Questions raised over heat network design practices


09 October 2017
bosch heat pump district heating
Pete Mills of Bosch
Consultants and contractors responsible for the design of heat networks and district heating schemes are being urged to avoid unnecessary oversizing by an industry spokesperson.

Pete Mills, Commercial Technical Operations Manager at Bosch Commercial and Industrial, is calling for designers to pay close attention to the sizing of the main heating source and pipework in order to maximise efficiency gains.
He said: “Unfortunately, it has become relatively common for heat network schemes in the UK to fall short of industry expectations through oversizing of appliances and pipework. Oversizing a heat network from the outset can have huge ramifications for the long-term efficiency, overall performance, and return on investment of a system. This is before we consider the reputational damage that incorrect design is having on heat networks’ credentials as efficient and cost-effective heating and hot water solutions for multi-residential and commercial buildings.” 

According to the Association for Decentralised Energy (ADE), there are currently more than 17,000 heat networks in the UK, of which around 91% are located in England and 6% in Scotland.  With the Government’s £320 million Heat Networks Investment Project (HNIP) set to provide financial support to up to 200 district heating projects by 2021 and lever in up to £2bn of wider investment, uptake of this heating approach is showing no signs of slowing.

Best payback
Mills added: “Many heat network designs we are seeing are not incorporating any renewable energy, waste heat, or low carbon technologies, which should be the foundation of a good scheme that is to provide heat and carbon savings for tenants. We are still lacking a wide base of design experience in the UK and this is something we must start to improve upon. Building developers, too, have a role to play in ensuring their developments will deliver good value for their tenants with fair priced heat that starts with a well-designed heat network.

“Heat pumps can be used for heat networks, particularly gas absorption heat pumps. Oversizing can still be an issue, but here it is more about the capital cost against coverage of the annual heat demand profile.

“Essentially you have to weigh up the cost/payback benefit from having an expensive plant sitting there just to cover a few days of very cold weather when there is high demand. We usually recommend somewhere in the region of 40% to 60% coverage from the heat pumps against the calculated peak demand. The remaining heat requirement on very cold days can be met with condensing boilers. This generally achieves the best payback periods.

“The UK, particularly its local authorities and housing associations, has the potential to benefit greatly from district heating schemes. It is therefore paramount that plants and pipework are correctly sized according to heat demand. Smaller pipes, shorter pipework runs and good insulation practices will keep heat losses in a network to a minimum, while benefitting the end-user from the word go.

“Those in doubt should remember that no two heat networks will ever be the same, and that manufacturers will often prove to be an invaluable source of help during the design process.”
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