For some years, the most popular heat pump variant in the UK has been air source. It is understandable: their installation is simple and relatively inexpensive too. But is their widespread deployment sensible for the electricity system and the environment?

A ground source heat pump (GSHP) installed at every suitable UK property – estimated to be over 85 per cent of the total – is likely to offer the lowest cost pathway to net zero carbon in the nation’s building stock. Such a strategy would provide the lowest cost and lowest carbon heat supply to users but, more importantly, would mean far more modest additional system costs associated with the additional generating capacity and strengthening of the existing electricity distribution network.

Very simply, it should have been the approach adopted 15 years ago when GSHP’s were the most popular low carbon heating technology.

In the interim, too much policy, specifically the Renewable Heat Incentive, has presumed the lowest cost solutions must somehow provide the best value. It is foolish. As a consequence, air source heat pumps (ASHPs) have been favored, perhaps because their seasonal efficiency, at around 275 per cent, is not hugely different from a GSHP at 340 per cent. For this reason, it might appear there is limited value in subsidizing a ground array but this narrow analysis wholly misses the point.

On the coldest day, with sub-zero air temperatures, an ASHP is only around 180 per cent efficient. By contrast, a GSHP will be operating at a far superior 300 per cent efficiency because the prevailing air temperature has not impacted its source temperature. This huge efficiency advantage, at a time when most heat pumps will be running, underpins the attractiveness of the ground source option to other stakeholders.

Of course, electricity and heat storage will increasingly impact operating profiles but the fact remains that an ASHP’s woeful efficiency when heat is most needed is a huge issue. Storage might help

Fifth Generation District Heating with Ambient Shared Borehole Ground Loop Arrays and Kensa Shoebox heat pump
Fifth Generation District Heating with Ambient Shared Borehole Ground Loop Arrays and Kensa Shoebox heat pump

in the short-term but it will do little if the cold weather persists and it is exhausted. This undeniable weakness has fuelled an odd campaign to support a hybrid system featuring a gas boiler and an ASHP. Whilst it is clear why the incumbent gas network companies might promote this option, it is hard to see how anybody else might benefit, especially any householder who is lumbered two appliances with poor efficiency and only modest durability.

Instead, the optimum strategy is a Government-backed mass ground array installation programme, which unlocks all the benefits, provides critical national infrastructure and creates a valuable 100-year plus legacy for the subsidy spend. In most cases, shared ground arrays, the 21st century low carbon equivalent to the gas infrastructure, should be deployed with most taking the form of a borehole field.

Such a system architecture will allow users to select their own preferred electricity supplier and ‘switch’ at will, an important benefit given more and more suppliers are now offering novel time-of-use tariffs, which can further reduce running costs and carbon emissions. Maximum savings are achieved if heat storage, perhaps using vessels equipped with phase change salts, is deployed so the heat pump only has to operate when electricity costs are low.

Ground arrays are entirely hidden from view so their mass deployment cannot upset anyone. They also have modest and very predictable on-going maintenance costs. For these reasons, many entities, including energy companies, water companies and private investors, are keen to own such assets as they provide a long-term income potential via an Annual Connection Fee, the equivalent of a gas standing charge. Importantly, even having paid this charge, householders will be better off as they will benefit from the lowest running and ownership costs: they can also benefit from free passive cooling, an increasingly desirable feature as summer temperatures continue to rise, and another unique feature of GSHPs.

Clearly, emerging business models, which divorce the cost of the ground array from the user are hugely disruptive to the current market, and the dominance of ASHPs. Why would any consumer prefer an unsightly and noisy ASHP to an identically priced GSHP if the ground array cost was paid by others?

Obvious early opportunities exist in the social housing retrofit and new build markets where a single decision-maker can require all properties to connect to the shared ground array. As costs fall, it will then be possible to tackle the private housing retrofit market in the second half of the decade, probably via long-term ‘heat as a service’ offers where the superior reliability and durability of the GSHP will support its adoption.

In the short-term, some Government subsidy towards the cost of the ground arrays will be necessary and will deliver unrivalled value regardless of the metric – UK jobs created, carbon saved, fuel poverty alleviated, renewable heat generated. Yes, more subsidy is required but private investment will mitigate the cost to the public purse, and, in a post-Covid world, where an economic recovery is critical, the vast majority of the investment would directly benefit UK Plc. Only UK based drillers can deliver the ground arrays and the majority of GSHPs currently installed in the UK are manufactured in Cornwall.

In conclusion, any holistic analysis of the total system-wide costs required to deliver zero carbon heating will reveal that the mass deployment of GSHPs is the optimum strategy. It works for the environment, the community, the supply chain and the energy system. And it is the only approach, which works for households. More efficient, more reliable and more durable GSHPs are the only low carbon technology that can provide a compelling alternative to gas boilers and the smarter network operators, here and in North America, have already seen reason to support their adoption.

Simon Lomax is CEO of the Kensa Group, a fast-growing collection of award-winning businesses involved in the manufacture and installation of ground source heat pumps and the ownership of associated underground infrastructure. Now employing over 90 people the Kensa Group wholly owns Kensa Heat Pumps Limited and Kensa Contracting Limited.Kensa Heat Pumps remains the UK’s only manufacturer of ground source heat pumps and is the long-established market leader according to BSRIA annual reports. Kensa Contracting is a specialist installation business which focuses on large-scale new build and social housing retrofit programs.
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