Chapter 27 - Heat Pumps and Heat Recovery

Abstract

All refrigeration systems are heat pump (HP) such that heat is pumped from a cool environment to a warmer one, so the sole purpose of a heat pump is to deliver heat. The HP type and performance is characterized by the nature of the source, that is, the medium from which heat is extracted by the evaporator, and the sink, that is the distribution of heat in the building. The two main sources of heat are ground and air. The ground source heat pump (GSHP) has a typical source temperature of 5–10°C and is the most commonly quoted technology when heating-only systems are being considered. One way of extracting the heat is to circulate a glycol solution through plastic pipes, laid in trenches, and the ground source then behaves in a very similar way to the water source. An alternative method, which may be used where space is restricted, is to drill a borehole, and to circulate brine to sufficient depth to gain the necessary heat. GSHPs capture solar heat stored in the ground. It is also possible to circulate the refrigerant directly by inserting the copper tube evaporator in the drilling. This eliminates one of the heat barriers, but increases refrigerant charge, and there is always the danger of underground refrigerant leakage, which can be costly to rectify.