Heat Pumps: the future of heating
In our quest for a carbon-friendly future, decarbonising some industries is proving far more challenging than others. One of the UK's biggest challenges is home heating, which is yet to be electrified (so unable to reap the benefits of cleaner, greener electricity), and accounts for 14% of our total carbon emissions.
17 million UK homes still use gas boilers, burning tonnes of fossil fuels to stay warm. With over 1.5 million people replacing their boilers every year, there are huge gains to be made, but we need affordable alternatives - hardware that helps us bring the benefits of cleaner, greener renewable energy to these hard-to-reach sectors.
When it comes to heating, heat pumps are the solution we’ve been waiting for
Or, have they been waiting for us? Heat pumps are a tried and tested technology. They’ve actually been around for 160 years (making them older, even, than gas boilers) and we already use them every day. A fridge, for example, is a reverse heat pump. So is the air conditioning in a car. Now, heat pumps offer a ludicrously efficient, far greener electrical alternative to traditional boilers. In the past, we didn’t have the right tech to make them small or efficient enough to heat a home, but all that's changed in recent years, and Peter Konowalczyk, the newest brain behind Octopus Energy’s efforts to decarbonise heat, reports from the centre of it all.
Peter - a heat pump sage - is level-headed, good humoured, and devastatingly clever. He was born in Poland, but these days he describes himself more of an in-betweener: "London is such a mixture - a proper Camden Market soup. Together we have a good taste, and I’m happy to be an ingredient”. He first became interested in tech as a kid, after sneaking into factories that made brackets for coal mine harvesters:
When I was 14, I faked my ID to sneak into a factory and see how it all worked. In Poland, you could work for 3 weeks during the summer when you were 16. I was 14, but this was Communist time, and children did not have proper ID, so I faked mine. My parents said ‘are you sure this is ok?’ And of course I just said ‘yeah, yeah, yeah’, and so off I went.
A lot’s changed since then - Peter has been many things, and the tech he’s working on has got a lot greener - but his inquisitive spirit hasn’t changed a bit. ‘I am a very curious person’, he tells me, ‘I always have been.’
Eventually Peter trained as a physicist and spent years investigating complex problems on production lines and in R&D labs. After 30-odd years, he moved to the UK, just before the credit crunch hit. He ended up taking an entry-level job at one of the very first companies to specialise in selling domestic heat pumps:
"Every time that the engineers parked up, I would look at their drawings, and very occasionally I would say, ‘sorry to stick my head in, but what if you were to do things this way?’ For fun, they tried what I said, and a couple of years later I was acting as the technical director of the company."
So what exactly are heat pumps?
Peter knows heat pumps inside-out. He explains that they’re what’s known as ‘active heat exchangers’. In other words, with a little bit of electrical power, they can extract energy from a ‘cold side’ (the air outside) and move it to a ‘hot side’ (into your home).
This is because, as Peter says, ‘Heat pumps don’t just use electricity to produce heating, they also use it to harness extra energy from the atmosphere, and this is how they appear to produce more energy than you put in’. Indeed, for every kW of electricity you give a heat pump, creates between 2-4 kW of heat (and sometimes even more!), making them up to 4 times more efficient than traditional boilers (which generate 0.9 kW of heat per kW of gas). In some ways, this seems almost magical. When I ask Peter, he explains that there’s nothing magic about it, but his eyes light up all the same:
Right now, our world relies on stealing energy and natural resources that we can’t give back. If you want to continue to be a part of the natural world, you have to act like nature. With heat pumps, you don’t have to burn anything, you don’t have to steal anything - we’re mimicking nature. Even when it’s cold outside, we can take some of that energy and produce something with it.
Heat pumps run a little differently to gas boilers
Where boilers waste tons of excess power to heat super-fast on demand, heat pumps learn from weather conditions and your home's usage patterns to heat your home gradually, over a longer period. As Peter explains: “Combi Boilers are massively oversized and overpowered. For a house that can be heated with 4 kW of energy, we have 30 kW boilers. This is because traditional Combi boilers are designed to be ‘reactive’. You say ‘heating on’ and a boiler will wastefully burn loads of dirty fossil fuels at several hundred degrees to heat your water up right then and there."
Heat pumps, on the other hand, heat your water gently, for longer, and much, much more efficiently. Electricity, plus that extra bit of energy drawn from the outside world, is used to compress and heat up fluid inside the heat pump. That hot fluid is used to warm the water which will then heat your home via your existing pipes, radiators, and underfloor heating. It’s worth mentioning that like system boilers, heat pumps use a tank (and so long as your tank is sized correctly, you’ll never run out of hot water).
Misinformation currently being spouted by certain sources claims that heat pumps aren’t capable of matching the same 60-70°C water temperatures produced by traditional boilers. “This is just blatantly untrue”, Peter rebukes, “these days heat pumps can and do achieve these temperatures. The real question, however, is whether your water really needs to be this hot in the first place.” Heat pumps are still fairly efficient at higher temperatures (at 60°C they are still over twice as efficient as gas boilers), but at low temperatures they are even better than that, potentially saving you tonnes of energy, and cash. By running your radiators at slightly lower temperatures, but for a little longer, a heat pump can easily heat your home to the same temperatures as a gas boiler, but it can do so far more efficiently.
If you come home at 5:30pm, your heat pump can start pre-heating your house half an hour before, so that we don’t have to put tonnes of energy in at the last minute to heat the house as you’re walking up the driveway. Or, even better, we can start two hours before, and heat up the water even more gently (and so efficiently, and cheaply).
Heat pumps are much smarter than traditional boilers
Heat pumps don’t need to use short sharp bursts of extreme heat to warm your home, they are much smarter than that. An electronic heat pump controller decides your heating schedule, learning from your behaviour and taking into account other factors like the weather so that your home is always just the right temperature.
What’s more, you can combine a heat pump with a smart tariff, like AgileOctopus (which has half hourly rates based on the price of wholesale energy) to heat your home for pennies with cheaper, greener off peak-energy (any time other than 4-7pm).
As Peter explains:
We don’t have to create extreme temperatures to heat our homes - we don’t have to use more than we need. We can be very gentle. Heat pumps are all about understanding and working with nature - about forecasting. All we need to do is start heating our houses a little bit earlier, that’s all. This is the beauty of heat pumps.
How do heat pumps actually work (tech level: 🌶️ )
Inside a heat pump is a sealed circuit (this circuit comes into close contact with the circuit of water pipes that run throughout your house, but the fluids inside don’t actually mix). The circuit inside the heat pump is filled with one of several fluid substances, usually the refrigerant R410, but increasingly CO2 (R744), difluoromethane (R32), or propane (R290) - which is able to reach the highest temperatures.
- First let’s say it’s 4°C outside the house. A fan, powered by a small amount of electricity will blow that 4°C air into the heat pump, onto an ‘evaporator heat exchanger’. This way the air outside can begin to heat up the fluid inside the sealed circuit (which starts off very cold, and in a liquid state).
- From there, the fluid (let’s say we’re using propane) travels through a pipe to a compressor, powered by electricity, where it continues to be heated by compression. In this case, let’s say it’s heated to 95°C. The propane will leave the outlet as a hot, high pressure gas.
- The heated gaseous propane travels through a ‘condenser heat exchanger’ - a series of plates designed to bring this hot propane into close contact with the water in the pipes that make up your house’s central heating system. This way, your water will begin to heat up. That warm water will then travel through your home. The propane will have cooled slightly before it reaches the condenser heat exchanger (from 95°C to 75°C), and this will heat the water in your home to 55°C, so in this case you have 55°C in your water tank and your radiators (although, as we’ve said before, the temperature can go higher.) By the time the water has finished circulating your home, some of the heat will have been transferred to your home, so the water will return to the heat exchanger at about 45°C, where it will be heated back up to 55°C, and continue to cycle around your home.
- By the time the propane has finished travelling through the heat exchanger, warming the water in your home, it will have dropped from 75°C to 50°C. After that, it travels into an expansion valve, where it is allowed to expand rapidly, dropping from 50°C to a temperature below the temperature outside (let’s say -7°C), and returning to a liquid state.
- Finally, back where you started, this -7°C liquid propane returns to the first heat exchanger, where air outside (earlier we said 4°C) begins to warm it back up. This is the moment at which a heat pump ‘takes’ energy from the atmosphere. From there, it goes back to the compressor, and the cycle begins again.
Can heat pumps take over the world?
There are several factors that currently hold heat pumps back. The largest is to do with the running economy - or how much it costs to run a heat pump. Given how efficient heat pumps are, they already operate fairly cheaply, but in the UK they are still constrained by taxes on electricity. Electricity is taxed heavily compared to gas (costing 13-16p per kWh compared to gas’ 3-4 per kWh). Much of this comes down to carbon taxes, despite the fact that electricity is now 40% renewable, but gas is 100% fossil fuel. If we were to swap some of the taxes from electricity over to gas, heat pumps would become significantly cheaper to run, allowing owners to rapidly make up for installation and manufacture costs.
By the time I was done talking to Peter, he had won me over. These days everyone should have the support to buy an electric car rather than a gas powered car, or to insulate their homes, or install solar panels on their roofs, and it should be exactly the same for heat pumps. They are already a great option, being so much more efficient than boilers, and far greener too. If we can streamline installation and encourage the government to swap taxes from electricity to gas to cut running costs, by the time you need to replace your boiler, switching to a heat pump will be a no brainer.
Heat Pump FAQs
Will heat pumps work in all homes? (yes, but you’ll have to insulate homes with massive heat losses first)
If you’re going to install a heat pump, some homes require a little more work than others. One potential challenge is to do with how much heat your home loses over time. In homes with average heat losses, heat pumps have to work harder, but even then, it's usually only for few days a year, and they're still far more efficient and effective than gas boilers. In an ideal world, we’d all have energy efficient homes that work like closed objects and retain heat for a long time. But, in Peter’s words, “we have a few houses in the UK that have similar heat losses to bloody Stonehenge. In a modern world, where we want to do right by the planet, where we want to spend less money on energy, where we only heat up our homes (and not Guildford out the window) it’s good to stop heat losses.”
For the vast majority of homes in the UK - even those with typical heat losses - heat pumps are still clearly a great option. Homes with some heat losses are capable of staying warm with a heat pump, it just depends on whether you’re willing to spend a little bit more to run them. Over winter, on especially cold days, you might want to run your heat pump for longer (and at a higher temperature) than usual, but there's still a good chance that you'll save money over the course of the year.
In extreme cases, however, there’s a chance that the house might lose heat faster than a heat pump can warm it up. In the UK, a 3 bedroom house should have heat losses of 6kW max, but some older houses have heat losses of up to 10-15kW. In this case, you’ll need to reduce heat losses first. At the end of the day, it will be worth it. You’ll be paid back over time, it will raise the energy rating of your home, and in these cases, it would be worth insulating your home whether you had a heat-pump, or stuck with a boiler.
How much do heat pumps cost to run?
This depends entirely on what kind of home you have. If your home has a decent energy efficiency, there’s no doubt that a heat pump will already be cheaper to run than a traditional boiler. The average home in the UK, however, is fairly leaky. Without insulation and other measures to improve energy efficiency, Peter's data suggests that it will cost the average leaky homes 40% more to run a heat pump on an average, middle-of-the-range electricity tariff than a traditional boiler. By taking advantage of the AgileOctopus smart tariff’s dirt-cheap off-peak rates, this drops to about 20%. However, it's worth remembering that with insulation you can easily ensure that your heat pump runs cheaper than a traditional boiler, and with solar panels, or a smart home battery, you could save tonnes of cash. What's more, running costs are set to drop massively if carbon taxes are shifted over from electricity to gas, but in the meantime, plenty of people are already saving money, and many are still happy to pay a little extra in order to go fossil fuel free!
Will I have to turn my radiators down? (Nope, but you might want to anyway)
You will sometimes hear naysayers claim that if you have a heat pump, your radiators will have to run 10°C cooler than if you had a boiler, which suggests that your house will be chillier - but this isn’t the case. First of all, heat pumps can heat your water to the same 60°C, or even 70°C degree temperatures that boilers can. However, because heat pumps are extremely efficient at lower temperatures, you would save money by running your heating at cooler temperatures for longer, and your house will stay just as warm as if you had a gas boiler. It’s worth mentioning that there are actually ongoing campaigns to lower radiator temperatures anyway. Overheating your water can be wasteful, and in care homes, for example, radiator temperatures are limited to 48°C to limit the risk of scalding.
Do heat pumps still run when it is really cold outside? (Yes!)
Thanks to the heat pump’s internal compressor, it will always be able to heat the fluid inside (propane, for example) to the same temperatures, regardless of the temperature outside. When it is extremely cold outside (we’re talking -15°C), the heat pump can’t extract quite as much energy from the atmosphere as usual – but that doesn’t mean your house won’t get as warm as normal. On these incredibly rare, freezing days, the heat pump would just use a little more electricity to create heat, or in other words, work a tiny bit less efficiently, but it will still reach the same temperatures as ever. We see temperatures below -10°C only a few days per year, and even at these temperatures, heat pumps still function more efficiently than gas boilers do.
Will I need new radiators? (Probably not, but there is a small possibility)
A radiator is a heat emitter. The larger a heat emitter is, the lower the temperatures it can handle while still keeping your house warm. In an average sized room (usually about 3 meters by 4 meters) your standard twin wall radiator setup should be fine to handle a heat pump. Occasionally, however, you might need to replace a smaller radiator with a slightly larger one (though it won’t have to be massive), or if you have any really big rooms, an engineer might recommend putting another radiator in.
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