A new perspective for understanding actual anthropogenic heat emissions from buildings

Abstract

The magnitude and timing of heat emissions from buildings can be substantially different than the corresponding energy consumption profile. Indeed, the definition of anthropogenic heat needs rethinking if our goal is to understand the role of buildings in heating of the urban environment, and to identify opportunities to reduce that heating. Here, we introduce a new definition of anthropogenic heat emissions from buildings. Specifically, we contend that a more useful definition must compare total sensible heat emissions from a building and its surrounding land with the emissions that would have been generated from the same land without a building. This definition includes convection from all building surfaces, heat emissions from the building air conditioning system, and infiltration/exfiltration of heat. It also considers shading of other buildings and the ground surface. The proposed framework is intended not to replace existing waste heat emissions approaches within atmospheric models, but rather to provide a separate approach for truly understanding the role of building construction, materials, and operations in affecting the urban environment. We implement this framework through urban building energy model simulations to estimate the actual hourly profiles of anthropogenic heat from an archetype office building of 3 different heights in four US cities in varied climate regions. In the summer season, 6 story buildings are responsible for a sensible heating of the environment that is three to four times the magnitude of their energy use. For 2 story buildings 62 to 69% of this sensible heating in summer is due to convection from the roof surface alone, while less than 29% is due to waste heat from air conditioning systems. So, the rooftop surface is twice as important as the building energy use in determining the extent to which a building warms the surrounding environment. These results demonstrate the flawed nature of thinking of anthropogenic heat from buildings solely from the perspective of energy use or emissions from heating and cooling equipment. The proposed framework is of crucial importance in understanding how buildings affect their surrounding thermal environments. Ultimately, it can inform strategies to mitigate heat emissions as it quantifies the role of façade and rooftop construction materials and their thermal and radiative properties.