Review and Critical Analysis of International UHI Studies

These studies were founded primarily on numerical simulations (depending on the scaling they
used different granularity of models that often made use of the DOE2/3 building energy analysis
program) and not the outcomes of data collection from large scale implementation. It was found
that temperature increases above a certain threshold would result in steady increase in peak
urban electric demand. For case specific city studies and hypothetical scale‐up scenarios (often in
hot climates with collective countermeasure implementation) that energy consumption and peak
power at the building, city and national scales can be decreased significantly both directly and
indirectly. It was also found that the primary energy saving technologies could generate greater
energy savings than UHI countermeasures and also have the potential to contribute to the
mitigation of UHIs. The studies that examined the CO2 reduction due to mass modification to
existing cities with urban green areas, reflective roofs and pavements demonstrated that
significant reductions in CO2 levels were achievable. Results for energy use, peak power and CO2
as a consequence of UHI mitigation measures were not easily transferable from one
region/climate zone to another and in scaling up such estimates to a global scale it was evident
that there is still significant research and refinement is required.
4.2.3 Energy/Peak Power/CO2 Literature Review
There are twenty references which addressed the energy, peak power and CO2 emissions as
defined above in the literature reviewed. Of these studies 65% emanate from the Lawrence
Berkeley National Laboratory Urban Heat Island Group [021, 027, 028, 033, 034, 035, 059, 066, 070,
079, 112, 142, 171] with a majority of studies focusing in North America and Japan but also
Singapore.
Of these nine studies addressed energy use [009, 015, 021, 022, 027, 033, 066, 079, 171,], thirteen
studies address peak power [021, 028, 031, 033, 034, 039, 059, 066, 070, 079, 111, 112, 171] and four
address the CO2 emissions [035, 041, 066, 142].
Nine studies addressed energy use were predominantly based on numerical simulations and
were not results of large scale implementation and measurements [009, 015, 021, 022, 027, 033,
066, 079, 171]. A selection of studies that help highlight the key conclusions are reviewed here. A
study produced by LBNL on Canada examines the heat island effect of the implementing UHI
mitigation measures in mass in the form of shade trees strategically position such that they
provide not just shading but also wind shielding and the use of cool roofs across the Greater
Toronto Area – the annual energy savings of the building sector are calculated using an hourly
building energy simulation model. The results show that annual energy savings of over $11m can
result from the mass implementation of UHI strategies across the Greater Toronto Area – the
potential annual electricity savings are estimated to be in the region of 150GWh. It demonstrated
that the combined use of reflective roofs and strategic shade trees reduces the summer cooling
energy use but also potentially incurs a penalty increase in the winter heating energy use,
however the approach yields results that are highly sensitive to the prices of cooling and heating
energy fuels (i.e. gas and electricity). It was evident that the research used to conduct this study
was better suited for addressing the mass effects of shading as opposed to shading effects of
trees; the DOE‐2 model has been addressed in both this paper and others to underestimate the
cooling‐energy savings and potential of reflective roofs (by as much as a factor of two); the
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