Decarbonising the UK’s Heat Supplies with District Heating

A fiendishly simple concept, district heating (DH) has been in the UK for many decades - however, it’s only relatively recently that it has gained prominence as a means by which the UK can tackle its sizable carbon emissions from heating and hot water production.

On its own, all DH will do is deliver heat energy to multiple consumers in the form of hot water, via a highly-efficient, buried pre-insulated pipe network – offering an economy of scale that both increases efficiency and lowers energy costs. Couple this to a low- or zero-carbon heat source such as combined heat and power (CHP) system or a biomass boiler and things really do start to get interesting – particularly in terms of the carbon reductions achievable.

Recognising this potential, the Department of Energy and Climate Change (DECC) has recently published the long-awaited strategy document outlining its plans for decarbonising heat supplies. As expected, DH is set to play a central role and a new Heat Networks Delivery Unit is being established to provide expert advice to local authorities.

Although the technology works well at a large scale, there are also gains to be made at the smaller end of the market – where a two or more buildings are connected together and fed by a centralised energy centre.
Smaller distribution systems and branch connections - from 25mm up to around 125mm OD - are likely to consist of pre-insulated PEX (cross-linked polyethylene) pipes, with larger dimensions utilising pre-insulated steel pipes. The choice of system has a bearing on the maximum continuous operating temperatures – around 85°C for PEX and 120°C for steel. These factors also have a direct influence on the life expectancy of the pipe system, so are important considerations.

Design must take into account the system’s ability to satisfy current and future heat loads, plus cater for the thermal expansion – something best done with computer-simulated stress analysis to enable designers to fully understand the life expectancy of the network during repeated temperature cycles.

However good the design and planning, the approach to the installation of buried DH networks is critical to the long-term reliability of the systems. It is imperative that the below-ground jointing of pipes is carried out by trained, competent operatives in strict accordance with manufacturers’ recommendations and, furthermore, that they are independently monitored and the process documented to avoid short cuts being taken.

Once out of the ground, supplies to consumers should be metered in order to encourage sensible consumption and incorporate good quality heat interface units to afford hydraulic separation and easy-to-use controls that ensure that both comfort levels and heating bills can be managed – without disadvantaging some of the more vulnerable members of society.

For the last 20 years or more, we’ve been predicting that DH would one day take off in the UK and it would seem to be finally happening. Let’s make sure that it delivers on all fronts!

Mark Whettall is managing director of CPV Ltd
Manufacturers of pre-insulated pipe systems.