Abstract
In most countries, PMV is the reference index for the assessment of thermal comfort conditions in mechanically conditioned environments. It is also the basis to settle input values of the operative temperature for heating and cooling load calculations, sizing of equipment, and energy calculations according to EN 16798-1 and 16798-2 Standards. Over the years, great effort has been spent to study the reliability of PMV, whereas few investigations were addressed to its calculation. To study this issue, the most significant apps devoted to its calculation have been compared with a reference software compliant with EN ISO 7730 and the well-known ASHRAE Thermal Comfort Tool. It has been revealed that only few apps consider all six variables responsible for the thermal comfort. Relative air velocity is not considered by ASHRAE Thermal Comfort Tool and, finally, the correction of basic insulation values due to body movements introduced by EN ISO 7730 and EN ISO 9920 Standards has only been considered in one case. This implies that most software and apps for the calculation of PMV index should be used with special care, especially by unexperienced users. This applies to both research and application fields.
Highlights
In case of the app E, which returns only the PPD and the sign of the thermal sensation, the PMV has been calculated from the standard equation [7,9]: PPD = 100 − 95 · exp −0.3353PMV 4 − 0.2179PMV 2 (4)
Tool and web app are in agreement with each other only when the effects of the body contribution of the air boundary layer to the total clothing insulation is less significant)
Software for the evaluation of thermal comfort conditions by means of PMV index, presently on the market, have to be used with special care. This is for software designed by Academics and posted on Universities web pages in the absence of clear specifications for input values
Summary
The building stock in the world uses approximately 40% of the total energy and it is responsible for one third of the global greenhouse gases emissions [1,2]. Several studies have been undertaken to highlight the limitations of PMV in predicting thermal comfort conditions in naturally ventilated buildings (and in hot and humid climates) where adaptation phenomena have to be considered Despite this interest that has led to the formulation of modified PMV indices (e.g., ePMV [19] and aPMV [20,21]), two issues remain unresolved in the scientific debate: the effect of measurement uncertainties and its calculation. To calculate PMV and PPD indices, the evaluation/measurement of six variables are required: the air temperature, the mean radiant temperature, the relative humidity, the air velocity, the metabolic rate and the clothing insulation [8] These quantities can be measured or evaluated according to the Standards in the field of the Ergonomics of the Thermal Environment [22,23,24,25].
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