REHAU event puts retrofitting residential heat networks in spotlight


15 January 2024
Heat Pumps Today attended a recent REHAU Retrofit 231 event, where a panel of industry experts discussed retrofitting low-carbon technologies in residential projects, including district heating and heat.


The event took place at The Building Centre, it featured sessions by speakers including Bean Beanland, Director of Growth & External Affairs for the Heat Pump Federation; Simon Eddleston, Director of Construction at Switch2 Energy and Steve Richmond, Head of Marketing & Technical at REHAU.


Topics covered in the event, included how the new Government targets and current installation skills gaps would affect the adoption of district heating technologies. In all three presentations, the speakers looked to dispel myths surrounding heat networks and what buildings they can be deployed in.

Steve said: “I think the biggest step we as an industry have to take is demonstrating that district heating isn’t an unproven concept, and this event is a key part of this.

It’s actually the opposite as there are low-carbon schemes going on in the UK all the time, whether that’s fourth-generation or fifth-generation heat networks.

“There is a lot of interest in these schemes and as I said on the night, we just need to increase the supply chain and get more contractors involved in the sector. By doing so, we can help bring costs down further and get more district heating networks installed across the UK.

“There can be misconceptions on which buildings they can be used in, and that naturally impacts a second major topic that came up on the night – namely, how we turn fossil fuel district heating networks into low-carbon heat networks.

“What the event made clear is that the industry is seeing growing interest in the technology, with professionals often asking how to join existing community-led heat networks, and who they need to speak to. The reason we hold these sessions is to provide additional clarity in this important area, and I believe we achieved our goal.”


Panel expert Bean highlights and discusses key points from his session with us.


Heat Pumps in District Heating and Retrofit

Gay-Lussac's Law2 states that the pressure of a given mass of gas varies directly with the absolute temperature of the gas. The principle is related to both Boyle’s Law3 and Charles’s Law4. These three beautifully simple laws of physics underpin the gas refrigeration that makes possible the lives of convenience that we all enjoy. Imagine how different the daily routine would be if we all had to go to the farm for fresh milk each morning and if we couldn’t enjoy the comfort of our air-conditioned offices and cars. Heat pump technologies are ubiquitous. In the modern vernacular, the fridge, the freezer, A/C, and even heat pump tumble dryers.

The range of heat pumps available on the market today is enormous, from those designed for highly insulated micro- apartments, at 1.5kW, through to the largest commercial units at up to 10MW. All these devices can be cascaded to deliver heating and cooling for massive industrial and community-wide systems.


A look at district heating systems

District heating systems are commonplace in many parts of Scandinavia and Europe. Many started out based on energy from waste, biomass or fossil fuel sources, but these are now being retrospectively converted to run on heat pump technologies as the high temperature output range increases through refrigerant and compressor innovation. Conventional chemical HFC refrigerants are destined to be phased out as the implications of high Global Warming (GWP) and Ozone Depleting (ODP) Potential are recognised. CO2, Propane (R290) and ammonia (R717) all have an ODP of zero and ultra-low GWP of 3 or less. By comparison, R32,

the current dominant HFC has a GWP of 675. The UK has a number of innovative, industry leading commercial heat pump manufacturers working with natural refrigerants which are increasingly demanded by climate conscious clients. These refrigerant developments are delivering viable economic solutions with flow temperatures up to 150°C, using any source, and combined with an increased ability to scavenge waste heat, this is bringing heat pump technologies to the fore in retrofit scenarios.

The other factor that has previously held back heat pump technologies has been the myth of incompatibility with conventional heat emitter systems. Low environmental impact, high flow temperatures and economic efficiencies, mean that retrofitting and decarbonising period and Listed buildings are now routinely possible.

Many such historic structures are found at the heart of medical and educational campus sites where smaller and micro- district schemes are now finding a ready market, supported by government funding, previously under the Non-Domestic Renewable Heat Incentive5 and latterly under the Public Sector Decarbonisation Scheme6. The National Trust and the Church of England are notable entities increasingly turning to heat pump technologies to decarbonise their estates and these high-profile exemplars are providing real encouragement to the communities that they serve. The concept of Bath Abbey as a low, and ultimately zero, carbon Grade I Listed building was unthinkable, but is now a reality, thanks to a water source heat pump system.

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Whilst carbon dioxide is the problem for the climate, it is other emissions derived from burning fossil fuels for heat, NOx, SOx and particulates, which are so damaging to health. Urban air-quality will be the beneficiary as existing heat networks are progressively retrofitted with heat pump technologies, many of which are specifically designed to include the harvesting of waste heat. The Bunhill scheme in Islington captures waste heat from the London Tube system and heats homes, a school and two leisure centres. There is sufficient waste heat in London to heat nearly 800,000 homes, levels of profligacy with fossil fuels that we can no longer afford. Waste heat is all around us, from industry, power generation and water treatment. As emissions start to dominate the retrofitting of mechanical services at all scales, scavenging waste will be a huge part of the economics.


A significant element

In the retrofitting of existing district heating schemes and the development of completely new networks, a significant element will be the messaging to consumers. Essentially, most homes and commercial buildings are already on a network – we call it the gas grid, where premises each have their own “converter”, a boiler. A heat network isn’t that different, there is a communal energy carrier and each building has a different type of “converter”, be this an individual heat pump on an ambient loop system, or a heat interface unit (HIU) on a 4th generation network. The optimised heat pump network scheme for any given community will be down to a number of factors, including access to beneficial assets, such as a source of waste heat or a major river, and the analysis of the loads. The rate at which this transition is adopted will largely be driven by our ability to demonstrate benefit and security of comfort to consumers. If we get this right, the current government assumption, that 20% of UK homes will be on some sort of heat network by 2050, could be an underestimate.


This all sounds too good to be true, so why do fossil fuels continue to dominate in the UK?

Essentially, this is down to the tax regime and the existing market relationship between the wholesale price of gas and the wholesale price of electricity. The combined impact is historically high electricity costs, whilst the gas price does not attract anything like the scale of social and environmental levies. For a typical domestic dual fuel bill, less than 2% of the gas price derives from levies, whilst the levies on electricity still sit at around 22%. Under the current domestic price cap, electricity is nearly four times the price of gas, per kWh. Even with increasingly efficient heat pump technologies, this presents a major obstacle leaving the UK at the bottom of the league in Europe for heat pump deployment per 1,000 households. For commercial customers, outside the protection of the OFGEM price caps the “spark gap”, the price differential between gas and electricity, can be even more challenging.



But change is coming

In Powering Up Britain, the major policy release in March this year, government committed to the Review of Electricity Market Arrangements (REMA)7 and to the rebalancing of the social and environmental levies. Both seem to have survived the Prime Minister’s latest pronouncements, and both should result in lower electricity prices, commercially and domestically. As set out above, the harvesting of waste heat should also improve the economics of electrification using heat pumps. Local generation capacity, again at both commercial and domestic scale, effectively reduces the average cost of electricity. Finally, recognition of the value to be derived from matching demand to increasingly intermittent zero carbon generation from wind and solar PV is also coming to the markets in multiple ways. This “flexibility” again has enormous economic potential. The challenge is to optimise the balancing mechanisms and to fairly distribute the economic value to encourage participation at all levels. A report published by the Carbon Trust and Imperial College in May 2021 put a value of £16.7bn per annum on net savings from flexibility across all scenarios. This is serious money.


In conclusion

It was once said that the Stone Age did not end because we ran out of stone, and that the fossil fuel age will not end because we run out of oil and gas. All heat pump technologies draw primary energy from the sun, whether stored in air, the ground or water. As the stars of decarbonisation policy, technical innovation and consumer engagement with the energy systems of the future, start to align, so combustion for heat will eventually be consigned to the history books.


In the next issue, we will hear from Simon Eddleston, who discussed retrofitting homes, in particular looking at district and communal heating technologies and the benefits to end-users as a result of their retrofit work.