Cities consume over 75 percent of global energy and inevitably release a large amount of heat waste into urban environments which threatens environmental and human health by enhancing rising temperatures and heat risks in urban areas. To understand how waste heat can impact a city’s climate during a heatwave, researchers modeled waste heat emitted from over 1 million buildings in Los Angeles. The results showed that waste heat from heating, ventilation and air conditioning (HVAC) systems, as well as building exhaust, increased temperatures, particularly during the evening and night hours, by as much as 1.3 °C.
Studying the heating effects of human activity and development is essential to predicting and addressing the impact of rising temperatures in cities. This research can equip scientists and urban planners with a better understanding of waste heat’s role in enhancing heat risk in cities. The researchers show that heat emitted from HVAC systems is only one component in the complex heating profile of a city caused by human activity. Additionally, buildings release a comparable amount of waste heat through ventilation and exhaust with a distinct heat profile. This study provides a roadmap to predicting the composition of waste heat in an urban environment, and its role in urban climate dynamics under extreme heat conditions like heatwaves.
Cities account for a majority of global energy consumption – inevitably, buildings and vehicles emit waste heat, resulting in rising urban temperatures and enhanced environmental and human health risks. As temperatures increase due to climate change, demand for cooling systems increases. This results in a positive feedback loop where HVAC systems and buildings consume more energy and in turn release more waste heat that further increases temperatures. The researchers modeled the effects of heat emitted from buildings in Los Angeles and how they contribute to rising temperatures. They showed that the heat emitted from building exhaust compared to HVAC systems led to different heating effects that are mostly nocturnal. This information enhances knowledge needed to address heat emissions as global temperatures and energy consumption increase with climate change.