Review and Critical Analysis of International UHI Studies

� The degree to which the change in air temperature associated from using cooling
pavements will affect the buildings and their cooling loads;
� Whether or not the building stock has both active cooling/heating systems installed
(otherwise the impact is only felt through changes in thermal comfort);
� The energy efficiency of active‐cooling and heating systems;
� The control regime of the active‐cooling and heating systems.
4.5.2.2 Cool Pavements Summary of Literature and Findings
A majority of the studies emanated from the LBNL Urban Heat Island Group and were North
American centric. The term pavements were loosely defined but this review classified them as
urban streets, driveways, parking areas and footpaths. It was demonstrated predominantly by
modeling and simulation case studies that the use of cool pavements can have a reduction on the
near ground temperatures of cities. It was however, difficult to isolate and attribute the indirect
energy and peak power savings from pavements due to the nature of indirect measurements and
the fact that cool pavements were often studied in combination with other UHI countermeasures.
The indirect savings potential (achieved by reflective roofs/pavements and vegetation) forms
only a small fraction of the total potential savings – it was concluded that higher priority should
therefore be given to measures that have both direct and indirect effects on the temperature and
thus energy savings and CO2 e.g. roofs and shade trees.
A large range of different cool pavement alternatives exist and are to varying degrees constrained
by their intended end‐use. Apart from the reflectivity and thermal emittance the cool permeable
pavement designs have the capacity to remain cooler than non‐permeable equivalents when wet.
Due to the immaturity and complexity of the cool pavement technology few studies addressed
the associated costs – however, early indicators show that they are more costly than conventional
designs. It was acknowledged that there was a loss of pavement performance (in terms of
reflectivity) due to weathering, dirt accumulation/pollution, use, age, etc but this requires further
case specific evaluation. The benefits, complexity and lack of data on cool pavements
performance in certain climates/conditions has meant research has tended to take precedence
over policy.
4.5.2.3 Review of Cool Pavements
There are twenty‐six references which addressed the use of cool pavement technology to mitigate
the urban heat island effect. Cool pavements were loosely defined by most papers, thus in this
review the papers reviewed define pavement technologies to include: paving for urban streets,
driveways, parking areas and footpaths. Over 50% of the papers emanated from the Lawrence
Berkley National Laboratory Urban Heat Island Group [021, 027, 028, 033, 035, 061, 066, 068, 070,
079, 105, 112, 128, 134]. The results of the LBNL studies tended to some degree form the
foundation for much of the remaining work/conclusions drawn for the other studies.
Nine studies examined the effects of albedo and other design parameters on lowering the
ambient temperature and thus the associated energy savings, peak power and power related
emissions of which five studies were conducted by LBNL [002, 021, 033, 035, 066, 073, 079, 112,
142]. The studies collected data on the local scale and then used models and simulations to
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