[en] solar collector ; heat storage ; heat pump ; coefficient of performance ; solar fraction
[en] An experimental solar-assisted heat pump system with a hybrid ground-coupled storage at the F.U.L. in Arlon, Belgium, is described. It includes a 382 m2 solar roof, two types of water storages, heat storage in earth by horizontal exchangers, and heat pumps. One operating period (1984–1985) is analyzed. The data processed has shown that each of the subsystems has apparently performed adequately: annual collector efficiency is 0.41, heat pump C.O.P. range around 4. Despite important energy losses from the underground storage, the storage efficiency reaches 0.7. This effectiveness is mainly due to heat recovery below natural soil temperature and also to the use of buried tanks for short-term storage. The main difficulties are controlling the flow between these subsystems and developing an operating strategy that matches both the building's heat requirements and a good solar fraction.