If heat networks are to form a significant part of the UK’s low carbon energy infrastructure in the future, they need to be designed, built and operated to a high standard.
To help achieve this, a new voluntary code of practice on heat networks has been produced by CIBSE and the Association for Decentralised Energy (ADE), previously the Combined Heat and Power Association.
Heat networks: A Code of Practice for the UK will be published this summer and is structured around a new cradle-to-grave heat networks plan of work. As well as helping to specify minimum standards in the tendering/contracting processes, its adoption by developers could give assurance to property purchasers that the district heating scheme has been designed, installed and commissioned to a specific set of standards. In the longer term, a condition of receiving private investment or public funding could be following the code.
Work is under way to introduce training, accreditation and registration of heat-network professionals, to ensure that the skills to implement the code are available across the sector.
From ‘could do’ to ‘must do’
The code represents a new approach for CIBSE in terms of style, structure, presentation and approach. It moves away from ‘could do’ guidance towards ‘must do’ minimum standards.
Structuring the code around a heat networks plan of work is also a significant departure, with a new colour-coded layout that could be used for other technologies or techniques in the future.
Where certain standards were thought too onerous as a minimum, they are presented as best practice, with the intention that these might become the minimum in future.
The industry lacks standards around the feasibility of heat networks. Feasibility is essential to achieving sufficient accuracy of peak heat demands and annual heat consumptions. It also requires identification of the most suitable, low carbon heat energy sources and location of an energy centre with top-up and standby boilers where necessary.
The feasibility study should select suitable operating temperatures, and define heat network distribution routes, pipe sizes and costs. It should conduct a consistent economic analysis, and options appraisals with full risk and sensitivity analyses across all environmental impacts and benefits. The study should also develop preferred business structures, contract strategy and procurement strategy.
Rehau's district heating pipework at Gaunts Estates
Well-designed schemes often perform badly because of poor commissioning. The code requires schemes to achieve consistently low return temperatures through commissioning building heating systems/controls.
One of the most critical aspects of the design and operation of a heat network is the return temperature, although – in existing systems –this is something over which the operator has relatively little control. So the commissioning is vital because it is harder to change settings once the system is in operation.
This is, in part, a cultural change. Operatives commissioning heating systems using gas-fired boilers in a building are more concerned with high flow rates and ensuring radiators deliver their output. As a result, there is a tendency to set flows and return temperatures higher than the design value. With heat networks, the main commissioning objectives should be to achieve the correct return temperatures and make sure flow rates are balanced to no more than the design value.
The code represents an entirely new approach for CIBSE in terms of style, structure, presentation and approach
To the future
Demand for standards means the code of practice is already being used by some local authorities in tendering for heat network schemes. Questions have been raised about how implementation of the code might be policed, and it could be that district heating schemes will be accredited, perhaps with an attached rating or compliance level. It is hoped the code will be regularly reviewed to upgrade standards with current best practice, eventually becoming minimum standards.
This article is based on a CIBSE Technical Symposium 2015 paper by Paul Woods,Tim Rotheray and Phil Jones www.cibse.org/symposium
DECC has funded a new CIBSE Surface water source heat pumps: A Code of Practice for the UK – produced in partnership with the Heat Pump Association and the Ground Source Heat Pump Association – to be published in late 2015. See page 7 in the Products Special.
Phil Jones FCIBSE is an energy consultant and chair of CIBSE Energy Performance Group