Thermal comfort evaluation in residences with natural ventilation: an application in the Brazilian hot and humid climate

A recent approach to human thermal comfort under warm-to-hot conditions indoors includes dynamic airflows, whose mean air velocities vary in time. The dynamic airflow background is based on the features of the widely accepted natural wind, recognised as more pleasant than constant mechanical airflows. Natural wind-induced airflows may occur inside buildings if climatic and building design characteristics are favourable. Moreover, natural ventilation is a primary conditioning strategy in Brazilian residences – an optimal scenario to assess dynamic airflows. This research addresses natural ventilation and thermal comfort in hot and humid climates based on two main approaches: the impact of air velocity from dynamic airflows on households‘ thermal delight and satisfaction (1) and the routine adoption of natural ventilation at home based on preferences, motivations and economic background (2). The research methods involved an online national survey and a local field campaign conducted in São Luis, Brazil‘s Northeast, during the local wind regime. The field campaign started with a visit to residences (point-in-time surveys with air velocity measurements) and ended after long-term indoor air temperature and relative humidity monitoring. A thermal delight condition from natural ventilation was defined based on sedentary activity and light clothing in residential environments in a hot and humid climate. Households‘ optimal evaluation corresponded to air velocities of at least 0.4 m/s under an operative temperature range of 27-30 °C. The outcomes indicated that if the minimum air velocity threshold was maintained, the fluctuations in air movement intensity did not impair thermal delight, resulting in households‘ satisfaction with air movement at the end of the point-in-time survey. Households‘ routines, economic constraints and environmental conditions of indoor air temperature and outdoor wind speed were behind adopting a conditioning strategy at home. Air-conditioning usage and preference increased, whilst fan usage and preference decreased towards the highest income range. Nevertheless, income did not significantly affect the preference for natural ventilation only. Preference and usage patterns regarding a conditioning strategy were also aligned so that those who prefer natural ventilation at home are prone to use it more frequently. The results of this study indicate the relevance of air movement from natural ventilation to households‘ thermal comfort, particularly in well-ventilated homes. The relevance arises within the favoured adoption of natural ventilation in the Brazilian residential sector.