Impact of façade design on indoor air temperatures and cooling loads in residential buildings in the tropical climate

Abstract

Thermal comfort and energy efficiency in residential buildings in tropical climate or summer are becoming increasingly important, in the context of global climate warming and occupants’ growing reliance on air-conditioning. In this study, a parametric study based on a validated model was carried out using EnergyPlus to evaluate the impacts of various façade design factors on indoor air temperatures and cooling loads. In particular, the façade performance was evaluated under five different ventilation or air-conditioning scenarios, namely 1) window-closed (WC) and 2) window-open (WO) scenarios for indoor air temperatures, as well as 3) 24-hour air-conditioning (AC), 4) nighttime air-conditioning with daytime closed window (WC + NA), and 5) nighttime air-conditioning with daytime open window (WO + NA) scenarios for cooling loads.It is found that, compared with the worst-performed unshaded façade with full-height clear glass, reducing the façade’s window-to-wall ratio (WWR) from 1 to 0.4 could achieve the largest indoor air temperature reductions under both WC and WO scenarios, followed by reducing the glass solar heat gain coefficient (SHGC) from 0.82 to 0.47, and by adding a 1.5-m horizontal overhang above the window. For space cooling energy-saving purpose, reducing the façade’s WWR from 1 to 0.4 and reducing the SHGC of window glass from 0.82 to 0.47 could achieve the largest cooling load reductions under the AC and WC + NA scenarios respectively. Moreover, window openings could effectively reduce the indoor air temperatures and nighttime cooling loads, as they facilitate heat dissipation during the daytime. In addition, the impacts of window glass and wall insulation on indoor air temperatures and cooling loads were analyzed. The more insulated windows and walls could have adverse effects on indoor thermal comfort and cooling loads if the internal surface temperature of façade becomes higher than its external surface, which could occur during the daytime when the indoor temperature is high under the WC scenario, or at night when the outdoor air temperature drops. For better thermal comfort and energy efficiency, it is thus advisable to conduct an optimization study to find the optimal facade insulation levels for tropical buildings, with considerations on the air-conditioning modes (operation period and set-point), window size and shading, glass SHGC and outdoor weather conditions.