Abstract
It is inherent in the process of producing mechanical and hence electrical energy from a heat engine that much of the energy input is released as relatively low temperature heat. By various techniques it is possible to produce reject heat at a temperature useful for space heating or industrial process heating, giving a much higher overall efficiency of conversion and saving fuel over separate production of electricity and heat. Heat from combined heat and power plant, or from another central source, can be piped in the form of hot water or steam to users' premises, in district heating networks