The range of temperatures over which the majority of persons feel comfortable (neither too hot nor too cold).
The ranges of indoor temperature, humidity, and air movement, under which most persons enjoy mental and physical well-being.
As represented on comfort charts of the American Society of Heating and Air Conditioning Engineers, comfort zones are areas bounded by curves of effective temperature and relative humidity. The limiting conditions vary somewhat according to season and to the native climate of the person or group. In the United States the comfort zone with normal ventilation lies between air temperatures of about 17° and 24°C (63° and 75°F) at a relative humidity of 70%, and 19°C (67°F) at a relative humidity of 30%, giving an effective temperature within a few degrees of 19°C (67°F). The limits, however, vary with the season, being higher in summer than in winter. In the United Kingdom, the comfort zone is centered on an effective temperature of about 16°C (60°F). In the Tropics the comfort zone lies between the same limits of relative humidity, but at air temperatures around 26°C (78°F).
Comfort Zone has been defined 3 different ways in documents like Glossary of Terms, Glossary of Energy Terms, Glossary of Meteorological Terms.