Switching to a heat pump to warm your house might not be as green as you think...
Why 'eco-friendly' heat pumps increase, not reduce, your carbon footprint
8th October, 2010
Switch to heat pumps to warm your home and you'll qualify for the Renewable Heat Incentive subsidy. But new research reveals the pumps release potent hydrofluorocarbon (HFC) gases, says Eric Johnson, significantly increasing the true carbon footprint of this supposedly green technology
It will come as no surprise that heating Britain's homes and offices causes major greenhouse gas emissions, and that a key target of climate-change policy is to improve the associated carbon footprint. One possible way to do this, under certain conditions, is to replace conventional heating systems with heat pumps. In principle, the aim is to substitute a heat pump in cases where its 'cradle-to-grave' or life-cycle footprint is significantly lower than its alternatives.
So the UK government has proposed to offer its Renewable Heat Incentive subsidy to home and office owners who switch from conventional fuels - gas, fuel oil, liquefied petroleum gas (LPG), electricity and coal - to heat pumps. The European Union stands behind this, with similar rules laid out in its Renewable Energy Directive (RED).
However, both of these regulations omit the inconvenient truth that heat pumps use, and emit, hydrofluorocarbon (HFC) gases that are as much as 2,000 times more potent in heating the atmosphere than garden variety carbon dioxide. And these are not exceptional cases. Other relevant rules, such as EU eco-labels for heat pumps, the Energy Using Products Directive, and the UK Standard Assessment Procedure for Buildings are all written as though a heat pump's only greenhouse gas emissions come from the power plant making electricity for it.
Well, they're not. At least six published studies, including one from a heat pump and refrigeration centre in Germany way back in 1994, have pointed out that HFCs leak from heat pumps both during their typical 15-18 years of operation and upon decommissioning.
The HFC kick
Armed with not just these studies, but also with the latest leak rate estimates from the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee (RTOC), of the United Nations Environment Programme, Atlantic Consulting - my company - set out to calculate how significant this 'HFC-kick' is to a heat pump's footprint. We modelled an air-source heat pump, typical for the UK, which works similarly to a refrigerator in reverse.
Based on inputs from the Energy Systems Research Unit from the University of Strathclyde, and the Buildings Research Establishment, we estimated footprints for space and hot water heating across the range of UK climate and homes, from one-bedroom flats up to four-bedroom detached houses.
Across this range we found that HFCs consistently add about 20 per cent to the footprint caused by power-generation. There is some variation by size of the home, type of construction and specific HFC, but the answer stays robust. HFCs add a serious chunk of carbon to a heat pump's profile.
Serious enough, in fact, that on a lifetime 'per kWh of delivered heat' basis, heat pumps are about as carbon intensive as natural gas or LPG in heating. If heat pumps run on continental European efficiencies, then they come in-between gas and LPG (which are pretty close together in the first place).
If they run on UK efficiencies (as demonstrated in recent trials
sponsored by the Energy Saving Trust) then heat pumps are higher carbon than either of the gas fuels - and that is a direct comparison to figures published by the Department of Energy and Climate Change.
Even compared to the classic 'dirty' fuel - coal - heat pumps fail to beat the 60 per cent carbon reduction subsidy threshold prescribed by RED. At European efficiencies, they barely beat the 60 per cent mark against electric resistance heaters.
Critically, our analysis is based on a UK power generation average. If heat pumps were instead evaluated on electricity production at the margin (which heat pumps would draw, and which recent work by Imperial College suggest may have a 40 per cent higher footprint) then our findings are even more robust.
Our findings are important, and they are not alone. A similar, peer reviewed, study was just published by researchers from the Netherlands' University of Delft, who concluded that 'a heat pump is actually not more environmentally friendly than a gas-fired boiler.'
And the implication is, that in countries with relatively high-carbon power generation (such as Netherlands, the UK and Germany), this will generally be the case now - and that just might be a surprise.
Eric Johnson is a director of Atlantic Consulting, an independent
consultancy based near Zurich, Switzerland. +41 44 772 1079,
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