Environmental thermal loading on urban buildings is expected to increase owing to the combined influence of a warming climate, increasing frequency and severity of extreme heat events, and the urban heat island (UHI) effect. This paper presents how a computationally efficient estimation pathway could be utilised to understand UHI influence on building energy simulations. As an example, this is examined by considering UHI influence on the space-conditioning loads of office buildings within urban and suburban conditions, and how the trend of replacing heavyweight facades with lightweight alternatives could affect their surrounding microclimates, as well as building energy use. The paper addresses this through simulations of street canyons based on the urban Moorgate and suburban Wimbledon areas of London. Results show that with all scenarios including the UHI within a dynamic thermal simulation presents between 2.5 and 9.6% net increase in annual space-conditioning. The study also demonstrates that the trend in urban centres to replace heavyweight facades with lightweight insulated alternatives increases space-conditioning loads, which in turn increases UHI intensity to create a warming feedback loop. The study therefore stresses the significance of including microclimate loading from the UHI in estimating urban and suburban energy use, and the combined simulation approach is presented as a computationally efficient pathway for use by built environment designers.

It has long been recognised that cities exhibit their own microclimate and are typically warmer than the surrounding rural areas. This ‘mesoscale’ influence is known as the urban heat island (UHI) effect and results largely from modification of surface properties leading to greater absorption of solar radiation, reduced convective cooling and lower water evaporation rates. Cities typically contain less vegetation and bodies of water than rural areas, and existing green and bluespace is often under threat from increasing population densities. This paper presents a meta-analysis of the key ways in which green and bluespace affect both urban canopy- and boundary-layer temperatures, examined from the perspectives of city-planning, urban climatology and climate science. The analysis suggests that the evapotranspiration-based cooling influence of both green and bluespace is primarily relevant for urban canopy-layer conditions, and that tree-dominated greenspace offers the greatest heat stress relief when it is most needed. However, the magnitude and transport of cooling experienced depends on size, spread, and geometry of greenspaces, with some solitary large parks found to offer minimal boundary-layer cooling. Contribution to cooling at the scale of the urban boundary-layer climate is attributed mainly to greenspace increasing surface roughness and thereby improving convection efficiency rather than evaporation. Although bluespace cooling and transport during the day can be substantial, nocturnal warming is highlighted as likely when conditions are most oppressive. However, when both features are employed together they can offer many synergistic ecosystem benefits including cooling. The ways in which green and bluespace infrastructure is applied in future urban growth strategies, particularly in countries expected to experience rapid urbanisation, warrants greater consideration in urban planning policy to mitigate the adverse effects of the UHI and enhance climate resilience.

A warming climate, increasing frequency and severity of extreme heat events, and the urban heat island (UHI) effect, are all expected to intensify thermal loading on buildings. This paper examines how the heat island affects space-conditioning loads within urban and suburban office buildings, and how the trend of replacing traditional heavyweight facades with lightweight alternatives can affect the magnitude and timing of the heat island experienced, as well as building energy use. This paper addresses this through simulation studies of street canyons based on the urban Moorgate and suburban Wimbledon areas of London. The results showed that including the heat island in dynamic thermal simulations to have an adverse effect on annual space-conditioning for urban canyon scenarios including stone facades, as well as a glazed alternative. With the suburban condition, a modest decrease in annual space-conditioning was shown for buildings with brick facades, while a white-painted timber alternative showed a marginal increase. The study demonstrates that the trend in urban centres to replace heavyweight building facades with lightweight insulated ones can increase space-conditioning loads, and thereby adversely affect the heat island to create a warming feedback loop. Within a suburban context however, the same change decreased space-conditioning loads to present a beneficial effect. The study in turn stresses the significance of accounting for heat island loads when estimating urban and suburban energy use, for which a combined simulation approach has been presented as an analysis pathway.