Effect of a Secondary Building Envelope on Cooling Loads in Hot Climates

Abstract

Cooling buildings represent a major environmental issue, especially during summers. Although thermal insulation can decrease cooling loads, the presence of thermal bridges, infiltrations, windows, and other openings pose a continuous challenge. In the Middle East and North Africa (MENA) region, for instance, most windows are made of aluminum, a thermal conductor. This paper uses two methods to evaluate the alternative solution of enveloping buildings, including windows, with a secondary layer. The first method involved small-scale models; two test rooms were built, with one (the reference room) being based on regular municipal thermal guidelines and the other (the enveloped room) including an extra, secondary surrounding layer. The second test staged a similar scenario via software simulation. Both sets of results showed a significant reduction in electricity consumption in the enveloped room, which became more notable as the weather grew hotter. At the high end of the temperature scale, the power consumption of the enveloped room was 47%–54% lower than that of the reference room. However, such a secondary building envelope would increase the width of the wall structure and present the downside of adding to construction costs. While adopting this system in Dubai may save the city an estimated 16.6% in electrical energy, based on current prices, a house would likely need between 10 and 15 years to recuperate the associated capital investment.