Comfort is in the mind of the beholder: a review of progress in adaptive thermal comfort research over the past two decades

The classic or deterministic understanding of thermal comfort contends that it is driven exclusively by the physics of the body’s heat exchange with its immediate thermal environment. But in recent decades there has been widespread recognition that a person’s thermal history and adaptation level, including behavioral, physiological and psychological processes operating on various timescales, also influence whether indoor climatic conditions will be deemed comfortable and acceptable, or not, as the case may be. This contextual view of the comfort construct is referred to as the adaptive model, and its empirical basis is an extensive body of field studies conducted in diverse occupancy and building types located across a broad cross-section of the world’s climate zones. The basic research design of the comfort field study consists of paired observations of objective indoor climatic parameters and their subjective evaluation by building occupants using comfort rating scales. The first global adaptive comfort standard, ratified by ASHRAE in 2004, was based on a statistical analysis of approximately 21,000 complete sets of objective indoor climatic observations and their “right-here-right-now” subjective evaluations by the building occupants who were exposed to them. Over a decade has elapsed since ASHRAE Standard 55-2004 was published and since then there has been an escalation in adaptive comfort field research activity around the world. Recently ASHRAE’s thermal comfort technical committee (TC 2.1), in collaboration with the International Energy Agency (Annex 69), have taken on the challenge of systematically collating and harmonizing the raw data collected in recent comfort field studies from around the world into an expanded, quality-assured database. When the project is completed this public-domain resource will underpin myriad inquiries by the thermal comfort community, researchers and practitioners alike. The aim of this presentation is to describe the DB-II proj