PERFORMANCE AND OPERATING CHARACTERISTICS OF COMPACT SOLAR THERMAL AND GEOTHERMAL HYBRID HEAT PUMP SYSTEMS FOR A ZERO-ENERGY HOUSE

In this study, the operating characteristics and thermal performance of a geothermal heat pump for a compact solar thermal and geothermal hybrid heat pump system that had been developed through previous studies for a zero-energy residential house were experimentally analyzed.This hybrid system was installed in a passive three-story house with a heating area of 194m 2 .The geothermal heat pump was used as backup for heating and cooling and the solar hot water system.Monitoring results showed that the daily heating COP of the geothermal heat pump was 3.7 to 4.6 and the cooling COP was 3.9 to 4.7, depending on the temperature of the heating medium supplied from the borehole heat exchanger to the heat pump and the temperature condition of the buffer storage tank.The operation pattern of the geothermal heat pump during the winter season showed continuous intermittent operations from the evening to early morning hours.One of the operation times was as short as about 10 minutes.Even during the summer, when the cooling load is high, the operation pattern of the heat pump showed intermittent operation characteristics similar to those of the winter season.The operation time of the heat pump was about 7 minutes.From such monitoring results, it is considered that the compact-type solar thermal and geothermal hybrid heat pump system needs to increase its buffer tank volume for heating and cooling or slightly reduce its heat pump capacity.If a variable output heat pump is used, the output of the heat pump can be adjusted to accommodate the instantaneous thermal load (not only the full load, but also the partial load), so that a solar thermal and geothermal hybrid system can be made more compact by eliminating the buffer storage tank for cooling and heating.