Double skin facade overall thermal transfer value correction factor in hot humid climate

Abstract

The ongoing discussion on the use of Naturally Ventilated Double Skin Façade (NVDSF) has been propelled by continuous advancements in building envelope design. Existing studies on NVDSF include the impacts of cavity depths, glazing types and wall types on the thermal performance of the building. However, only a few studies have focused on its cooling load, heat transferred and the building Overall Thermal Transfer Value (OTTV). Therefore, this research evaluated the impacts of the NVDSF design parameters such as window-to-wall ratio (WWR), cavity depth (CD) and glass shading coefficient (SC) on heat transfer and cooling load and developed a dataset of correction factors to calculate OTTV for buildings with NVDSF for four cardinal orientations (east, north, south and west). An experiment was carried out using a simplified 5-storey air-conditioned commercial office building with a total area of 5,760-meter square as the base-case model. Computer simulations were conducted using DesignBuilder v5.0.1.024 with EnergyPlus v8.3 simulation engine. The validation test conducted by comparing measured cavity air temperature with the simulation results showed that the software simulation is in good agreement with the measured data. Analysis of the study results revealed that naturally ventilated double skin façade was effective to minimize the solar heat gain and thermal transmittance. Proper combination of appropriate outer and inner glass panels will significantly reduce the solar heat gain as well as the resulting cooling load. The simulation model case with 0.2 m cavity depth outperformed all other tested cavity depths (0.2m, 0.4m, 0.6m and 0.8m) both in value of heat transferred and cooling loads reduction. Furthermore, the study showed that heat transmitted through both single skin façade and NVDSF will increase as window to wall ratio and the glass shading coefficient increases. The findings corroborate the fact that a carefully designed NVDSF would save a considerable amount of building energy use in hot humid climate. Based on analysis of the simulation results, the study concludes by generating a set of 8192 correction factors to calculate the OTTV of buildings with NVDSF in Malaysia. These correction factors are expected to ease the designer’s burden of simulation and speed up the construction documentation process for building with NVDSF as OTTV become a compulsory requirement for construction approval in Malaysia.