Small gas engines and open-type compressors with high efficiency and excellent durability were developed in the three-year project started in 1981 for seven types of gas engine heat pumps (GHPs)(1-10 refrigerating ton, by three gas utilities, five engine manufacturers, and seven heat pump manufacturers, with support from the Ministry of International Trade and Industry (MITI). After the project, the utilities and manufacturers continued developing GHPs to the level of commercialization and completed large-scale field tests with successful results.

About 2300 GNPs (1.3-5 RT) were marketed between September 1987 and March 1988, and sales of 10,000 units were expected in fiscal 1988. To provide maintenance work, a large gas company in Tokyo founded the GHP Service Center comprising a special maintenance team for small GHPs in the Tokyo area. Maintenance setups are gradually being established throughout Japan.