In the cold region of Hokkaido area, most of today's heating systems are using fuel oil. For this area, adequate heat pump solutions shall be developed for the low energy houses field. A ground-coupled system is in field-monitoring conducted and evaluated by Hokkaido university. However, 80% of the Japanese people live in the medium climate zone IV (Region Tokyo, Osaka, Fukuoka), where heat pumps in reverse operation for space heating in winter and air-conditioning in summer are very popular. These systems have a large market share in Japan. They shall be further developed for the application in low energy houses with regard to capacity range and control issues for different building types. Therefore, currently a load analysis by TRNSYS simulations is done and comparison to a central heating system with exhaust air heat pump and floor heating distribution is accomplished.