The Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD)

This chapter shows how Fanger (1970) extended his comfort equation from a method for determining comfort conditions for any combination of air temperature, mean radiant temperature, humidity, relative air velocity, clothing and activity to a method that predicted the mean vote of a large group of people who would be exposed to any combination of those variables. The predicted vote is in terms of a rating on a thermal sensation scale (3, hot; 2, warm; 1, slightly warm; 0, neutral; −1, slightly cool; −2, cool; −3, cold). This is the famous Predicted Mean Vote (PMV) index which is accepted across the world. How to predict the percentage of dissatisfied with that environment (PPD) and the Lowest Possible Percentage of Dissatisfied (LPPD) that could be achieved are also described. The chapter concludes with a discussion of the limitations of the PMV/PPD indices and what the next paradigm shift in thermal comfort will be.