Energy‐Saving Effect of Hot Water Supply Preheating System That Utilizes Unused Wells in Traditional Japanese Houses

ABSTRACT It is expected that unused wells in traditional Japanese houses can be utilized to save energy. In this paper, we examine a hot water supply preheating system that utilizes unused wells in traditional Japanese houses. In this system, the pipe supplying water to the water heater passes through the well water and is preheated by heat exchange with it. We show the results of measuring the well‐water temperature in an actual well for a period of 1 year and propose a method for estimating the well‐water temperature. Furthermore, we show the results of a heat exchange experiment in the actual well and propose a method for estimating the temperature change of water passing through a coil used for the heat exchange. Finally, using methods of estimating the well‐water temperature and the temperature change of water passing through the coil, we estimate the rates of reduction in energy needed to supply hot water via this system when the preheated water supply is heated to 50°C–60°C by this system, as opposed to the case where the unpreheated water supply is heated to 50°C–60°C. These reduction rates are about 7%–17%, depending on the flow rate and the coil length.