THERMAL EFFICIENCY
The inherent thermal mass of reinforced concrete increases the potential for energy efficient buildings.
The potential of concrete's thermal mass to realise fabric energy storage (FES) solutions for improving the energy efficiency of buildings and so reduce their carbon emissions is being increasingly recognised. Concrete offers a free thermal sink that absorbs heat during the day and can be cooled during the night. Steel conducts heat rather than absorbs.
The UK Climate Impacts Programme predicts that by the 2080s, annual temperatures for the UK may increase by up to 3.50C. In London, peak summertime temperatures are likely to increase by around 70C taking a warm summer day to over 400C. This will have a considerable impact on the internal temperatures within the buildings that we are designing and building today, especially those that do not expose thermal mass. Growing concern over climate change, increasing energy prices, and changes to the Building Regulations are increasing pressure on designers and clients to realise the potential of Fabric Energy Storage (FES). FES is the ability of heavyweight materials, such as concrete, to absorb and store heat.
Typically, using concrete's FES can result in internal temperatures being some 80C cooler than peak external summertime temperatures. The provision of a cooler and more comfortable internal environmental would have a positive effect on the workplace.
The optimal thickness of concrete floors to maximise FES is greater than 250mmm. This relies on exposure of both sides of the slabs. The top surface of the slabs can be 'exposed' by passing air through a floor plenum and having floor diffusers.
A FES system using exposed concrete soffits provides a cooling capacity of up to 25W/m2 of floor area. Active FES systems, using ducted air within the concrete slab, can provide cooling of up to 40W/m2. Alternatively, water can be used in an active concrete system as an effective cooling (or heating) medium. Embedded pipes in floor slabs can achieve a cooling capacity of 64W/m2. These figures compare with typical heat gains in office dues to equipment, lighting and people of 20 to 30 W/m2 and solar gains of up to double this.
FES is by no means a new technology, indeed the principle is the basis behind the construction of 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 new buildings. The high thermal mass of concrete can contribute positively and cost effectively to a significant reduction in the energy consumption of buildings by minimising the need for air conditioning. Best of all, this is a performance advantage that you get for free from concrete construction.
