22 May 2008

DEVELOPMENT OF HEAT PUMP WATER HEATER USING CO2 FOR COMMERCIAL USE


New heat pump water heater system using CO2 has been developed to spread the electrical heat pump water heater from the point of view of the global warming prevention. Most of the conventional water heaters for commercial use are combustion heaters using fossil fuel. The developed system consists of a water tank, the refrigeration circuit with a suction line heat exchanger(SLHX) ,a bypass line and heat recovery heat exchanger(HRHX) for the defrost. This system has three operating modes; hot water storage mode, heating up mode and defrost mode using HRHX. In the hot water storage mode, 17? tap water is heated up to 65? hot water and sent into the tank and 40kW heating capacity is generated. In addition, in the heating up mode, 60? hot water supplied from the tank is heated up to 80? and 19kW heating capacity is generated. The SLHX can make the inlet quality of the evaporator lower than the conventional cycle without the SLHX,
therefore excessive amount of refrigerant can be stored in the air heat
exchanger(evaporator) without accumulator under the various condition. Furthermore, in the
defrost mode, the HRHX makes defrost capacity increase and the air heat exchanger is used as the condenser. The SLHX are used as the gas cooler (high pressure side) and the evaporator (low pressure side) by the bypass line. This defrost circuit can prevent the liquid return to the compressor and ensures high reliability without accumulator.