Providing renewable cooling in an office building with a Ground–Source heat pump system hybridized with natural ventilation & personal comfort systems

A ground–source heat pump system (GSHP) can be an alternative to air–source heat pumps (ASHP), as exchanging heat with the ground instead of with the air can result in higher coefficients of performance (COP). However, unbalanced loads can significantly shift the temperature profile in the ground, decreasing the GSHP’s overall performance. Hybrid systems can reduce the imbalanced loads and improve performance. This study proposed the use of personal comfort systems (PCS) and natural ventilation (NV) to decrease the thermal load imbalance in a cooling–dominated building. Building energy simulations were used to assess the performance of eight renewable heating and cooling solutions in three Portuguese cities (Porto, Lisbon and Faro): (1) ASHP, (2) GSHP, (3) ASHP–PCS, (4) GSHP–PCS, (5) ASHP–NV, (6) GSHP–NV, (7) ASHP–PCS–NV, (8) GSHP–PCS–NV. The simulation results show that without hybridization, the use of the GSHP resulted in an increase in ground temperature of more than 20 °C, over 50 years, which decreased its COP and rendered it unable to supply the full cooling load, and may not be acceptable in environmental terms. The use of either PCS or NV for hybrid cooling decreased the thermal cooling load and increased the energy efficiency of the GSHP system relative to the equivalent ASHP–hybrid. However, full coverage of the cooling load was still not always possible, as ground heat build–up was still high. Hybridization with both NV and PCS allowed full coverage of the thermal load by the GSHP. Both the cooling load and final energy needs decreased by over 90%, and the increase in ground temperature was limited to about 6 °C.