Inter-building effects on thermal management performance of cool walls in the tropical climate

The thermal management performance of cool roof may be limited when buildings are multi-story, because heat may penetrate through much larger wall areas, thus making cool walls a potential solution. Nonetheless, inter-building effects including mutual occlusion and reflection complicate the potential effectiveness of cool walls especially in urban context. However, study of inter-building effects on thermal management performance of cool walls is lacking. Therefore, numerical simulation was conducted in this study based on an experimentally calibrated model. When there are no surrounding buildings (very sparse density scenario), as wall to roof ratio increases from 2.0 to 10.5, the relative contribution to total cooling load reduction by cool walls becomes dominant (from 59 % to 89 %). For naturally ventilated building, cool roof + walls strategy can ensure that thermally uncomfortable time percentage is below 20 % judged by the standard of 20 % PPD (predicted percentage of dissatisfied). When buildings always have equal height, the effects of building layout typology and density are small under the minimum spacing requirement. For unequal building height scenarios, different fraction of cool coating application has different effects, but even under the worst-case scenario the total cooling load reduction can still reach 36 % maximum. Cool walls’ negative externality effects on adjacent building are also small: total cooling load increases are all below 4.6 % for air-conditioned building, and thermally uncomfortable time percentage increases are all below 1.5 % for naturally ventilated building. Financial return periods of cool coating application are satisfactory under different inter-building scenarios, which further emphasize the benefits of cool walls.