Study on High-Efficiency Heat Source System Using Thermal Storage

<p>In this study, we proposed a high-efficiency heat source system using a thermal storage system that stably improves the efficiency by providing a condition with low energy consumption with INV equipment using thermal storage. We proposed a method to reduce the pump and refrigerator heads of INV equipment and to increase the efficiency by using pipes and equipment that are not operated during thermal storage and with a low load of multiple channels. In addition ,we have proposed a heat source system with high-efficiency thermal storage that stably improves the efficiency by providing a condition with low energy consumption by INV equipment using thermal storage. We examined the method for calculating the partial load characteristics of the refrigerator based on the cooling water outlet temperature, which can be linearly regressed with high accuracy. Although it is clear that changing the flow rate of auxiliary equipment has a great energy-saving effect, it is necessary to pay attention to the reduction in efficiency at low rotational speeds. Further, we demonstrated this effect by the heat source operation that could be performed without a decrease in efficiency at a certain head and flow rate at the time of thermal storage. Although the cooling water variable flow has the disadvantage of increasing the chiller power, it is effective in reducing the cooling water pump power, and it has been shown that comparing the variable flow with the constant flow reduces the system efficiency and the energy saving capacity. The method and effect of operating with a reduced pump head at a low flow rate in a thermal storage are described. As a method to saving energy in multiple flow paths, we have proposed “Divided Double Flow System (DDF)” and “Divided Multiple Flow System (DMF)”. We showed an improvement in efficiency when the cooling water temperature in the INV refrigerator was lowered, and we proposed to operate at a lower cooling water temperature for the thermal storage that provides a stable load. We proposed the effect prediction control as a control method to lower the cooling water temperature, and the possibility of the effect of the over-cooling of the cooling tower was shown. It was confirmed by the annual simulation that the proposed energy-saving thermal storage system could be a high-efficiency heat source system exceeding 2.6 with the annual primary system COP (conversion factor 9.76MJ/kWh). We showed that the proposed system could be applied gradually to existing thermal storage tanks by means of retrofitting. It is necessary to carry out this study for actual operation and to develop equipment for high-efficiency thermal storage.</p>