The Albedo Effect and Energy Efficiency in Cities
How a simple model revealed why cities are getting warmer.
Urban areas around the world have been known to be as much as 5 °C warmer than nearby sub-urban areas. The Urban Heat Island (UHI) effect is prevalent in many cities, the temperature increase being due to a combination of factors, including human activities. This effect is mostly noticeable at night, when surfaces constantly release heat into the atmosphere. The primary cause of the urban heat island effect is the alteration of land surfaces, and as a secondary contributor of waste heat from energy usage.
Not only does the heat island effect contribute to an increase in energy consumption it also contributes to complex air quality problems such as ground-level ozone known as smog, fine particulate matter, and acid rain.
Albedo Effect
The Norwegian Polar Institute indicates that the “albedo is an expression of the ability of surfaces to reflect sunlight (heat from the sun). Light-coloured surfaces return a large part of the sun rays back to the atmosphere (high albedo). Dark surfaces absorb the rays from the sun (low albedo).”
Humans have altered the natural albedo effect primarily with constructions, ultimately decreasing the albedo. Asphalt roads, buildings and roofs are the most exposed surfaces to solar radiation, making them very important to increase their energy efficiency by means of the application of the albedo effect.
The albedo effect has a significant influence on climate change and the urban heat island effect since approximately 50% of the solar radiation reaches the Earth’s surface, where it will be either absorbed or reflected, depending on its albedo. The more radiation the Earth absorbs, the hotter it becomes, favouring global warming. A city with inappropriate albedo management with surfaces that attract and absorb solar radiation should have an increased temperature.
Data Collection
Implementing a simple model, that consisted in painting 10 cardboard boxes, each with a different gradient from white to black. We then measured each boxes inner temperature at 10:30 am, 1:30pm and 4:30pm for several days.
Table 3 illustrates how temperature increases depending on the surface colour gradient, the lightest colours having the lowest temperatures and the darkest colours the highest temperatures. In spite of this it is not possible to say this trend is completely accurate but it does show some correlation. With enhancements, more precise and accurate results could be achieved.
Graph 2. Demonstrates the relationship between the albedo and temperature, illustrating that surfaces with low albedo absorb the most solar radiation, increasing the inner box temperature.
On the other hand, surfaces with a high albedo reflect most solar radiation maintaining the temperature lower. Indicating that the darker the colour of the cardboard box, the higher the temperature. Nonetheless this effect is intensified when solar radiation is higher, and the effect is lower when there is not as much solar radiation.
Conclusions
The surface colour and colour gradient of an urban building does affect the internal air temperature either positively or negatively.
Darker surfaces (black) absorb the most solar radiation, producing an increase in heat, contrary to surfaces with a lighter colours (white), which reflect more solar radiation ultimately absorbing less heat and keeping internal air temperature cooler. Signifying that darker surfaces absorb more energy and transfer it as heat into the air causing temperatures to increase.
A solution that could help reduce the Urban Heat Island effect and reduce economic cost of energy consumption by air conditioning would be to use albedo friendly roofs and surfaces. Using white or light colour paint with a high gloss can help reflect more solar radiation maintaining a stable and cool internal air temperature of urban buildings. Using roofs with lower albedos can help maintain buildings cooler, this practice has been done in many coastal and desert countries. Why not implement it in our modern cities?
References
- Agency, E. -U. (n.d.). EPA. Retrieved from Heat Islands — Heat Island Impacts: https://www.epa.gov/heat-islands/heat-island-impacts
- Colorado Edu. (n.d.). Retrieved from Measuring Albedo: http://cires.colorado.edu/outreach/sites/default/files/curriculum/Worksheets%20%28Module%201%29.pdf
- Institute, N. P. (n.d.). Norwegian Polar Institute. Retrieved from Albedo effect: http://www.npolar.no/en/facts/albedo-effect.html
- Muñoz, A. Z. (2012). Albedo Effect and Energy Efficiency of Cities . http://cdn.intechopen.com/pdfs/29929/InTech-Albedo_effect_and_energy_efficiency_of_cities.pdf.
- Aniceto Zaragoza Ramírez and César Bartolomé Muñoz (2012). Albedo Effect and Energy Efficiency of Cities, Sustainable Development Chaouki Ghenai (Ed.), ISBN: 978–953–51–0165–9, InTech, Available from: http://www.intechopen.com/books/sustainable-development-energy-engineering-and-technologiesmanufacturing-and-environment/albedo-effect-and-energy-efficiency-of-buildings
