Abstract
Introduction
In cold climate area, the number of houses with high energy efficiency and high airtightness continues to increase. Most of the heating loads for such houses are caused by fresh air which has large temperature differences. Reducing ventilation load, preheating is effective with natural resources. Therefore, in this research, we aim to develop a preheating system for ventilation combining a solar thermal collector and a heat storage. Initially, we verified PCM panels for mounting in a heat storage. Next, we made a numerical model related to the heat storage. Finally, we investigated the performance of multilayer thermal storage using PCM panels and the availability of this system using the numerical model.
Thermal Heat Storage System with PCM Panel
Warm air heated in solar thermal collector flow into the heat storage chamber in which one PCM panel shown in Figs. 4, 5, and 6 was installed, and the heat was stored in the PCM panel. After heat storage periods, the cold fresh air flow into the heated heat storage chamber, and heat exchange is carried out by passing the cold air through the PCM panel. Figures 8, 9, and 10 show the measurement results of inlet temperature and outlet temperature during the procedure. The difference between the inlet temperature and the outlet temperature shows the effect of heat storage and preheating.
Numerical Model Outline
Based on the experimental results of the above system, we made a numerical model and verified the consistency between the experimental value of the exit temperature and the analytical value. The numerical models are shown in equations (1), (2) and (3). Based on the comparison of the experimental value and analysis value shown in Fig. 12 and the result of RMSE shown in Table 4, we judged that the model had enough consistency.
Analysis of Cascade System and Conclusion
In order to expand a range of the heat storage temperature and increase the PCM weight per installation area, PCM panels in the heat storage chamber were arranged at a certain interval. In addition, we changed the combination of melting points of PCM panels and investigated the influence of the range of the heat storage temperature. In this analysis, the solar radiation and the outside air temperature obtained from the standard weather data were used through the system, the room air warmed by the solar air collector flows into the heat storage chamber during the day, and outside fresh air was heated by heat storage chamber before it flows into the room. The findings obtained by this analysis are shown below.
(1) According to the results showing in Fig. 14 and 15, no significant difference between the inlet temperature and outlet temperature was confirmed regardless of the change in the heat storage temperature.
(2) According to the results showing in Fig. 16, 17 and 18, the distribution of outlet temperature from the heat storage chamber and the radiation time had the difference at the range from 15 to 30 °C.
(3) No significant difference was observed in the distribution and the total heat dissipation in typical one week shown in Figs. 19 and 20.
