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

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 degrees 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. (C) 2019 Elsevier B.V. All rights reserved.