AIR SOURCE & GROUND SOURCE HEAT PUMPS
The future of heat networks – the 4th generation
Heat networks have come a long way since the steam-powered originals of the 1800s – and are destined to become a widely used tool in the drive to the decarbonisation of heating and hot water in multi-dwelling buildings, writes Ian Bradley, managing director at Modutherm
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ometimes you have to look backwards to see how far you’ve come. Recently, I was going through some old files and it occurred to me that we were talking a lot about heat networks
over a decade ago – referencing things like geothermal heat networks in Iceland and apartment blocks with cascades of commercial condensing boilers. But the world has moved on over the intervening years, as has heating and hot water technology. You could also argue that the climate change issues we were reading about back then have become even more urgent and important.
So, what have we learned from the past, that is helping shape systems for the future? As the title of this article hints, we’re talking about the fourth generation of heat networks. The first steam-powered generation was back in the late 1800s. During the war years the second generation used pressurised hot water at over 100oC. The 1970s saw the introduction of the third generation – using boilers and water below 100oC. These systems were further developed by incorporating ever more efficient condensing boilers, but still relied on natural gas to fuel them. Now, as the world begins to decarbonise as it
Modutherm managing director, Ian Bradley
targets Net Zero emissions, we embark on the fourth generation of heat networks (and look further forward to what the fifth generation may bring). With CIBSE’s CP1 2020 Heat Networks Code of Practice dictating the direction, manufacturers, specifiers and heating engineers are now gearing up for the fourth generation. These new heat networks no longer feature gigantic boilers in the basement of a building; instead, they embrace the renewable technology of heat pumps. As you would expect with the utilisation of heat pumps, these networks operate at a lower temperature than previously seen in the days of boilers. All of these aspects contribute to higher system efficiency, lower carbon emissions and a reduction in air pollution. In practice, the commercial heat pump (or pumps) – often installed on the outside of the building – are connected via the heat network to next generation Heat Interface Units (HIU) installed within each apartment. One important thing to note is these new HIUs are designed specifically to work with the lower temperatures associated with heat pumps and optimise performance in a well-insulated, newly built apartment building. They are therefore considered “heat pump ready”. Let’s take a new build apartment building as an example – designed and built to the latest building regulations, well insulated, with effective ventilation and occupant comfort at the forefront. In this situation, consulting engineers could specify a relatively high- capacity commercial air source heat pump for the primary circuit, such as Modutherm’s Alira
HTS high temperature appliance, which has a heating capacity of up to 98kW (cooling up to 89.6kW) across five models. Considering a typical southern UK outside design condition of -4°C, such a unit can produce hot water up to 62°C, which makes it the perfect partner of the “heat pump ready” HIUs.
Practically speaking, multiple heat pumps or a cascade of appliances should be installed, taking a similar approach to fitting condensing boilers. This gives flexibility – not only in terms of specification, but also for easy installation. On-board cascade controls can also manage up to four boilers, while multiple blocks of four appliances can be controlled with the help of a heat network’s BMS system. So, that’s the heating source. Next to consider is the HIU, which needs to be “heat pump ready. Modutherm’s MTA PLUS features the latest best performing heat exchangers to ensure it delivers lots of instantaneous domestic hot water (DHW) and provides the necessary heating requirement, even if it sees relatively low temperature water provided to it via heat pumps.
It can easily deliver DHW to satisfy most sizes
of property, at the CIBSE CP1 2020 value of 50°C but higher temperatures can also be accommodated. If lower temperature domestic water is sought, then the HIU can still deliver with network primary temperatures as low as 50°C. CIBSE’s CP1 2020 now calls for the temperature of the water that returns to the network, from the DHW heat exchanger, to be no more than 25°C, with a recommendation that 20°C is not exceeded. Similar parameters are mentioned in CP1 for the heating heat exchanger sothe heat exchanger has been engineered with low water return temperatures in mind. It is this combination of low returns from both heat exchangers that delivers the best heat network efficiency. The HIU has also been specifically designed to provide high outputs, when operating at low network temperatures, and still achieve low temperature returns. This powerful combination of features makes the unit exceptionally efficient and works in perfect harmony with heat pumps. With multiple dwelling buildings, ease of installation (particularly at first fix) and servicing are important considerations, in addition to metering, billing, controls and compatibility with smart home thermostats thanks to the ubiquity
12 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JUNE 2022
of mobile apps. Even Alexa can have a say. All of these can be achieved with the correct HIUs and careful planning; not to mention consulting with manufacturers, who would be happy to look at projects and help engineers achieve optimal results.
But what of the fifth generation of heat networks mentioned earlier? You won’t be unsurprised to know that we’re ready for that too! The fifth generation will see networks include perhaps cooling – using reverse cycles with heat pumps and keeping internal temperatures at a comfortable level all year round. However, I think that’s probably best left to another article at another time…
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