The Comfort Zone
Learning Objectives - After this course, you should be able to:
- Explain the difference between the conventional and adaptive theories of thermal comfort.
- List the variables that affect adaptive thermal comfort.
- Understand when ASHRAE Standard 55's optional method for determining acceptable thermal conditions in naturally ventilated spaces is applicable.
- Discuss the range of research that still needs to be undertaken to optimize thermal comfort.
Prior to the age of cheap fuel, the model now known as "adaptive thermal comfort" was the rule: In warmer weather people logically opened up windows to increase air circulation and, in certain cultures, during the hottest part of the day. In cooler weather, families huddled closer together, limiting the rooms they needed to heat, and individuals added extra layers of clothing.
According to Michael A. Humphreys, emeritus professor of architecture at the School of the Built Environment at Oxford Brookes University in Oxford, UK, and an early pioneer in the field of adaptive thermal comfort, "100 years ago a wealthy London gentleman would have considered an inside temperature of 15ÂºC (60ÂºF) to be comfortable in winter," because his normal attire on a cold day would include long johns, under-vest, thick flannel shirt, waist coat, and lined jacket and trousers. In short, the adaptive thermal comfort model describes the age-old situation in which people naturally and incrementally adjusted to the typical variations in temperature associated with their region through behavioral modifications and variable expectations and preferences.
During the 20th century, at least in the most highly developed countries, new technologies running on seemingly abundant fossil fuels led to a built environment that was increasingly disconnected from the outdoors. This, coupled with new research into thermal comfort and the standards that evolved from such research, created the expectation of a fairly constant and narrow range of indoor temperatures year-round among building occupants in industrialized countries.
Illustrations by Headcase