Experimental investigation of a ground-source heat pump system for greenhouse heating-cooling

One of the important heating criteria of a greenhouse in the Northern hemisphere countries is heat availability, particularly in the winter season. Among other heat storage types, seasonal soil-based energy storage performance is auspicious. However, the performance is affected by the length and depth of borehole pipes used, which are very expensive for growers. Therefore, this study investigates the performance of a shallow seasonal soil-based energy storage heat pump, in a greenhouse. Thick insulations were installed to reduce soil heat loss. The soil thermal imbalance ratio was calculated to know the thermal recovery resulted. Based on the results, the heat pump's seasonal coefficient of performance (COP) heating and cooling varied between 1.48-2.97 and 1.20-3.45, respectively. The COPsys heating and cooling were observed to be 1.51 and 1.55, respectively. However, the system successfully maintained indoor temperature >16 degrees C in other seasons, except for winter. Due to low brine input in winter, the average indoor temperature dropped to 11 degrees C, indicating a thermal soil property problem. Moreover, the proposed system achieved soil thermal imbalance ratio of 32.76%.