The higher the outdoor temperature, the higher the cooling load of a building. Especially in cities, the cooling load can be higher compared to the surrounding countryside because of higher temperatures by 2 to 3 degrees Celsius. Peak temperature differences can be even higher. The urban heat island effect is the reason for this phenomenon. The high concentration of dark surfaces with high heat capacities like roads and buildings absorbs much more solar radiation. Little greenery and no water bodies cause a lack of evapotranspiration which would have a cooling effect. Additionally, many forms of pollution like waste heat from industries, cars and air-conditioning systems are increasing the external temperature.
How to determine appropriate urban heat island mitigation strategies?
Peak temperatures of 45 °C (113 °F) or more during the summer season cause heavy cooling loads in the United Arab Emirates. In Abu Dhabi, about 60 percent of the annual energy expenses are caused by air-conditioning systems. It can even rise up to 75 percent on peak days. The urban heat island causes up to 15 percent of the emirate’s yearly cooling load in Abu Dhabi. Reducing the urban heat means cutting energy costs.
Researchers at MIT and the Masdar Institute are creating a three-dimensional urban microclimate model to investigate the impact of several urban heat island mitigation strategies
“The more cooling you have, the more heat air-conditioning systems release into the urban environment, which then elevates the ambient temperature and further increases the cooling demand. It’s a vicious cycle,” said Masdar Institute’s Afshin Afshari, professor of practice of engineering systems and management, who is a member of the Masdar Institute-MIT research team.
Scientists at Massachusetts Institute of Technology (MIT) and the Masdar Institute, a graduate-level technology university in the UAE, are searching for ways to reduce the urban heat island effect. The development of a new three-dimensional urban microclimate model for the downtown area of Abu Dhabi shall enable to investigate the impact of various strategies to mitigate the urban heat island. It could be a valuable urban planning decision-making tool. Influencing factors like geometric effects of buildings, materials, street layouts, green spaces, shading strategies, and water points can be taken into account.
“Very few research teams in the world approach the problem as an integrated phenomenon,” Afshari explained. “Most microclimatologists assume buildings are simple geometric obstacles with a constant temperature, and don’t look at the energy and heat the building produces, while building physicists are not interested in the urban climatology. But we see that the two phenomena are closely coupled and that their dissociation can lead to large modeling errors.”
According to MIT, the 3-D computational model shows the complex process of heat flows between buildings in Abu Dhabi’s downtown area. It is possible to conclude important climatic variables like air temperature, building façade temperatures, wind speed, solar radiation, and ground temperature.
The researchers considered local weather data, the accurate geographical city structure and other remote sensing data. They estimated the cooling demand of the buildings as well as the released heat from air-conditioning systems and integrated the climatic data, building data, and, to some degree, motorized traffic data. To get a clearer picture, more detailed information, and in order to improve the model, the researchers install dozens of in-house developed weather sensors in downtown area.
Urban heat island mitigation is an important component to reduce the country’s high energy costs and carbon footprint. An affordable way to optimize “Abu Dhabi’s smart infrastructure systems through a tool that enables city planners to design a cooler, more productive city, which will in turn increase the city’s competitiveness and prosperity.”
“The impact from this research project is spreading to the students we teach at both MI and MIT,” Norford said. “The broader and more important impact we hope our research achieves is on professional practice. If architects, developers, and planners use our software to evaluate alternative designs and make informed decisions to locate, design, and operate buildings in ways that minimize urban heat releases and improve the thermal comfort of urban dwellers, we will have achieved our goal.”