Dual source heat pump systems: Operation and performance

Dual source heat pump systems comprise of a main cold source heat pump that is supported by an additional heat source. Two arrangements have been studied in detail: air source heat pumps combined with solar collectors; and ground source heat pumps coupled with solar collectors. In addition to a situation where solar collectors are devoted solely to direct heating, the solar system can be used with the heat pump in either a series or a dual source scheme. When set up in series, a higher COP can be achieved, but there is often a lower free energy fraction. This is due to the lack of direct solar heating, meaning that auxiliary energy is required more frequently. A careful analysis of all the plant elements, including location, heating and cooling demand, solar collector area, thermal ground probe length, etc. is fundamental for achieving the best outcome in terms of both good primary energy savings and profitable economical performance.