Numerical analysis on the production of cool exergy by making use of heat capacity of building envelopes

This paper describes a method to calculate cool and warm exergies stored by building envelopes and the result of a case study in terms of passive cooling strategy using the building envelope heat capacity. The concept of exergy enables us to show explicitly the cooling potential of a substance that is colder than its ambient. We call the cooling potential “cool exergy” and the heating potential “warm exergy”. The value of either cool or warm exergy is positive without exception. We made a case study to examine the combined effects of shading and natural ventilation on making a better use of heat capacity of concrete walls for passive cooling during the nighttime in summer in Tokyo. The amount of cool and warm exergies stored by the building envelopes and the variation of their rate of storage were calculated. It was confirmed that the cool exergy could be obtained from the concrete walls even during the daytime of a hot day in summer, provided that an appropriate combination of shading, natural ventilation, and the heat capacity is designed.