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District heating systems in the UK

Commonplace in many other countries, district heating systems are gaining traction in the UK. Here they are becoming an increasingly popular means of efficiently providing reliable services to hospitals, schools, college campuses, retirement villages and other housing developments.

As with any HVAC system, the specific demands of a district heating project needs to be considered to determine the optimum pipework installation method. Factors include the physical site, along with the operation and maintenance of the system and possible future expansion.

In most such systems there are likely to be many hundreds of metres – sometimes kilometres – of pipework, which may include large-diameter pipes (350mm and above).

Often pipes will be located in inaccessible trenches or buried, requiring solutions for accommodating thermal movement. While welding is commonly used to join pipework, on large projects with poor access, not only the welding itself, but the essential site preparation and the need to move welding equipment during the job will take considerable time.

To accommodate thermal movement in welded systems, U-shaped expansion loops and welded offsets are commonly used, together with linear axial bellows. These can be costly and time-consuming to install and may require periodic maintenance.

Using grooved mechanical pipe joining is a quicker, simpler, safer option. Where pipes need to be joined, contractors can make economies of scale in time and cost-saving by selecting couplings in preference to welding. For added convenience, pre-insulated carbon steel pipes, which are typically used in district heating systems, can be supplied pre-grooved as standard by manufacturers.

Plantrooms for district heating and building-specific systems are similar, but district heating systems generally run at a higher temperature. If the normal low-temperature hot water operating temperature of 82°C were used, the water would be cool by the time it reached pipework furthest from the plantroom.

District heating systems therefore operate at 90 – 95°C to ensure sufficient heat at the end of the run in a large system. Contractors need to ensure that the system will operate reliably at these temperatures. EPDM gaskets used in couplings are designed to withstand such temperatures.

The inherent linear movement/angular deflection capabilities of flexible grooved couplings can be used as a cost-effective, maintenance-free alternative to accommodating thermal movement. Mover expansion joints, which are simple to install and adjust as required before installation, can also be used.

A trend is for large energy suppliers to purchase and then deliver heating and cooling services, with typical delivery and maintenance contracts lasting for decades.

Reliability is a key criterion, as suppliers can risk substantial financial penalties if the system is down for all but minimum periods – including planned maintenance. Grooved mechanical couplings not only last the life of a system, but provide a union at every joint.

A system that requires little maintenance, where valves, filters and other components can be changed simply and speedily without the need for total system shutdown, has clear advantages. The same benefits apply if there is a requirement to expand the system to include more buildings in the future.

Andy Carter is product engineer at Victaulic

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