Abstract
The window-to-wall ratio (WWR) significantly affects the indoor thermal environment, causing changes in buildings’ energy demands. This research couples the “Envi-met” model and the “TRNSYS” model to predict the impact of the window-to-wall ratio on indoor cooling energy demands in south Hunan. With the coupled model, “Envi-met + TRNSYS”, fixed meteorological parameters around the exterior walls are replaced by varied data provided by Envi-met. This makes TRNSYS predictions more accurate. Six window-to-wall ratios are considered in this research, and in each scenario, the electricity demand for cooling is predicted using “Envi-met + TRNSYS”. Based on the classification of thermal perception in south Hunan, the TRNSYS predictions of the electricity demand start with 30 °C as the threshold of refrigeration. The analytical results reveal that in a 6-storey residential building with 24 households, in order to maintain the air temperature below 30 °C, the electricity required for cooling buildings with 0% WWR, 20% WWR, 40% WWR, 60% WWR, 80% WWR, and 100% WWR are respectively 0 KW·h, 19.6 KW·h, 133.7 KW·h, 273.1 KW·h, 374.5 KW·h, and 461.9 KW·h. This method considers the influence of microclimate on the exterior wall and improves the accuracy of TRNSYS in predicting the energy demand for indoor cooling.
Highlights
The residential energy consumption in China accounts for about 21% of China’s total energy consumption [1,2], and 70% of that energy is consumed for the purpose of modifying the indoor thermal environment [3]
In urban planning and building science, the window-to-wall ratio (WWR) is a spatial parameter usually determined by aesthetic, energy-saving, and daylight considerations [8,9]
From a methodological perspective, coupling the CFD-based software Envi-met with the Transient Systems Simulation program TRNSYS fills in the gap between urban planning and building science [39]
Summary
The residential energy consumption in China accounts for about 21% of China’s total energy consumption [1,2], and 70% of that energy is consumed for the purpose of modifying the indoor thermal environment [3]. Many studies have researched how WWR influences the building energy demand [17,18,19], most of those have been conducted on single buildings, without considering microclimate factors, which greatly affect the indoor air temperature [20,21]. WWR studies are mostly conducted using CFD software (Computational Fluid Dynamics) [22,23,24], which is capable of simulating the thermal behavior of various materials under various morphological conditions, calculating their influences on local wind speed, air temperature, and relative humidity [25,26,27]. TRNSYS calculates the indoor cooling demand without considering the changes in wind speed and air temperature caused by the urban microclimate. There is no standard threshold for cooling-energy initiation, which is affected by the body’s tolerance to temperature, and Hunan people sense 30 ◦ C as the boundary temperature between slightly warm and warm, 30 ◦ C has been adopted as the threshold of refrigeration start-up in this study
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