The heat pump¿an economical method of producing low-grade heat from electricity

The paper deals with a method¿which so far has not received the attention of engineers¿of converting electrical energy into heat energy. The method is based on the general principle that the efficiency of the heat engine working in the normal cycle is given by (T1 ¿ T2)/T1, where T1 is the high temperature and T2 the low, and that the heating efficiency of a reversed-cycle heat engine is given by T1/(T1 ¿ T2). The reversed-cycle heat engine (or heat pump) is described, and it is shown both from theoretical considerations and from practical tests on refrigerating plant that where heat at a comparatively low temperature is required, heating efficiencies of the order of from 300 to 500 per cent or even more may be obtained, the heating efficiency being defined as the ratio of the heat produced by the heat pump to the heat equivalent of the electrical energy consumed. The application of this principle to the heating of buildings and for such purposes as the heating of public baths is discussed, and estimated figures for a public-bath installation are given. The paper concludes with a description of experiments which the author has been carrying out during the past 2 years, and which have demonstrated the soundness of the general principles on which the heat pump is based.