Abstract

In the current design and operation of residential houses, indoor humidity is often left unregulated because, unlike temperature, it is more difficult to sense, quantify, and control. High indoor RH may increase the risk of respiratory problems such as rhinitis and asthma, reduce perceived air quality, propitiate mold growth, and cause building damages. Low indoor RH may cause discomfort due to dryness of nose, eyes and skin. Indoor humidity in each room of multizone buildings depends on the moisture generation by sources, moisture transport by air leakage and ventilation, moisture buffering by indoor finishing materials and furniture, moisture transport through the envelope, and moisture transport between rooms due to interzonal airflows. Most of these aspects have been extensively studied, but the moisture transport due to interzonal airflows through doorways or staircase openings has received less attention. The aim of this investigation is to study the interzonal air and moisture transport through a large horizontal opening in a full-scale two-story test-hut involving buoyancy-driven flows (due to temperature differences only) and combined buoyancy and forced airflows (due to mechanical ventilation). To accomplish this objective, experiments and Computational Fluid Dynamics (CFD) simulations are performed. The main parameters tested are the temperature difference between the lower and the upper rooms, ventilation strategies, ventilation rates and locations of the moisture source. Interzonal moisture exchange and interzonal airflows are analyzed based on two quantities that represent both phenomena, the difference between the average humidity ratios of the two rooms and the interzonal mass airflows, respectively. Experimental and CFD simulation results show that higher interzonal mass airflows and moisture exchanges through the horizontal opening are found when the upper room is colder than the lower room, while lower interzonal mass airflows and moisture exchanges occur when the upper room is warmer. Also, it is shown that the mechanical ventilation significantly restricts interzonal mass airflows in comparison with cases without ventilation. Based on CFD results, empirical equations representing the upward mass airflow through the horizontal opening are developed at different ventilation rates and ventilation strategies