Building Anthropogenic heat flux in Singapore

Abstract

Buildings are amongst the biggest sources of anthropogenic heat in cities. In Singapore, buildings consume close to 28 TWh/year, which is eventually rejected as heat into the environment. It is believed that this amount may contribute to raising temperatures in the city state and thus urban warming. In order to provide a better understanding this phenomenon, this work characterizes the distribution of anthropogenic heat flux from buildings in Singapore. The focus lies in the analysis of the heat generated by different building morphologies and typologies throughout a typical year across the island. The methodology is divided into two parts. In the first part, we assess the energy consumption of over 13,000 buildings in Singapore across diverse building typologies (commercial, private housing and public housing [HDB]) and local climate zones. The result is the mean sampled energy use intensity for three main typologies: commercial buildings, public housing (HDB) and private housing. The mean sampled energy use intensity for each typology is validated against energy statistics. The second part combines this information with a Local Climate Zone (LCZ) - Land Use map, resulting in a map of Singapore’s building anthropogenic heat flux and an estimation of total anthropogenic heat released over one year, also validated against reported energy consumption. The analysis of Energy Use Intensity (EUI) revealed that commercial buildings (mean EUI of 267 kWh/m²/yr) can be four to five times more energy intensive than public (50 kWh/m²/yr) and private housing (72 kWh/m²/yr). The EUIs for each typology tend to remain nearly constant for different LCZs, which is expected, given that the effect of different morphologies is not evident when normalizing the energy of buildings per gross floor area. The EUI is converted into anthropogenic heat density (AH Density) with the use of the Floor Area Ratio (FAR) index, which is the ratio between gross floor area and site area. The AH density, expressed in annual heat per site area, is then converted into anthropogenic heat flux (AH Flux), assuming a constant distribution of power throughout the year. In terms of AH flux, the highest flux is generated in compact high-rise areas (LCZ1), with AH flux of commercial buildings (105 W/m²) being 6 to 7 times higher than private (18 W/m² ) and for public housing (15 W/m²). The lowest anthropogenic heat flux is observed in sparsely built regions (LCZ9), with AH flux ranging from 2 W/m² in residential buildings to 7 W/m² in commercial buildings. In Singapore, open lands (LCZ3, LCZ4 and LCZ5) comprises 70% of the built-up spaces, with 34% of the site area from buildings corresponding to high rises (LCZ4) and 27% to open mid-rises (LCZ5). In those regions, the average heat flux from commercial buildings (55 – 91 W/m²) is estimated to be 8 to 11 times higher than private housing (5-11W/m²) and 6 to 7 times higher than public housing (HDB) (9-13W/m²). The spatial distribution of AH flux presents a clearer distinction between commercial and residential areas. Commercial areas are, as expected, the most heat intensive areas, with a range of AH flux between 70 and 110 W/m² in business and retail areas such as Central Business District (CBD), Orchard Road, and the Mapletree Business City, but also with a significant amount (40-90 W/m²) in university campuses. Although residential buildings have an AH flux five to twenty times lower than the commercial sector (2-20 W/m²), residential buildings are distributed over an area three times larger than that of commercial buildings. Therefore, residential buildings are still significant, representing around 30% of the total AH emitted in Singapore. In terms of total anthropogenic heat, LCZ4 and LCZ5 present the highest share of aggregated heat released, due to their larger site area coverage. Up to 62% of the AH released coming from buildings is observed in those urban morphologies. From that, 65% is due to commercial (10.69 TWh/yr) and 35% is due to residential (5.80 TWh/yr), also indicating how much more intensive the commercial sector is in Singapore. Our results provide a visual representation of the direct contribution of buildings to anthropogenic heat emissions across Singapore, highlighting the hotspots across the island. It also establishes the basis for the evaluation of “what-if” scenarios, such as changes in the Master Plan or assessing the potential impact of new developments. Future work will explore the incorporation of building energy models in this framework, accounting for hourly variation throughout the day and a potential to explore a wider range of “what-if” scenarios related to building technology.