thermal comfort
Definitions according to ASHRAE 55 : thermal comfort: that condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation. predicted mean vote (PMV): an index that predicts the mean value of the thermal sensation votes of a large group of persons on a sensation scaled expressed from -3 to +3
The conditions that provide thermal comfort. It states that there are physiological and psychological variations from person to person so the acceptable thermal conditions are different for everyone (from Appendix E):
There are six primary factors to be considered:
- Metabolic rate (individual) - since someone with a faster metabolic rate can create more heat
- Clothing insulation (individual) - An obvious one, since if someone wearing shorts and someone wearing sweatpants will feel the environment differently
- Air temperature (environment) -
- Radiant temperature (environment) - One that is not always noticed
- Air speed (environment) - Because the more air speed the faster the hot air will get replaced ?
- Humidity (environment) - The one that gets you to the bone
The predicted mean vote (PMV) which is a model that predicts the mean value of the thermal sensation votes of a large group of persons on a sensation scale between -3 to +3:
- -3: cold
- -2: cool
- -1: slightly cool
- 0: neutral
- +1: slightly warm
- +2: warm
- +3: hot
Note: If you are interested, the document provides a JavaScript code to calculate the PMV! Look for “NORMATIVE APPENDIX B”
The whole document is well worth a read!