Heat networks
Delivering optimum effi ciency within a heat network
The transition to heat pump technology in heat networks has created its challenges, especially in the specifi cation of suitable HIUs. Here, Ian Bradley, managing director of Modutherm, discusses the regulatory framework surrounding fourth generation ‘heat pump ready’ HIUs, and the importance of specifying units with the lowest possible return temperature in order to deliver optimum effi ciency within a heat network.
H
eat pumps continue to be a central pillar in facing down the challenges of increasing energy prices and the ever-intensifying drive
towards net zero. However, individual heat pumps are not necessarily practical or cost-eff ective in multi- occupancy buildings like apartment blocks. Therefore, heat networks powered by heat pumps are the ideal solution for homeowners, or utility customers, who will be focusing on the bottom line of their bills. Nevertheless, energy effi ciency is still the key to their success. The good news is that we have a regulatory
framework which is already heading in the right direction. Specifi ers and engineers are using the revised legislation to build heat networks that are not only placing heat pumps at the heart of them but use heat interface units (HIUs) to deliver heating and DHW to a building’s occupants with optimum effi ciency.
The regulations
If you look at the revision to CIBSE’s Guide to Heat Networks (CP1 2020), you will fi nd that guidance on operating heat networks using HIUs at low temperatures is prominently featured. Manufacturers
are already creating advanced HIUs for heat networks powered by renewables, and this is where annual volume weighted average return temperature (VWART) becomes so crucial. Not only is the CIBSE guide important for manufacturers like Modutherm, it’s equally important for heating engineers and specifi ers to consider when designing heat pump- based heat networks. For those who are less familiar with VWART, a
defi nition is useful: it is a measure looking at a heat network’s effi ciency. In simple terms, a lower return temperature results in a larger delta T, which means lower fl ow rates are required to achieve the same kW delivery. In practice, this allows smaller pumps and pipes to be used – and smaller pumps mean lower capital expenditure and power consumption. Smaller pipework also reduces surface area and related heat losses.
Replicating typical UK conditions
VWARTs are embedded into the regulatory framework thanks to BESA’s (British Engineering Services Association) UK Standard for Heat Interface Units, which was developed in collaboration with the industry. The BESA standard benchmarks HIU performance and verifi es it against a set of tests that replicate typical UK operating conditions. A key factor
16 May 2023
of those tests is VWART, which is an amalgamation of estimations of the annual individual VWARTs for domestic hot water, space heating and keep-warm functions.
By measuring the performance data of diff erent HIUs within the context of typical UK operating conditions, it enables heating engineers and heat network system designers to compare the performance of specifi c HIUs – not only against design requirements but also competing manufacturers. That’s why specifying equipment that delivers
low return temperatures is the best approach to improving the effi ciency of a heat pump led heat network. Of course, system designers will need to remember that the CIBSE Code of Practice states, as a minimum requirement, the VWART should be no higher than 33°C. Here at Modutherm, we’re proud that our MTA PLUS TWIN HIU recently achieved top marks in the BESA standard, registering the lowest return temperature (VWART) tests of any heat interface unit, with values of 26 (high) and 24 (low) respectively. That’s superior to any other HIU previously tested, so we’re justifi ably proud to claim that our HIU is the most effi cient on the market. So, there are many diff erent ways to design an
energy effi cient heat network, depending on the needs of any given situation, and all the many variables that contribute to the best performance of each system. By using VWART, consultants are able to specify the most effi cient HIUs – especially when they are combined with highly effi cient heat pumps. The team at Modutherm is always searching for
ever more effi cient and innovative ways to build heat networks. And we’re happy to work in tandem with specifi ers and consultants on fi nding the best approach to maximise effi ciency in heat pump powered heat networks.
Left: Ian Bradley,
managing director of Modutherm
www.heatingandventilating.net
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