Development of groundwater circulation heat pump system

In general, water pumped from a well used in a groundwater heat pump (GWHP) system is discharged to the well or the other wells. However, long-term pumping and injection may cause clogging of the wells, which is a major problem encountered when injecting groundwater into a well. Reverse circulation has been proposed as a solution to this problem, but this only results in temporary improvement of the injection efficiency and is not a permanent solution. With the aim of reducing the environment load and conserving groundwater resources, a groundwater circulation heat pump system was developed that is well suited for long-term use. This article provides an overview of the system and the results of real-scale experiments carried out at two sites (Chiba and Nagoya, Japan). These experiments have been conducted to evaluate the heating and cooling performance of the system. The system used at the Chiba site is equipped with two submersible pumps and two wells because of the deep groundwater level (-11 m (36 ft) G. L.). However, in the system at the Nagoya site, where the groundwater level is -4 m (13 ft) G.L., a land pump and a single well (for both production and injection) are used. Results show that the coefficient of performance (COP) of the groundwater heat pump is higher than that of the air-source heat pump. Furthermore, an automatic reverse circulation system was introduced that prevents clogging of the return well. Also, the effectiveness of a packer is confirmed for preventing short circuiting of the temperature in the aquifer in the case of the single well system. Finally, it is concluded that a small pumping rate and large temperature difference are very effective for reducing pumping-energy consumption and improving the coefficient of performance.