The basic function of a heat pump is to transfer energy from a low-temperature heat source to a higher temperature medium. This function may be carried out for a range of 50 to 120°F temperatures, although not with the same efficiency. A large heat pump installation for district heating or process heating usually must be specifically adapted to the heat source and the requirements of the heat consumers. Small heat pumps for domestic use are quite standardized, often designed for inexpensive mass production, easy operation, and maintenance