Dual source heat pump systems: operation and performance

In dual source systems the heat pump main cold source is aided by another source. Two combinations have received a special attention and have been studied: air and solar collectors; ground and solar collectors. Apart the parallel disposition where solar collectors are devoted to direct heating only, the solar contribution to the heat pump can be according to the series or dual source scheme. The series disposition allows a higher COP but it often produces a lower free energy fraction, as it lacks of direct solar heating and the resort to auxiliary energy is more frequent. A careful analysis of all the plant elements, location, heating and cooling demand, solar collector area, thermal ground probes length, etc. is fundamental for reaching the best result both looking for a good primary energy saving or for a profitable economical result.