Across the UK, district heating is experiencing a resurgence. Once again, it has become popular, driven mainly by energy modeling and planning authorities promoting the energy efficiency benefits that are synonymous with district heating.

But are district heating systems efficient?

Perhaps one of the primary reasons for district heating systems not being as efficient as they should be is due to a lack of access to data. Effectively, designers specify systems without using any operational data to help inform their decisions. Instead, they rely on specified standards (namely CP1 and the legacy Danish standard, DN44) to guide and inform their sizing. These standards cannot accurately assist with the sizing required for any given site and as a consequence, systems can often be vastly oversized.   

The drive for twin plate heat interface units means that networks must be kept hot, resulting in very large system heat losses. Because pump manufacturers are unable to turn down pumps to below 25%, it can often trick designers into making allowances for very large flow rates. This is despite the fact there is no demand on the size at all. This oversizing can result in systems running above 50% efficiency, especially on district heating systems designed in the last ten years. This is obviously not what the Energy Standard or the Greater London Authority (GLA) had in mind when they decided to promote the use of district heating systems.

So how do we solve it and what does the future of district heating look like?

Operational data must be shared and conventional diversity curves must be regularly kept updated. This way, the designer can start from the smallest base available. Smaller primary plants equals smaller primary and secondary networks. Flow must be carefully calculated and modelled, only running around the smallest parts of the networks to ensure not too much hot water is retained.

Encouraging the installation of demand based controls, perhaps Heat Interface Units (HIU), that demand an increase in flow and return during operation is another option. Many versions of the modern HIUs come equipped with smart controls to limit operation of some parts of the system during peak demand.

Increase the diameter of the pipe insulations - the thicker, the better. Our team have been to many sites where we have discovered no insulation on valves or different parts of the network.

And finally, system efficiencies must be used in the Standard Assessment Procedure (SAP) and the Simplified Building Energy Model (SBEM) and not just defaults. This method must be realistic and have sensible calculation parameters that match real life situations.

District heating will not be obsolete anytime soon. We hope that in the near future, the district heating system can restore its reputation as an energy efficient solution and we will be discussing district heating systems in the same context as a ‘clean and efficient method of delivering heat for all’.

The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag

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