Comparative analysis of PMV Models accuracy implemented in the ISO 7730:2005 and ASHRAE 55:2023

Abstract

The Predicted Mean Vote (PMV) model, developed by Fanger, is included in the ISO 7730:2005. It has a low prediction accuracy, especially outside thermal neutrality. Several other formulations have been proposed to compensate for its limitations. One is the PMV calculated in accordance with the ASHRAE 55:2023 (PMV CE ) standard. The ISO 7730:2005 and ASHRAE 55:2023 are the most widely referenced thermal comfort standards worldwide, hence, we compared the accuracy of the two PMV models, against 49 245 thermal sensation votes collected in buildings. We found that overall both models only predict Thermal Sensation Vote (TSV) correctly only one-third of the time. The PMV CE has a higher bias than PMV in predicting thermal sensation in the subset of data with relative air speed ≥ 0.2 m/s. Both models have an accuracy lower or equal to 5% when predicting either ‘warm’, ‘hot’, or ‘cold’. This value is lower than random guessing (14%), meaning they are misleading users. A PMV value higher than 0.5 or lower than -0.5 only indicates that people’s thermal sensation is on the ‘warm’ or ‘cold’ side, respectively. Hence, we suggest reducing the applicability limit of both models within the range ∣ PMV ∣ ≤ 0 . 5 . Finally, the assumption that individuals who feel ‘slightly warm’ or ‘slightly cool’ can be considered thermally neutral leads to under-counting thermal discomfort. In the ASHRAE Global Thermal Comfort Database II, 68% of participants who were ‘slightly warm’ wanted to be ‘cooler’ and 54% of participants who were ‘slightly cool’ wanted to be ‘warmer’. • We compared the accuracy of the PMV models in ISO 7730:2005 and ASHRAE 55:2023. • Both models have low and similar prediction accuracy (PMV = 32% – PMV CE = 34%). • The PMV CE has a higher bias than PMV in predicting thermal sensation. • We recommend limiting the applicability range of the models to ∣ PMV ∣ ≤ 0 . 5 . • It is misleading to classify slightly warm/cool individuals as thermally comfortable.

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