Predicted Mean Vote

ISO EN 7730 standardizes the PMV-PPD index as the method for evaluation of moderate thermal environments. To quantify the degree of comfort, the PMV (predicted mean vote) index gives a value on a 7-point thermal sensation scale -t-3 hot, +2 warm, +1 slightly warm, 0 neutral, -I slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors (clothing, activity, air and mean radiant temperatures, air speed, and humidity). 

FIGURE 6.2 Predicted percentage of dissatisfied (PPD) as a function of predicted mean vote (PMV). 

Predicted percentage of dissatisfied Category (PPD) Predicted mean vote (PMV) Percentage of dissatisfied due to draft (DR) Percentage of dissatisfied due to vertical air temperature difference Percentage of dissatisfied due to warm or cooi floor Percentage of dissatisfied due to radiant asymmetry... 

Predicted mean vote index (PMV) An index used to predict the mean value of thermal sensation votes of a large group of persons, expressed on a 7-point scale. 

Fanger correlated L with the Predicted Mean Vote (PMV) to determine comfort ... 

In 1970, Danish scholar Fanger summed up the two widely used evaluating indicators of heat comfort which are PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) (Bo S S et al. 2011). These two indicators combine six factors which are air temperature, average radiant temperature, air velocity, air humidity, human body metabolism and heat-resistance of clothes, so they are the most comprehensive evaluating indicators of heat environment until now and have been compiled into international standard ISO7730. 

Thermal comfort is a subjective judgment often classified in a scale from —4 (very cold) to 4 (very hot). This is called the Predicted Mean Vote (PMV). Also, the percentage dissatisfied (PPD) can be estimated from the formulae. ISO 7730 is mainly used by engineers to predict and evaluate climate comfort in buildings. 

FI G U RE 13.2 Graph showing how predicted mean vote (PMV) values map onto the predicted percentage of people thermally dissatisfied a value of 10% or less is desired. (Permission to reproduce figure from BS/EN/ISO 7730 1995 is granted by the British Standards Institution.)... 

Yao, R., Li, B., Liu, J. (2009). A theoretical adaptive model of thermal comfort— Adaptive Predicted Mean Vote (aPMV). Building and Environment, 44(10), 2089-2096. doi 10.1016/j.buildenv.2009.02.014. Zingano, B. (2001). A discussion on thermal comfort with reference to bath water temperature to deduce a midpoint of the thermal comfort temperature zone. Renewable Energy, 23(1), 41 7. doi 10.1016/ 80960-1481(00)00101-4. 

There are two other indices called the Fangers PMV (Predicted Mean Comfort Vote) and the P4SR (predicted 4 hour sweat rate). 

The PMV index predicts the mean value of the thermal preferences of a large group of people exposed to the same environment. But individual votes are scattered around this mean value, and it is useful to predict the number of people likely to feel uncomfortably warm or cool. The PPD (predicted percentage of dissatisfied) index establishes a quantitative prediction of the number of thermally dissatisfied people. The PPD predicts the percentage of a large group of people likely to feel too warm or cool, i.e., voting hot (-t-. , warm (4-2), cool (-2), or cold (-3) on the 7-point thermal sensation scale. 

This is similar to the approach used by the political pollsters above when they sample the population using a poll to predict the results of an upcoming election. The poll results are reported as the mean predicted votes plus a margin of error which defines the confidence interval. The larger and more diverse the poll, as well as the closer to election day, the narrower the confidence interval and more precise the prediction. The election is the real measurement of the population, and then only a single number (the actual votes cast) is needed to describe the results. There is no uncertainty when the entire population is sampled. Unlike in politics, this option is not available in toxicology. 

Software diversity has been advocated as a means of improving the reliability of safety related software and in particular safety systems that react to a demand, where a 1 out of 2 or a 2 out of 3 voting scheme can be used to ensure that some safety action is performed. This approach is used in industry (e.g. for railway interlocking), but development and maintenance is costlier than for a non-diverse system and it is not easy to predict in advance the likely safety improvement that can be achieved. 

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