PMV - PPD and Acceptability in Naturally Ventilated Schools

The assessment of moderate thermal environments provided with HVAC system is usually car-ried out by means of the PMV and the PPD indices. The reliability of the PMV to predict the ther-mal sensation in non-air conditioned environments has been criticized in the past. Particularly, Fanger himself, realizing the difference in the expectations between people not used to occupy con-ditioned environments and people used to, proposed to widen the use of PMV even in non-air con-ditioned environments by means of an expectancy factor. This factor, multiplied by the PMV value, returns a corrected vote that keeps into account the difference in expectancy of occupants of non-air conditioned environments. In this paper an expectancy factor value for the Mediterranean climate is proposed. This value has been obtained by carrying out a combined subjective and objective investigation on about 200 Italian classrooms and more than 4000 students both in winter and in summer season. All investi-gated school buildings were non-air conditioned and ventilated by operable windows. The subjec-tive investigation has been carried out by means of a special questionnaire also containing a direct question on the acceptability to verify the agreement between the percentages of dissatisfied con-sistent with the votes assigned to the thermal environment and the acceptability. Obtained results seem to show similar distributions with only a slight overestimation (15% about) of the percentage of dissatisfied under neutrality conditions.