STUDY ON ENERGY CONSUMPTION OF A GROCERY STORE (PART2): CALCULATION OF COOLING LOAD AND REFRIGERATOR POWER CONSUMPTION USING DISPLAY CASE COOLING CHARACTERISTICS

Abstract

　From changes in Japan's final energy consumption, the overall increase rate from 1973 to 2013 was 1.2 times, but the increase in business divisions 2.4 times, so that energy saving is required.

　Refrigeration equipment with a high energy consumption density is exposed to cost competition in the food store industry, so that energy-saving equipment is slow to spread. Therefore, it is important to save energy by devising operation and design.

　Many open display cases are installed in grocery stores because of their availability. The open display case maintains the internal temperature with an air curtain, but cold air in the refrigerator leaks from the display case from a part of the air curtain, affecting the air enthalpy in the store and deteriorating comfort. At the same time, the air enthalpy that enters the display case affects the freezing load of the display case. For these reasons, the load of the open type display case interacts with the load of space conditioning, and it is difficult to think about energy saving.

　In this study, we will devise a method to give the enthalpy of the intrusion air into the SC considering the amount of heat leaked from the SC. The SC refrigeration load is calculated by combining the enthalpy of the air entering the SC and various SC characteristics obtained from the experiment. Furthermore, by combining with air conditioning load calculation, store air conditioning, ventilation, and SC energy consumption are calculated, and the impact of various energy saving measures on store energy consumption is clarified.

　In this report (2nd report), the enthalpy characteristic formulas of total heat and latent heat of SC shown in the first report were used to examine the method of predicting the SC load and refrigerator power consumption of actual stores. At the same time, the validity of the calculation model was evaluated by comparing the calculation result of the power consumption of the refrigerator with the energy consumption of the actual store.

　We also devised a method for calculating the amount of heat leaked from the SC to the store and evaluated its validity by comparing it with the calculation results of the building cooling load in the interim period.

1.　From the results of the constant temperature and humidity experiment, the maximum load, stable load, rise time, and stable time were expressed as functions of in-store enthalpy, and the load change of each SC including defrost was modeled. Each SC model was combined to create an SC load calculation formula for the entire store. At the same time, we devised a method to calculate the sensible heat and latent heat leaked into the store by using the enthalpy characteristics of the sensible heat ratio of SC.

2.　The SC load was calculated using the in-store air enthalpy, and the power consumption of the refrigerator was predicted using the SC load and the measured outside air temperature. Comparing the predicted value and the measured value, the error during the daytime in summer when the power consumption is large was within 10%, which was almost reproducible. However, some SCs may be stopped at night, but they are not reflected in the calculation, so the calculated value is about 20% larger than the measured value.