Long term performance of different SAGSHP solutions for residential energy supply in Finland

• I assess different SAGSHP solutions for a cold climate with many borehole depths.
• I consider the conventional solar thermal collector typologies for each solution.
• How to use solar thermal energy has to be planned carefully.
• The use of the unglazed and flat plate collectors is suggested for short boreholes.
• For deep boreholes the use of flat plate or evacuated tube collectors is suggested.

The presented paper focuses on different control strategies of a solar assisted ground source heat pump (SAGSHP) for cold climate. Dynamic simulation approach has been used through TRNSYS software. In particular, a SAGSHP solution operating with the strategies suitable for cold climate found in literature, a conventional ground source heat pump (GSHP) solution and a GSHP with solar thermal system only for building heating supply have been compared to the SAGSHP proposed system. The impact of the considered system solutions on seasonal performance factor and primary energy ratio in case of a gas boiler as auxiliary system has been evaluated as a function of the boreholes depth, the conventional solar thermal collector typologies and the size of the solar thermal system.Results have shown that the proposed strategy is effective from a specific borehole depth. Moreover, the solar thermal collector typology has to be selected accordingly to the borehole depth and to the used auxiliary source. Furthermore, the temperature difference between solar collectors and the ground, which has to be exceeded for driving solar heat into it, has to be kept low for system with short borehole in order to drive more heat into the ground and it has to be incremented with the increasing of borehole length, especially for small solar thermal system size when flat plate and evacuated tube solar collector typologies are adopted.