Thermal comfort in practice

Since the early twentieth century when air-conditioning began penetrating the market in a serious way, there has been a need for human factors research upon which HVAC engineering practice could be based. Now we have nearly a century of thermal comfort research from climate chambers and much has been learnt in that time. By stripping the research problem back to essential cause-and-effect variables, climate chamber methods have delivered results that are amenable to rigorous data analyses leading to unequivocal conclusions. However, in the minds of HVAC practitioners there are persistent doubts about the experiential realism of the chamber methodology, and the external validity of their findings, in particular, their relevance to building occupants going about their normal daily routines in fully-engineered indoor climatic environments. In response to this methodological concern in the 1990s, ASHRAE commissioned a series of thermal comfort studies aimed at field validating the findings of climate chamber research and the HVAC standards based upon them in a variety of climatic contexts around the world. This paper discusses the methodological benefits and constraints of conventional climate chamber research in comparison to the field-based alternative. In particular, issues such as sample size and demographics, research design, instrumentation and indoor climatic measurement procedures, questionnaires, clothing insulation and metabolic rate assessment techniques are analyzed. The discussion of methodology is then extended to the discipline of environmental psychology, which should have made a much more significant contribution to the topic of thermal comfort, and yet has remained relatively silent. The paper finishes by considering why engineers, most notably P.O. Fanger, have come to dominate a research topic that falls so clearly within the scope of psychology. HVAC engineering is the profession most directly occupied in the practice of thermal comfort, and therefore an engineer such as Fanger has been ideally qualified to design and conduct research, and even more important, presents its results in a way most directly useful to thermal comfort practitioners.

The paper gives practical advice on evaluating and designing for thermal comfort.