Review and Critical Analysis of International UHI Studies

In a study in China, researchers found the residential electricity consumption in the largest case
study city was 1.6 times higher than the national average. In terms of coal and gas, again
consumption in the largest city was considerably higher than the rest [155].
Another study in China acknowledged each case study city’s characteristics and the influencing
factors of energy use, these were: city locale, housing type, space cooler and water heater
distribution, household characteristics and indoor thermal environment [153]. These variables
affected a city’s energy consumption differently from city to city, one having a dramatic effect on
one city and no or little affect in another.
However, a study in Quebec, Canada on the impact of urban density on energy use found that
cities with the largest densities consumed less gasoline and electricity per capita. They found that
policy factors affected energy consumption such as services offered by a city, street lighting and
building requirements. Factors that weren’t included in their study were variables such as energy
price, time series analysis, standard of living, geographic situation and economic activities [154].
An increase in urban population by 1% causes an increase in energy consumption by 2.2% [150].
In US cities with populations over 100,000 a 1°F increase in daily maximum temperatures means
that peak energy demand rises by 1.5‐2%. Air conditioning use accounts for up to 10% of urban
peak electrical demand [157]. Based on the calculations of electricity demand and temperature
increases across the US in 1992, heat islands alone were estimated at costing $1 million an hour or
over $1 billion a year in electricity costs [157].
Since 1920 Los Angeles’ temperature has increased by 2.5°C which represents a 1500 MW
increase in energy demand.
Rising temperatures increase the demand for cooling in the use of air‐conditioning units and fans.
In the USA a sixth of all electricity generated was used to air condition buildings. This equates to
80 million metric tonnes of carbon emissions and approximately $40 billion a year in energy bills.
Of these figures roughly 50% occur in cities that have been classed urban heat islands [080,
figures from 2001]. In the last 40 years air conditioning use has risen by 10% [080].
Another study in the USA has shown that the temperature increases relating to UHI account for
5‐10% of urban peak electricity demand for air conditioning use [112]. Peaks are generally on hot,
summer weekday afternoons [078].
A study in Brazil looked at a residential area of a medium sized city and mapped its energy
consumption against its thermal environment. The study used air temperature data, rural
temperature data, electrical energy consumption of the houses and the income levels of the
residents. Then GIS tools produced maps for analysis. In the results when comparing thermal
maps to energy consumption those areas showing larger UHI intensity showed increased levels
of energy consumption, up to 20% more than other areas regardless of income level. However,
when maximum air temperature levels were compared to energy consumption no such
correlation existed [149].
In Athens, heat island intensity often reaches 10°c. In Athens the increase in energy use as a result
of this temperature increase was studied, the building’s cooling load nearly doubled, peak
electricity load nearly tripled for higher set point temperatures; however, heating loads were
reduced by up to 50% compared to suburban buildings [150].
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