Control methods for a direct-ground cooling system: An experimental study on office cooling with ground-coupled ceiling cooling panels

Abstract

This article experimentally investigates the performance of two control methods (the supply water temperature method and the water flow control method) for a direct-ground cooling system. The control methods were implemented through three types of indoor feedback controllers: 1) an on/off controller, 2) an on/off controller with a deadband and 3) P controller. The performances of the control methods were evaluated regarding room temperature stability and pump energy use. Ceiling cooling panels were employed to keep the test room air temperature at 25.0 °C under periodic heat gain conditions. The cooling system used a ground heat exchanger with a U-pipe in an 80-meter-deep borehole as a cooling source. The findings show that room air temperature was maintained close to the set-point with both control methods, but it was more stable with the temperature control method. In addition, condensation risk was easily preventable with the temperature control method. A parametric study showed that pump energy use when using two-position controllers could be as low as when using modulating controllers if the on-state flow rate of the circulating pump is selected in relation to the ground temperature and heat transfer characteristics of the heat exchanger.