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apps:biomet_pmv [2014/09/15 13:39] – enviadminapps:biomet_pmv [2014/09/15 13:42] – enviadmin
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 The **PMV Model** (=Predicted Mean Vote Model) is probably the best know human thermal comfort model especially for indoor applications. It is based on Fangers (1972) comfort model and relates the energy balance of the human body with the humans thermal impression using a straight empirical function (see below). PMV was originally developed for steady-state indoor situations, but by extending the exergy flux related parts of the model with solar and longwave radiation and allowing wind speeds above an indoor room situation, PMV can also be applied -with limits- to outdoor situations (see e.g. German VDI 3787 Part 2, 2008). As the original PMV/PPD uses an empirical function to relate the bodys energy balance to a thermal sensation, it can be discussed, whether it is valid to extend this model above its original context or not. In addition, the clothing temperature is the only parameter of the PMV model that reacts on the environmental conditions, the skin temperature only depends on the activity of the person (see below). The **PMV Model** (=Predicted Mean Vote Model) is probably the best know human thermal comfort model especially for indoor applications. It is based on Fangers (1972) comfort model and relates the energy balance of the human body with the humans thermal impression using a straight empirical function (see below). PMV was originally developed for steady-state indoor situations, but by extending the exergy flux related parts of the model with solar and longwave radiation and allowing wind speeds above an indoor room situation, PMV can also be applied -with limits- to outdoor situations (see e.g. German VDI 3787 Part 2, 2008). As the original PMV/PPD uses an empirical function to relate the bodys energy balance to a thermal sensation, it can be discussed, whether it is valid to extend this model above its original context or not. In addition, the clothing temperature is the only parameter of the PMV model that reacts on the environmental conditions, the skin temperature only depends on the activity of the person (see below).
  
-PMV is, like most other thermal comfort indices, a stationary value. This means that the assessed person is assumed to be exposed long enough to a constant climate situation until all energy exchange processes at the human body have become stationary (if possible). While this the normal case for a person in an indoor environment, it is the exception for most people in an outdoor environment. The validity of stationary indices in an outdoor setting is therfore limited to either non-moving persons or to large isothermal environments where the microclimate stays constant even if moving. +PMV is, like most other thermal comfort indices, a stationary value. This means that the assessed person is assumed to be exposed long enough to a constant climate situation until all energy exchange processes at the human body have become stationary (if possible). While this is the normal case for a person in an indoor environment, it is the exception for most people in an outdoor environment. The validity of stationary indices in an outdoor setting is therfore limited to either non-moving persons or to large isothermal environments where the microclimate stays constant even if moving. 
  
 In addition to the PMV value, ENVI-met BioMet provides the associated **PPD value** (//=Predicted Percentage of Dissatisfied//) which tells the percentage of people who would be dissatisfied with the climate conditions found. PMV and PPD have a linear relationship (=they can be directly transformed into one another). Therefore the PPD maps have the same spatial structure as the associated PMV maps, but different units. In addition to the PMV value, ENVI-met BioMet provides the associated **PPD value** (//=Predicted Percentage of Dissatisfied//) which tells the percentage of people who would be dissatisfied with the climate conditions found. PMV and PPD have a linear relationship (=they can be directly transformed into one another). Therefore the PPD maps have the same spatial structure as the associated PMV maps, but different units.
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 ==== Extention to outdoor conditions ==== ==== Extention to outdoor conditions ====
  
-As mentioned above, the concept of PMV/PPD as established by Fanger (1982) was designed for indoor applications. This did affect two fundamental aspects of the PMV mode: the design of the equations and the transition from energy balance units to comfort votes.+As mentioned above, the concept of PMV/PPD as established by Fanger (1972) was designed for indoor applications. This does affect two fundamental aspects of the PMV mode: the design of the equations and the transition from energy balance units to comfort votes.
    
 First, using the clothing surface temperature as the only environment sensitive variable may be acceptable under office conditions in the absence of direct sun light and almost no ventilation. In an outdoor setting in warm to hot climates, relevant fractions of the human body are not covered by clothing but are exposed to the outdoor envionment with varing radiative loads and higher wind speeds. For those parts of the body, the skin temperature will be substantially different to the values estimated by the equations above.  First, using the clothing surface temperature as the only environment sensitive variable may be acceptable under office conditions in the absence of direct sun light and almost no ventilation. In an outdoor setting in warm to hot climates, relevant fractions of the human body are not covered by clothing but are exposed to the outdoor envionment with varing radiative loads and higher wind speeds. For those parts of the body, the skin temperature will be substantially different to the values estimated by the equations above. 
  
-Secondly, the PMV equation relates physical values (energy balance) to a personal comfort assessement. This has been achieved through tests using  volunteering persons in a climate camber. As a matter of fact and humanity, the PMV range was only checked within the range of -4 to +4, so the volunteeres were neither deep frozen nor grilled. From a schentific point of view, the transition from an energy balance to a comfort vote based on an an empirical study is only valid withing the range of the original study. Applying the PMV equation to outdoor conditions in summer heat stress situations can easily produce PMV values high above +4 (+8 and more). While this result is numerically correct, it violates the range of the original PMV system.+Secondly, the PMV equation relates physical values (energy balance) to a personal comfort assessement. This has been achieved through tests using  volunteering persons in a climate camber. As a matter of fact and humanity, the PMV range was only checked within the range of -4 to +4, so the volunteeres were neither deep frozen nor grilled. From a scientific point of view, the transition from an energy balance to a comfort vote based on an an empirical study is only valid within the range of the original study. Applying the PMV equation to outdoor conditions in summer heat stress situations can easily produce PMV values high above +4 (+8 and more). While this result is numerically correct, it violates the range of the original PMV system.
  
 Despite these problems, PMV in its outdoor version is able summarize the effects of air temperature, radiation, humidity and wind on the persons energy balance in one value each of it weighted with level of influence.  Despite these problems, PMV in its outdoor version is able summarize the effects of air temperature, radiation, humidity and wind on the persons energy balance in one value each of it weighted with level of influence.