Urban Heat Island Effect
Elevated temperatures from urban heat islands, particularly during the summer, can affect a community’s environment and quality of life. The United States Environmental Protection Agency (US EPA 2008) has listed the negative impacts of the urban heat islands as follows:
- • Increased energy consumption
- • Elevated emissions of air pollutants and greenhouse gases
- • Compromised human health and comfort
- • Impaired water quality
Heat island effect has a great impact in exacerbating cooling energy requirements in warm to hot climates in summer. Previous research (Akbari et al 1992; US EPA 2008) showed that for US cities with population larger than 100,000, peak urban electric demand increases 1.5-2 % for every 1 °F (0.6 °C) increase in summertime temperature (i.e., 2.5-3.5 % for every °C increase in temperature). Steadily increasing downtown temperatures over the last several decades mean that 5-10 % of community-wide demand for electricity is used to compensate for the heat island effect. During extreme heat events, which are exacerbated by urban heat islands, the resulting high demand for cooling can overload systems and require a utility to introduce extra measures to avoid power outages. The costs for summer heat island were estimated over $1 million per hour, or over $1 billion per year (Akbari et al 1992).
Santamouris et al. (2001) investigated the impact of the urban climate on the energy consumption of buildings in Athens, Greece. The study depended on analysis of weather data retrieved from almost 30 urban and suburban stations and performed specific measurements in ten urban canyons. The findings of the study showed that higher ambient temperatures caused by urban heat island could result in:
- • Doubling the cooling load of the urban buildings.
- • Tripling the peak electricity load for cooling purposes.
- • Decreasing of the COP value for air conditioning (up to 25 %).
- • Reducing the airflow rates inside urban canyons up to ten times compared to those when undistributed ambient meteorological data were used.