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Fine tuning heat networks – a Code of Practice

Fine tuning heat networks – a Code of Practice

With the Government planning to supply 14% of the U.K.’s heat via heat networks, the publication of CP1 Heat Networks: Code of Practice must be seen as a very welcome development.

The Code of Practice has been developed jointly by the Association for Decentralised Energy (ADE) and the Chartered Institution of Building Services Engineers (CIBSE). It was drafted by AECOM with input from a steering group of industry experts from various organisations, including SAV Systems.

As Phil Jones, Chairman of the CIBSE Energy Performance Group, explains: “These standards, with the associated training, will help change the face of district heating in the UK. Alongside a lot of good DH networks we are still seeing too many poorly implemented schemes in practice.

“The new code of practice will help prevent this and ensure that DH systems do what they say on the tin. It will also give the tools and confidence to developers to encourage greater use of heat networks and take the sector to the next level. With the right standards and skills in place, DH will become the solution of choice in high heat density areas.”

In practical terms, it will ensure that specifiers are provided with the best practice guidance they need to deliver optimum efficiency through heat networks, or district heating systems as they are sometimes known.

One of the key elements of this best practice is the need to reduce flow and return temperatures in heating systems. This is because combined heat and power (CHP), condensing boilers, heat pumps and solar thermal systems all operate more efficiently at lower return water temperatures. So, instead of the traditional 80°C flow/60°C return, the Code recommends flow/return temperatures of 70°C/40°C.

This development means that the difference between the flow and return water temperatures (the ‘Delta T’) now becomes the overriding design consideration. This is achieved by ensuring that sufficient heat is removed from the system by the terminal units, thereby reducing the return temperature.

This higher level of heat transfer to the space being heated is greatly facilitated by reducing the flow rate of the water, so that it spends more time in contact with the heat exchange mechanism.

Achieving a good Delta T therefore involves the use of a variable speed pump so that the flow rate of the water can be reduced to maximise heat transfer at the terminal unit. An added benefit of this is that it enables use of a smaller pump that costs less to buy and operate.

In turn, variable speed pumping necessitates the use of two-port valves such as thermostatic radiator valves (TRVs). However, two-port valves are not designed to function with variable pressures, so differential pressure control valves (DPCVs) should also be included to enable the two-port control valves to operate as designed.

SAV FloCon pressure independent commissioning modules are designed to facilitate achieving a high Delta T by addressing all of these issues, even where ultra low flows are in use. Where a network is serving heat interface units within individual apartments or other spaces, our FlatStation units will also help to underpin optimum performance and high Delta T.

Fine-tuning performance

Another crucial area to optimise the performance of heating networks is equipping building operators with the ability to measure and understand the way in which their systems are performing, and the ability to re-configure them in line with changes to building usage. Indeed, this is a key element of the Government’s ‘soft landings’ aspirations.

This has long been a challenge for the building services industry and experience has shown that the most cost-effective way to achieve this is by incorporating metering in commissioning modules that serve zones of terminal units.

With its profound understanding and experience of delivering low carbon heat networks, backed by a comprehensive range of products, SAV was able to make a significant contribution to the development of the Code. These same principles are at the heart of the 70/40 campaign we have been running for several years as part of our wider-ranging ‘Waste Not, Want Not’ programme to reduce energy waste.