Combined Heat & Power & District Heating
I
t’s probably safe to say that ancient Greek philosophers are rarely quoted in the building services media. But one such philosopher, who went by the name of Heraclitus, actually captured how it feels to be in the industry these days: “Change is the only constant in life.” He’s not wrong. It seems like every day there’s a new acronym or advisory to pay attention to – especially in the pioneering world of heat networks. Of course, the driving force behind all this change is the concerted move away from fossil fuels and decarbonisation. Combined with the inexorable energy price rises over the last year or two, the industry has experienced an increased demand for heat pump-based heat networks. Since the third generation of heat networks in the 1970s, we’ve moved to the fourth generation – which use renewables like heat pumps and other electrification to maximise output and minimise harmful emissions. The exponential growth of heat networks that integrate heat pumps has changed the regulatory framework. This ensures the latter are designed to maximise the latest technological developments and manufacturers’ ingenuity in combining ever more efficient appliances with renewables. We have seen this with the revision to CIBSE’s Guide to Heat Networks (CP1 2020). As you would expect, the emphasis currently is on operating heat networks that utilise heat interface units (HIUs) at low temperatures. As a result, manufacturers are creating advanced HIUs and this is where annual volume weighted average return temperature (VWART) becomes so crucial; equally it is important for specifiers and heating engineers to get to grips with when designing heat pump-based heat networks.
Ian Bradley is managing director at Modutherm
Modutherm’s Alira HTS heat pump is available in four models with heating capacity up to 98kW
The return is king As heat networks continue to rise in popularity it’s important for specifiers to understand the importance of annual Volume Weighted Average Return Temperature (VWART), writes Ian Bradley
Standard benchmarks
Back in 2016, BESA (British Engineering Services Association) launched a UK Standard for Heat Interface Units, which had been developed in collaboration with industry experts. The BESA standard benchmarks HIU performance and verifies it against a set of tests that replicate typical UK operating conditions. A key factor of the test is VWART, which is an amalgamation of estimations of the annual VWARTs for domestic hot water, space heating and keep-warm functions.
Modutherm’s MTA PLUS TWIN heat interface unit is claimed to be the most efficient on the market
The BESA testing has been an important step towards improving the performance of UK district heating schemes. By measuring the performance data of different HIUs within the context of typical UK
operating conditions, it becomes valuable in enabling heating engineers and heat network system designers to consider the performance of specific HIUs – not only against design requirements but also the many
competing manufacturers. In simple terms, VWART measures return temperature, which is one of the best ways to consider a heat network’s efficiency. A lower return temperature results in a larger delta T, which means lower flow 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. To conclude, specifying equipment that delivers low VWARTs is the best approach to improving the efficiency of a heat pump led heat network, remembering, of course, that, the CIBSE Code of Practice states, as a minimum requirement, the VWART should be no higher than 33°C.
Designing heat networks
Here at Modutherm, we’re very happy that our MTA PLUS TWIN HIU recently achieved top marks in registering the lowest VWART in both the high and low temperature tests of any heat interface unit, with values of 26 and 24 respectively. That’s better than any other HIU previously tested. We can claim that our HIU is the most efficient on the market. There are multiple ways of designing heat networks, depending on the needs of any given situation, and a myriad of variables that contribute to the best performance of each system. By using VWART, consultants are able to specify the most efficient HIUs – especially when they are combined with matching heat pumps. This gives engineers and specifiers the ability to create incredibly energy efficient heat networks that deliver generous amounts of heating and DHW to a building’s occupants. And they do all of this while contributing to decarbonisation goals, reduction in harmful emissions and the wider use of renewables. The team at Modutherm is always searching for ever more efficient and innovative ways to build heat networks. It’s our ambition to be the very best at what we do, which brings us neatly back to that ancient Greek thinker again, who also once wrote: “Big results require big ambitions.” In the coming years the fifth generation of heat networks will see networks include perhaps cooling – using reverse cycles with heat pumps and keeping internal temperatures at a very comfortable level all year round.
22 | ENERGY IN BUILDINGS & INDUSTRY | JULY � AUGUST 2022
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