MEASUREMENT UNCERTAINTIES INFLUENCE ON THE THERMAL ENVIRONMENT ASSESSMENT

ISO 7726 Standard describes in a very careful way both the measurement techniques and the related metrological performances of instruments required for the thermal environment assessment. On the contrary hand, the analysis in situ of assessment indices rarely takes into account the evaluation of the single measurement uncertainties and their inevitable effect on the thermal environment assessment. The reasons of these lacks are several: the high costs for the calibration of devices, the complex metrological traceability, the variety of measurement parameters, the late application of both ISO GUM on the accuracy assessment and the related Standards for the management and certification of measurement hardware of laboratories. Concerning thermal comfort assessment, another critical facet is related to the limit values for the percentage of dissatisfied for each comfort category required by ISO 7730 Standard. As a matter of fact, such values (especially for the category labelled as “A”) can be so strongly prescriptive to make almost impossible their practical use, especially if the high uncertainty of some quantities involved for the assessment is taken into account. As far the mean radiant temperature and the radiant asymmetry is concerned, ISO 7730:2005 suggests three direct (black-globe, two-sphere radiometer and constant air temperature sensor) and two indirect (view factors and plane radiant temperature) measurement methods. Although this Standard sets up their different and not easily comparable ranges of accuracy, there is no clear reference about the effect of such values (differentiated in “required” and “desirable”) on the environment classification (“A”, “B” or “C”). This work deals with the effect of measurement accuracy of both physical (the air temperature, the mean radiant temperature, the air velocity and the relative humidity) and subjective parameters on the assessment of moderate thermal environment. A compared assessment of comfort indices in most significant environments carried out by means of different measurement techniques and devices is also reported. This procedure can highlight both the compatibility of measurement and the suitability of devices required for the verification of comfort classes settled by ISO 7730 Standard.