23 September 2011

PERFORMANCE OF A HEAT PUMP WATER HEATER AT VARIABLE CONDITIONS


This study investigates the performance of R410A heat pump water heater at
various weather conditions. A household heat pump water heater with R410A refrigerant has
been developed in ITRI. The tube-in-fin evaporator, tube-in-tube heat exchanger have been
designed with in-house software based on R410A system. Meanwhile, all components have
been manufactured and supplied by local companies. The assembling, optimizing tuning and
performance also have been executed in a certificated laboratory in ITRI. The refrigeration
system was judged according to the variable inlet temperatures of water and the weather of
hot water demand. At specified condition of Taiwan domestic requirement which the water
inlet and outlet temperature are fixed at 15 ?and 55? respectively, the tested heat pump
water heater had the heating capacity of 6.4 kW and the coefficient of performance (COP)
was equal to 4.07. The operation of heat pump has shown that refrigerant subcooling was
increasing with decreasing water inlet temperature. The result has also indicated that
evaporator had larger pressure drop in the winter test condition because of the large volume
of vaporized refrigerant which with a large specific volume resulted in a high flow resistance.
It is suspected that the refrigerant subcooling at condenser outlet was limited by the high
condenser water inlet temperature. The optimal operation conditions for the heat pump
system, after a carefully examination of the measuring data, have concluded as following that
the water inlet temperature should be kept as low as possible to obtain a larger subcooling,
and the pressure ratio between the compressor inlet and outlet can be reduced such that the
compressor power input is reduced as well.