MASTERPLANNING LOW CARBON CITIES


and therefore tends to reflect little solar radiation towards occupied zones. This means that unshaded water absorbs a lot of solar radiation; but this does not necessarily produce a significant increase of water temperature due to the large thermal capacity of water and evaporation at its surface.


Cool spaces Courtyards can be designed as well- shaded, sheltered places where localised air temperature reduction due to heat sinks can be contained and improved. The addition of vegetation or water features into such spaces can provide significant improvements to the environment. As a result of this, a building opening onto a courtyard is likely to have lower radiative and convective fluxes. Transition spaces between air-


conditioned buildings and the outside can protect entrances while providing pleasant climatic transitions for people. Large buffer spaces can replace vestibules to capture air conditioning leakage at entrances while using passive techniques to improve conditions, leading to zero-energy public areas. Retail circulation can occur outside of conditioned malls in passively improved areas to reduce the total conditioned area.


Centralised systems Lower external temperatures can improve the efficiency of heat rejection. It is suggested that heat rejection may be centralised and carefully placed to reduce further anthropogenic heat input. Such planning of systems at an urban scale offers the potential to place heat-rejection devices in better ventilated environments and improve their efficiency, further reducing energy consumption. Centralisation provides improved scope for the use of new technologies such as solar-powered district systems.


Renewables The potential for renewable energy production associated with buildings is limited by the availability of resource: urban form should ideally be devised to provide buildings with elements facing the sun. In sunny climates, the unshaded surface area available for solar water heaters should be guaranteed, and space for future solar plant reserved. The installation of renewables should be considered on a regional scale when masterplanning, to achieve the most economic solution. Building-integrated


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Urban design


Materials Vegetation Water


Geometry etc


Improved external comfort


Reduce urban heat island effect


Improved air quality


Reduce energy consumption


Fewer cars


More natural ventilation


Centralise heat rejection


Reduce cooling loads


Figure 2: Positive feedback mechanisms in urban design for reduced energy consumption


generation should be addressed in context of the site, but compared to centralised options when available.


Conclusions The aim of microclimate design in climates with very hot seasons is to extend the usability of the external environment further from the cold season towards the hot season. In many locations this can produce outdoor spaces that are usable all year round. It is unlikely that passive measures will provide external comfort in extreme Middle Eastern summers, and this should not be a design aim for sustainable developments. For the maximum impact on designs,


and therefore the largest impact on energy use, it is necessary to consider the urban design principles discussed here at the earliest stage of a project through design workshops and outline studies. As designs progress, analysis may be carried out in order to support the implementation of energy-saving site-wide strategies. We ought to think bigger about our


designs, beyond the usual low-energy mantra of ‘passive building design first, then efficient systems, then building integrated renewables’. We need more consideration of context and more sustainable masterplans. Encouraging designers to think on an urban scale is crucial: the impact of masterplanning will be enormous and very long term.


l Becci Taylor works for Arup


The installation of renewables should be considered on a regional scale when masterplanning, to achieve the most economic solution


August 2011 CIBSE Journal


27


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