3052 -- A Prototypical Direct-Expansion Solar Heat Pump System PDF

This paper presents a phototype for a direct expansion solar heat pump system for domestic water heating and its performance date. The prototype system consists of refrigerant-filled solar collectors as an evaporator, a variable-capacity compressor, a double-wall copper tube heat exchanger as a condenser, an electric expansion valve, and a thermal storage tank.

The collectors, which are made of anodized extruded aluminum, are bare (without cover glass and insulation) and can be integrated into a house structure (roof, wall) or (fence). The aperture area of the roof-integrated collector is 6.0 m² ( 65 ft² ). The compressor is a rotary type, and its capacity modulation is done by a frequency controller. The electric expansion valve can handle a wide range of refrigerant (R-22) flow rate in order to obtain an appropriate superheat in the collector. A thermal storage tank of 470 liters is used for the system.

Results of indoor experiments with a solar simulator in an environmental room show that the system can heat water up to 55°C with a high coefficient of performance, 3.7-4.2 throughout the year. Outdoor field tests resulted in coefficients of performance of 3.1-3.7 for the four systems tested throughout the year.

Units: Dual