For the past few years, the specification of a heating system for an off-gas grid development has not been simple. Traditional oil or LPG boilers are not hugely favoured by purchasers. Housebuilders aren’t that keen either as their presence complicates compliance with increasingly stringent building regulations. What to do? Many house builders have gambled with air source heat pumps, a technology that not only disfigures the appearance of the property but also often requires planning permission to safeguard against noise disturbance at neighbouring properties. Worse, their efficiency has often not matched expectations which is hardly surprising given the fanciful performance claims bandied around by some manufacturers and the somewhat generous ERP test regime. And there are inevitable concerns about reliability and durability given the appliance must be continuously exposed to the elements. All in all, it isn’t a great solution.
In desperation, some developers have even embraced communal LPG systems which impose hideous running costs and emit far more carbon than the leading providers would have you believe. Claiming to be ‘greener’ than an oil boiler is hardly an endorsement for the widespread use of LPG! The proposed carbon intensity factors for SAP 10 demonstrate that a ground source heat pump would emit less than one quarter the carbon of a LPG boiler. Running costs would be less than half. The leading LPG provider may have some marketing muscle but they promote a fuel that must be quickly condemned to history.
Of course, ground source heat pumps would offer the lowest running costs, maintenance costs and carbon emissions. Aren’t they the obvious answer? History tells us they have rarely been considered primarily because of the added cost of the ground array, typically a borehole for a new-build dwelling given the modest size of most gardens. Thankfully, this will change as ground arrays can be provided at zero cost to the house builder. Yes, no cost at all. In other words, ground source heat pumps are now no more expensive than air source variants.
With the split ownership model – where an external funder can cover the cost of the ground array – funders can make a decent return especially as they could charge an annual connection fee. In some cases, this allows a subsidy towards the cost of the ground source heat pump too. And housebuilders and their SAP consultants are figuring out the specification of a ground source heat pump can allow savings to be made elsewhere in the build without compromising compliance with building regulations. What used to be the most expensive heating system choice actually turns out to be the cheapest.
And the appeal doesn’t stop there. House purchasers will like the solution too. Each householder is free to source their electricity from their preferred provider so they can switch at will to secure the lowest cost heat. The government likes this flexibility. And the emergence of flexible tariffs, such as Octopus Agile, and the development of novel (and compact) thermal storage featuring phase change salts will allow owners to focus heat pump operation during periods of low cost (and low carbon) electricity. The government likes this too.
If there are to be 3m heat pumps installed in the 2020’s – and multiple studies from the Committee for Climate Change, National Grid and other key stakeholders reveal this to be necessary to meet over-arching carbon targets – it makes sense to choose the most efficient variant in order to limit the strain on generating capacity. Crucially, ground source heat pumps clearly have far more potential to participate in load shifting initiatives as their efficiency is not reduced during night-time operation. By contrast, an air source heat pump is stymied by the cooler night-time air temperature – it is typically 3C cooler at 2am than 2pm – which further exacerbates the efficiency difference. What’s more, most people are trying to sleep so won’t appreciate the noise from whirring air source fans.
Whilst air source heat pumps are currently dominant, sales have stagnated and there is increasing appetite for ground source heat pumps to reclaim their position as the most popular variant. Government has recognised the ground arrays represent key strategic infrastructure which provide a long-lasting legacy for the subsidy spend. Better still, each installation is unobtrusive so there is no sensitivity around the mass deployment of ground source heat pumps. Unlike wind, or solar PV, or, for that matter, air source heat pumps, there is simply nothing that can spoil the landscape.
And if you want one final benefit, the coolth in the earth during the summer months will allow the dwelling to be passively cooled. You will need to fit radiators incorporating fan coils but it will be possible to take a few degrees off room temperatures for the cost of running a circulation pump. In reality, some of these costs will actually be recovered during the winter as the summer heat rejected into the ground will bolster heating efficiency and reduce running costs.
In summary, air source heat pumps really can’t stack up as an alternative to their less expensive, more efficient, more reliable and durable cousin and the real question is the timescale for gas boilers to submit too.