Center for the Built Environment

Much has been done in order to understand when air movement enhancement is unwelcome. Traditionally, air velocity has been framed in terms of maximum permissible limits in order to avoid occupants’ complaints due to ‘draft’. Numerous authors have proposed a variety of maximum acceptable indoor air velocity, ranging from 0.5 to 2.5m/s, and 0.8m/s has been deemed as maximum allowable air velocity by ASHRAE 55-2004. In hot humid climates, however, it is likely that higher air velocity values would be preferred by occupants. This project aims to understand the relevance and applicability of maximum air velocity limits, focusing on occupant’s thermal comfort, preference and acceptability, within naturally ventilated buildings. The methodological approach focuses on field research design, based on the proximity, in time and space, of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. The two field experiment campaigns took place in naturally ventilated buildings in Maceio, located at the north-east hot-humid zone of Brazil, during the cool (Aug/Sep) and also hot seasons (Feb/Mar), resulting in 2075 questionnaires. Air movement was investigated based on two goals for acceptability: 80 and 90%. Minimal air velocities values obtained based on this analysis were close to, or above 0.8m/s, which is currently mandated as the maximum air velocity for ASHRAE 55-2004. Findings also indicated occupant’s rising comfort expectations; resulting from constant air-conditioning exposure, militate against the implementation of adaptive comfort principles in bioclimatic buildings. Findings also indicated that air movement definitely assumes a major significance in terms of preference and acceptance of the indoor thermal environment. Thermal acceptability alone was not enough to satisfy occupants. And combining thermal and air movement acceptability is the key challenge that must be faced in these indoor environments. Based on these results, this project suggested a set of guidelines for a Brazilian standard for naturally ventilated buildings, considering air movement enhancement as a welcome breeze in hot-humid climates.