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In the UK, a competition is shaping up between different ways to reduce carbon emissions from buildings. In one corner of the ring is the techno-fix of air source heat pumps and in the other, eco-retrofitting with insulation and draughtproofing

The UK Government has recently come under attack from multiple sides for its failure to act sufficiently on the challenge of climate change, particularly with respect to emissions from buildings.

Prime Minister Boris Johnson has pledged to cut carbon emissions by 78 per cent by 2035 compared to 1990 levels, taking the UK more than three quarters of the way towards hitting net zero.

The Committee on Climate Change (CCC), which is legally obliged to regularly mark the government’s homework on climate change, has slammed its inability to match action to words. “An ambitious heat and buildings strategy that works for consumers is urgently needed,” it says.

Even homes constructed just four years ago are not up to the required standard and will need refurbishing according to Labour’s shadow housing secretary, Thangam Debbonaire who said: “Families will spend years in homes [that] are colder and more expensive to heat. Every year of delay is costing billions of pounds and pumping millions of tonnes of carbon into the atmosphere. The government needs to wake up to the importance of warmer, more efficient and sustainable homes”. 

A new Office for Budget Responsibility (OBR) report puts the cost of making buildings net zero by 2050 at nearly £400 billion, with replacing gas boilers with heat pumps and installing better insulation raising a £250 billion bill for homes and more than £140 billion for all other buildings.

It says the amount pledged so far is insufficient. While unmitigated climate change would spell disaster, the net fiscal costs of moving to net zero emissions by 2050 could be comparatively modest, it says, because the savings from reduced energy costs across the whole economy would be around £1.08 trillion, leaving a £400 billion bill over 30 years.

The 242-page report also warns that not tackling climate change would “ultimately have catastrophic economic and fiscal consequences”.

Air source heat pumps: a disaster in the making

Both reports unquestioningly repeat the mantra that buildings need to have electricity-powered air source heat pumps installed to decarbonise heat by replacing gas or oil-fired boilers.

The government target is 600,000 heat pump installations per year by 2028, with the CCC calling for half as many again.

Unfortunately air source heat pumps are only effective in well insulated buildings, which the majority of buildings are not, yet the CCC is not calling for a programme of refurbishment in its required “headline actions”.

Energy performance certificate assessors will tell you, as one told me recently, that you need an efficiency rating of C or above to make air source heat pumps worthwhile, otherwise homeowners will find themselves saddled with high electricity bills as the pumps struggle to reach the temperatures set on the thermostat while heat is still leaving the building.

The efficiency of any source heat pump depends both on the difference between the target the source temperature, and the rate at which heat leaves the building.

It’s more efficient to use heat from underground or a water source (since these rarely reach below 2-4 degrees Celsius) and to use it for underfloor or warm air heating, typically no more than 20 degrees Celsius (a difference of 16 degrees Celsius), than it is to use air as a source (which in winter may reach well below zero) and to send that heat to radiators or domestic hot water which might be up to 50 degrees Celsius (a difference of roughly 55 degrees Celsius).

Combine this with draughts and poor insulation, and those air source heat pumps really have their work cut out. There are already stories of people being shocked at how much their electricity bills have risen.

Meanwhile building owners are being pestered by installers and suppliers of air source heat pumps who hope to make a fortune out of the fact that the technology is backed by the government. 

It’s certainly not in their interest to inform poorly informed building owners that the technology is inappropriate if their property is not well insulated.

Besides thousands of disappointed customers, this is going to result in a large ecological footprint caused by the supply chain and eventual disposal of these units when they are unnecessary.

We’ve seen this before, when rooftop wind turbines were recommended by a former Government energy minister, Brian Wilson, and sold in DIY shops, when in fact they were useless, generating almost nothing because of the turbulence that exists around buildings, leading to many customer complaints.

In both cases we see the solution to climate change being sold as a techno fix. 

Technology is in part responsible for climate change, so it is reasonable to conclude that the first stop in looking for solution is not to use technology, but to avoid the need for it.

This is called energy efficiency.

The retrofit challenge

The Conservative Governments has been remarkably reluctant to back energy efficiency. Why? 

Could it be because it is easy in the short term to make a business case for manufacturing and selling technology, whereas the business case for energy efficiency is harder to make without public subsidy?

But the evidence shows that if you factor in the reduced costs of tackling climate change plus the reduced energy costs due to implementing energy efficiency, then refurbishment becomes a financially sound investment, as well as an environmentally and ethically sound investment. 

However this only works on a long-term basis. Long-term is longer than a few years. But why should we be limited by this thinking? The difference in age between a grandchild and grand mother can be 90 years. Combining their lifespans, we are looking at around 200 years given today’s longevity. 

This gives us a proper perspective. What kind of a life do you want your grandchild to be living? What kind of a world do you want them to inhabit?

The tipping point for the kind of solution to be used in a building to reduce overall life-cycle greenhouse gas emissions is influenced by geographical location, climate and the local energy mix supplying the building and therefore varies between different buildings.

To investigate which kind of solutions to use one can simply look at the climate zone map for passive house refurbishment. 

Map of world climate zones for passive house style refurbishment of buildings

Most of Australia for example is classed as “very hot”, with the remainder as “hot” or “warm temperate”. Different solutions are needed for each zone and supplied by regional passive house trusts. 

There is now no shortage of good examples.

Passive house retrofits in Darmstadt Germany

But as long as people are more attracted by the allure of new technology and ignore or remain unaware of the upfront and life-cycle emissions associated with it, the energy efficiency message will remain hard to sell.

Air source heat pumps do have a part to play in a zero carbon future, but they should be second in line to improving building energy efficiency.

David Thorpe is the author of Passive Solar Architecture Pocket Reference,  Energy Management in Buildings and  Sustainable Home Refurbishment. He lives in the UK.

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  1. Good article, David. Agree 100% that targeting the EE of the building is the first priority. The sustainability message is too easily muddied by not assessing the whole problem holistically, and this promotion of air-source heat pumps is a classic example.