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Air Conditioning System

Air conditioning for people is the control of temperature, humidity, air movement and air

cleanliness, heat radiation sometimes [e.g. by chilled ceiling ], normally with mechanical means,

to achieve human thermal comfort

Air Conditioning System Design involve 1. Selecting a proper system

2. Sizing the system

These are done in the following steps

1. Calculate cooling load

a) Sensible heat load due to

1. heat gain through walls, etc

2. solar radiation

3. heat emission of occupants

4. infiltration of outside air

5. heat emission of lights and machinery

b) Latent heat load due to

1. moisture given off by occupants

2. infiltration of outside air

3. moisture from process machinery

2. Select air treatment process

3. Determinate air quantities

4. Layout and sizing of ducts

5. Determinate capacity of air treating units

6. Determinate refrigerator and boiler duties

7. Determinate pump and fan duties

Air conditioning systems can be categorized according to the means by which the controllable

cooling is accomplished in the conditioned space. They are further segregated to accomplish

specific purposes by special equipment arrangement.

In selecting a suitable air conditioning system for a particular application, consideration should

also given to the following:-

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- System constraints : Cooling load, Zoning requirements, Heating and ventilation

- Architectural Constraints : Size and appearance of terminal devices, acceptable noise

level, Space available to house equipment and its location relative to the conditioned

space, acceptability of components obtruding into the conditioned space

- Financial Constraints : Capital cost, Operating cost, Maintenance cost

There are four basic system categories:

1 Central chilled water air conditioning systems - All Air Systems 1.1 Single zone

1.2 Reheat

1.3 Variable Air Volume

1.4 Dual Duct

1.5 Multizone

2 Central chilled water air conditioning systems - Air-and Water Systems 2.1 Induction

2.2 Fan Coil

2.3 Two-pipe

2.4 Three-pipe

3 Central chilled water air conditioning systems - All Water Systems, including cooling

towers which can also be applied to systems 1, 2 above

3.1 Fan-coil units

3.2 Central chilled water air conditioning system with fan coils and other devices

3.3 Water cooling tower

4 Direct expansion Systems [i.e. direct expansion of refrigerant, without the chilled water

cooling medium ]

4.1 Window air conditioners

4.2 Unitary and Rooftop Air Conditioners

4.3 Split type and package air conditioning systems

4.4 Heat pumps

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1. Central chilled water air conditioning systems - All Air Systems

An all-air system provides complete sensible and latent cooling capacity in the cold air

supplied by the system. Heating can be accomplished by the same air stream, either in

the central system or at a particular zone. All-air systems can be classified into 2

categories:-

-Single duct systems

-Dual duct systems

System Advantages

1. The central plant is located in unoccupied areas, hence facilitating operating and

maintenance, noise control and choice of suitable equipment.

2. No piping, electrical wiring and filters are located inside the conditioned space.

3. Allows the use of the greatest numbers of potential cooling seasons house with

outside air in place of mechanical refrigeration.

4. Seasonal changeover is simple and readily adaptable to climatic control.

5. Gives a wide choice of zonability, flexibility, and humidity control under all

operating conditions.

6. Heat recovery system may be readily incorporated.

7. Allows good design flexibility for optimum air distribution, draft control, and

local requirements.

8. Well suited to applications requiring unusual exhaust makeup.

9. Infringes least on perimeter floor space.

10. Adapts to winter humidification.

System Disadvantages

1. Requires additional duct clearance which can reduce the usable floor space.

2. Air-balancing is difficult and requires great care.

3. Accessibility to terminals demands close cooperation between architectural,

mechanical and structural engineers.

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Distribution systems have a number of important components:

1. The Air Handling Unit is a cabinet that includes or houses the central furnace, air

conditioner, or heat pump and the plenum and blower assembly that forces air through

the ductwork.

2. The Supply Ductwork carries air from the air handler to the rooms in a house. Typically

each room has at least one supply duct and larger rooms may have several.

3. The Return Ductwork carries air from the conditioned space back to the air handler.

Most houses have only one or two main return ducts located in a central area.

4. Supply and Return Plenums are boxes made of duct board, metal, drywall or wood that

distribute air to individual ducts or registers.

5. The Ductwork is a branching network of round or rectangular tubes generally

constructed of sheet metal, fiberglass board, or a flexible plastic and wire composite

material located within the walls, floors, and ceilings. The three most common types of

duct material used in home construction are metal, fiberglass duct board, and flex-duct.

6. Flex-duct is installed between the register and plenum box, or plenum box and air

handler, usually in a single, continuous piece. While flex-duct has fewer seams, the inner

lining and outer insulated covering can tear or be pinched closed. Also longer flex-duct

runs can restrict the flow of air; proper design and installation is very important.

7. Both metal and fiberglass duct board are rigid and installed in pieces. Fiberglass duct

board, like flex-duct, is made of an insulation material. Ducts are built of sections of the

duct board. The seams in the duct board should be carefully sealed with mastic or high

quality duct tape.

8. Rectangular metal duct, especially the kind used for plenums and larger trunk runs, is

often insulated on the inside with fiberglass duct liner. If it is not insulated on the inside,

metal ducts should be insulated on the outside using a fiberglass batt with an attached

metal foil vapor retarder. The insulation should be at least two inches thick, and the vapor

barrier installed on the outside of the insulation facing away from the duct.

The seams in the insulation are usually stapled together around the duct and then taped.

All of the seams should be sealed before insulation is installed. All return and supply

ducts located outside the conditioned space, in attics, crawlspaces, or basements, for

example, should be sealed and insulated.

9. Ductwork Joints join pieces of ductwork.

10. Elbows are manufactured pieces of duct used for turns.

11. Boots connect ductwork to registers.

12. Registers and Grilles are the coverings for duct openings into the conditioned

space.

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Fig 1b. shows the control of chilled cooling coil and fan

These are components will bring about:-

-Heat balance: The amount of heat extracted out of the air conditioned room (by the cooling

system, exhaust air systems, building leakage, must be equal to the amount of heat generated

inside the room (by human being, electrical appliances, etc.) and transferred into the room (by

conduction through the building envelope, radiation via the glass, hot air leakage into the

room through gaps in windows, doors, fresh air introduced into the room, etc.) i.e. Total kW

going into room = Total kW going out of the room.

-Air balance: The mass flow rate of the air going into the room = The mass flow rate of air

going out of the room. Fresh air coming into the room : 2.5 l/s per person, non-smoking, 5 l/s

per person for smoking accommodation, good indoor air quality (IAQ) is important.

1.1 Single Zone System

The all-air single-zone air conditioning system is the basic central system which can

supply a constant air volume or a variable air volume at low, medium or high pressure.

Normally, the equipment is located outside the conditioned space but can also be installed

within the conditioned are if conditions permit. Typical applications include:-

-Space with uniform loads

-Small spaces requiring precision control

-Multiple systems for large areas

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Fig 1.1

1.2 Reheat System

The reheat system is a modification of the single-zone system. It provides:-

-Zone or space control for areas of unequal loading.

-Heating or cooling of perimeter areas with different exposures.

-Close control for process or comfort applications. In the reheat system, heat is added as

a secondary process to either preconditioned primary air or recirculated room air. The

heating medium can be hot water, steam or electricity.

Advantages : Closely controls space conditions

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Disadvantages : Expensive to operate

Fig 1.2

1.3 Variable Air Volume System

The variable air volume system compensates for varying cooling loads by regulating the

volume of cooling air supplied through a single duct.

(a) Simple Variable Air Volume (VAV)

Simple VAV systems typically cools only and have no requirement for

simultaneous heating and cooling in various zones.

Fig 1.3a

(b) Variable Air Volume – Reheat

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It integrates heating at or near the terminal units. It is applied to systems

requiring full heating and cooling flexibility in interior and exterior zones.

Heating is turned on when the air flow reaches a predetermined minimum.

Fig 1.3b

Advantages

a) When combined with a perimeter heating system, it offers inexpensive

temperature control for multiple zoning and a high degree of simultaneous

heating-cooling flexibility.

b) Capital cost is lower since diversities of loads from lights, occupancy, solar and

equipment of as much as 30% are permitted.

c) Virtually self-balancing.

d) It is easy and inexpensive to subdivide into new zones and to handle increased

loads with new tenancy or usage if load does not exceed the original design

simultaneous peak.

e) No zoning is required in central equipment.

f) Lower operating cost because

(i) Fans run long hours at reduced volume

(ii) Refrigeration, heating and pumping matches diversity of loads

(iii) Unoccupied areas may be fully cut-off

g) Reduced noise level when the system is running at off-peak loads.

h) Allows simultaneous heating and cooling without seasonal changeover.

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1.4 Dual Duct System

The dual-duct system employs two air ducts to supply cold air and warm air to a mixing

terminal unit which proportions the cold and warm air in response to a thermostat located

in the conditioned space. The system is well suited to provide temperature control for

individual spaces or zones.

Fig 1.4

Advantages (in addition to those common to all air systems)

1. Systems with terminal volume regulation are self-balancing.

2. Zoning of central equipment is not required.

3. Instant temperature response is achieved because of simultaneous availability of

cold and warm air at each terminal unit.

4. No seasonal changeover is necessary.

Disadvantages

1. Initial cost is usually higher than other VAV systems.

2. Does not operate as economically as other VAV systems.

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1.5 Multi-zone System

The multi-zone system applies to a relatively small number of zones served by a single,

central air-handling unit. Different zone requirements are met by mixing cold and warm

air through zone dampers at the central air handler in response to zone thermostats.

Fig. 1.5

Advantages (in addition to those common to all-air systems)

1. Easy to balance.

2. Air transmission and distribution is simplified.

2. Central chilled water A/C systems - Air-and-Water Systems

An air-and-water system is one in which both air and water (cooled or heated in central

plant room) are distributed to room terminals to perform cooling or heating function. The

air side is comprised of central air conditioning equipment, a duct distribution system,

and a room terminal. The supply air, called primary air, usually has a constant volume

which is determined by:

1. The ventilation requirement.

2. The required sensible cooling capacity at maximum cooling load.

3. The maximum sensible cooling capacity following changeover to the winter

cycle when chilled water is no longer circulated to the room terminal.

The water side consists of a pump and piping to convey water to heat transfer surfaces

within each conditioned space. The water is commonly cooled by the introduction of

chilled water from the primary cooling system and is refereed to as the secondary water

loop. Individual room temperature control is by regulation of either the water flow

through it or the air flow over it.

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2.1 Induction System

The inducting system is designed for use in perimeter rooms of multi-storey, multi-room

building that may have reversing sensible heat characteristics. It is especially adapted to

handle the loads of skyscrapers with minimum space requirements for mechanical

equipment.

In the induction system, ducted primary air is fed into a small plenum chamber where its

pressure is reduced by means of a suitable damper to the level required at the nozzles.

The plenum is acoustically treated to attenuate part of the noise generated in the duct

system and in the unit. The primary air is then delivered through nozzles as high velocity

jets which induce secondary air from the room and over the secondary coil.

Induction units are usually installed at a perimeter wall under a window. Some hotel

rooms are provide with induction coils.

Fig. 2.1

The induction system employs air ducts to convey treated air with higher pressure levels

and of the right adjustable quantities to various cooling/heating coil units. These coil

units are built in with induction nozzles such that when high pressure air goes through

them, air room the room is inducted across the fin surface of the water-circulated coils.

This inducted air stream is either cooled or heated after passing through the coil, and then

mixed with the air coming out of the nozzle. The right quantity of high pressure air is

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adjusted automatically in response to a thermostat located in the conditioned space. The

system is well suited to provide temperature control for individual spaces or zones.

Advantages

1. Individual room temperature control.

2. Separate sources of heating and cooling for each space available as needed to

satisfy a wide range of load variations.

3. Low distribution system space required as a result of reducing the air supply by

use of secondary water for cooling and high velocity air design.

4. Reduced size of central air handling equipment.

5. Dehumidification & filtration performed in a central plant room remote from

conditioned space.

6. Outdoor air supply is positive.

7. Minimal maintenance required for individual induction units which have no

moving parts, i.e. no fans

8. Air duct dimensions are smaller than VAV systems or CAV systems

9. Zoning of central equipment is not required.

10. No fan comes together with the coil, making the conditioned space quiet.

Disadvantages

1. Limited to perimeter space.

2. The primary air supply is usually constant with no provision for shutoff.

3. Not applicable to spaces with high exhaust requirement.

4. Higher energy consumption due to increased power required by the primary

pressure drop in the terminal units.

5. Controls tend to be more complex than for all-air systems.

6. A low chilled water temperature is needed to control space humidity adequately.

7. Seasonal changeover is necessary.

8. Initial cost is usually higher than fan coil systems.

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2.2 Fan-Coil System

The fan-coil system is similar to the inducting system, with the induction unit replaced by

the fan-coil unit. The basic elements of the fan-coil units are a finned-tube coil and a fan

section. The fan section recirculates air continuously from within the perimeter space

through the coil which is supplied with either hot or chilled water. Auxiliary air may be

delivered to the conditioned space for dehumidification and ventilation purposes.

Fig 2.2a

Fig 2.2b

Advantages (in addition to those for induction units)

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1. System can be operated with the primary air turned off.

2. The air velocity is fairly constant regardless of the primary air quantity.

3. Primary air can either connect directly to fan-coil unit or supply the room

separately.

2.3` Two-pipe Systems

In two-pipe systems for induction coil, fan-coil or radiant panel systems, the water

distribution circuit consists of one supply and one return pipe. The secondary water is

cold in summer and intermediate seasons and warm in winter. The primary air quantity is

fixed and the primary air temperature is varied in reverse proportion to outside

temperature to provide the necessary amount of heating during summer and intermediate

seasons. During winter cycle operation, the primary air is preheated and supplied at

about 10°C to provide a source of cooling.

Fig 2.3

Advantages

1. Usually less expensive to install than four pipe systems.

Disadvantages

1. Less capable of handling widely varying loads or providing widely varying

choice of room temperature than four-pipe systems.

2. Cumbersome to change over.

3. More costly to operate than four-pipe systems.

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2.4 ` Three-pipe Systems

Three-pipe systems for induction coil, fan-coil and radiant panel systems have three pipes

to each terminal unit, a cold water pipe, a warm water pipe and a common return. These

systems are rarely used today because they consume excess energy.

Fig 2.4

2.5` Four pipe Systems

Four-pipe systems have a cold water supply, cold water return, warm water supply and

warm water return. The terminal unit usually has two independent secondary water coils,

one served by hot water, the other by cold water. The primary air is cold and remains at

the same temperature year-round.

Fig 2.5a

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Fig 2.5b

Advantages (as compared with two-pipe systems)

1. More flexible and adaptable to widely varying loads.

2. Simpler to operate (No summer-winter changeover and primary air reheat

schedule).

3. Higher efficiency due to lower operating costs.

Disadvantages

1. Higher initial cost.

3. Central chilled water air conditioning systems - All-water Systems

All-water systems are those with fan-coil, unit ventilator, or valance type room terminals

with unconditioned ventilation air supplied by an opening through the wall or by

infiltration. Cooling and dehumidification is provided by circulating chilled water

through a finned coil in the unit. Heating is provided by supplying hot water through the

same or a separate coil.

System Advantages

1. Flexible and readily adaptable to many building module requirements.

2. Provides individual room control.

System Disadvantages

1. No positive ventilation is provided unless wall openings are used.

2. No humidification is provided.

3. Seasonal change over is required.

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4. Maintenance and service work has to be done in the occupied areas.

3.1 Fan-coil units

A fan-coil unit basically consists of a finned tube coil, a filter and a fan section. The fan

recirculates air continuously from the space through the coil, which contains either hot or

chilled water.

Fig 3.1a

Fig 3.1b

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3.2 Central chilled water air conditioning system with fan coils and other devices

In this system, the following circuits do not mix with each other, and heat exchange is

performed via various metal surfaces:-

-the chilled water circuit – nominally 12 deg .C entering water chiller, 7 deg. C leaving

chiller, i.e. nominally 7 deg .C entering fan coil units [FCU] /air handling unit[AHU]

/primary handling unit[PAU]- for treating fresh air, 12 deg. C leaving these devices –

chilled water pumps move water through this circuit – CH. W. F- chilled water flow ;

- CH. W. R- chilled water flow return.

-refrigerant circuit – refrigerant compressors move the refrigerant through this circuit

-cooling water circuit - nominally 35 deg .C entering water cooling tower , 30 deg. C

leaving cooling tower, i.e. nominally 30 deg .C entering condenser of chiller assembly,

35 deg. C leaving condenser of chiller assembly – Condenser water pumps move

condenser water through this circuit

3.2 Water cooling tower

A water cooling tower cools the water entering it from 35 deg. C to 30 deg. C nominally.

The warmer water is sprayed inside the cooling tower admidst the stream of an upward

air flow produced by the fan at the top of the tower. The air stream going out carries

water particles. These water particles should not be taken into buildings, to avoid

Legionnaire disease to occur. Condenser water pumps move condenser water through this

circuit. Water in this circuit has to be treated. There is water loss to atmosphere in using

cooling towers

4. Direct expansion Systems

[i.e. direct expansion of refrigerant, without the chilled water cooling medium ]

4.1 Direct expansion Systems [i.e. direct expansion of refrigerant , without the chilled

water cooling medium ] -Window Air Conditioners

A window unit is an encased assembly designed primarily for mounting in a window,

through a wall, or as a console. These units are designed for comfort cooling and to

provide delivery of conditioned air to a room either without ducts or with very short

ducts. They include a prime source of refrigeration, dehumidification, means for

circulating and cleaning air, and may also include means for ventilating, and/or

exhausting and heating.

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Fig 4.1a

Fig 4.1b

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Fig 4.1c

Fig 4.1d

In a window air conditioner, the indoor unit and outdoor unit of the split system is put

into one single unit. The refrigerant compressor now is part of the machine locating at the

window area. Since this compressor gives out most noise, among other components, the

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window unit will make the room acoustically inferior to other air conditioning systems.

Fresh air exchange for the room can be provided by :-

-(1) setting the “ventilator” switch of the window air conditioner to “open” position

-(2) installing a ventilating extract fan in the room to extract room air to outside –

caution- not to oversize the fan

-(3) naturally leaking of air in and out of the room

4.2 Direct expansion Systems [i.e. direct expansion of refrigerant , without the chilled water

cooling medium ] -Unitary and Rooftop Air Conditioners

Fig 4.2

• These are commonly air-cooled units.

• The units are the floor – standing type designed for installation outdoors or on the

roof.

• A supply air duct and a return air duct are to be connected to the cooling unit.

• Application: For general air conditioning of stores, residences, schools, offices,

etc. particularly suitable for single flat building with extensive floor areas.

• A remote controller should be installed on an easily accessible wall,

incorporating a temperature selection switch & thermostat.

4.3 Direct expansion Systems [i.e. direct expansion of refrigerant , without the chilled water

cooling medium ] - Split type and package air conditioning systems

• package air conditioning systems - Factory assembled (floor mounting) package,

placed indoor, containing direct expansion coil, controls, fan and compressor,

with the condenser remotely placed outdoor ; commonly used in Malaysia for

restaurants, café shops, factories, etc

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•

• • Fig 4.3a

•

• • Fig 4.3b

•

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split air conditioning systems - Factory assembled (ceiling mounting) indoor unit of fan

and direct expansion coil, controls, with the condensing unit [i.e. compressor and

condensing coil ] remotely placed outdoor

4.3.1. The basic concepts of a split air conditioning system [ Small system]

a. A split air conditioning system consists of an indoor unit and an outdoor unit

connected together by refrigerant pipes. The refrigerant circulates between these 2 units

[i.e. 2 parts of the system] to take heat from indoor to outdoor, by firstly having heat of

the room air absorbed into the refrigerant via an air-refrigerant heat exchanger which is

the indoor unit, then conveying the heat to the outdoor unit for disposal.

b. The indoor unit comprises a finned coil and a fan which is driven by an electric

motor. Refrigerant is circulated inside the finned coil to the outside unit and then back to

the indoor unit. The fan pulls or pushes air around the outer surfaces of the coil inside the

indoor unit, taking warm air from the room and injecting cooled air into the room in

summer. The refrigerant has no direct contact with air. So the heat of the room air is

transferred into the refrigerant in the indoor unit. Inside the coil, refrigerant evaporates,

and the indoor unit is therefore commonly called an evaporator by the engineers. The

indoor unit is wall-mount or ceiling mount unit.

c. The outdoor unit The refrigerant then takes the heat from the indoor unit to the outdoor unit, which is

commonly called a condensing unit. [ i.e. a unit for refrigerant to condense] In an air-

cooled outdoor unit, heat exchange occurs in the same way as the indoor unit. However,

the outdoor unit contains a refrigerant compressor, in addition to having a finned coil and

motor-driven fan. The refrigerant does not have direct contact with air. Refrigerant going

through this outdoor coil is losing its energy across the metal surface of the coil to the

atmosphere, as outside air is drawn pass the surface of the finned coil by the fan. By

passing through this finned coil, the outside air is heated up, by normally about 5 deg.

rise in temperature. The outside air passing through the outdoor unit is an open circuit.

That is, air path is not recirculated.

The refrigerant compressor, which usually is installed inside the outdoor unit, is pumping the refrigerant through the indoor unit and the outdoor unit. [ In the split

system therefore the compressor – generating noise when pumping refrigerant- is

located outdoor, inside the outdoor unit] The refrigerant takes up energy as it goes

through the indoor unit, and rejects energy to the outside atmosphere as it goes

through the outdoor unit. Energy rejected is the sum of the energy taken indoor plus the energy consumed by the compressor in pumping the refrigerant through

the refrigerant circuit. This refrigerant circuit is a closed circuit, and if pipe joints

are well installed , no leakage of refrigerant should occur.

d. Air circuits for the indoor environment. The air passing through the indoor unit is

cooled, say to 15 deg. C, before recirculated back to the room. A large part of air heated

up in the room, say to 25 deg. [ Note : Design room temperature is 23 deg C in general

for human comfort ] then goes back to the indoor unit for cooling. A small part of room

air is extracted to outside by an exhaust fan, with an amount of fresh outside air coming

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in to replenish this amount exhausted. Now this make up air can be supplied by

connecting a small air duct from an external opening to the indoor unit. See diagram

attached

e. Single splits and multiple splits -single split – one indoor unit is connected to one outdoor unit by insulated copper

refrigerant pipes

-multiple splits– several indoor units are connected to one outdoor unit by insulated

copper refrigerant pipes

f. Energy saving options

If heat rejection in the outdoor unit is taken care by cooling water , there would be a

saving of 30% of energy. In urban areas,. cooling water can be provided by fresh water

cooling towers. The water cooling tower can be placed at the top of a building, with a

pump drawing water from it to circulate the condensing water to the outdoor units of the

split system. After taking up heat from the outdoor unit, with an increase of unusually 5

deg. C, condensing water is circulated back to the cooling tower for cooling again. Of

course the finned coil f the outdoor unit has to be replaced by a water –cooled condenser.

g. A variant of split air conditioning system - A packaged system If the refrigerant compressor of the outdoor unit of the split air conditioning system is

installed together with the indoor unit, it is called a packaged system. The compressor now is put indoor, making the machine less quite than the split system. However this

will allow a larger cooling capacity for the indoor unit, which then will be floor-mount

usually. A packaged system is needed if the outdoor unit, now called a condenser, is put

on the roof top, with the indoor unit a few floors below.

h. Direct expansion air conditioning equipments consist of factory-matched refrigeration

cycle components for inclusion is air-conditioning systems which are field designed to

meet the needs of the user. The following list of variations is indicative of the vast

number of types of unitary air conditioners presently available.

1. Arrangement: single or split.

2. Heat rejection: air-cooled, evaporative condenser, water-cooled.

3. Unit exterior: decorative for in-space applications, functional for equipment

room and ducts, weatherproofed for outdoors.

4. Placement: floor standing, wall-mounted, ceiling suspended, roof-mounted.

5. Indoor air: vertical upflow, counterflow, horizontal, 90° and 180° degree

turns, with fan, or for use with forced air furnace.

6. Locations: Indoor - Exposed with plenums or furred in ductwork; concealed

in closets, attic, crawl spaces, basements, garages or equipment

room.

Wall - Built-in, window, transom.

Outdoor -Rooftop, wall-mounted or on ground.

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4.4 Heat Pumps

The term ‘heat pump’, as applied to a year-round air conditioning system, commonly

denotes a system in which refrigeration equipment is used in such a manner that heat is

taken from a heat source and given up to the conditioned space when heating service is

wanted, and is removed from the space and discharged to a heat sink when cooling and

dehumidification are desired.

Heat pumps for air conditioning service may be classified according to

a) type of heat source and sink.

b) Heating and cooling distribution fluid.

c) Type of thermodynamic cycle.

d) Type of building structure.

e) Size and configuration.

4.3.1 Air-to-Air Heat Pumps

The air-to-air heat pump is the most common type of heat pumps. It is particularly

suitable for factory-built unitary heat pumps, and has been widely used for residential and

commercial application. Air is used as the heat source and heat sink. Extended surface,

forced convection heat transfer coils are normally employed to transfer the heat between

the air and the refrigerant. When selecting or designing an air-source heat pup, two

factors in particular must be taken into consideration:

1) the variation in temperature experienced in a given locality.

2) the formation of frost.

4.3.2 Water-source Heat Pumps

The water-source heat pump uses water and air as the heat source or heat sink depending

on the mode of operation. When cooling, water is used as the heat sink, and the heat

pump operates as a water-cooled air conditioner. When heating, water is used as the heat

source and the equipment operates as a water chiller.

The water-source heat pump is suitable for many types of multi-room buildings,

including office buildings, hotels, schools, apartment buildings, manufacturing facilities

and hospitals.

Advantages

1. Affords opportunity for energy conservation by recovering heat from interior

zones and/or waste heat and by storing excess heat from daytime cooling for

night time heating.

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2. No wall openings required.

3. Longer expected life than air-cooled heat pumps.

4. Lower noise level because condenser fans are eliminated.

5. Energy for the heat pumps can be metered directly to each tenant.

6. Total life cycle cost frequently compares favourably to central systems when

considering relative installed cost, operating costs, and system life.

Disadvantages

1. Space required for boiler, heat exchanger, pumps and heat rejector.

2. Higher initial cost than for most other multiple-packaged unit systems.

3. Reduced air flow can cause the heat pump to cycle cutout. Good filter

maintenance is imperative.