The comfort and energy impact of overcooled buildings in warm climates

Abstract

Around 18% of global carbon emissions can be attributed to building heating or cooling, driven by the adoption of “international” thermal comfort standards such as ASHRAE-55, which imply an homogenous indoor environment. We argue that the importation of such standards to warm climates results in indoor cold discomfort due to “overcooling”: a phenomenon anecdotally recognised worldwide but not studied or defined systematically. Unlike under- or over-heating, overcooling is the purposeful over-expenditure of energy, that creates conditions of cold thermal discomfort. We examine data for warm and temperate climates from a global thermal comfort database spanning 27 countries with over 90,000 occupant responses to investigate overcooling of air-conditioned buildings. We suggest that overcooling is best defined by taking the intersection of thermal sensation and preference and, using this definition, we find that 17% of building occupants in the examined data can be classed as being overcooled. We estimate the cooling energy demand of overcooling imposed through the adoption of the ASHRAE-55 standard using computer simulations that move building occupants from being overcooled to comfortable. The results suggest around 15% of cooling energy demand could be saved through a simple upward adjustment of set-point temperatures by 2 °C in warm climates. Such an adjustment in the Global South, which contains the majority of the warm regions of the Earth, could have a dramatic impact on the evolution of future cooling energy demand which is expected to triple by 2050.