Detecting heat loss
October 1st 2005

by Paul Sacker, UK sales and marketing manager, FLIR Systems

"Uncontrolled heat loss and gain through the walls and roof of a building is no longer acceptable. It leads to excessive use of fuel, causes pollution and increases CO2 emissions. UK and European regulations have now been tightened up so that not only must good insulation be designed and specified, but achievement of the required performance and the quality of installation must be proven."

This is the opening statement from a new best practice guide for continuous insulation published by BSRIA, the UK's leading centre for building services research. It draws clearly on proposed new legislation regarding the energy efficiency of buildings being developed by the Office of the Deputy Prime Minister - in particular the Building Regulations Part L. So how can you ensure you are complying with these new rules? The ideal method of detecting heat loss through a building structure is infrared thermography. But how does it work? What are its benefits? And what training do you need?

Any object that is not transmitting, generating or absorbing heat will take on the surrounding air temperature. So cold air leaking into a building - or missing insulation on a heated building - will cause cold patches on the wall, floor or ceiling. Conversely, warm air leaking from a building will cause warm patches on the outside of a wall or roof. The air tightness testing requirements for new buildings are being significantly tightened.

But it is not just through air leakage that heat energy is lost in building structures. Thermal bridges and slippage of insulation materials also cause energy loss and these are harder to detect without a thermal imaging camera.

Thermal imaging cameras are designed to enable you to see these temperature differences through a viewfinder or on an LCD display. The sensing medium they use is infrared.

IR radiation is emitted by all objects warmer than -273°C.

The measurement results are shown instantly and on some cameras you can take both a thermal and a visual image of the problem area, making evaluation even easier. It is also possible to record voice and text comments.

Some infrared camera systems are more suitable for building surveys than others. So what are the basic credentials? Firstly it should be a longwave camera, less sensitive to solar reflection than a medium wave IR camera. It also helps to be fully radiometric to facilitate measurement of surface temperatures. While many thermal imaging cameras are available, most do not have the narrow temperature range required to determine the frequently small temperature differences that indicate a potential problem. The temperature span setting must be displayed and provide minimum detectable temperature solutions of better than 0.1°C at an ambient temperature of 20°C. The ability of the camera to record thermal images to a digital memory is also important.

Three key elements need to be borne in mind when carrying out infrared surveys to assess the heat loss characteristics of a building envelope. Firstly the camera operator needs good knowledge of the construction being surveyed to predict the thermal patterns likely to be induced when an air leakage or thermal insulation weakness occurs.

It will also help determine whether an internal or external survey is most appropriate.

Ideally the survey should be performed at night or with little direct solar radiation. Sufficient time must elapse to allow heat previously builtup from solar gain to be emitted from the building. Temperature differences across the building enclosure, ambient temperatures and wind speed all need to be monitored and all building surfaces must be inspected dry.

The final element is recording the acquired survey data. Documenting results is easy with good quality infrared cameras. They allow the user to download information straight onto their PC.

Guidance on all these aspects as well as setting and operating the camera is naturally given within the training programmes offered by the top manufacturers. International recognized certification on three levels is now available and in the UK training to PCN standard is offered by Approved Training Organisations certified by the UK Thermography Association.

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