Numerical analysis of a ground-source heat-pump system in traditional Japanese “Kyo-machiya” dwellings

Kyo-machiya, which is a traditional wooden dwelling in Kyoto, is generally equipped with a shallow well. The well water can be potentially utilized as a heat source with a geothermal heatpump system without incurring a high drilling cost. Hereby, more energy saving in the traditional dwelling can be realized with the heat-pump system. However, an appropriate technique to utilize geothermal heat from a shallow well has not been established yet in Japan. To promote the geothermal use, we have continued an experiment to evaluate the practicability of a simple geothermal heat-pump system installed in a shallow well since the winter of 2013. In this study, the condition of the water flow in the well was examined using the computational fluid dynamics (CFD) technique, and the velocity of flow of the groundwater into the well was also estimated. We show that constant buoyancy was generated because of the temperature difference due to the heat-pump operation. Based on the results, a three-dimensional heattransfer numerical analysis model, proposed in the previous study, was developed so that moisture transfer in the ground could be considered. Using the estimated buoyancy of the well water and the groundwater velocity, the calculated results seemed to reproduce the characteristic of the measured value. Furthermore, we show that the groundwater velocity has a large influence on the well water temperature.