PLEA2009 - 26th Conference on Passive and Low Energy Architecture, Quebec City, Canada, 22-24 June 2009 Air Movement Preference and Thermal Comfort A survey in classrooms during summer season in Brazil CHRISTHINA CÂNDIDO 1,4 , RICHARD DE DEAR 2 , ROBERTO LAMBERTS 1 , LEONARDO BITTENCOURT 3 1 Federal University of Santa Catarina, Florianópolis, Brazil 2 The University of Sydney, Sydney, Australia 2 Federal University of Alagoas, Maceió, Brazil 2 Macquarie University, Sydney, Australia ABSTRACT: This research aims to explore the relationship between thermal and air movement preferences inside naturally ventilated buildings in the north-east of Brazil. Questionnaires relating to thermal acceptability were given whilst measurements (air velocity, air temperature, radiant air temperature and humidity), were simultaneously taken inside classrooms. This paper summarizes results for the summer season when 915 questionnaires were answered for the buildings’ occupants. Results suggest that occupants demand far more air movement as an essential strategy in order to improve their thermal comfort conditions. In addition, it is also possible to notice a significant demand for complementary cooling strategy, such as fans. Keywords: air movement preference, thermal comfort, air velocity, warm and humid climate. INTRODUCTION Many of the justifications for that shift from naturally ventilated indoor climates to HVAC during the late 20th century emphasised the risk of local discomfort, or draft, in situations where indoor air movement relies on natural processes instead of controllable mechanical ones. Previous studies have attempted to define when and where air movement is desirable and when it is not (i.e. draft). As concept, draught means an unpleased air movement and it is related with air temperature and air speed but also of several factors such as area and variability and part of the body which is exposed [1]. Wind chill in cold conditions is considered detrimental but air movement in neutral to hot environments is considered beneficial. This is because normally under conditions with air temperatures above 23°C, the body needs to lose heat in order to maintain a constant internal temperature [2]. Thermal comfort research literature indicates that indoor air speed in hot climates should be set between 0.2 - 1.50 m/s, yet 0.2 m/s has been deemed in ASHRAE Standard 55 [3] to be the upper limit of draft perception allowed inside air-conditioned buildings where occupants have no direct control over their environment [4]. The new standard 55 is based on Fanger’s [5] draft risk formula, which has an even lower limit in practice than 0.2 m/s. None of the previous research explicitly addressed air movement acceptability, instead focusing mostly on overall thermal sensation and comfort [6]. Much of Brazil’s territory is classified as having a hot, humid climate. In such regions, natural ventilation combined with solar protection, are the most effective building design strategies to achieve thermal comfort without resorting to mechanical cooling. However, the use of air-conditioning as the main cooling strategy inside the buildings has been increasing. Governmental data suggest that buildings are responsible for circa 30.7% of the energy final-use in Brazil (public and commercial sectors combined), [7]. However the benefits of people spending more time inside artificial and controlled environments during their daily activities in order to keep than “neutral” have been questioned. If we agree that thermal environments that are slightly warmer then preferred or neutral, can be still acceptable to building occupants (as the adaptive comfort model suggests [8, 9], then the introduction of elevated air motion into such environments should be universally regarded as desirable because the effect will be to remove sensible and latent heat from the body, so body temperatures will be restored to their comfort set- points [8]. The weight of research evidence to date suggests that neither the “risk” of draft nor the possibility of negative