Solar assisted ground source heat pump performance assessment for residential energy supply in southern European climates

The awareness about environmental problems due to fossil fuel consumption is increasing widely; therefore, efforts are being made to develop energy efficient and environmentally friendly systems by utilisation of non-polluting renewable energy sources. Ground source heat pumps (GSHPs) belong to this category. Many variations of geothermal system typologies exist, with different configurations suitable in different situations and most locations around the world. One emergent configuration is the solar assisted GSHP (SAGSHP). The paper focuses on different control strategies of a solar assisted ground source heat pump (SAGSHP) for different Italian locations. Dynamic simulation approach has been used through TRNSYS software. The impact of the considered strategies on the seasonal performance factor has been evaluated. Results have shown that the strategy strongly affects the system consumption; therefore, it needs to be chosen appropriately in the design phase. Furthermore, when solar energy is driven into the ground, the temperature difference between solar collectors and the ground, which has to be a positive value to charge the ground, plays a fundamental role. In particular, solar thermal energy injected into the ground decreases to zero moving from a humid sub-tropical (Cfa) to a dry-summer subtropical (Csa) climate. Therefore, a compromise between the operation of the circulation pumps used for supplying free cooling energy and for driving solar thermal energy into the ground has to be found for each climate