Thermal Comfort

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ASHRAE Model of Thermal Comfort

The American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) indicates that thermal comfort as a set of building thermal conditions that, when implemented, will satisfy 80% of occupants. Thermal comfort is affected by many factors including heat conduction, convection, radiation, and evaporative heat loss; factors that help determine “comfort” are personal factors such as metabolism and clothing as well as environmental factors such as air temperature, relative humidity, and air movement/velocity. Thus, thermal comfort is not dependent on air temperature alone. The ASHRAE standard for thermal comfort is fairly narrow, and still does not satisfy up to 20% of building occupants. This static definition of thermal comfort indicates that air temperature and comfort does not depend on outdoor air temperature or seasons. That is, it states that one set of conditions should be comfortable for most people all year round.


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Lead Author(s): Heather Burpee

Adaptive Models of Thermal Comfort

Adaptive models of thermal comfort take into account that variable conditions that relate to outside temperature and conditions can shift what is perceived as comfortable. It considers that people can adapt to different sets of thermal circumstances depending on what the weather is like outside. For example, in the summer, warmer temperatures may be more tolerable indoors and cooler temperatures may be more acceptable in the winter. Adaptive models of comfort also take into consideration that occupants of buildings who have more control over their thermal environment may be more likely to accept a wider range of temperature and thermal conditions. Research has shown that occupants in naturally ventilated buildings accept (and prefer) a wider temperature range than do occupants of fully mechanically conditioned buildings.

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Lead Author(s): Heather Burpee

Effects on Energy

This widened comfort range has a direct relation to energy use in buildings. Conditioning the air temperature of buildings mechanically uses a significant amount of energy. Widening the temperature comfort range can decrease the amount of mechanical modification of the airflow that is required. Secondly, utilizing natural ventilation can significantly decrease or eliminate the amount of mechanical heating and cooling all together.

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Lead Author(s): Heather Burpee

Effects of Envelope

Perception of comfort can be significantly changed when environmental factors such as direct solar radiation (short-wave radiation) enters the building envelope. An occupant that is washed with a ray of sunlight will feel significantly different than another occupant that is not in direct sunlight in the same building at the same interior temperature. Similarly, direct radiation off of windows (long-wave radiation), heat in the summer and coolness in the winter, can significantly affect an occupant’s sense of comfort. These factors suggest that control of solar radiation and radiant air flow near the envelope is important to satisfy occupant thermal comfort criteria.

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Lead Author(s): Heather Burpee

Page Key Resources
  • Boyce, P., Hunter, C., Howlett, O. (2003). The benefits of daylight through windows. Troy (NY): Lighting Research Center.
  • Brager, G., and G. Paliaga. (2004). Operable Windows, Personal Control, and Occupant Comfort. ASHRAE Transactions 2004, Vol 110, Part 2.
  • Huizenga, C., Zhang, H., Mattelaer, P., Yu, T., Arens, E, and Lyons, P. (2006). \ Window Performance for Human Thermal Comfort. Final Report to the National Fenestration Rating Council. Center for the Built Environment, Berkeley and ARUP, Melbourne Australia.
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