Different strategies for long term performance of SAGSHP to match residential energy requirements in a cold climate

Awareness about serious environmental problems due to fossil fuel consumption is increasing widely. Furthermore ground source heat pumps (GSHP) have increasingly been used for residential building heating and cooling in recent years and one promising configuration for cold climate is the solar assisted ground source heat pump (SAGSHP), where solar energy could be used for supplying heating energy to the building or for recharging the boreholes. Scientists pointed out that a key role is played by the strategy to control the solar-ground loop (Zhai et al.; Rad et al.; Kjellsson et al. ; Stojanovic and Akander). The presented paper focuses on a new control strategy for such systems aiming to maximize the solar energy use and energy savings. In order to compare different proposed and current operating modes and strategies of SAGSHP systems, simulations have been carried out with the simulation program TRNSYS. Results have shown that the proposed strategy is effective from a specific borehole depth; furthermore the temperature difference between solar collectors and ground source, which has to be exceeded for driving solar energy into the ground, has to be chosen prudently as a function of the borehole depth, the solar filed size and the auxiliary system typology.