Evaluation of the Passive Cooling Potential of Mass Inherent in Medium to Large Commercial Buildings

Abstract

While the literature on thermal mass and passive cooling is rich, what it means for a building to be thermally massive is not well defined or consistently applied. Most research has been conducted with mass depths far greater than would be seen in typical construction.  Meanwhile, some research suggests that because the heat transfer rate at the surface is limited, the focus should be on surface area of exposed mass. Since even lightweight commercial construction typically has large surface areas of mass in the floor slabs, this research investigates how effective that mass is for passive cooling, relative to other mass depths. In all climates analyzed it was found that there was a pronounced shoulder where energy savings from passive cooling of increasing mass depths was steep until roughly 7.5 cm to 10 cm, and thereafter the energy savings diminished rapidly. When considering the embodied energy of concrete, the incremental benefit of added mass beyond a typical topping slab of 10 cm does not justify the incremental embodied energy cost from an energy standpoint alone, unless a very long embodied energy payback period was adopted.