Cooling mode experimental analysis of a direct expansion geothermal heat pump with a control depending on the discharge pressure

Highlights: • A specific control depending to the discharge pressure have been implemented. • DXGHP performance has been improved. • Performance analysis in cooling mode of the DXGHP have been performed. • Oscillations zones and operating limit zone have been identify. -- Abstract: This work presents an experimental study of a direct expansion geothermal heat pump in cooling mode. The three geothermal loops are installed in parallel. To improve the system performance, a specific control depending on the discharge pressure was implemented to select the geothermal loops to serve as condensers. The fundamental question is whether this particular heat pump can operate continuously? So the goal was to determine the operating limits in order to develop the best strategies for the most efficient use of this recent geothermal heat pump. The analysis of experimental results enabled us to reach a maximum of 12 h continuous for this heat pump with the implemented control. During this optimal period of operation, the coefficient of performance reaches an average of 2.60 with maximum values of up to 3.40. The average cooling capacity is 9.60 kW for an average ground heat rejection rate of about 290.8 W m⁻¹. Beyond this period, the performance of the DX GHP decreases and some phenomena like the oscillation loop, soil saturation, were identified and presented. The experimental results allowed also generally reveal that the controls implemented promotes geothermal loops cooling and helps increase the performance of the DX GHP. This article represents a logical continuation of our previous published study on heating mode.