A new flexible pipe system with plastic service pipe is the result of Kingspan LOGSTOR’s participation in the COOL DH development project. This is the pipe system the district heating industry has been waiting for. The main objective of the COOL DH development project was “to support cities in their endeavor to plan and deploy new, efficient district heating and cooling (DHC) systems and extend and refurbish existing ones to higher standards and thus, allowing greater uptake of renewables, recovering of excess heat or cold while improving the overall efficiency of the systems.”

By Peter Jorsal, Product & Academy Manager, Kingspan LOGSTOR

Published in Hot Cool, edition no. 8/2023 | ISSN 0904 9681 |

District Heating as a concept has a vital role in the green transition in Europe, a journey towards fossil-free energy electricity, district heating production, and lower CO2 emissions.

The green transition has kickstarted a massive need for expanding existing and building new district heating pipe systems.
In many countries, this results in a lack of contractors to do the job.

Therefore, the district heating market is looking for a solution that can be a good alternative to traditional steel pipe systems in relevant dimensions where there is no dependency on steel welders. Or, to be more specific:

High speed of installation
Less dependency on steel welders
Sustainable solutions
Low heat loss over a lifetime

PertFlextra is a result of the COOL DH development project.

More than three years ago, together with other companies, we joined an EU development project, COOL DH.

The Kingspan LOGSTOR objective for the COOL DH project was to “Design and build a low-temperature district heating grid with non-conventional pipe materials. Test new innovative pipe components introduced by COOL DH”.

The focus of the development project was the following:

Develop a plastic service pipe that should have a more robust performance on temperature and pressure than the present standards on the market, service pipe 25 – 110 mm SDR 7,4
Secure low heat loss in the entire lifetime of the pipe system
• Develop a system with plastic service pipe with the possibility of having an integrated surveillance system
The plastic service pipe shall be weldable, leading to the possibility of using electro-fusion couplings when connecting the service pipe
The flexible pipe shall be easy to install with a focus on the work environment

During this project, LOGSTOR developed PertFlextra, and 1900 m TwinPipe was installed in a project in Høje Taastrup, and 1900 m single- and TwinPipe was installed in Lund.

For further information about the COOL DH project, please see: https://www.cooldh.eu/this-is-cool-dh/

PertFlextra in details

PertFlextra is a complete range of diffusion-tight, flexible, pre-insulated pipe systems for community heating and district heating, according to prEN17878-1/2.

The service pipe in PertFlextra is made of polyethylene PE-RT type II SDR 7,4 featuring an aluminum diffusion barrier that prevents the diffusion of oxygen into the media and water vapor from the water into the PUR foam, thereby ensuring that the foam stays dry over a lifetime and heat loss remains low.

The service pipe is insulated with PUR foam, and the outer casing of HDPE has a built-in EVOH diffusion barrier that will ensure that heat loss property will not deteriorate over the lifetime.

The following describes the outcome of the targets defined in the COOLDH project.

Lifetime and performance of the PE-RT service pipe

Lifetime on a plastic service pipe can, according to EN15632-1 Annex A, be calculated according to Miner’s rule when knowing the typical temperature and pressure profile of the pipe system.

The service pipe in PertFlextra is SDR 7,4 PE-RT, whereas the service pipe on PEX pipes on the market is SDR 11. SDR 7,4 will have a higher wall thickness than SDR 11, and when doing the calculations according to Miner’s rule, PE-RT SDR 7,4 will have better lifetime performance compared to PEX SDR 11.

In other words, a system with PE-RT SDR 7,4 can be operated with higher pressure than a system with PEX SDR 11 at the same temperature profile.

Low heat loss during the entire lifetime of the system

There are three contributors to the low heat loss over a lifetime.

Low lambda value of the PUR foam
Diffusion barrier for water vapor on the PE-RT service pipe
Diffusion barrier in the corrugated casing for the PUR foam insulation gasses

Low lambda value of the PUR foam:

The PUR foam with where cyclopentane is the blowing agent.

Cyclopentane is accepted in the REACH regulations and does not conflict with any future additional restrictions, e.g., related to PFAS restrictions. Cyclopentane leads to insulating properties that are far better than, for example, pure CO2-blown PUR foam.

The latest lambda test on FlextraPipe has been carried out at the institute IMA Materialforchung und Andwendungstechnik GmbH, according to requirements in the EN standards, show a lambda50 on 0,0201 W/mK.

Diffusion barrier for water vapor on the service pipe:

The aluminum diffusion barrier on the PE-RT service pipe shall prevent oxygen diffusion into the water and avoid water vapor diffusion into the PUR insulation.

Concerning heat loss, the European standard for flexible pipe systems EN15632-1 Annex C defines that if a supplier does not have the diffusion barrier for water vapor on the service pipe, the declared lambda value shall be multiplied with a factor 1,1 to achieve the design lambda value.

Reference is made to a report done by the Danish Technological Institute, “Fleksible præisolerede rør med fugtig isolering” (Translated to English as “Flexible pre-insulated pipes with wet insulation”). The pipes tested in this project are flexible with PEX service pipes (without water vapor diffusion barrier) operating for some years.

Diffusion barrier in the casing for diffusion of insulation gasses:

An EVOH diffusion barrier co-extruded into the casing of PertFlextra shall prevent the diffusion of insulation gases out of the PUR foam and the diffusion of atmospheric air into the PUR foam.

About heat loss, the European standard for flexible pipe systems EN15632-1 Annex C defines that if a supplier does not have the diffusion barrier for insulation gasses, the declared lambda value shall be multiplied by a factor of 1,25 to achieve the design lambda value.

Possibility of having a surveillance system on a pre-insulated flexible pipe system with a plastic service pipe

With an integrated surveillance system on a flexible system with plastic service pipe wet foam can be detected whether the moisture is coming from a leaking service pipe or from outside due to wrong joint installation or due to damage on the casing.

On pre-insulated flexible pipe systems with a plastic service pipe without a water vapor diffusion barrier, it will make no sense to include a surveillance system as an integrated part of the flexible pipes. This is because it is known (see above) that there will be water permeation into the foam, and the foam might get wet over a lifetime.

PertFlextra has a water vapor diffusion barrier on the service pipe, enabling the possibility of integrating a surveillance system in the pre-insulated flexible pipes, PertFlextra.

In the COOL DH project, the pre-insulated flexible pipes were delivered with the 3dc surveillance wires for an impedance surveillance system.

On the project in Høje Taastrup, a Detector type X6 for impedance measurement is connected to the 3dc wires in the flexible pipes.

Flexibility of the pre-insulated flexible pipe

High flexibility is secured by combining the design with a corrugated casing and a soft PUR foam.

We have tested the flexibility of PertFlextra by bending tests and compared it to the flexibility of the corresponding dimensions of PexFlextra and AluFlextra. The dimensions of the service pipes are 32 mm, and the casing dimension is 90 mm.

Tests show that the flexural stress needed to bend PexFlextra (SDR 11) is 19% lower than bending PertFlextra (SDR 7,4), and the flexural stress needed to bend PertFlextra is 18% lower than bending AluFlextra.

Qualifying an electro-fusion coupling for connection of the PE-RT service pipes:

This was defined as part of the COOL DH project, but time was too short to do this qualification during the development period of this project.

Tests done to qualify PertFlextra

Before the launch of the new pre-insulated flexible pipe system, it is necessary to conduct several tests on the service pipe itself, the service pipe together with couplings, and tests on the pre-insulated pipe.

This is to ensure that the pipe system with components will live up to the requirements in the standards and ultimately have the expected lifetime.

All below tests are done, and requirements in the standards are fulfilled.

Thermal stability test of the PE-RT service pipe (Danish Technological Institute):

Each pipe dimension is tested with 2,4 MPa and 110 °C for 15.000 hours. No break on the service pipe is allowed.

Coupling test of press couplings and compression couplings installed on the PE-RT service pipe (Danish Technological Institute):

Thermal cycling test of the coupling installed on the PE-RT service pipe for each pipe dimension. 2000 cycles up to 32 mm and 1000 cycles from 40 mm and bigger dimensions. No leakage allowed.

Oxygen diffusion tightness of the PE-RT service pipe (KIWA):

Oxygen diffusion shall not exceed 1,8 mg/m2*day at 80 °C. On the test was measured 0,06 mg/m2*day

Water vapor permeation (Danish Technological Institute):

We have tested water permeation (mg/m/day) on PE-RT type II SDR 7,4 with an aluminum diffusion barrier and on PEXa SDR 11 at 95 °C. Dimension of pipe 32 mm.

On a PEXa SDR11, water permeation was tested at 367 mg/m/day.

On PE-RT type II SDR 7,4 with an aluminum diffusion barrier, the water permeation was tested to 2,3 mg/m/day, which is considered within the measurement uncertainty.

At lower temperatures, the water permeation will be lower. At 75 °C, the water permeation will be approximately 50% lower than at 95 °C.

The conclusion is that on plastic service pipes without a water vapor diffusion barrier, there is considerable water permeation, and on PE-RT with an aluminum diffusion barrier, the issue with water permeation is solved.

To secure the water vapor diffusion tightness of the entire installed system, couplings shall be wrapped with an alu wrap before installing the casing joint. Please see the below picture:

Linear water tightness (Type test, internal):

The requirement is that the amount of water leaking through any of the pipe ends shall not exceed 100g after 168 hours.

On the test of PertFlextra, no water was leaking through the pipe ends after 168 hours.

Axial shear strength (Type test, internal):

Axial shear strength shall be a minimum of 0,08 MPa.

On the test of PertFlextra, the axial shear strength was measured to 0,22 MPa.

Complete range of roducts for the PertFlextra system , service pipe dimension 25 – 63 mm

PertFlextra is available as single pipe and TwinPipe systems and includes all press couplings, casing joints, fittings, and tools needed to establish a complete pre-insulated piping network.

The dimensions of the service pipe will be 25 – 63 mm,and the casing dimensions will be 90 – 180 mm.

Further development to meet the full potential of the COOLDH project

The reason for not introducing dimension 75 – 110 mm at the first launch is that during production of these dimensions for the COOLDH project (Deliveries to Lund) was observed safety issues for the production employees that should be solved before introducing these dimensions.

At a later stage, larger dimensions of PertFlextra and electro-fusion couplings will be introduced.

For further information please contact: Peter Jorsal, Peter.Jorsal@kingspan.com

Meet the author

Peter Jorsal

Product & Academy Manager, Kingspan LOGSTOR

“PertFlextra – A new flexible pipe system to improve the efficiency of District Heating” was published in Hot Cool, edition no. 8/2023. You can download the article here:

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