Urban cities like Chicago are experiencing increasing temperatures due to the urban heat island effect, caused by elements such as concrete sidewalks, black asphalt streets, and brick buildings that retain heat. To help combat this issue, researchers at the U.S. Department of Energy’s Argonne National Laboratory have studied different roofing strategies and their impact on near-surface temperature and cooling energy demand in the Chicago metropolitan area. By understanding these strategies, decision makers and communities can make informed choices to keep their residents cool during the summer months.
The study examined three different types of roofs: cool roofs, green roofs, and solar panel roofs. Cool roofs are painted white to reflect heat, green roofs have vegetation, and solar panel roofs generate electricity from sunlight. The researchers used regional modeling to simulate the Chicago metro area and assess the effectiveness of each roofing strategy.
The study found that all three types of roofs had a cooling effect on the near-surface temperature and reduced the demand for air conditioning during daytime hours when the air temperature is highest. Cool roofs had the most significant impact, reducing the near-surface temperature by 1.5 degrees Celsius, followed by green roofs (1.2 degrees) and solar panel roofs (0.6 degrees) across the Chicago area. In terms of energy consumption, cool roofs also outperformed the other two options, reducing AC energy demand by 16.6%, compared to 14.0% for green roofs and 7.6% for solar panel roofs.
Cool roofs were found to be the most cost-effective option, as they cost less than green roofs and solar panel roofs, and they do not require additional water. However, green roofs have the added benefit of managing stormwater loads, which cool roofs cannot do. The study’s findings can assist stakeholders in making sustainable development decisions, reducing summertime cooling energy demand, and minimizing greenhouse gas emissions in the long term.
Implications for the Future
The research conducted as part of the Community Research on Climate & Urban Science (CROCUS) Urban Integrated Field Laboratory will help communities in the Chicago region plan and test mitigation options. The researchers plan to develop city-scale and global-scale models for each of the roofing options, which will allow for more comprehensive analysis. To achieve this, more measurements for green roofs are necessary to understand their energy and water usage. The researchers will also improve the resolution of the models to analyze the impact of individual rooftops and streets on nearby buildings and pavement.
The study utilized supercomputing resources at the Argonne Leadership Computing Facility (ALCF) and the National Energy Research Scientific Computing Center (NERSC). These facilities, located at Argonne and Lawrence Berkeley National Laboratory, respectively, are DOE Office of Science user facilities. The use of supercomputing allowed for accurate and detailed simulations of the Chicago metropolitan area.
Understanding the impact of different roofing strategies on the urban heat island effect is crucial for creating more sustainable and resilient cities. The research conducted at Argonne National Laboratory provides valuable insights into how cool roofs, green roofs, and solar panel roofs can reduce near-surface temperature and decrease energy demand for cooling in urban areas like Chicago. By implementing these strategies, decision makers and communities can work towards a more comfortable and environmentally-friendly future.