Modern Building Services

MODERN BUILDING SERVICES NOVEMBER 2021 17 FEATURE NET ZERO While the bigger and wider schemes tend to be completed to a better standard, there is still a need to decarbonise on a smaller scale as many of these larger schemes have been built using Combined Heat and Power, which is fast losing its carbon savings rating. The situation is starting to become a little clearer as to how existing CHP schemes that are currently being built out will be treated, with a proposed grace period to June 2022 most likely. In comparison, the smaller networks tend to get designed by developers wanting to work in a particular area, however, do not receive the same funding, as money is directed to larger heat networks. The Green Heat Network fund is an example of this, where a minimum 2GWh/year energy use or 100 dwellings, if off grid, sets the qualifying entry. Smaller communal heat networks will need to decarbonise as they many are built around gas boilers currently, which makes them an obvious sector to focus in on. It is inevitable that these schemes might incur the costs to make this transition possible within the ambitious timescales. What issues will we face? With this said, there will be some issues in converting both types of networks, and as a result, improvements will need to be made on the return temperatures and the insulation levels they are getting. The first step to achieve a low carbon target is to get all heat networks operating more efficiently than they are today, and this will need to be done by reducing heat loss from these schemes. The second step would be to start thinking about how renewable technology can be incorporated. We know that heat pumps are the technology of choice, but we also know that they need to operate at lower temperatures (ideally below 60°C) to meet the seasonal efficiencies that will be needed. In addition to challenges facing insulation levels, there is likely to be space constraints with allocated plant rooms on smaller schemes, which could present a challenge for installers and certain equipment might need to go external to cope with this. It will be interesting to see how developers will get around this challenge. Hybrid heat networks An alternative to the challenges that we are facing with heat network schemes, will be the use of hybrid systems to get good decarbonisation levels. If you have 40% of the heat load covered by heat pumps, then you can cover an excess of 80% of your kW hours. This means that 80% of the energy is going across to a renewable source, which will be a way to achieve a reasonable level of decarbonisation on some of these harder to achieve schemes. The main benefit of including a hybrid system instead of a sole heat pump is that it can support future carbon emission reductions. It is looking increasingly likely that current boilers will be replaced by hydrogen-ready appliances in the coming years, so much so it could become a mandatory requirement. One of the best solutions to take advantage of this would be a hybrid approach to heat networks. Take for example, a plant room where a heat pump takes the lead supported by a peak-load boiler, this would offer a practical option to keeping capital costs under control while still delivering significant carbon savings. Heat networks typically operate below 25% of their peak demand for over half of the year, which is why heat pumps are well-suited to larger schemes. By having peak-load boilers on standby, and introducing a hybrid heat network, when the outside temperature drops to its coldest during the winter months the hybrid heat network will provide end users with instant peak time hot water and heating. By carefully considering the design of heat network plant rooms now and the types of heating technology that are installed, will ensure that heat networks continue to achieve their full potential as we continue moving towards a net zero future. Hybrid systems do just that and help heat networks pave the way for a net-zero future. Although we have been set a timescale for decarbonisation by 2035, we will only just see hydrogen start to develop at some sort of level as we move closer to that date. While it will not be nationwide in the UK by then, it is anticipated that several of these schemes may have to limp along until hydrogen is able to pick up the load, and hybrid heat networks will be able to do just that to help things move along until we reach the net-zero target. Hydrogen might come in earlier in some areas; however, this is just another angle, in addition to the introduction of hybrid systems, of what might come into play when decarbonising heat networks.