BRE BR431 PDF

Introduction

BRE has been developing guidance for building designers on low-energy design solutions which maximise the application of solar access and passive cooling strategies in the urban environment. This guide and the design tool it includes have been produced to enable the construction industry to move towards reducing the impact of the urban heat island on peak cooling-energy demand in buildings.

Central areas of London can be significantly warmer than the surrounding areas, a phenomenon known as the heat island effect. These increased temperatures have an important impact on the cooling loads in buildings. Average cooling demand in a central London site is more than that at a rural site, and the efficiency of air-conditioning plant is decreased at higher temperatures. So the use of rural temperature data to calculate cooling loads can result in significant underestimates.

This guide presents the results of a unique long-term monitoring experiment to measure air temperatures at 80 sites spread around London. Summertime temperatures from some of the sites were then used in a model for a typical office building. The resulting design tool on the diskette included with this guide allows the designer to modify temperature data from Bracknell (the reference site for temperature data on pages 2–71 of CIBSE Guide A[1]) for the calculation of peak summertime cooling loads at 80 different locations in London.

The guide also outlines a range of techniques to reduce or even eliminate the effects of the heat island by careful design of the building and its surroundings, including:

• Alternative cooling strategies such as natural ventilation, night cooling, mixed mode

• Building layout to encourage wind flow and ventilation

• Landscaping and vegetation using trees and green areas, vines and other plants on walls

• Water features

• Surfaces with high albedo, to reduce heat build up

• Solar shading

• Reducing casual gains; avoiding unnecessary cooling caused by inefficient equipment and lighting