Exploring the best practices around District Heating Schemes

District heating systems are suitable for use with conventional energy sources but there is an increasing trend towards the use of renewables.  Commercially, this may be driven by a company’s carbon reduction plan, while for residential schemes it may be prompted by reduced costs, with the Renewable Heat Incentive (RHI) funding and Feed in Tariffs (FIT) supplementing the financial benefits of lower heating bills.

For some renewable energy sources, such as ground source heat pumps, the energy output may be lower than conventional boilers, and this must be optimised in the design and layout of the infrastructure.  The goal for the specifier should always be to ensure that the heat energy from the centralised plant reaches its destination at each property as rapidly as possible to maximise the heat energy input to the local network from the centralised plant output. This requires early engagement of the pre-insulated pipe supplier and a collaborative approach  -involving the design team, the utilities provider, the civils contractor and the pre-insulated pipe supplier - to ensure the most efficient underground network is specified, taking into account the routes of existing underground services networks and any additional obstacles below ground.

Usually, working with the pre-insulated pipe supplier in this way will not only ensure the underground pipe layout is optimised to maximise the energy efficiency of the system but may also reduce the cost of materials

District heating and cooling systems require the installation of an underground network of pre-insulated pipe and this should be durable enough to offer a long service life and resist abrasion during installation, while offering excellent flexibility so that it can be routed around obstacles and natural contours in the ground.

The insulation performance of pre-insulated pipe manufactured specifically for district heating installations varies considerably and a pipe supplier should be able to advise on the most appropriate choice.  This will depend on a range of criteria, including the energy source, the distance between the energy source and the end point user and the size of the network. Insulation performance will also impact on the cost of the installation, as pipe with lower thermal conductivity will be more expensive.
There are other ways to bring down the capex cost of the project, however. In addition to taking advice from the pre-insulated pipe supplier on configuration and optimised routing, specifiers should seek their advice on the diameter of pipe required. Each section of pipe has a flow and return pipe within the insulated casing and this should be sized to meet the anticipated demand from end user. Usually, there will be a ‘spine’ of larger diameter pipe leading to a network of smaller diameter pipe ‘branches’, and early engagement with the pre-insulated pipe specialist can help to avoid over-specification.

The pre-insulated pipe supplier can also advise on the most appropriate approach to installing pipe connections. For example, Uponor offers Wipex coupling connectors that offer a conventional approach to joining two sections of pipe by fitting over the join, or a Q&E (Quick and Easy) fitting, which is installed using a special expander tool, fitting securely inside the pipe. With training and use of the specialist tool, the Q&E fitting can reduce installation costs by speeding up installation.

Historically, many district heating systems have failed to achieve their potential energy efficiency because the centralised plant has been oversized.  This is because the calculations used to assess the energy output required have been based on maximum load requirements, rather than actual usage patterns. On a residential development, energy demand for hot water is two or three times greater than the requirement for heating and, while all residents may switch their heating on at the same time during a cold snap, it’s unlikely they will all take a bath at the same time! Consequently, even if the maximum output of the energy source is 20% lower than the maximum demand (calculated using raw occupancy data) it may still only be required at 70-80% capacity at times of peak demand (calculated based on usage patterns).

Similarly, contemporary pipe systems like Uponor’s Ecoflex, do not allow calcium build up so the pipe bore should never be oversized when using a polyethylene-based pipe system as there will be no reduction in bore over time.

 Why not read more about our latest involvement in the Orchard House Social Housing Scheme.