According to EU figures, approximately 40 per cent of the UK’s energy consumption is expended on heating, cooling and lighting buildings. In the face of pressure to cut carbon emissions, reducing this figure is now a key government target.
The Code for Sustainable Homes, published by the Department for Communities and Local Government in 2006, set a target of producing zero carbon homes by 2016. Meanwhile, later this year the government’s Climate Change Bill will become law. This aims to set a legal framework for ensuring reductions in CO2 emissions by 2020 with a final aim of achieving a 60 per cent reduction of 1990 carbon emission levels by 2050.
But it is not just the government that is interested in reducing energy loss — and its associated bills. Measuring the insulation properties of building materials and structures began in the 1940s and 1950s, but was thrust into the spotlight during the energy crisis of the 1970s. Now, soaring energy costs and the introduction of Energy Performance Certificates that allow prospective homebuyers, and soon, renters, to see a home’s energy use have once again brought insulation to the fore.
Further legislation and regulations aimed at minimising energy use in new buildings, and eventually older properties, are expected. This means everyone from manufacturers, regulatory authorities and builders to architects and designers must prove their products and designs meet stringent guidelines for thermal performance, without which they will not be able to sell the products.
However, the measurements used to judge this thermal performance must be accurate and traceable to accepted measurement standards, and the expertise and equipment to undertake the mammoth task of certifying everyone lies with just a few specialist sites.
‘Apart from the major insulation manufacturers, which have apparatus for measuring the thermal conductivity of their products for quality control, there are only seven organisations that are accepted by the United Kingdom Accreditation Service (UKAS) to measure the thermal properties of materials and two that are UKAS accredited to measure the thermal performance of structures, and the National Physical Laboratory (NPL) is one,’ said Ray Williams, principal NPL research scientist.
To determine materials’ thermal performance, the organisation has developed apparatus that is capable of accurately measuring the thermal performance of insulation materials from -170°C through room temperature and on up to 800°C. Meanwhile, NPL houses the UK’s only pipe insulation thermal performance measurement facility.
It is also home to one of the few HotBox facilities for measuring the thermal performance of sections of structures ranging from masonry walls to windows, doors, roofs, wall and floor structures.
The apparatus can thermally measure both building materials and structures, including traditional and innovative insulation materials, pipe insulation, walls, windows, roofs and doors, allowing users to see clearly how their use can contribute to the development of low energy buildings.
Using its resources, NPL can provide a level of accuracy and confidence in its measurement that will be vital to the certification of low-energy construction materials and products and, ultimately, to the industry’s ability to compete in an increasingly regulated market.
The thermal conductivity of homogeneous materials, such as masonry and insulation, as well as the thermal transmittance of structures such as walls, roofs, floors, windows, skylights and curtain walls can also be measured by the apparatus.
Measurements can be carried out at all orientations, which is vital as convection is affected by the heat transfer direction relative to gravity. In total, the data produced includes information on 37 different parameters including airflow, heat flux, and emissivity.
‘The materials are essentially tested by driving temperatures through them,’ said Williams. ‘There is a warm and a cold chamber, and a specimen is clamped between them within a polystyrene wall whose properties are known exactly. Then the air temperature on each side is measured, as well as the temperature of the surfaces. We also measure air movement. The trick is to make sure all the power goes through the sample without loss or gain, to ensure the result is not invalid.’
One user of the facility is Web Dynamics, a company that manufactures construction materials, notably TLX multi-foil insulation and WEB UV-breathable roofing underlays. Using NPL’s facilities, they tested the thermal performance of a roof section insulated with TLX.
‘We built a small section of a roof consisting of three rafter widths. Below the rafters a foil-backed plasterboard was fitted,’ said technical manager John Payne. ‘Above rafters, TLX was fitted, then battened in place and a breathable underlay added on top.’
The thermal transmittance, or U value, of this roof section was measured in the HotBox, providing a result of 0.53 w/m2K.
‘This test result allowed us to derive the thermal resistance, or R value, of TLX installed in this way,’ said Payne. ‘This in turn meant we could develop roof structures based on TLX that meet the building regulation standards for roof insulation.
‘It also allowed us to gain the first-ever BBA certificate for a multi-foil insulation for TLX. The HotBox was beneficial — as it is an ISO standard test method, the results are widely accepted. If we had developed our own test method it would not have as much credibility.’
The benefits of NPL’s systems and the data it can deliver are clear, especially when faced by dweller demand and increased legislation. All that is needed now is for industry to submit materials for accurate testing.
‘In a building there are huge savings to be made over the course of 50 years by putting in insulation,’ said Williams.
‘In the UK we waste a higher percentage of the country’s energy consumption through our homes than we use in manufacturing.
‘There are also future issues including how to correctly evaluate the benefits of buildings utilising high thermal inertia or how to maximise the benefits of the use of good passive solar design; both currently rely on fairly complex calculations to demonstrate their value.
‘In the meantime, centres of expertise like NPL will be leading the drive towards greener housing — but it is up to industry to make the most of the resource.’
As UK energy waste continues to go through the roof, a handful of organisations is leading the drive towards greener housing. Julia Pierce reports.