Body-Near Climate Control Systems and Thermal Ergonomics
Assessing thermal comfort according to ISO 14505-2
06/2012 to 06/2014
Usually, attempts to assess overall thermal comfort in rooms are based on the two indices “Predicted Mean Vote” (PMV) and “Predicted Percentage of Dissatisfied” (PPD) according to the DIN EN ISO 7730 or the ASHRAE Standard 55. The mathematical model framework focuses on calculating the energy balance between the human being and the surrounding indoor climate. The required physical input variables to assess the current local climatic situation – such as average air speed, operational temperature, and relative humidity – can be evaluated using commercially available instruments. PMV and PPD are only applicable for steady indoor climate conditions near thermal neutrality, so it is not possible to assess local inhomogeneities in the indoor environment caused by fluctuating air currents, radiation, or temperature asymmetries.
The international standard DIN EN ISO 14505-2 offers a measurement method that allows to assess local air stimuli affecting a human being with the help of a reference value (“ Klimasummenmaß ”) and measurements by using flat heated sensors. Here, the reference value serves as a so-called equivalent temperature, which can be described as a function of the surface temperature of a heated sensor and other parameters (Resultant Surface Temperature, RST). The RST is the result of locally acting microclimates (sensitive heat loss). Drawing on a body-part-specific comfort zone definition, the so-called “Local Mean Vote” (LMV), this effect can be transformed into an objective statement regarding thermal comfort. Resulting from extensive subject studies, these comfort correlations are to be seen as valuable background data. On behalf of the industry, the Institute performs measurements under steady-state and transient conditions – in vehicles, for example.