Review and Critical Analysis of International UHI Studies

the insulated house to 43% savings in the un‐insulated house [061]. Most simulations accounted
for insulation when defining the prototypical house, others however, rejected the impact of such
building design factors [021, 033, 072].
Most models generate useful estimates from mitigating measures such as cool roofs but the exact
energy savings are difficult to compute for a given site. Many factors come into play apart from
roof albedo: daily energy patterns; energy efficiency of cooling systems (lack of presence of
cooling systems – as is the case for poorer regions and some non‐commercial buildings); and the
type of insulation [021, 025, 058]. Such parameters are important considerations that have to be
accounted for in conducting scale up of micro phenomena. There was little attention given to
control in cooling/heating systems, though it was mentioned that A/C are often difficult to
regulate to produce comfortable temperatures and thus a cool roof system would help to reduce
the A/C intensity and assist with the control of the building temperature [025].
Four studies indicated that there have been significant design efforts in adapting the more
traditional colored roofing materials by identifying and characterizing pigments to
include/exclude in the colored cool roofing material design. Cool colored roof material on
average had 0.22 higher albedo than their traditional counterpart – resulting in a maximum of
12K reduction in the material surface temperature. This temperature reduction was tested and
thus quoted to equate to a maximum of 600W peak power savings and an annual cooling energy
saving of 650kWh – with the cost of heat loss in the winter months from reflected incident solar
gain less than 30% of the cooling savings [025, 061, 071, 072, 112].
Four Studies demonstrated that roofs are typically repainted or replaced every 10‐20 years, and
high albedo alternatives are available at little extra cost with the exception of some newer
materials (e.g. asphalt shingle roofing with ceramic coated granules). Typical payback periods for
a majority of high albedo materials ranged from 0‐10 years again with the exception of the very
latest products quoted to be 8‐19 years. High albedo roofing options for new builds may require a
higher initial investment but are often more attractive when life‐cycle costs are examined – due to
longer roof life and energy savings [021, 025, 061, 071].
Limited studies addressed the cool roof penalties in hot vs. cold conditions and similarly these
conditions at different geographical locations. A simulation study for Toronto, Canada found that
for residential buildings the cooling energy savings were written off by penalties in heating
energy use [033]. Another study, concluded that there was no winter penalty for the US state of
Mississippi for employing cool roofs [072]. In general it was acknowledged that it depended
upon the aggregation of a complex set of influential factors such as the geographical location,
time of year etc. This hasn’t been extensively reviewed for other climates but is indicated that
savings are greatest for buildings located in climates with long cooling seasons and short heating
seasons, but this requires data collection and field experimentation as conducted in the US, Japan
and parts of Europe – note: over 90% of the studies referred to experiments and models were
conducted for North American or Canadian cities [015, 025, 027, 033, 034, 061, 066, 071, 072, 113,
114].
The acknowledged benefits of cool‐roofs in certain climates (predominantly in equatorial, arid
and warm temperate climates) have resulted in several incentive programs, product labeling and
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