part 1: overview of cogeneration and its status in asia - Fire

State of art review of cogeneration 21
2.6 Working Principle of Absorption Chillers
Like the vapour compression chiller (VCC), the vapour absorption chiller (VAC) extracts heat
in the evaporator which is placed in the space to be cooled and rejects this heat in the
condenser. However, VAC needs a heat source as the driving force while VCC requires
mechanical power or electricity for the same duty. Figure 2.8 shows the schematic diagrams
of VCC and VAC.
High Pressure
High Pressure
Vapour
Vapour Refrigerant Refrigerant
Condenser Condenser Generator
Vapour
Compressor
Figure 2.8 Comparison between vapour compression and absorption cycles
The improved version of the VAC, commonly known as the double effect type, is designed
such that it utilizes the vaporized refrigerant as an extra heat source. The generator is divided
into high and low temperature sections. The refrigerant vapour produced in the high
temperature generator gives up its latent heat to the partially refrigerant-rich solution in the
low temperature generator that operates at a low pressure, hence the lower boiling point of
the refrigerant. The energy consumption of a double effect VAC is approximately half that of
the single effect VAC for the same cooling effect. Moreover, heat rejected in the condenser is
also reduced, resulting in smaller condenser and cooling tower.
The performances of absorption chillers strongly depend on the thermo-physical properties of
the working pair, i.e., the refrigerant and absorbent. Binary working pairs such as ammoniawater
(NH3-H2O) and lithium bromide-water (LiBr-H2O) have been employed commercially in
absorption chillers for a long time and these are in commercial use. A single effect LIBr-H2O
absorption chiller requires about 0.8 m 3 /h of hot water at around 90ºC or 8.3 kg/h of steam at
1.5 bar to provide 1 RT. On the other hand, a double effect chiller requires only 4.5 kg/h of
steam, though at a higher pressure between 6 and 8 bar.
2.7 District Heating/Cooling Network
Heat
Mechanical Input
Heat
Power/Electricity Exchanger
Evaporator Evaporator Absorber
Low Pressure Low Pressure
Vapour Refrigerant Vapour Refrigerant
(i) Vapour Compression Chiller (ii) Vapour Absorption Chiller
Individual buildings and industries may lack economies of scale when setting up cogeneration
facilities and it may not be always possible to optimize the design parameters due to the
peculiarity of the energy demand patterns. In such cases, one may think of developing a
facility that caters to several user-groups with varying demand patterns that can be
complimentary. In the building sector, for instance, offices are active during the daytime