Conference Year

2012

Keywords

thermal comfort long-term evaluation, glazing systems, cooling and heating needs

Abstract

Although the presence of large window surfaces could be preferable during the heating season when solar gains through the glazed components can overcome heating losses from the same surfaces, during the cooling season more attention has to be paid in order to limit the inlet of solar radiation which causes the increment of cooling load. Generally the optimal tradeoff for energy optimization, as already underlined in a previous paper by the authors, is using low thermal transmittance and high solar factor glazing, even if higher solar transmittance considerably worsens the cooling performance. However, the choice of glazing type and the design of windows on a façade may depend on comfort consideration besides energetic evaluations. Thermal sensation of an individual is mainly related to the whole thermal balance of the human body. Comfort limits can in this case be expressed by two indexes proposed by Fanger in 1970: the Predicted Mean Vote, PMV, and the correlated Predicted Percentage of Dissatisfied, PPD. The PMV depends on four environmental parameters (air temperature, air humidity, air velocity and mean radiant temperature) and two variables connected with human being (physical activity and clothing). The air temperature, the air humidity and the air velocity inside a building are directly under the system control. In contrast, the mean radiant temperature is strongly conditioned by the envelope surface temperature, and in particular, by the presence of glazed surfaces whose insulating performance is lower than the opaque components one. In this paper the study of heating and cooling energy needs of an open-space office with different windows’ characteristics has been carried out controlling the internal comfort conditions with appropriate setpoint of the system. An office module with windows on a single façade, or on opposite façades, oriented towards 3 different orientations has been simulated, varying the glazed area (2 sizes), the glazing systems (4 types) and considering three localities of central and southern Europe. The PMV have been calculated for each hour of occupation of the whole year assuming two season as regards the setpoint conditions and clothing level. Calculations have then been repeated considering also the effect of the diffuse and beam solar radiation through the windows directly reaching the occupants. The evaluation of the long-term comfort conditions (on seasonal basis) has been conducted considering some statistical indicators of distribution (the median, minimum, maximum and the interquartile range) and the energy performance of the different glazing solution have been compared accounting for the comfort one.

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