Double effect
absorption chiller is an improvement in single effect lithium bromide chiller (read here all about Single effect absorption chiller ) . Double
effect water chillers have more coefficient of performance and enhanced utilization
of input energy.Basic working principle of these dual effect absorption chillers
remains same as single effect but with addition of some components to vapor
absorption cycle. Absorption cooling is enhanced using the system energy which
would have been otherwise wasted as in case of single effect industrial chiller.In order
to produce chilled water in these double effect chillers,water remains as a
refrigerant and lithium bromide as absorbent in these HVAC water chillers. As
compared to single effect absorption chillers,double effect vapor absorption chiller has an
additional heat exchanger and generator/concentrator.
HVAC double effect absorption chiller |
Basics of Double effect Absorption Chiller Operation
HP Generator Process in Double effect Absorption Chiller Operation
In double effect
absorption chiller,both in direct and indirect fired chiller operation, weak
solution from the absorber is pumped into the HP generator through LT,
condensate and HT heat exchangers. It is heated by operating steam and
concentrated to the intermediate solution, and high temperature refrigerant
vapor is produced.Instead of steam ,hot exhaust gases or waste heat may also be used as in case of direct fired absorption chillers.
LP Generator and HT exchanger Process in Double effect
Absorption Chiller Operation
In next step of chiller operation,Intermediate
solution enters LP generator through HT heat exchanger in exchanging heat with
weak solution which is passed through the tubes. Intermediate solution in LP generator is heated by the refrigerant
vapor from HP generator, concentrated to the strong solution, releasing
refrigerant vapor at the same time.
LT Heat exchanger
Process in Double effect Absorption Chiller Operation
The strong solution
passes through the outside tube space of LT heat exchanger, enters absorber,
transmitting heat to the weak solution from absorber. In absorber the strong
solution absorbs refrigerant vapor again.
Condenser Process in Double effect Absorption Chiller Operation
Refrigerant vapor from HP generator is condensed in LP generator to form condensate, which enters condenser through throttle. Refrigerant vapor formed in the LP generator flows to the condenser to form condensate also.
Evaporator ,Refrigerant
Pump and Absorber Process in Double effect Absorption Chiller Operation
At normal
temperature and pressure water boils at 212oF but as pressure is
lowered sufficiently below atmospheric pressure then boiling temperature is
also decreased .Same thing is used in evaporator of absorption chillers(single
and double effect ).
These two parts of refrigerant condensate flows into the flash chamber through U pipe. A part of refrigerant water is flashed to form vapor, which flows into the re-absorption chamber at the bottom of absorber, while another part of refrigerant water is cooled, and enters evaporator refrigerant pan. Refrigerant from evaporator refrigerant pan is pumped over the evaporator tubes for the refrigeration effect, and evaporates to form vapor by absorbing heat of chilled water flowing through tubes.
These two parts of refrigerant condensate flows into the flash chamber through U pipe. A part of refrigerant water is flashed to form vapor, which flows into the re-absorption chamber at the bottom of absorber, while another part of refrigerant water is cooled, and enters evaporator refrigerant pan. Refrigerant from evaporator refrigerant pan is pumped over the evaporator tubes for the refrigeration effect, and evaporates to form vapor by absorbing heat of chilled water flowing through tubes.
Produced refrigerant
vapor enters absorber, and absorbed by strong solution in the absorber. Chilled
water is cooled and return to the HVAC system of customer. Strong solution is
diluted by absorbing refrigerant vapor in absorber and absorbing flashed
refrigerant vapor in the re-absorption chamber.
Solution Pump in
Double effect Absorption Chiller Operation
Weak solution is then transferred by solution pump to HP and LP generator for concentration. Heat generated is carried to atmosphere by cooling water. This process is continued, and refrigeration effect is repeated.