BRE FB9 PDF

Introduction

Overheating in buildings can happen for a number of reasons including poor ventilation and high internal heat gains. However one of the most common causes of overheating is excessive solar gain, particularly in buildings with large glazed areas.

Introducing air conditioning and comfort cooling is a common way to control overheating. Cooled floorspace area is increasing by 6.5% annually in the UK. This can substantially increase, though, a building's energy consumption. A BRE case study, Comfort without air conditioning in refurbished offices^[1], estimated that installing air conditioning in a typical 1960s open plan office would require an extra 55 kWh/m² per year, resulting in overall air conditioning running costs of £15/m² per year.

The same study showed that, in many cases, comfort could be achieved at zero cooling energy consumption with a combination of solar shading (either mid-pane or external) and night ventilation. The extra cost of these measures will usually be substantially less than that of installing cooling. But the calculations showed that, even in a building where cooling had already been fitted, the shading could pay for itself in under five years.

Choosing the best form of solar shading is not always easy, however. The effectiveness of shading will depend on the orientation of the window, the location of the shading device (external, internal or mid-pane), and its detailed geometry and optical properties.

This report provides data that can be used to quantify the ability of windows and shading devices to control summertime overheating. Chapter 2 describes the different terms that are used to quantify solar control. Chapter 3 explains the different approaches that can be used and gives generic data for the most common system types. Chapter 4 gives more detailed data for a range of systems. Finally, Chapter 5 explains how the data can be used to compare different device types and as input to simple calculation methods.

The data in this report are intended solely for the assessment of solar overheating in summer. They cannot be used to evaluate the benefits of glare control, or reduction of winter solar gain or daylight. A previous BRE report^[2] covers these issues.