Optimum Operation of the Open-loop Systems of Ground Source Heat Pump by the Controlled Pumping Water Flow Rate

Abstract

In the open-loop systems of the ground source heat pump, the decrease of pumping water flow rate enables to lower its power consumption as the air conditioning load decreases, so that it’s SCOP is improved than the constant rate of pumping water. The pumping water flow rate can be controlled by the temperature difference between inlet and outlet pumping water (hereinafter referred to as GW⊿T) in the heat exchanger, between the pumping water and the heat pump, to be consistent. The optimum GW⊿T would be different depending on the air conditioning load pattern and the pumping water conditions such as temperature and water level of where the system installed. The purpose of this study is to estimate the value of SCOP at a certain GW⊿T and verify it with demonstration experiment systems so that the optimum GW⊿T can be estimated in any system. We conducted the demonstration experiment at three sites; Gifu, Yokkaichi, and Nagoya, where the air conditioning load and pumping water conditions are different. The calculated SCOP comes from the estimated power consumptions of the heat pump and groundwater pump. The former is calculated by the pumping water temperature, the capacity and power consumption of heat pump including partial load conditions, and the heat output to primary side of heat pump system. The latter is by the relationship between power consumption of groundwater pump and pumping water flow rate. The measured SCOP comes from demonstration experiments in the several GW⊿T at the three sites and monitoring the capacity and power consumption of the heat pump and the power consumption of the groundwater pump. The calculated SCOPs with the change in GW⊿T have similar tendencies to the measured ones at each site. The difference of the optimum GW⊿T between the calculated and measured SCOPs is within 2 K at each site. This result shows that it is possible to estimate the optimum value of GW⊿T at the design stage based on air conditioning load pattern, groundwater temperature and water level.