District heat networks – the overlooked urban solution?

While hydrogen certainly offers great potential, it’s often overlooked that it is untested technology at present and, meanwhile, the clock is ticking.

One approach that was overlooked in the 10-point plan but could be found among the 170 pages of the subsequent Energy White Paper, is district heat networks. Proven, mature technology that works; could this community wide approach offer the silver bullet in our fight to decarbonise?

We spoke to Matthew Trewhella, managing director of GSHP specialists, Kensa Contracting:

What sort of district heat network solutions do you offer?

The energy whitepaper describes a heat network (sometimes called district heating) as “…a system of insulated pipes that takes heating and cooling generated from a central source and distributes it to a number of domestic and non-domestic buildings”. Kensa has pioneered a subtly different approach to heat networks; shared ground loop arrays serving individual ground source units connected by ambient temperature distribution pipework.

Kensa heat pumps in home

This shared ground loop system acts as a thermal energy supply grid, circulating low-grade heat from the ground, water or waste heat processes, around a network of pipes to individual heat pumps in separate dwellings. The heat pumps then upgrade this heat at the point of use to deliver heating and hot water whenever it is needed. Distributing the heat harvested from the ground at ambient temperatures (-5°C to 20°C), delivers exceptional efficiencies, minimising heat losses and avoids the common overheating problems associated with central plantrooms and riser pipework in corridors.

The result is a system that on the surface looks more like a traditional gas system – with a white box appliance in every property producing hot water (35-65°C) that is fed energy using a network of pipes. However, this architecture is a true district heating system – 65-85% of the heat being given out by the heating system comes from low grade heat delivered by the district, shared network. Only 15-35% of the energy is added by the heat pump using the householder’s electricity.

To what level do you see district heat networks playing a part in our road to net zero?

At Kensa believe that shared ground arrays should be regarded as the 21st century equivalent to the gas network, creating a renewable heat infrastructure that effectively mimics the existing mains gas model and allows the householder to have a ‘white box GSHP’ inside the property that mimics the familiar boiler market. Boiler installers do not have to worry about the sizing or installation of the gas grid and boilers from all manufacturers are compatible with the network. This also solves another major concern about the transition to net zero – training. By splitting the design and implementation of the ground/network infrastructure from the installation of the heat pump the existing skills of boiler installers are retained which minimises the training required.

What are the barriers to implementation on a wider scale?

Some of the barriers are real and some are perception based. There is a common misconception that many properties won’t have space for the ground array that a ground source heat pump system requires. That may be partially true if you are limited to gardens only and every property having its own ground array. However, even in Victorian terraced properties – the densest low-rise housing in the UK – there would be plenty of space if we used deeper boreholes installed in the street.

Currently ground source heat pumps compete well with mains gas on running, operating and replacement costs but still cost more to install which is a barrier. However, once the underground infrastructure is in place, households could simply call their local heat pump installer and connect to the shared ground loop array on their street as and when their existing boiler needs replacing. We think that Government subsidy should support the infrastructure deployment just like when the gas network was rolled out.

The industry is calling on government to recognise that networked ground source heat pumps are the best low carbon heating solution available, and by providing the right support they can unlock the potential of shared ground array infrastructure, allowing the industry to rapidly and effectively scale up to reach the volumes needed to deliver 600,000 per year.

What do you say to the hydrogen advocates who argue that we do not produce enough electricity for widescale heat pump deployment?

paper examining the impact of largescale deployment of heat pumps on national demand was published in the international peer-reviewed journal, Energy Policy. Decarbonising domestic heating: What is the peak GB demand?  concluded peak heat demand is 170 GW, around 40% lower than previously thought, and the maximum ramp rate is 60 GW/h, around 50% lower than previously thought. The paper says, ‘a shift towards heating GB’s homes using electricity rather than natural gas will put much less pressure on the electricity supply system than previously anticipated’.

These predictions, together with considerations of the way in which UK housing stock will evolve, advances in heating technology, and changes to the UK demographic, have far-reaching implications.

Heat pumps produce more heat than the electric that they consume, and therefore impose a reduced load on the grid. When using ground source heat pumps in particular, this strain is further reduced because they are typically 20-25% more efficient than air source heat pumps. To supply the 170GW of peak heat demand currently supplied by gas would only require 40-50GW of electricity to harvest the remaining 120-130GW from the ground. The current peak electricity supply is around 50GW so it would mean building the same capacity again to fully decarbonise all UK homes.

Conversely, to produce truly green hydrogen from electrolysis using renewable electricity, requires generating many times more energy, typically 0.5-0.6 units of heat are produced for every 1 unit of electricity generated which makes it 6 times less efficient than using a heat pump.