulate air as part of a H@5! system. The primary function of an 5H is to transmit processed air from the air conditioning plant to the conditioned space and distribute it properly within the conditioned space. 5n 5H is usually a large modular metal box containing various sections li6e 0 •
Filter 9ection with prelters
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!ooling !oil 9ection with copper tubes and aluminium ns.
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$lower section with !entrifugal fans and :otor.
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5ccessories include drain pan, dampers , @F>, 9tarters, @ibration isolators etc
The air is rst passed through lters to remove dust particles and then over to the cooling coils wherein the air is cooled and dehumidied. The blowers then convey the pressuri%ed air to the ducts which in turn distributes to the area to be airconditioned through grilles and di-users..
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COOLING TOWER In a water cooled system the heat to be reCected is pic6ed by water. =ow to cool the water a cooling tower is used. 5 cooling tower is an e/uipment used to reduce the temperature of a water stream by extracting heat from water and emitting it to the atmosphere. !ooling towers are used to reCect heat through the natural process of evaporation. &arm recirculating water is sent to the cooling tower where it is sprayed through no%%les into the air. 5 portion of the water is evaporated into the air passing through the tower. 5s the water evaporates, the air absorbs heat, which lowers the temperature of the remaining water. This process provides signicant cooling to the remaining water stream that collects in the tower basin where it can be pumped bac6 into the system to extract more process or building heat, thereby allowing much of the water to be used repeatedly to meet the cooling demand. The two types are 0
Natural draft tower : =atural draft towers are constructed of wooden louver held on wooden uprights. =owadays plastic louvers are also available. The space enclosed by the louvers has a water spray system on the top. &arm water from the condenser is sprayed by no%%les 1 This nely atomi%ed water Bows by gravity into a small collecting basin. 9ince its performance depends on existing air currents, ordinarily, a roof top is an excellent location. Aouvers must be placed on all sides of a natural draft tower to reduce drift. The drift loss " loss of water due to wind movement # and space re/uirements of a natural draft tower are much greater than for other cooling tower designs.
Meca!"cal draft tower : These towers use a motor and fan to pull " induced draft # or push " forced draft # a constant volume of air through the tower. The water is sprayed through no%%les into the draft thereby evaporating rapidly and cooling the rest of the water. The heat transfer area is enhanced due to ;@! lls. &ater is collected at the base and again sent to the condenser for cooling.
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UNIT II : AIR CONDITIONING : SYSTEMS AND APPLICATIONS
AIR CONDITIONING SYSTEM FOR SMALL 'UILDINGS : (INDO( AIR)CONDITIONERS: &indow air conditioners employ hermetic compressors and are available in capacities ranging from J to ( T<. They are factory assembled and can be directly installed in the room to be cooled and are ready for operation.
In window 5irconditioners, the compressor, condenser, evaporator and expansion valve are all enclosed in a single cabinet. The unit is to be installed in a wooden frame either in a window or in a hole in the wall. The whole assembly of the window air conditioner can be divided into two compartments 0 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. &indow air conditioners are mainly used for residences, small oKces and shops. 5dvantages are easy to install and cheaper. >isadvantages are no fresh air and not suited for large areas. The units are also noisy.
SPLIT AIR)CONDITIONERS: The 9plit airconditioner is split into two basic components, the Indoor unit and the utdoor unit. These two units are connected by refrigeration tubing. The indoor unit " evaporator unit # is 6ept inside the conditioned area whereas the outdoor unit " condensing unit # is 6ept outside. Thus noise level inside the conditioned area is reduced. The indoor unit comprises the evaporator or cooling coil, expansion valve and cooling fan. f late the expansion valve is shifted to the outdoor unit to avoid hissing noise. For this unit you don8t have to ma6e any slot in the wall of the room. Further, present day split units have aesthetic appeal and do not ta6e up as much space as a window unit. The outdoor unit, tted outside the room, houses components li6e the compressor, condenser and of late even the expansion valve. There are many versions of the indoor units li6e High &all, Floor mounted, !eiling mounted, @ertical, !oncealed, !assette etc. The outdoor unit has the Bexibility to be installed either on the roof or on a ledge or on the Boor.
EVAPORATIVE COOLERS : In lowhumidity areas, evaporating water into the air provides a natural and energy eKcient means of cooling. Evaporative coolers rely on this principle, cooling outdoor air by passing it over watersaturated cellulose pads, causing the water to evaporate
into it. The cooler and humidied air is then directed into the area to be used and pushes warmer air out through windows. &hen operating an evaporative cooler, windows are opened part way to allow warm indoor air to escape as it is replaced by cooled air. 5ir conditioning systems re circulate the same air, however evaporative coolers provide a steady stream of fresh air into the area to be used. Evaporative cooling is a common form of cooling buildings for thermal comfort since it is relatively cheap and re/uires less energy than other forms of cooling. However, evaporative cooling is only e-ective when the relative humidity is on the low side, limiting its popularity to dry climates. Evaporative cooling raises the internal humidity level signicantly, which dry climate inhabitants may appreciate as the moist air re hydrates dry s6in and sinuses. Evaporative coolers should not be used in humid climates because they add humidity to the air in your home.
PAC*AGED AIR CONDITIONER + DUCTA'LE SPLIT AIR CONDITIONERS , SEMI) CENTRAL -: a. Air coo"e/ 0!0te1: The heat pic6ed up from the conditioned space and the heat of compression has to be ultimately reCected to the atmosphere. This heat can only be reCected to the ambient air or water. Thus systems using aircooled condensers are classied as aircooled. 2. (ater coo"e/ 0!0te1: 9ystems using watercooled condensers wor6ing in conCunction with cooling towers for recirculation of the water are called watercooled systems.
;ac6aged 5irconditioners are shaped li6e cupboards and need to be located in a separate plant room adCoining the area to be airconditioned. They are connected to the conditioned area by ducting. They employ either aircooled or water cooled condensers. They use scroll compressor and operate on D+4@ 5! ' phase 4* cycles power supply. They are generally available from 4.4 T< to (( T< capacity. The indoor cabinet unit comprises of !ompressor, Evaporator, expansion valve and relatively a powerful blower. The outdoor unit comprises of air cooled condenser which reCects the heat. $oth the units are connected by copper pipes to facilitate refrigerant Bow.
&ater cooled option is also available. The water cooled condenser is located in the indoor unit. The heat is reCected to water and thro pumps the water goes to the cooling tower, reCects heat and goes bac6 to the condenser for pic6ing up more heat. ;ac6aged units are mainly used for oKces and show rooms. 5dvantages are these units are rugged, multiple units can be used for large areas, easy and fast installation, can handle long duct runs and higher air /uantity re/uirements, the services are restricted to the unit room. >isadvantages are multiple units for larger applications, Boor space is re/uired for locating the units. 5 variation of the above is the >uctable split units are mainly used for oKces and show rooms. In this version the indoor unit is ceiling suspended and comprises the evaporator and expansion valve. The outdoor unit comprises of the compressor and aircooled condenser. 5dvantages are this unit does not occupy Boor space and can handle di-erent areas. >isadvantages are too many units are used for large spaces, restriction on the length of refrigerant piping, too many outdoor units, limitations on static pressure available, limitations on the air /uantity available, diKculty in servicing3cleaning the coils, high noise level in the wor6 areas.
CENTRAL AIRCONDITIONING SYSTEM: D& CENTRAL PLANT : The system uses multiple scroll compressors and the capacity varies from 4 T< to * T<. In this system the refrigerant gas directly cools the air hence >? " >irect Expansion #. The 5H is customi%ed hence it can be used for heavy duty and non standard applications. They use aircooled or water cooled condensers. 5 >? plant is most eKcient from the thermodynamic point of view since the heat transfer is directly between the refrigerant and air.
CHILLER PLANT :
&henever it is not possible to install a single >? plant, because of restriction on the length of the refrigerant piping, in such cases chilled water system is used. 5lso when large number of smaller %ones are re/uired to be airconditioned then the practical arrangement will be a chiller system. In a chilled water system the chiller plant chills water. Then the water is pumped to the cooling coil in the 5ir Handling nit 1 5H. The chilled water then cools the air. This is an indirect system of cooling. &ater can be easily pumped for long distances without any loss. In case of multistoried buildings or multiple buildings a chilled water system with a single air conditioning plant, it is possible to aircondition the entire building with multiple air handling units and fan coil units. This also gives Bexibility of usage. !apacities available are from +* to +4** T< in single machine, multiple units can be used for larger installations. 5nd available in air cooled and water cooled versions with 9croll, 9crew and !entrifugal type !ompressors. 5dvantages are these types of machines can handle easily system diversities thus reducing the total installed capacities li6e in hotels, oKces and multi storied buildings. They have a better response to part loads o-ering better control, very rugged systems, better humidity control as compared to pac6aged and split units. >isadvantages are slightly longer lead times, extensive site wor6,costlier than >? systems, pac6aged 3 split units especially for small Cobs. 5lso needs trained manpower to operate.
D%cta2"e Sp"it Unit0 :
PAC*AGED AIRCONDITIONERS
D& CENTRAL PANT :
!HIAAE< ;A5=T
ALL AIR S#STEMS In this system conditioned air is produced in one location of a %one in a Boor and then distributed through ductwor6 running above false ceiling. There is only a centrali%ed control of cooling and each spot cannot have its own inside design conditions. Ideal for large oKce areas, IT par6s, 5irports, !inema Theatre, 9tadium etc. In case there are smaller rooms within large areas then they can be controlled with VARIA'LE AIR VOLUME SYSTEMS , VAV - as detailed below .
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The collar which connect the duct and terminals should be properly lin6ed. In many cases it is found that there is gap and this leads to improper cooling. 5 coordinated layout should be prepared by super imposing various services li6e false ceiling, H@5! ducts and pipes, air terminal units, lighting, re sprin6ler pipes and electrical cables. 5ny clash can be avoided in the planning stage itself . The walls of the 5H room adCoining the area to be airconditioned should be acoustically treated. Fire dampers to close the supply ducts and return air entry to 5H room should be provided for Fire 9afety. Finally Testing 1 5dCusting 1 $alancing should be carried out.
)ARIA*LE AIR )OLUME S#STEMS + )A) ,
5 variableairvolume "@5@# airconditioning system varies the volume of constant temperature air that is supplied to meet the changing load conditions of the space. The @5@ system controls air from a single supply duct and varies the airBow to each %one or room based upon the temperature in the room. 5 @5@ system consists of four basic parts0 a thermostat, a precision actuator controlled damper, an airBow sensor, and a controller. &henever the load comes down in a particular room the thermostat senses it and send signal to the controller and in turn the damper tends to close and air supply is reduced. >ue to the closure of the damper pressure builds up in the ducting system. 5 pressure sensor sends this signal to @ariable Fre/uency >rive
" @F> # and in turn the @F> reduces the speed of the fan. For example by reducing (* M of the speed we can expect 4* M reduction in the energy cost of the fan.
ALL WATER S#STEMS : In this system the !hilled water will be pumped to various small areas to be individually airconditioned. The chilled water will be sent to the Fan !oil nits for each room. The conditioned air thus produced will be directly fed to the room without any air distribution system. Ideal for multi%one applications with small rooms li6e Hotels, Hospitals etc. In case of part load operation the chiller will get the message by sensing the return water temperature . If the return water temperature is lower than the set point then the plant senses that production can be reduced. The capacity control mechanism ensures that the compressor will run only in part load and save energy. !onse/uently all the downstream components need to run only in part load. This should be ta6en care of in the rst design itself. :any a times this is overloo6ed due to budget constraints but a basic rives " @F># for ;umps.
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;iping system should be properly installed and insulated. If not condensation will be a perennial problem. >rain pipes are very critical and should not run for long lengths as natural gravity slope is re/uired. 9uKcient space for carrying out piping wor6 should be provided li6e space above false ceiling and shafts crossing the Boors. Isolation @alve for each 5H and F! to be provided. :ost important Isolation valve for each Boor has to be provided. >uring the design stage itself pipe openings can be given in the beams itself. Thus saving valuable space which will be occupied by chilled water pipes below the beam.
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5lways design the pipes with low pressure drop. This will ensure that pumping cost is reduced . 5lso any future expansion can be easily carried out without maCor alterations.
ALL WATER S#STEMS : $AN COIL UNITS $OR GUEST ROOMS
ALL WATER S#STEMS : AIR HANDLING UNITS $OR LARGER ROOMS
CONFIGURING + SI3ING OF MECHANICAL EQUIPMENT :
TYPE OF EQUIPMENT
COMMONLY AVAILA'LE RATINGS
&indow and 9plit 5!
:in 0 + T< 1 :ax 0 ( T<
;ac6aged 5irconditioners
:in 0 4.4 T< 1 :ax 0 (( T<
>uctable 5irconditioners
:in 0 4.4 T< 1 :ax 0 (( T<
>?9ystem
:in 0 +( T< 1 :ax 0 2* T<
5ir !ooled 9croll !hiller
:in 0 +* T< 1 :ax 0 * T<
&ater !hiller
!ooled
9croll :in 0 ++ T< 1 :ax 0 4 T<
5ir !ooled 9crew !hiller &ater !hiller
!ooled
:in 0 +** T< and :ax 0 D** T<
9crew :in 0 +(* T< and :ax 0 D4* T<
.EQUIPMENT SPACING : &hile planning for the space re/uirements of 5! E/uipment rooms the following guidelines may be used.
TYPE OF EQUIPMENT
SPACE REQUIREMENT
;ac6aged unit room
'm x (m 1 9ingle unit 'm x D m 1 Two units ' m x 4 m 1 Three units
5H
Dm x 'm 1 upto '* T< Dm x 4 m 1 upto L* T<
&ater !ooled chiller plants
Lm x Lm for each plant and pumps. 'm x 'm open space for cooling tower.
5ir cooled chiller plants
+* m x m open space for one plant and pumps.
Note t4e $o""o#in : Height of pac6aged unit room or the 5H room should be the same as that of the area to be airconditioned.
>utable split units re/uire minimum L** mm clear space above false to locate the indoor units and to run the ducts. E/uipment placing should be done with an eye on maintenance. ;ac6aged unit should have + m space in front of the unit for unit servicing . If it is water cooled ( m at the side also re/uired for condenser tube cleaning. 9hafts should be si%ed properly for installing the pipes based on site conditions.
UNIT III : AIR CONDITIONING : DESIGN ISSUES AND HORIZONTAL DISTRIBUTION OF PIPES
De0in Criteria $or 0e"ectin t4e air con/itionin 0!0te1 $or "are 2%i"/in0 : D& CENTRAL PLANT : (4en to %0e : +. If re/uirement exceeds D** s/.m. (. For heavy duty oKces, showrooms, industries etc. '. 9ingle %one areas.
(4en not to %0e : +. :ulti%one areas. (. &hen copper pipe length is more than 4* feet
CHILLER PLANT : (4en to %0e : +. If re/uirement does exceeds (*** s/.m. (. If used for heavy duty commercial and industrial applications li6e IT ;ar6s, 9tar Hotels, Hospitals, :aCor oKces, :aCor showrooms, Industries, nonstandard application etc. '. :ulti%one one areas. D. If plant has to be located far way from usage
(4en not to %0e : If re/uirement is highly variable and may go down to less than D* M.
ENERGY CONSERVATION MEASURES : +. 9elect proper system ta6ing the usage into account. (. Ensure design is based on low pressure drop in piping and ducting system. '. !onsider latest insulation materials li6e elastomeric in place of berglass 3 expanded polystyrene. D. o for variable fre/uency drives for all motors. 4. o for preinsulated pipes in place of site insulation. L. o for factory fabricated ducts in place of site fabrication. 7. o for double s6in 5H in place of single s6in 5H. . o for direct drive plug fans in place of belt driven centrifugal fans. 2. o for @5@ 1 @ariable 5ir @olume systems to control air in smaller rooms which are part of a bigger oKce. +*. o for Energy
o for building management systems 1 $:9.
HORI3ONTAL DISTRI'UTION OF SERVICES FOR LARGE 'UILDINGS The hori%ontal distribution system for mechanical and electrical services in a large building should be planned simultaneously with the structural frame and the interior nish systems, because the three are strongly interrelated. The Boor1toBoor height of a building is determined in part by the vertical dimension needed at each story for hori%ontal runs of ductwor6 and piping. The selection of nish ceiling, partition, and Boor systems is often based in part on their ability to contain the necessary electrical and mechanical services and to adCust to future changes in these services. 5ll these strategies involve close cooperation among the architect and the structural and mechanical engineers.
CONNECTING HORI3ONTAL AND VERTICAL DISTRI'UTION LINES Hori%ontal mechanical and electrical lines must be fed by vertical lines through smooth, functional connections. ;lumbing waste lines, which must be slopped to drain by gravity, have top priority in the planning of hori%ontal service linesO if they are conned to vertical plumbing walls, they will not interfere with other services. 9prin6ler heads, which have the second highest priority in the layout of hori%ontal
services, are served from the re standpipe by hori%ontal piping that seldom exceeds D in. "+**mm# in outside diameter. The spacing of the heads is coordinated with the placement of walls and partitionsO the maximum coverage per head is about (** s/.ft"+.Lm(# in lightha%ard buildings. !overage in industrial and storage buildings ranges from +'* to 2* s/.ft"+(.+ to .D m (# per head, depending on the substances handled in the buildingO 5ir conditioning ducts is the next priority. In the 5H room the return air will mix with outside fresh air and then will be ta6en inside the 5H. The 5H will lter the air, cool and dehumidify it and then feed it to the ductwor6 for further distribution. The supply air ducts will be ta6en above the false ceiling and fed to the area to be air conditioned through grilles3di-user. i-users are generally re/uired at the rate of one for every +4* s/.ft.
GROUP HORI3ONTAL DISTRI'UTION IN CENTRAL CORRIDORS 9ometimes the maCor runs of ductwor6, piping and wiring can be grouped in the ceiling area above the central corridor of each Boor of a building, leaving the ceilings of the surrounding rooms essentially PcleanQ. This wor6s especially well in hotels, dormitories, and apartment buildings that rely on above ceiling allwater system. 5 low corridor ceiling is readily accepted in exchange for high, unobstructed space in the occupied rooms, where the structure may be left exposed as the nish ceiling, saving cost and BoortoBoor height.
FLOOR(ISE HORI3ONTAL DISTRI'UTION In broad expanses of Boor space, particularly where all electrical and communications services must be available at any point in the area, an entire hori%ontal layer of space is reserved on each story for mechanical and electrical e/uipment.
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DISTRI'UTION A'OVE A SUSPENDED CEILING 5bove a suspended ceiling, all services can be ta6en li6e 0 • • •
Fire 9prin6ers Electrical wiring !ommunication >ata
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;lumbing H@5! piping H@5! ducts " supply air, return air, fresh air and exhaust air #
DISTRI'UTION A'OVE THE STRUCTURAL FLOOR 5 raised access Boor system allows maximum Bexibility in running services because it can accommodate piping, ductwor6, and wiring with e/ual case. It is especially useful in industrial or oKce areas where large numbers of computers or computer terminals are used and where fre/uent wiring changes are li6ely. It is also
valuable in retrotting old buildings for modern services. Though Boors can be raised to any desired height above the structural dec6, heights of '**D4*mm . ndercarpet Bat wiring may be used instead of a raised access Boor in buildings with moderate needs for future wiring changes. Flat wiring does not increase the overall height of the building, as raised access Boors usually do, but it does not o-er the unlimited capacity and complete freedom of wire location of the raised Boors. Flat wiring is used in both new buildings and retrot wor6.
In case of any further assistance required please do not hesitate to get in touch with the undersigned : D.BALAI
!"AC Consultant shreesr#$yahoo.com %&'''())))
