In earlier studies, we developed a PCM-plastered wall, which is a novel finishing material with a high thermal storage capacity. In addition, previous experiments by our research group have shown that the PCM-plastered wall significantly improves indoor environments and saves energy when an experimental module is used. In the present study, we developed a radiant heating－cooling hybrid system shown in Fig. 1 and measured its thermal performance. The indoor environment and the amount of energy saved from two experimental housings were also measured.
 First, as shown in Photo1 and Fig. 2, we constructed the hybrid system by combining a PCM-plastered wall and capillary tubing mats. We proposed a method for using the new system that combines natural energy for the effective use of the PCM through the application of a thin tube, which increases the contact area. In the summer, the system is used with a geothermal coil, whereas in the winter, solar heat obtained via a solar collector is effectively used. Fig. 3 depicts the renewable energy utilization.
 In the basic thermal performance test, the experimental device was installed in a room thermostat, and hot water from the refrigerant was circulated using a pump (Photo 3, Fig. 4 and Fig. 5). The temperature of the water, the surface temperature of the front and back of the PCM, and the surface heat flow on the PCM layer were measured in one-minute intervals (Fig. 6 and Fig. 7). The heat dissipation ability of the prototype was calculated from the difference between hot water and room temperatures, as shown in Fig. 8 to Fig. 10 and in Table1.
 Next, the basic thermal performance was tested using a geothermal coil to measure the heat storage and the temperature distribution of the soil. Photo 4 and Fig. 11 show the test device, which is a polyethylene pipe and a sensor installed inside the soil and covered with a heat insulating material. As shown in Table 2 and Fig. 12, the temperature was measured by a thermocouple, and an analysis was conducted by calculating two-dimensional non-steady heat conduction. Fig. 13 shows the temperature of the water, which was approximated by a sixth-order polynomial. Measurements results and analysis data were indicated that a position close to the pipe (30mm) was approximately the same (Fig. 14). All of the values approximately match after 30 hours.
 Finally, the energy savings and indoor environments were measured on the two experimental housings. The two buildings installed the hybrid system and geothermal coil. Table3 gives an overview of the experimental housing. The system diagram is shown in Fig. 16. Water is used as the refrigerant, and the heat source is a heat pump unit. The solar collector would be a secondary construction. One building is used by the office, and the other is a model house. Both buildings are in Sapporo, Hokkaido and plans for these buildings are shown in Fig. 17 and Fig. 18.
 In the summer, the room temperature of the N-project was stable and near the PCM melting point (Fig. 19). Even when the outside temperature reached 35 °C, P-project's room temperature remained approximately 26 °C. Therefore, it was confirmed that it had the cooling capacity required during the summer in Hokkaido (Fig. 20 and Table4). In the winter, the heating required for the experimental house is generally reduced to between 4% and 6% of the high thermal insulation and the significantly airtight house. It also demonstrated the reduction of the heating period. Furthermore, as shown in Fig. 21, Fig. 22, and Table5, there was a demonstrated decrease in heating. We confirmed, as shown by the graphs in Fig. 23 and Fig. 24, that the equivalent heat loss coefficient decreases owing to the PCM-plastered wall.

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