bs 2 hvac air conditioning 3
TRANSCRIPT
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BUILDING SERVICES TWO (BLD60503)
HVAC Systems & Building
Prepared by Tan Hee Chai
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Air Conditioning 3
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Contents Fans Refrigeration Air Conditioning methods Air Conditioning systems
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Fans
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Three (3) common types of fan
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Shape of centrifugal fan
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Centrifugal fansAlso called ‘radial flow’ fansPerformance is affected by the shape of the blades and shape of the casing.
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Centrifugal fans
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Fan drives and motorsAC or DC powered
AC uses mains power but noisy due to nature of supply.Speed variation and harmonies easier and cheaper to control using micro processors.
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DC motorsQuieter speed control constant but expensive.AC DC rectifier (see right photo)
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Fan drive
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Axial flow fans Consist tubular casing with
aerofoil section blades arranged at an angle to form helix
Motor contain inside hub or outside casing driven by V belt
Centrifugal fan with forward curved blades develop higher pressure than axial fans
High running speed favours small motor
Latest blades provide quiet operation
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Shape of axial flow (screw) fan
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Axial flow fan
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Bifurcated axial flow fan
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Mixed flow fans Combine advantages of
centrifugal & axial fan Air flows over rotor
provides both radial and axial velocity components.
Higher pressure and quieter
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Fan characteristics
Performance of fans is analysed and recorded on ‘characteristic chart’ used to select fans for particular duties
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Refrigeration
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Refrigeration
Air conditioning systems for cooling comes with a refrigeration system
Cooling by refrigeration achieved by causing a change of state of a refrigerant between gaseous and liquid phases.
Gases at normal atmospheric temperatures and pressure, boils at low temperature and high pressure
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Two principal of refrigeration system
1.The Vapour compression cycle2.The absorption cycle
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BUILDING | SERVICES | TWO (BLD60503)Basic vapour compression cycle
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BUILDING | SERVICES | TWO (BLD60503)Vapour compression cycle
https://youtu.be/nKZ2DPvvua8
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Vapour compression cycle Uses a compound – boil and condense at
different temperatures when subjected to different pressures.
Two devices is used – one compresses the gas. The other allow it to expand plus heat transfer
matrices. One suck heat in (on evaporation) The other to reject it (condenser)
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Condenser
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BUILDING | SERVICES | TWO (BLD60503)Cooling towers
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Cooling towers
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BUILDING | SERVICES | TWO (BLD60503)Condenser
Condensers are heat rejectors of the cycle Can be air cooled or water cooled. Water cooled usually cooled by a cooling tower which
continually recirculates water over packing infills panels, increasing surface area for heat transfer.
Make up water to balance water lost in evaporation is made up from the mains approx. 1% of recirculated water volume.
Cooling towers use both air flow and water flow for rejecting heat to atmosphere using latent heat of evaporation and sensible heat transfer of water.
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Condenser Recirculating water systems treated using chemicals and/or ultra- violet emitters to reduce bacterial contamination.
HEPHe
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Expansion valve
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Expansion valve Situated as close as possible to the evaporator. Control refrigerant flow into evaporator, excessive
cause flooding and damage Compressor draws up gas from evaporator- slight
pressure & temperature decrease within felt by bellows.
Bellows exert slight weaker force against the spring, moving the needle to open the valve.
Additional refrigerant is admitted to the evaporator, increasing the pressure, overcoming the force of spring, moving the needle to close the valve.
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Expansion valve
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The evaporator
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Evaporator
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The evaporator Cool, high pressure refrigerant liquid is
expanded so that boiling takes place due to pressure drop
Latent heat of evaporator is taken from the water, air or brine in the secondary circuit.
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Compressor
Reciprocating Compressor
Rotary Compressor
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BUILDING | SERVICES | TWO (BLD60503)Compressor
Reciprocating Compressor
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BUILDING | SERVICES | TWO (BLD60503)Compressor
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BUILDING | SERVICES | TWO (BLD60503)Compressor
Single or multi stage centrifugal, reciprocating by piston action or rotary to develop a compression of the refrigerant gas
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Absorption refrigeration
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Absorption refrigerationDessicant-A substance, such as calcium oxide or silica gel, that has a high affinity for water and is used as a drying agent.
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BUILDING | SERVICES | TWO (BLD60503)Absorption refrigeration
Absorption cycle utilises property of certain liquids to absorb
gases/vapours Heat energy to separate the refrigerant from
its carrier fluid
Heat rejection – via a condenser Cooling effect – via an evaporator where
refrigerant is vapourised.
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Absorption refrigeration Compressor of the vapour compression
cycle – replaced by refrigerant ‘generator’ where two fluids are separated.
Absorber – absorb the refrigerant by carrier liquid.
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BUILDING | SERVICES | TWO (BLD60503)Absorption refrigeration
Typical refrigeration/carrier fluid combinations:
Ammonia/Water
Where temperature above 0 degree Celsius Water/Lithium bromide Water/Lithium Chloride
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The End