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AIRCONDITIONING
TYPES OF AIR CONDITIONERS
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TYPES OF AIR CONDITIONERS
I. Self-contained room units:
Cooling only units Cooling & Heating Units Heat pump units
II. Central Systems:
Packaged Units Remote or Split Systems Combination Heating & Cooling Units Heat pump Units Built up Systems
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Cooling only units
A room AC has two separate & distinctive air circuits:Outside Air over Condensor: air drawn into the unit from outside,passes thru air-cooled condensor over motor compressor & back
outside, carrying with it the heat removed from condensor.
Cooled Room Air: air drawn from the rm. Into the unit thru a filter thatremoves dust & impurities, passes thru evaporator coil, where it givesup somr heat, then back into the room as conditioned air.
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Air Cooled&Water Cooled Condensor
Used in areaswhere free airsupply is limitedor non existant
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use of air to cool the
compressor & condenser coil
used to return the refrigerant gas
to a liquid state.
These split systems usually
have an inside evaporator
cooling coil installed to workalong with the blower & duct
system. The outside half of the
equipment contains the
compressor and condenser coil.
AIR COOLED AC SYSTEMS
schematic diagram shows how refrigerant
moving through the system as a gas orliquid moves heat from inside the building
(at the evaporator coil in an air handler) to
outside the building (at the condenser
unit's condensing coil).
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WATER COOLED AC SYSTEMS
use water as a chiller toremove heat from the high temp
gas in the (usually but not always
outside) compressor/condenser
unit.
uses refrigerant & coils to move
heat from indoors to outside. But
instead of moving heat from the
condensing coil into air blown
across the coil outdoors, we're
moving heat into water circulated
around a condensing coil.
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Combination Heating&
Cooling Units
some rm conditioners are offered withelectrical resistance, usually in the form
of strip heaters for supplying heat
during cool days, done instead of
incorporating reverse cycle system as
heat pumps.
strip heaters are placed in the air
stream beyond the evaporator,
manually operated, with fan operating
but compressor turned off.
with strip heaters all current drawn is
converted into heat. Additional heat isprovided by heat of fan motor.
Wattage is same as drawn by
compressor motor.
Strip heater for room unit
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Combination Heating & Cooling UnitsAdvatages:heating & cooling facilities in one package.
Blower serves both sections, only one duct system
is required.
Blower designed to handle larger usually reqd. forsummer cooling loads.
Both operations are independent & air from either
side does not pass thru other side.
minimum duct work required to connect unit to air
distribution system.
Compact unit takes up less space.Disadvatages:Sometimes over capacity results, space utilization,
initial cost & additional wiring.
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Heat Pump Units
electrically driven device designed toprovide heating & cooling in the same
basic unit but operation is entirely different& hence treated separately.
used for residential & light commercial
application.
Operation depends on two simple facts:1. There is always considerable heat in
air, at extremely low outside temp.
2. A cold object absorbs heat from
warmer one.Construction of a room air
to air heat pump unit
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Reverse Cycle:
Air to air heat pump Cycle:
in winter extracts heat from outside air &
uses it to heat the air inside the rm. in
summer operation is reversed to remove
heat from inside & release it outside.
Water to water system
water to water system takes heat from
water source such as deep well & transfers
it to closed circulation water system.
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PACKAGE AIR CONDITIONING: COOLING
In case of higher capacities the unit AC becomes larger in size. Needs network of supply & return. Capacity is 7 TR, 10TR, 12TR etc.Built up spaces between 1200 to 1800 Sft can be effectively served. include ceiling as well as floor mounted units.Commercial or residential uses. Consist of evaporator or cooling coil, compressor-condensorcombination.
& may include heaqting function also. Compressors are reciprocating type, cooling colis are direct expansiontype,Condensors can be air cooled or water cooled. Expansion devices are capillaryv tubes, thermostatic expansionvalves are also used.
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Air conditioning ducts
Uses: Air Distribution
efficient method of conveying & distributing cold air.Without ducting the effect of a fan, air conditioner or cooler islimited to a small area but ducting allows the cold air to bedirected to specific hot spots to provide localised cooling, ordiffused over a wide area to reduce temp. gradients. usually suspended overhead from steel wires.
Rows of small holes in the sides of the ducts produce jets ofcold air that mix with the warmer room air before falling tofloor level. Leading to draft free air movement thru out thebuilding and reduced temperatures. By using numerous small jets the air velocity is kept low,ensuring the workforce do not complain of uncomfortable cold
drafts.
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Desirable qualities: Smooth surfaces offer min.
resistance to flow Air tight for no leakageWater proof insulating qualities-min. 2-4thk Min. sound transmission
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Duct Materials: Galvanised Steel Aluminium
Copper & Brass Laminated asbestos Spring steel wire Woven fibre glass
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Insulation
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Commonly used System Conventional system: branch §ion sized on quantity of air to becarried.
Small pipe system: air is deliveredthru 31/2 or 4 round pipe with
prefabricated fittings & specialoutlets.
Extended Plenum system: large
main duct of uniform dimension thruout its length with branches taken offthru special fittings.
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Duct Layout
Commonly used System Conventional system: branch & section sized on quantity of air to be
carried. Extended Plenum system: large main duct of uniform dimensionthru out its length with branches taken off thru special fittings.Small pipe system: air is delivered thru 31/2 or 4 round pipe withprefabricated fittings & special outlets.
Duct Layout requirements: to determine air movement required in each room-found by sensiblecooling & heating load of each room. to determine supply air temperature-usually ranges from 50-65 degF for cooling & 100-150 deg F for heating. figuring sizes of various duct sections- round duct will carry moreair with less friction loss than other shape & same given cross
section. Square ducts are better than rectangular.