Supermarkets and grocery stores represent an important energy-intensive role in the commercial sector. In Japan, grocery stores occupy 8% of energy consumption in the commercial sector. Refrigerated and frozen display cases are widely used in grocery stores and those occupation of energy consumption in a store range from 50% to 67%. In addition, plenty of research illustrated that alterations in humidity and temperature affect the cooling load of display cases. Also, cold air leaking from display cases can influence the cooling and heating load of space conditioners because of affecting room temperature. Furthermore, the cold leakage air does harm to the thermal comfort of stores. Hence, it is essential to explore the interaction between space conditioners and display cases while analyzing energy consumption characteristics and thermal comfort in stores
Although some energy calculation software or methods such as Energy Plus have been used to simulate the energy consumption of space conditioners and display cases in stores in terms of indoor temperature, regarding a store as a temperature completely mixing space leads to a lack of accuracy for the reason of uneven temperature distribution in grocery stores. For the same reason, it is difficult to evaluate the thermal comfort of grocery stores without mastering the temperature distribution. Thus, hardly were energy-saving strategies evaluated in terms of both energy-saving potential and thermal comfort simultaneously.
In this study, focusing on space conditioners and display cases in grocery stores, CFD (Computer Fluid Dynamics), was utilized to try to build a method that can evaluate energy-saving strategies by mastering the indoor temperature distribution influenced by display cases and space conditions.
In the first report, based on a series of experimental results, 5 kinds of display case CFD models were built to imitate their cooling load and low-temperature leakage air in different temperatures or humidity environments. The results of this report are shown below.
(1) Detailed display case CFD models, in which even mock goods in display cases were reproduced, were built based on a series of experiments performed in a laboratory with constant temperature and humidity. And the positive reliability, satisfying the purpose of this study, of them was confirmed.
(2) According to the results obtained from detailed display case CFD models, especially the cooling load of refrigerated display cases can be influenced easily by altering indoor temperature or humidity.
(3) Simplified display case CFD models were built to decrease the computation load while setting them in a large space, for example, a store. Only leakage and influx surface were set in the front of a cube, and the relations between the temperature of influx air and boundary values of these surfaces were obtained from the results of detailed models.
(4) In spite of some bias, the simplified models were able to reproduce the detailed models properly in terms of the temperature space distribution. And the calculation load of computers can be reduced by 44% when replacing a kind of display case detailed model in a large space by the corresponding simplified model.
Above all, by employing the simplified CFD models for building grocery store CFD models, it is possible to evaluate kinds of energy-saving strategies adopted in grocery stores in terms of indoor thermal comfort and energy consumption, for example, altering space conditioners temperature, altering the numbers or types of display cases, and etc.