This paper describes the performance of a domestic hot water (DHW) supply and space heating system using CO2 heat pump (HP). Experiments were carried out under the same hot water demand by using the M1 standard mode. As a result of experiments, each coefficient of performance of the HP (HPCOP) was 4.91 in summer, 4.34 in the middle season and 2.75/2.82 in winter (high/low space heating load), respectively. Each system coefficient of performance (SCOP) was 3.59, 3.35 and 2.06/1.94. As a result of the comparison with the performance of HP for DHW only, it was shown that a space heating operation influenced a drop of SCOP. A rise of HP inlet temperature and increase of the heat loss from a hot water storage tank became the factor. As a result of having carried out an approximate evaluation, a value of the degradation ratio of SCOP compared with HP for DHW only was 20% in Tokyo.
