Absorption Chiller in HVAC system

Absorption chiller  occupies vital position in an HVAC system.Absorption chiller is an equipment which uses a heat source, a refrigerant and an absorbent for producing chilled or hot water. In the types of chillers,along with vapor compression water chiller or electric chiller ,absorption cooling system is also used in many applications.Absorption chillers produce chilled water under vacuum conditions for the purpose of air-conditioning and technology process.

Basic components of Vapor absorption chillers

Absorption chillers in its simplest form (single stage) consist of following main parts:

Steam absorption chiller

• Generator
• Condenser
• Evaporator
• Absorber
• Heat exchanger
• Refrigerant Pump
• Solution pump

Working Principle of Absorption Chiller

1. Function of Generator in absorption chiller

In generator of absorption chillers weak solution is heated by operating steam (steam absorption chillers),hot water or flue gases in indirect fired absorption chillers.While direct fired absorption chillers are Natural gas, Diesel or Kerosene Oil Operated.After heating in generator solution is concentrated and high temperature refrigerant vapors are produced.After generator process in a chiller high temperature and pressure refrigerant vapors travel to condenser. A strong solution enters absorber through heat exchanger in exchanging heat with weak solution .

2. Function of Condenser  in absorption chiller

vapor absorption cycle

Refrigerant vapor from generator is condensed in condenser by cooling water.Condensation is constant pressure process where refrigerant (water) gives off its heat to cooling water .In this way refrigerant heat is carried to atmosphere.In water cooled chillers , cooling water recycles after exchanging heat with air in cooling towers of same HVACsystem.

3. Function of Evaporator in absorption chiller

Refrigerant from condenser flows to evaporator .In this compartment of absorption chiller,refrigerant gets vaporized by taking heat from chilled water.Refrigerant from evaporator refrigerant pan is pumped over the evaporator tubes with the help of refrigerant pump.Flow of refrigerant over evaporator tubes evaporates the refrigerant thus producing refrigeration effect, and evaporates to form vapor by absorbing heat of chilled water flowing through tubes.In this way,evaporation takes place at constant pressure process where refrigerant gets latent heat from chiller water.Chiller absorption takes place here in absorber.Chilled water is cooled and return to the system of customer.

4. Function of Absorber in absorption chiller

Produced refrigerant vapor enters absorber, and absorbed by strong solution in the absorber.In this way,strong solution is diluted by absorbing refrigerant vapor in absorber . Heat generated is carried to atmosphere by cooling water.

5. Function of HVAC Solution Pump in absorption chiller

This weak solution is transferred by solution pump to generator for concentration.Pumps are components in absorption cooling systems which require electric energy for its operation.Weak solution from the absorber is pumped into the generator through heat exchanger. This process is continued, and refrigeration effect is repeated.

Must Read : Absorption Chillers vs Electric (Compression) chillers

Try here HVAC quiz related to absorption chillers or vapor compression cycle.

Water Chillers

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

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 ):

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 .

Must Read : Absorption Chillers vs Electric (Compression) chillers