PMV-PPD and acceptability in naturally ventilated schools

The assessment of moderate thermal environments provided with HVAC system is usually carried out by means of the PMV and the PPD indices. The reliability of the PMV to predict the thermal 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 conditioned environments and people used to, proposed to widen the use of PMV even in non-air conditioned 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 investigated school buildings were non-air conditioned and ventilated by operable windows. The subjective 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 consistent 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. (C) 2013 Elsevier Ltd. All rights reserved.