Predicted mean vote
The predicted mean vote (PMV) was developed by Povl Ole Fanger at Kansas State University and the Technical University of Denmark as an empirical fit to the human sensation of thermal comfort. It was later adopted as an ISO standard. It predicts the average vote of a large group of people on the a seven-point thermal sensation scale where:
- +3 = hot
- +2 = warm
- +1 = slightly warm
- 0 = neutral
- -1 = slightly cool
- -2 = cool
- -3 = cold
The properties measured and the maths required to create the empirical fit are very complicated, based on the deviation between heat loss and metabolic rate, and the equations generated only apply under constant conditions and at constant metabolic rates. However, as the conditions within the built environment will generally be within a small range, and the clothing, metabolic rates and so on of occupants can be predicted, standards have been produced indicating thermal conditions that will give a satisfactory predicted mean vote. For example, the ASHRAE Standard 55 Comfort Zone represents a predicted mean vote of of between -0.5 and +0.5 for buildings where the occupants have metabolic rates of between 1.0 met and 1.3 met and clothing provides between 0.5 clo and 1.0 clo of thermal insulation.
Fanger extended his concept to allow estimation of the predicted percent of dissatisfied people (PPD). The PPD increases as the predicted mean vote moves away from zero in either direction.
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