Risks of summertime extreme thermal conditions in buildings as a result of climate change and exacerbation of urban heat islands

• Under nominal AC operations, climate change minimally affects indoor comfort.
• Indoor air temperatures can rise well above ambient conditions when AC fails.
• Coincident climate change and equipment failure results in very poor indoor comfort.
• Maximum summer indoor air temperatures can increase by 10–14 °C when AC fails.

This study explores the role of global and local warming on indoor thermal environments of representative buildings in two warm climate cities in the U.S. (Chicago IL, and Houston TX). It uses downscaled climate change scenarios to drive whole-building model simulations of representative apartment buildings. Simulations were conducted under (a) current conditions; (b) conditions that include a global warming effect; and (c) conditions that include global warming with concurrent intensification of the urban heat island. Building thermal conditions are assessed for typical operating conditions, for conditions associated with failure of cooling equipment, and for complete power loss during a heat wave.Simulations show that warming by itself may have minimal effects on indoor thermal comfort in summer. For example, in Houston the Predicted Percent Dissatisfied (PPD) comfort metric was approximately 5–6% for current and future climate scenarios under normal operating conditions. Under conditions of AC failure, however, this increased to 61.9% for the current climate and 71.4% for the 2050 climate. In the case of Chicago PPD was between 6.2% and 7.9% for all climate scenarios when equipment operated normally. Under conditions of equipment failure, however, PPD increased to 34.1% for the current climate and 39.2% for the 2050 climate. In simulations for both cities, a complete power failure resulted in peak temperatures that were approximately 2 °C cooler than the case of AC failure only. This is due to reduction in internal gains during a power blackout.