Give us shelter

The timeliness of a report from The Concrete Centre: Thermal Mass: Concrete Solutions for a Changing Climate, is underlined by the prediction from the Met Office of unusually high temperatures this July and August.

The prediction follows a recent BBC documentary drama that showed what would happen if temperatures topped 38°C for more than a week. It was based on the 2003 heatwave, which is estimated to have caused 27,000 deaths across Europe, 2000 of them in the UK.

The report argues that one of our best defences against these dangerous temperatures is a building’s fabric energy storage (FES). This refers to the way a building can absorb energy during the day and release it at night. FES helps to reduce and even out the building’s internal temperature, and it should reduce the growing demand for air-conditioning and the resulting increase in energy use and carbon dioxide emissions.

Current predictions from the UK Climate Impacts Programme, an organisation based at Oxford University, are that annual temperatures in the UK may increase by up to 3.5°C by the 2080s. In London, this may be as high as 8°C, taking the peak summertime temperature to greater than 40°C, which is higher than the present average temperature of Cairo. This will have a considerable impact on the internal temperatures of the buildings we are designing today, especially those of a lightweight construction. Typically, the use of FES can result in internal temperatures being 8°C cooler than peak external summer temperatures.

Growing concern over climate change, increasing energy prices, and changes to the Building Regulations are putting increasing pressure on designers and clients to take full consideration of the use of energy-intensive air-conditioning. As global warming progresses, the demand for air-conditioning will also increase. This is bad news for the environment. However, the combination of high thermal mass and night-time cooling can provide a cost-effective alternative to air-conditioning, especially when steps such as solar shading have been taken to minimise heat gain.

Central to the FES approach is the thermal mass provided by exposed concrete. This absorbs internal heat gains caused by heating, lighting, computers and other electrical equipment on warm summer days, thereby helping to prevent overheating and ensuring a more stable and comfortable internal temperature. Night cooling is used to purge the accumulated heat from the slab in readiness for the next day. Where mechanical air-conditioning is still considered necessary, FES can significantly reduce the energy required to operate the plant – and the associated CO₂ emissions – by supplementing mechanical ventilation and cooling. Alternatively, floor slabs can be water-cooled to maximise FES performance.

In addition to reducing peak internal temperature, a building with high thermal mass can also delay its onset by up to six hours. In a typical office, this will usually occur late in the afternoon or the evening, once the occupants have left. As the evening progresses, the external air temperature drops, making night ventilation an effective means of removing accumulated heat.

The benefits of FES are not limited to the summer months. Buildings can be designed to capture solar gains during the winter and store them in their thermal mass. This technique has been used to good effect at the BedZed housing development in south London, where it is estimated that the use of heating energy has been reduced by up to 30%, and in recent projects such as Brighton library.

The new report from The Concrete Centre examines a range of FES solutions for buildings including natural ventilation with exposed soffits, underfloor ventilation with exposed soffits, permeable ceilings, hollowcore slabs with mechanical ventilation and chilled beams with exposed soffits.

The increased use of FES was advocated in 2004 by one of the first studies to make a quantitative assessment of the effect of climate change on the built environment. Commissioned by the DTI and based on CIRIA research led by Arup, the study warned against relying on air-conditioning as this would further increase energy usage and therefore carbon emissions, and predicted that by 2080, the temperature in a lightweight home could reach 40°C. Arup found that buildings with high levels of thermal mass would be easier to adapt to cope with climate change. Conversely, the research raises obvious question marks over use of lightweight construction systems.

FES is not a new technology – the principle has been used by ancient civilisations throughout the Mediterranean. With Britain predicted to have temperatures more associated with southern France, FES must become a key feature in the design of buildings. Best of all, this comes free with concrete construction.

Thermal Mass: Concrete Solutions for a Changing Climate is available free from The Concrete Centre, 0700 4 500 500, www.concretecentre.com