在国际贸易和工业部（MITI）的支持下，三家燃气公用事业公司、五家发动机制造商和七家热泵制造商于1981年启动了七种燃气机热泵（GHP）（1-10制冷吨）的三年期项目，开发出了效率高、耐用性好的小型燃气发动机和开式压缩机。项目结束后，公用事业公司和制造商继续开发GHP，使其达到商业化水平，并完成了大规模的现场试验，取得了成功。1987年9月至1988年3月期间，约有2300个GNP（1.3-5 RT）在市场上销售，1988财年预计销售10000个单位。为了提供维护工作，东京的一家大型天然气公司成立了GHP服务中心，该中心由东京地区小型GHP的特别维护团队组成。 日本各地正在逐步建立维护机构。引文:研讨会，ASHRAE交易，第95卷，pt。1989年，芝加哥

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.