The Modal Comfort Envelope and its Use in Current Standards

Abstract

A detailed study of thermal comfort was conducted by exposing 1600 subjects, in groups of 10 subjects each (5 men and 5 women), to 20 dry bulb temperatures at each of eight relative humidities (160 tests). From this study, 15 temperature-humidity conditions were selected (ET: 75.9-79.7°F) and identified as the Modal Comfort Envelope (MCE). Within this envelope 94% of the subjects were either slightly cool, comfortable, or slightly warm; 3% were cool and 3% were warm; and none were hot or cold. To validate these findings, a new sample of 150 subjects was tested and the results of this test agree favorably with the original findings. The MCE was used in a clothing study and in an investigation of thermal comfort in the elderly; the results of these studies are discussed, together with suggestions for the use of the Modal Comfort Envelope, as a tool for examining the thermal sensation as a function of such non-thermal factors as lighting, subject density, sex, and activity. A slightly modified version of the MCE is currently being used as a standard for thermal comfort by ASHRAE and this is examined together with ASHRAE Comfort Standard 55–66, the New ASHRAE Comfort Chart, and the new Effective Temperature Scale.