iPump anyone? How intelligent heat pumps could replace gas boilers

Heating a home using an Air Source Heat PumpHeat pumps are not a new technology; the principles underlying their operation were described by Lord Kelvin in the 1850s. On the wall of the boiler room of the Pimlico District Heating Scheme you will find a Times article from the 1950s proposing a heat pump as a replacement for the then common open coal fire.

But while they are common on the Continent, their uptake in the UK has been low, with cheap gas from the North Sea displacing most other domestic heating sources from the 1970s onward.

In basic terms, heat pumps work by extracting heat from the ground or air with a refrigerant and concentrating it into a much higher temperature by pressurising the refrigerant and running it through a heat exchanger. This is the same mechanism as a fridge but in reverse, keeping the desired space heated rather than cooled.

Low carbon heat
Now that the full cost of burning fossil fuels is apparent, heat pumps are on the march again. Their unique ability to supply three to four units of heat for every one unit of electricity consumed makes them much more efficient than ordinary electric heaters, and an ideal heating method in a world where the cost of gas-related carbon emissions is simply too high. Any heat pump that produces over 2.3 units of heat for every unit of electricity already has lower carbon emissions than a gas boiler. In the future, a decarbonised electricity system coupled with heat pumps will allow us to heat our homes with very low associated carbon emissions.

Unfortunately, we’ve become used to boilers we can switch off and switch on whenever we need them, and heat pumps don’t work quite like that. They can deliver the same comfort and amount of heat gas boilers can (and potentially for less money per unit of heat), but they require a bit more planning. You can’t just switch a heat pump on when you get in from work and expect it to deliver heat instantly, not without severely reducing its efficiency. Because heat pumps are more efficient when their output temperature is lower, it can be more cost-effective to run them all the time, as a room can be kept warm either by lower temperatures all the time or higher temperatures for a limited number of hours. This can seem counter-intuitive when you’re used to switching off the heating when there’s no-one in the house.

Performing below par
As a result, the performance of heat pumps in the UK has been mixed. Alongside some poorly performed installations, a lack of consumer education has led to heat pumps being treated by their owners as gas boilers, leading to them producing heat at very low efficiency levels and consequently causing bills to skyrocket. A range of projects have tried to understand the way in which consumers engage with heat pumps, and found some very odd things. For every two houses using their heat pump properly, there’s one in which the owner has taken to going out into their garden and switching their heat pump on and off at the socket.

There are at least two solutions to this problem. The first is a straightforward requirement that anyone installing a heat pump is required to fully train the customer in how to properly programme their heating system to deliver heat when they want it. Unfortunately, education alone doesn’t guarantee a customer won’t revert back to their old way of operating their heating device – and will blame the heat pump when the bill comes in.

Intelligent design
The second solution being put forward by some manufacturers is to simply design the customer out of the equation. Instead of the heat pump being programmed directly, the device learns to anticipate when the householder requires heat, and supplies it accordingly. This wouldn’t prevent people switching their heat pump on and off at the socket, but would perhaps forestall them thinking they needed to. In some commercial schemes, such as those in supermarkets, companies had found that staff were arriving in the morning, feeling cold, and attempting to switch the heat pump on, even though it was already lined up to deliver the scheduled heat. To accommodate this some models include a fan which switches on when staff attempt to interact with the device, but doesn’t actually deliver any heat. This gave staff the impression the device was switched on without causing additional running costs, while the pump still delivers the appropriate amount of heat.

Regardless of the eventual solution, it’s clear that in order to make heat pumps a viable alternative to gas boilers, a simple and easy to understand interface for them is necessary. It’s a great shame that Steve Jobs died before he could bring us the iPump.


  • If you have a heat pump. operating in the UK, that delivers anywhere near 5 units of energy for every 1 used, then you are very very lucky – 4 is very good.

    • Hi Bob,
      You’re absolutely right – an SPF of 5 would be extremely high for the UK, although it has been achieved on the continent. That’s why I went for 2.3 for the gas boiler comparison – it’s a much more realistic number!

  • The SPF figure of 2.3 ignores the fact that generating electricity and getting it into our homes is in itself only about 33% efficient. i.e. we burn 3kWh of coal/gas to create steam which is then used to drive a turbine to generate electricity which is then transported along cables to our homes where it provides 1kWh of electricity that can power a heat pump to generate 2.3kWh of heat. In total this process is only ~77% efficient (2.3/3). Whereas a modern combi boiler provides the same heat at >90% efficiency.

    I recommend watching out for the gas heat pumps being developed by manufactures across the continent. These run off the existing gas supply and early reports suggest can improve the efficiency to ~130%. Run a search for “IGWP heat pump” for instance.

    • P.S. I am searching for evidence that British boiler manufacturers are also developing new gas heat pump products. Hopefully our manufacturers will not miss out on this emerging opportunity. Please let me know of any you know!

    • The SPF figure presumes a carbon factor of grid electricity of 0.5246g/kwh, a carbon factor of natural gas of 0.1836g/kwh and a standard gas boiler at 80% efficiency. Pushing it up to 90% (which condensing boilers will only achieve at higher flow temperatures) is matched by a HP at 2.6 SPF and at 100% a HP at 2.9 SPF will match it. The efficiency of the power plant is taken into account in the carbon factor of the grid electricity.

      This being said, gas heat pumps and other hybrids/bivalent systems are a good option for larger dwellings, which might otherwise require a large heat pump.

      • The problem with using gas as a driver for a heat pump is that this requires the use of a combustion engine – internal or external – which requires more maintenance than an electric heat pump. The reduced maintenance keeps costs down – important as a GSHP and collector are already expensive to install.

      • I would recommend a web search for ‘Pathways for Decarbonising Heat’ by National Grid. Figure 2 on page 10 neatly illustrates the scale of the challenge if we are to move en-mass to power consuming heating solutions.

        Carbon is one thing. Having enough power is perhaps equally fundamental. Fantastic opportunity for providers of energy technology solutions !

  • Adam, a good article, I agree. I’m a member of the Green Alliance and looked at a Ground Source Heat Pump (GSHP) for myself 18 months ago. But to get good efficiency you need underfloor heating which in effect doubled the cost up front. This sparked an idea to see if it is possible to develop a GSHP which could produce heated water output at radiator temperatures. I believe this can be done an am now working with a heat pump expert to develop this. It’s called the GeoBoiler, the idea is to make it a direct replacement for and Oil or Gas Boiler. If you or any of your readers are interested in this please let me know. Assuming we can make this work it would be a breakthrough that could address the major problem of how to retrofit the 20m gas and 1m oil centrally heated homes in the UK. As I’m sure you know this is one of the major carbon-reduction challenges facing us in the coming decades. Yours, David Richards.

    • Hi David – many thanks for getting in touch. To clarify, you’re designing a GSHP for flow temperatures of 70-80C, is that right? What kind of SPF are you aiming for? I know Dimplex at least have a model in that range right now.

  • Adam, we are targetting a Co-Efficient of Performance (COP) of 4. Depending on the application and the ground source input the average flow temperature would either be at 70C (to meet EN442 standard for radiators, 74C out and 66C return flows) or at 60C as per condensing boiler specifications. We are aware of the Dimplex product and we suspect that at radiator temperatures it’s efficiency drops off similar to the problems you noted in your article. David

  • If you can hit an SPF (ie average annual average COP) of 4 using closed loop ground input temperatures (which are typically close to zero) and an output temperature of 70C – you will be doing extremely well. Lots of folk will be interested. However, bear in mind that the higher the SPF, the larger the ground loop that is required – and the more expensive the GSHP system.

  • Heat Pump systems were based on reverse cycle defrost systems, long based technology in the refrigeration market.

    In all honetsy I hate to burst the bubble here but there are already air to water heat pumps available that produce hot water at high levels (Altherma)using as cascade system. These have been available for at least two years.
    I agree about water temperatures being produced at 55 DegC as being more suitable for underfloor heating but, in a new installation the rads could be sized for the water temperatures delivered.

    To a certain extent current systems already deliver the desired level of heating to the client as and when it is required. The current batch of Heat Pumps should be supplied with inverter drive so that the amount of energy consumed is proportional to the heat required.

    The whole ethos of our renewable sector at the moment is geared to our energy generation future requirements and the fact that we are shutting down gas & coal generating plants in the near future. Our gas supplies are allegedly running down so why would you advocate using a gas fired heat pump and the turbine/engine that has to power it? As one person has already commented this will require more regular servicing, as in a car engine, and a suitably qualified engineer to carry that works out, in addition to a heating engineer. Best will in the world, do you want an engine, not matter how quiet running in your back yard?

    By the way, Heat Pumps have been used commercially in the UK for over 30 years and we have lead Europe in the commercial market for most of that time. We have also grown with the technology from electro-mechanical through to electronic and on to digital, currently.

    • When you say “we have lead Europe in the commercial market”, I take it that you mean non-domestic installations, because sales of domestic heat pumps in UK are a fraction of those in Sweden, France and Norway.
      Underfloor heating is not always the panacea it is cracked up to be, as it requires higher output pump or pumps (the ordinary kind, not heat pumps) because of the extra pressure involved in getting the distribution fluid around the much longer, thinner pipe network. Some heat pump controllers insist that this flow be maintained all the time to monitor system temperatures and this is an extra load.
      To some extent, if we manage to achieve a decarbonised electricity supply, despite the efforts of George Osborne, heat pumps are the only game in town that allows us to take advantage of it. Though if we could get our housing up to passivhaus standards, then simple electric heaters would be a lower-cost, simpler method of providing the small amount of heat required.

      • Hi Bob
        I was referring to the commercial market which in turns begats the domestic market. The technology used today in the domestic market has been honed and developed by the commercial market.
        The commercial market has been using inverter drive for over 20 years whilst the domestic market in Europe simply has not until very recent years.

        In all honesty the small commercial products have been modified, adapted and improved for the domestic market over the last few years. Many of them are in fact domestic products in their ‘home’ markets!

        When we first tried to enter the domestic market back in the early 90’s it was with the extensive support of the electricity companies in both financial and marketing support. Of course these companies do not exist in that form today. Their help got Heat Pumps in to things like the Ideal Homes exhibition and in to show houses and hugely increased the awareness. Now we have to pay for any help from the Big 6!

        I am a firm believer in Heat Pumps as one of many solutions for the future and the fact that underfloor is not the only solution to heating premises. An integrated renewable policy is far better and you will find that companies are widening their product offers to cover this.

        I also maintain, by the way, that the Coalition has at last put the horse before the cart and put the emphasis on energy efficiency to reduce our energy generation needs which should have been the priority in the first place. People ‘buy in’ to saving money!

  • Interesting to read the IGWP information. Adsorption heat pumps are not new but combining them with boilers is. It doesn’t address the problem and the costs of those ‘off grid’ which is where a big market for domestic heat pumps lie.

    Jager actually produce radiators specifically for Heat Pumps, by the way.

    • I agree that current GSHPs are fine for new build using underfloor, oversized or high-capacity radiators. But the biggest problem we face in the UK is the 21 million homes who need to shift away from oil and gas central heating to low and no-carbon solutions. European Governments like ourselves and Germany see three main renawable technologies to achieve this ‘de-carbonisation’, namely GSHPs, Air Source Heat Pumps(ASHPs) and Biomass. Ref GSHPs, retrofitting underfloor heating in existing housing stock is just un-economic. And running current-technology GSHPs at temperatures even above 45C makes them inefficient and questionably not carbon-reducing at all. There are in effect 2 problems. New- build (within which I would include significant renovation where new floor and plumbing can/is being done), for which all three solutions are well-suited. And the much larger problem of Retrofit ie established homes who need radiator-temperature water because of the fabric of the building and their existing radiators and plumbing. Biomass will do a good job here, but it’s not a particularly ‘clean’ technology (smoke and ashes) and there is the problem of sourcing and loading the biomass. ASHPs will do a good job for many, particularly in towns and cities, but it has limitations. There is therefore a gap, which is why I’m on a mission to develop a radiator-compatible GSHP!

      • Hi David. That is the Holy Grail that keeps all the major manufacturers of Heat Pumps supporting the market for ASHP whilst the RHI system dithers.

        I think there is not any likelihood of us touching a target of 21m households as most of them are on the grid and cannot afford to change to elaborate new systems at, currently, great cost.

        I agree that retro-fitting underfloor heating and replacing radiators is a step too far for the majority of households for a variety of reasons and the lack of much in the way of new builds doesn’t allow the industry room for movement.

        Perhaps one of the ways forward is the advent of ground water sourcing using mine shafts that is being trialed in Glasgow/Falkirk for District Heating systems.

        Biomass is not much use for the general housing market due to size and fuel but is very viable for District Heating, especially if the procurement people allow for future changes to the fuel supply in the system bought.

        Good luck with your development work.

  • Gents, I have spent a little time reading these comments – the heat pump guys know their onions on Heat Pump performance and I leave it to them.

    Think about using a heating engineer!

    I think that it may be worth taking a slight step back and take a more holistic approach – In my experience, the majority (I choose this word carefully) of heat pumps work well at low temperatures, perhaps even at ‘medium’ temperatures – up to 55degC.

    Designing Low/Medium/High temperature ASHP/Boiler, GSHP/Boiler and Boiler/Boiler combinations is not difficult, indeed the commercial world has been doing this as long as I can remember – as previously highlighted it just need consideration on the whole heating system.

    Finding emitters (such as JAGA) that can match heat source selection is not so difficult as long as you decide what route you want to go down and I think that emitter industry, as long as the heat source industry will move to assist here too – take a look at the MIS Heat Emitter (available now) and BRE Low Temperature (coming soon) Guides.

    Not wishing to be too controversial: I am not so sure about Biomass boilers – is it not just carbon offsetting? Use a heat pump and plant a tree? – don’t mob me with answers on this one, just interested in the concept!

  • Hello,
    Heat pumps are not a new technology; the principles underlying their operation were described by Lord Kelvin in the 1850s.
    Click Here

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s