Study on the impact of window size and proportion on indoor air temperature of bedrooms in apartments

Abstract

Globally, over one-third of total energy is consumed by the residential building sector (IEA, 2013). In Bangladesh, more than 40% of electricity is consumed in the domestic sector by air-conditioning (AC) and fans for comfort cooling (JICA, 2015). Windows, the drivers of natural ventilation, if designed and adopted properly can offset energy guzzling AC devices, while providing thermal comfort. During the design phase, sizing windows against room area and wall area have a considerable effect on achieving thermally acceptable indoor air temperature for occupants. This simulation based study analyzes the impact of varied window-to-floor area-ratio (WFR) and window-to-wall area-ratio (WWR), on bedroom air temperature in residential apartments, thereby providing possible design options for such spaces, to offset energy consumption, while keeping air temperature within a comfortable limit. Initially, a base-case bedroom simulation model was formulated by conducting a random questionnaire survey and case study analysis of high-rise apartment buildings of the upper middle income group of Dhaka along with a comprehensive literature review on comfortable air temperature in such rooms. Simulation was done in Ecotect Analysis and WinAir to figure out indoor air temperature and air movement pattern respectively for the base case, as well for varied WFR and WWR. Simulation outcomes were validated, by comparing with measured values from a pilot survey conducted inside a bedroom of the topmost floor of an existing high-rise residential building. Comparative analysis was used to predict the best possible WFR and WWR configurations for obtaining a comfortable air temperature within this space. The result reveals that WWR, ranging from 20% to 30%, is preferable for inducing lower indoor air temperature in the south west corner rooms of naturally ventilated buildings.