Anthropogenic heating of the urban environment: An investigation of feedback dynamics between urban micro-climate and decomposed anthropogenic heating from buildings

Cities consume 2/3 of global energy and consequently release a large amount of anthropogenic heat into urban environments, which are already vulnerable to extreme heat risk due to the compounding effects of urban heat island and the warming climate. In this study, we use detailed process-based building energy modeling of over 1.1 million buildings in Los Angeles along with a high-resolution urban micro-climate modeling framework to assess the implications of anthropogenic heating for urban micro-climate dynamics and the feedback process between them. We uniquely distinguish between two major components of anthropogenic heating from HVAC system rejections and exhaust/relief air from buildings. We show that the less-studied anthropogenic heating from building exhaust, compared to that from HVAC systems, is mostly a nocturnal phenomenon with more significant implications for local air temperature due to the lower and more stable planetary boundary layer at night. We demonstrate that anthropogenic heating from HVAC rejection and building exhaust not only have reverse diurnal profiles, they also exhibit offsetting behaviors under increasing outdoor temperatures. Our results show that a detailed understanding of the composition of anthropogenic heating, specific to an urban environment, is required to predict its' diurnal dynamics and its’ response to a warming climate.