Off-site District Heating connections: Key Considerations

Connection of housing development heat networks to external heat supplies is increasingly encouraged by local authorities. Successful delivery of this brings some opportunities as well as challenges.

Tougher carbon targets and the fact that alternatives to gas-boilers and CHP are generally more costly (to build, as well as heat costs for residents) are two of the reasons why an incoming heat supply may be a good option for developers, especially as the number of heat networks grows. Many of these expansive heat networks utilise very low carbon heat sources (e.g. waste to energy) that are unavailable at the scale of housing developments. However, there are technical and managerial aspects that need to be considered too.

An onsite heat network can only easily harness heat from another system if it operates at a lower temperature than the system it is connecting to. This is exacerbated by introducing hydraulic breaks to deal with incompatible system pressures. Conversely, the lack of hydraulic breaks means water from both systems will be mixing, which adds water quality, pumping and resilience considerations into the mix. With a sound design, however, all of these can be managed.

Service levels, such as response times, also need to be considered. Often large heat networks operate only to meet the minimum Heat Trust standards, which are lower than many new build housing developments deem to be acceptable.

Resilience of heat supply is also important. Utilising an off site heat supply may mean that there is no onsite heat generation plant at all. Before agreeing to make a connection, it is therefore critical to be comfortable with the technical capabilities and processes of the heat provider and that suitable contractual measures are in place to ensure a resilient supply of heat to customers as well as to quickly restore this if there is an outage.