CEFEP Technical Blog

Insulation of pipes and ducts is often an afterthought, seen as something that needs to be done but with little consideration given to the details of which materials or how they should be installed. This often leads to difficult or irregularly shaped parts of a pipe insulation system like flanges, valves, pipe supports and complicated bends or elbows being left un-insulated. In some cases these pipe fixtures are simply covered with PVC or duct tape to make them ‘look’ part of an insulated system without providing any of the energy saving benefits.

The FfE (Forschungsgesellschaft für Energiewirtschaft) in Munich conducted a study in 2012 to understand the impact of insufficient and incomplete (thermal) insulation on pipes and ducts. The institute examined the existing pipe insulation of six firms from different segments.

The findings are revealing: Retro-fitting all uninsulated components of the pipe systems could reduce energy losses by more than 20%(1).

Although the study is not representative of all building types, the results clearly demonstrate that applying thermal insulation to a pipe system in its entirety can have a significant impact when it comes to reducing the energy consumption and CO2-emssions of occupied buildings.

Source: (1) FfE Study - Energy saving potential by mechanical insulation, Final Report, November 2012 (only available in German)

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Keeping the surface of an insulation material above the dew-point temperature is key to stopping condensation.  Insulation thickness and thermal conductivity play major roles but, when it comes to controlling the surface temperature of insulation, no material property is more important than the surface emissivity.

Surface emissivity measures the potential of a material to emit energy in the form of thermal radiation.  Black, non-reflective, surfaces with a high emissivity finish are well suited to keeping the surface temperature above that of the dew-point.  Relatively small thicknesses of insulation can be used to reliably prevent condensation if the insulation material presents a high emissivity surface finish.

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Insulation made of flexible elastomeric foams (FEF) or polyethylene foams (PEF) can help to reduce the health risks associated with heating and plumbing pipework. Insulation is especially important when it comes to reducing bacterial growth inside domestic water supply pipes. "The Legionella bacteria grows at an accelerated rate in 'stationary' water at temperatures between 25 ºC and 60 ºC," explains Georg Eleftheriadis, Chairman of the European Association CEFEP.

"FEF or PEF thermal insulation can reduce temperature variations and so support the quality and 'purity' of drinking water.” Closed cell insulation with its in-built water vapour barrier saves energy efficiently and protects against moisture ingress at the same time.

International standards and strict EU regulations define how to supply drinking water in order to guarantee a high level of "purity". The European standard EN 806 defines precisely which measures should be implemented in order to supply safe, clean drinking water.

The legionella bacteria favours temperatures between 25 ºC and 60 ºC, a range that can be encountered in both hot and cold water pipes. When inhaled in small droplets - for example, as an aerosol in the shower - to the legionella bacteria can cause symptoms similar to those of pneumonia. "In order to counteract the risk of microbial contamination it is important that hot and cold water pipes are strictly isolated from each other by the appropriate technical insulation," explains Georg Eleftheriadis.

Reliable insulation protects against contamination

Appropriate pipe insulation helps to minimise the risk of hot water temperatures falling below 60 ºC and cold water temperatures increasing above 25 ºC. These are the safe water supply temperature limits defined within EN 806-2.

Alongside energy saving considerations, environmental factors like humidity, ambient temperature and pipe temperature will influence the pipe insulation thickness selected. Regardless of thickness, insulation should also be resistant to moisture ingress in order to ensure long term thermal performance.

This is where the advantages of FEF and PEF insulation are most obvious. For cold pipes the operating temperature is lower than the ambient air which leads to condensation. Using FEF or PEF insulation with an in-built water vapour barrier at the appropriate insulation thickness no condensation will form, either on the surface of the pipe or within the insulation itself.

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Condensation on pipework should always be prevented wherever possible. Moisture formation can damage the structural fabric of a building, promote mould growth and either cause or greatly accelerate pipe corrosion. In extreme circumstances corrosion attributed to condensation can even shorten the lifespan of a mechanical system.

Insulation is used to ensure that the surface temperature remains above the critical dew-point temperature so that condensation cannot form. “The properties of the insulation play an important role in preventing condensation and closed-cell materials have a clear advantage,” explains Ralf Springub from the European FEF/PEF Interest Group CEFEP (Celle, Germany).

Warmer air can hold lots of moisture as water vapour but this capacity is diminished as it cools. Eventually cooling air must relinquish some of the moisture it could hold at higher temperatures, creating what we know as condensation. Any surface cooler than the surrounding air presents the potential for condensation but the risks are greater as the temperature decreases, making it a particular issue for refrigeration and air-conditioning pipes.

Fortunately pipe insulation doesn’t just reduce energy loss – it can also be used to prevent the warm, moisture laden, air coming into contact with the cold surfaces of refrigeration and air-conditioning pipework.

Better in black

“The properties of an insulation material are important when assessing its suitability for refrigeration and air conditioning pipework,” explains Ralf Springub, “it’s essential to keep the surface temperature above the dew-point so that condensation cannot form”. Besides the specific thermal conductivity, the surface emissivity of the insulation material is critical. The surface emissivity describes the potential of a material to give off energy in the form of thermal radiation etc. With a non-reflective, high emissivity finish, black surfaces are well suited to controlling the surface temperature. In this way, relatively low insulation thicknesses can be used for the reliable control of condensation.

Keep water vapour out of insulation and off the pipe

Differences in partial water vapour pressure force moisture towards cold surfaces. If water vapour is free to pass through the insulation surface it can cause interstitial condensation within the material, dramatically reducing energy saving performance and increasing the risks of pipe corrosion.

For many insulation materials the only way to prevent this is to apply an external water vapour barrier – usually in the form of a thin and easily damaged Aluminium foil. Closed cell FEF and PEF materials are, however, so inherently effective at preventing the passage of water vapour that they can be considered to possess an in-built water vapour barrier and do not require an external foil to be applied.

The nature of this resistance means that surface damage to a closed cell FEF or PEF insulation material is unlikely to significantly impair or diminish its ability to prevent condensation moisture ingress.

Maximising flexibility, minimising thickness

Because FEF and PEF insulation materials are not reliant on an low-emissivity external water vapour barrier they are able to present a high emissivity surface finish. This can lead to notably thinner insulation solutions for controlling condensation when using FEF or PEF materials.

FEF insulation materials are particularly practical when it comes to insulating irregularly shaped pipework elements like valves and flanges. Thanks to the flexibility of the foam and the inherent water vapour resistance offered by the closed cell structure, FEF materials can be easily shaped and cut to size and aren’t reliant on a externally applied water vapour barrier for protection against moisture ingress.

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