This work shows the results of a field study about indoor thermal comfort, based on investigations in Portuguese secondary schools' classrooms. The surveys herein presented were carried out in a school in Beja, in the SouthEast of Portugal. The field study was conducted by physical parameters monitoring and survey questionnaires. Both field monitoring and subjective surveys were performed at the same time during the regular class period (either at the end or at the beginning of the class). The measurement campaign consisted in measuring the environmental parameters-air temperature (T a), air relative humidity (RH), CO 2 concentrations. Outdoor air temperature values were registered hourly at the nearest climatological station. Through these data, along with the actual people clothing and metabolic rate being know, both Fanger's comfort indices were calculated (predicted mean vote and predicted percentage of dissatisfied people). The subjective survey investigated the thermal acceptability, the thermal sensation and the thermal preference. The judgments about the thermal environment were compared with the results of the field measurements. Draught preference votes, air stiffness and global air quality votes were also collected. The results show that the students found temperature range beyond the comfort zone acceptable, and revealed the occupants' accommodation to CO 2 exposure, confirming the results obtained in other studies. Moreover, it was verified that running on naturally ventilation mode, CO2 concentration limits were highly exceeded.

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Maintaining suitable indoor climate conditions is a need for the occupants' well being, while requiring very strictly thermal comfort conditions and very high levels of indoor air quality in buildings represents also a high expense of energy, with its consequence in terms of environmental impact and cost. In fact, it is well known that the indoor environmental quality (IEQ), considering both thermal and indoor air quality aspects, has a primary impact not only on the perceived human comfort, but also on the building energy consumption. This issue is clearly expressed by the European Energy Performance of Buildings Directive 2002/92/EC, together with the most recent 2010/31/EU, which underlines that the expression of a judgment about the energy consumption of a building should be always joint with the corresponding indoor environmental quality level required by occupants. To this aim, the concept of indoor environment categories has been introduced in the EN 15251 standard. These categories range from I to III, where category I refers to the highest level of indoor climate requirement. In the challenge of reducing the environmental impact for air conditioning in buildings, it is essential that IEQ requirements are relaxed in order to widen the variations of the temperature ranges and ventilation air flow rates. In this paper, by means of building energy simulation, the heating and cooling energy demand are calculated for a mechanically controlled office building where different indoor environmental quality levels are required, ranging from category I to category III of EN 15251. The building is located in different European cities (Moscow, Torino and Athens), characterized by significantly different wheatear conditions. The mutual relation between heating and cooling energy demand and the required levels of IEQ is highlighted. The simulations are performed on a typical office room which is adopted as a reference in validation tests of the European Standard EN 15265 to validate calculation procedures of energy use for space heating and cooling. Keywordsindoor environmental quality, categories, energy demand, building energy simulation Article History

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