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The tool calculates the thermal mass and related properties of
construction elements such as walls and floors |
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Part L of the Building Regulations, which deals with the conservation of energy, is currently being revised along with the compliance tool for housing known as SAP (Standard Assessment Procedure). The changes to SAP include a more-rigorous treatment of thermal mass in housing and the role it can play in passive design. When used appropriately, thermal mass can improve energy efficiency during the heating season by providing a means of capturing and slowly releasing free heat gains from the sun and internal sources.
This cuts the load on the heating system and reduces CO2 emissions, particularly in well insulated, air-tight homes.
The revisions take better account of this passive heating effect and, to help designers take advantage, the Concrete Centre commissioned Arup to develop a free Excel-based tool for calculating the thermal mass in floors and walls, which can now be downloaded at www.concretecentre.com.
The methodology is based on BS EN ISO 13786, and is fully aligned with SAP, allowing thermal mass values (also know as Kappa values) to be easily calculated and used in SAP software. If required, admittance values are also produced, providing an alternative means of assessing thermal mass.
Another feature of the tool is its ability to calculate decrement. This is a property of thermal mass which describes the way in which the density, heat capacity and thermal conductivity (of a wall for example) can slow the passage of heat from one side to the other (decrement delay), and also attenuate gains as they pass through (decrement factor). Designing for a long decrement delay of around nine hours or more, and a low decrement factor can help reduce overheating problems in summer.
The motivation for producing this tool is the growing need among architects and engineers for more information about the thermal characteristics of construction elements, other than just their U-value. This information helps to inform passive design choices and optimise the energy efficiency of the building form and fabric. Going forward, we are likely to see more attention paid to getting this right as the building fabric will have to work harder to help achieve the challenging requirements of Part L and the approaching zero-carbon target for new buildings. A further driver is the need for climate change adaptation, which will also place greater demands on the performance of construction materials.
 
For further information please contact Tom De Saulles at
The Concrete Centre (01276 608714; E-mail: info@concretecentre.com).
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