Water chillers are
backbone of HVAC cooling systems.Water chiller is a refrigeration machine which
produces chilled water ( Approx 7 Degree C ~ 12 Degree C).The primary function of a chiller is to
lower the temperature of water to such value such that it can be used for producing
cooling effect in integration with other HVAC components. A water chiller is
just like a other refrigerator machine but instead of keeping your food cool or
making ice,it produces chilled water.The output of chiller is a water at lower
temperature usually around about 10 o C depending upon the Chiller design.
HVAC water chillers
play vital role in any HVAC systems along with other basic components. Chillers
have got much attention in recent years for its new designs and performance
improvement in existing designs. New designs have resulted in hvac chiller with
better efficiency and less operation and maintenance costs. Another desirable
features is energy saving and precise load or capacity control for new chillers. We see the chillers with
above features in market but as engineering professionals we hope to see more
with design improvements with less O & M cost. It is essential part of HVACsystem to have a chiller. Chiller manufacturers have also expanded their
production as well design capabilities to cater to the diversified demands of HVAC chillers.
HVAC Chiller Basics
Working Principle of Vapor Compression Chiller
Working Principle of Vapor Compression Chiller
An HVAC
chiller works on vapor compression or vapor absorption cycle.In vapor
compression cycle, refrigerant circulates in evaporator ,compressor, condenser
and expansion valve of a chiller. A thermodynamic process occurs in each of
above chillers.Theoretical working of Vapor compression or compression chillers
is explained below.
Heat addition to refrigerant in evaporator ( 1-2):
Refrigerant gets
vaporized by taking heat from chilled water in evaporator thus serving its
prime purpose. Refrigerant comes out of evaporator as vapors but on other side
chilled water is produced. Thus heat is added to refrigerant at constant
pressure but is extracted from chilled water. Both refrigerant and chilled
water don’t get mixed and are separated by some solid wall in between them in
evaporator like shell and tube design.
Compression of
refrigerant vapors in compressor (2 - 3 ):
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| Working Principle of Water Chillers |
Refrigerant vapors
come out of evaporator and then compressed by chiller compressor to high
pressure and temperature. Compressor requires energy input for its working and
hence electric energy is supplied to it.
Heat rejection by
refrigerant in condenser ( 3 - 4 ) :
Similar to evaporator
,but reverse is happening here. Refrigerant rejects its heat to outside cooling
liquid or air .In this way, refrigerant gets condensed and outside media is heated.
outside media e.g. cooling water may be cooled by cooling tower and recycled
again into condenser.
Expansion of
refrigerant in expansion valve ( 4 -1 ) :
Refrigerant in condensed form coming out of condenser is
expanded in expansion valve and its pressure and temperature is reduced to
level of evaporator so that above cycle is repeated again.
In above four
components of hvac
chiller ,evaporator is the part where we get chilled water after exchanging
heat with refrigerant .
