Warning of Two-Tier Heat Network Performance
With the dash to install heat networks gathering apace, the head of one of the UK’s longest serving manufacturers of pre-insulated pipe systems has highlighted a large disparity in the performance of commonly available flexible pipe systems – underlining the significant impact they can have on the operational costs for buried heat network owners.
Having been at the forefront of the recent campaign for the introduction of standards in UK district heating networks, Mark Whettall, managing director of CPV Ltd, wants to draw the attention of heat network owners and operators to the huge variation in heat loss between different types of insulation. “Although modern buried pre-insulated pipe systems generally perform well, the results of recent research that we have carried out has been quite astonishing as it’s highlighted a big disparity between two main types of insulation methods.”
He went on to explain that the two types of systems, one where the polymer service pipe – normally cross-linked polyethylene (PEX) – is bonded in a sandwich construction with the outer casing by a closed-cell polyurethane foam (PUR) and the other where a cheaper flexible foam insulation – quite often segmented – is loose inside the void between the outer casing and the service pipe.
He continued: “Although both of these types of pipe system are covered by the EN 15632 standards (parts 2 and 3 respectively), the thermal insulation performance is drastically different – in some cases by more than 100 percent worse in the ‘budget’ systems with an air gap when compared to systems with bonded PUR insulation. Clearly, this has a significant effect on the heat loss and therefore makes the operational costs very different – effectively a two-tier approach to performance.
“In our research, we found that using an example of a network with a total of 400 metres of 25mm diameter (OD) pre-insulated pipe (200 metres of trench), heated by a natural-gas-fired boiler, the extra cost of the average heat loss from systems with air gap increased the heat loss to such an extent that – over a 25-year minimum operational life, the additional gas cost alone would be in the region of £18k (*) – with carbon emissions proportional to the fuel consumed at an additional 84 tonnes.
When considering that the capital cost for this size of the non-PUR-bonded system is less than one percent cheaper than the bonded alternative, the initial saving would be consumed hundreds of times over by extra operational costs.
“Apply this example to a system fuelled by a wood-chip biomass boiler and factoring in the potential loss of income from the government’s RHI incentive payments can lift the operational cost by some £27k – which when applied to a larger, more complex system will of course increase even further.”
Whettall continued to say that, in most cases, the company selecting and installing a heat network is not going to be responsible for its operational costs, so it’s important that the system owners and operators are aware of the issues of heat loss and therefore specify systems that offer the best life cycle costs. What may seem a good CAPEX saving could turn out to be very costly for the future operation and replicate this across the country and the lost opportunities for maximising carbon reductions will mount up.
“All manufacturers publish their pre-insulated pipe systems heat loss figures as Watts per metre (W/m), so it’s relatively easy to check and compare”, Whettall concluded.
(*) Basis of Calculation
Assumed 200 metres trench (400m pipe), 25mm OD separate flow and return pipes buried to a cover depth of 800mm. Soil temperature 10°C, average flow temperature of media 70°C. Operating constantly. Gas tariff £0.03/kWh, boiler efficiency 80%.
Notes to Editors
Further Press Information
For further press information and photographs, please contact Tim Ward of Parker Ward Limited.
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Based near Romsey, Hampshire, CPV Ltd is one of the UK’s leading manufacturers of specialist engineering pipe systems for industrial and building-related applications. Founded in 1948 as the Chemical Pipe and Vessel Company (CPV), the company has established a worldwide reputation for its innovative range of products, including corrosion-resistant pipe solutions and pre-insulated pipe systems for district heating and cooling applications.