Cool roof technology is known to reduce the cooling energy consumption of conditioned buildings during hot periods, and widespread implementation of such roofs in a neighbourhood or precinct can mitigate the urban heat island effect. Established building energy modelling techniques are able in principle to predict the benefits of cool roofs due to reduced heat transfer through the roof structure. However, several scientific and industry publications have claimed that additional benefits can arise from the reduction in air temperature above cool roofs. Rooftop heating, ventilation and airconditioning (HVAC) equipment energy consumption would be reduced by such an effect, and the efficiency of rooftop photovoltaic (PV) panels would be improved.
A small number of studies have attempted to quantify the effects of cool roofs on above-roof temperature fields and the performance of rooftop equipment, but these studies have been relatively small in scope and have produced varying results. It is likely that some such effects exist, that are not currently taken into account in assessments of roof performance, but prior to the present project it was not possible to determine whether such effects are significant. This report summarises the work carried out under project RP1037, the aim of which was to generate experimental evidence, and other data, that may be used to more accurately quantify the benefit of cool roofs to Australian largefootprint buildings, including the generally unaccounted-for above-roof effects described above.
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Conventionally in building performance simulations (BPS), it is assumed that air entering outdoor HVAC equipment is at the outdoor ‘ambient’ temperature, obtained from a weather file. However, significant spatial variations exist in outdoor air temperature fields, especially within the thermal boundary layers that form near exposed surfaces like roofs.
The implementation of ‘cool’ roofing materials, with high solar reflectance and infrared emittance, has received significant attention in recent years, as a method to mitigate the urban heat island effect and reduce building cooling energy requirements. The effect of ‘cool’ roofs on heat transfer through the roof structure has been investigated by many researchers. However, the air temperature field above roofs and the influence of elevated above-roof air temperatures on the performance of rooftop air-conditioning equipment and photovoltaic panels have not been studied in depth.
This document presents the mitigation study for the CBD area of Darwin, performed by the High Performance Architecture Group of UNSW, Faculty of Built Environment.The first part of the report includes the methods and the results of the terrestrial and aerial monitoring campaign, the evaluation of the magnitude of the Urban Heat Island (UHI) and finally the main conclusions on the climatic context characterized with the monitoring.
This is the first interim report for project RP1037u1, an extension to the recently completed project RP1037 ‘Driving increased utilisation of cool roofs on large footprint buildings’. Progress so-far in the project and preliminary findings have been summarised in this report.