A green revolution — Part 2

The heating

Because “green” technology is still quite an expensive endeavour in terms of up front costs, it’s seen as prohibitive for people on lower incomes. I’ve heard it said the green revolution cannot only be for the middle classes, and that’s absolutely correct, but the point of these blog posts is to demonstrate it already isn’t. Last time out I wrote about our new Renault Zoé and did some maths to demonstrate a low-income family in France would find themselves financially better off with a new EV than a second-hand diesel. This time I’m parking transport (pun intended) and, as promised, exploring the cost of an air source heat pump.

When I first contacted a local company, EcoWatt, to come and talk to us about our central heating I was considering a hybrid system. The principle is straightforward enough, you leave your gas boiler in place, you have a heat pump heating the water in your existing radiators and if it gets too cold for the heat pump to cope, the gas boiler lights up and gives the radiator temperature an extra boost. In our case the boiler also provided on-demand hot water. This felt like a reasonably inexpensive way to significantly reduce our fossil fuel consumption without changing too much.

So the guy from EcoWatt came over, had a good look around, asked how old the boiler was (it was 8 years old, which is right on the tipping point for considering it “end of life”, as it happens), checked our insulation and suggested, instead of going hybrid, we replace the gas boiler entirely with a high temperature air-to-water air source heat pump.

I was initially sceptical of this idea, the gas boiler we had worked fine — although the cost of delivered propane is terrifying — and I’d never heard of high temperature air source heat pumps that can directly replace a gas boiler. This must be new!

Colour me surprised when I discovered Daikin, who are one of the leaders in this technology, have been making their high temperature air-to-water heat pumps for over 10 years! While researching what to do I found this blog about a family who installed the exact same system in a 1920s brick house in England back in 2011. They found their air source heat pump to be a perfectly adequate replacement for their old mains gas boiler, so if it could adequately provide for a single-skin brick house in the UK, I was far less concerned about being able to heat a relatively modern 1970s house with cavity walls in the south of France. Add to this we already have low-volume radiators, which we installed 8 years ago with the gas boiler, and I began to understand the air source heat pump as a replacement was an attractive option.

I still wanted to do some maths though…

Cost of fuel

The first thing to do is understand how much propane costs per kilowatt hour (kWh) equivalent. Propane, on average, cost me around €2.20 a kilo. There are several different answers for the number of kWh in a kilo of propane, but around 14 kWh seems to be a safe number. Optimistic, if anything. So a kWh of propane is costing me €0.157. I happen to have my electricity rates right in front of me, we’re on a 100% renewables plan which is a little more expensive than “normal” electricity but ensures our house is effectively zero emissions. I pay €0.2125 per kWh during the working day and €0.1257 per kWh at night and on weekends. So the cost per kWh of my propane gas is probably slightly lower than my electricity.

However, the heat pump is a little over three times more efficient than a modern gas condensing boiler, so in theory — even though the energy source is slightly more expensive — even at peak electricity prices I’m paying about 7¢ for the same amount of heat generated by a kWh of propane costing 16¢. We spent about €3,000 on propane gas in 2019 so, all things being equal, if you apply the 16/7 ratio to the cost of gas I would pay €1,340 for the same amount of heating with a heat pump. If I only heated at peak hours, which of course I won’t. But let’s be pessimistic, let’s keep that number. That means if I assume the heat pump and the gas boiler both have a life of 10 years, which seems to be about right in both cases based on real world installations, over those 10 years I’m going to save a whopping €16,700.

I should note that if I had mains gas, “gaz de ville” as it’s known in France, this would cost me about 7¢ per kWh, so I probably wouldn’t save much money, but I would be able to smugly know my carbon footprint is almost zero. If you have mains gas, you probably won’t save money — you’ll have to do your own maths — but if you have gas or fuel delivered for your heating, as many people in a rural setting do, you will certainly see significant savings.

Cost of plant

Which is just as well, because these machines ain’t cheap! I hope you’re sitting down. Ours cost €15,000, fully fitted. But there are some important caveats on that number. Firstly, we bought the biggest unit Daikin make for residential use. We have a big house and my wife likes a warm house, so we decided not to risk under-specifying the machinery. We could’ve got a perfectly adequate system for €12,000. Secondly, we had a combi boiler so we had to replace the hot water system as well and that cost another €2,000.

So if you have a “normal” family home and you already have a separate hot water heater, as is the case for my dad and a lot of other British homes, then you’re looking at a €10,000 system really. That’s still double the price of a decent gas boiler, but it’s not outrageous.

So to complete my scenario, on paper I’m going to pay €10,000 more than a replacement gas boiler for the machine, but I’m going to save €16,700 in energy costs over the next ten years. In case you’re wondering, maintenance costs, warranties, lifespan, and so on are all almost identical to a gas boiler, so when it all shakes out I should be around €7,000 better off. (I didn’t have €15,000 lying around, so there’s actually interest on a bank loan to consider, but there’s never been a better time to get very low interest personal loans for energy efficient home conversions, so it’s not much.)

To return to the point in the first paragraph, this isn’t something you should do if you’re rich. This is something anyone should do if they currently use resistance electrical heating (like storage heaters or electric heater panels) or have fossil fuel delivered. You will save money. Even if you have a small apartment, you can get reversible air-to-air air source heat pumps. You don’t have to be talking about replacing gas boilers for air source heat pumps to apply to you. My mother-in-law has a Mitsubishi one, it cost about €2,000 to install but it costs peanuts to run, produces loads of heat and provides cooling in summer as well.

Adding in solar panels

But what if you are on mains gas? Surely fitting a heat pump like mine is a pure luxury, reserved for people who can afford to spend €5,000 on feeling better about themselves? Well, yes and no. If all you do is install a high temperature heat pump, you’ll probably be worse off over 10 years, if personal finances are your only metric. However, if you have space for solar panels things get a lot more interesting.

We are also adding a 3 kW solar panel array. I will write in more detail about this later in the year, for now — thanks to the current health crisis — I am still waiting for the planning permission to clear.

Now solar panels have been around for quite a few decades, we know initial fears about them ceasing to function after a time have proven unfounded. They do lose efficiency, but even 30 year old solar panels are still sitting there generating decent amounts of electricity (around 80% of original generating capacity). And, as with all things, the technology gets better every single year that passes, so the latest solar panels take up less space and stay at maximum efficiency for even longer.

So back to our heat pump. A solar array like ours will more or less cover the cost of running the heat pump. Even on the very coldest days in winter we burned 10 kilos of propane. That’s 140 kWh, so we can expect our heat pump to use about 40 kWh to heat the house to the same temperature on that same cold day on a weekend. If it’s sunny (and the coldest days invariably are) we can expect our solar array to generate about 15 kWh. Doesn’t cover it, right?

But here’s where it gets fun: virtual power plant technology. When our solar panels are finally fitted, we will move to a supplier that offers a virtual battery. Probably Urban Solar Energy in Lyon, as they have excellent credentials and have been doing this for as long as anybody. Virtual batteries are incredibly clever and incredibly simple. Essentially, using your smart meter companies like Urban Solar Energy can track exactly how much energy you’re putting into the grid. They keep a log of your electricity “balance” and they know how much electrical “credit” or “debt” you have. When you “owe” electricity you simply buy it from them as usual. When you have “saved” electricity, your consumption is free until you’ve used it all up.

So while I use, say, 60 kWh on a cold day in mid January, while I’m away on holiday I’m only using 1 kWh to run my fridge! I can expect to save up about 300 kWh in my virtual battery while I’m away on a 2 week summer holiday, for example. Even when we’re here, we’re not using enough energy from June to October to consume all our PV output, so all the extra gets saved in your virtual battery for a monthly fee of a couple of Euros. On balance, I should have almost no electricity bill, once it all shakes out over the year.

Revisiting the maths and assuming you’re €5,000 out of pocket, having replaced your mains gas boiler with an expensive heat pump, plus you’ve probably paid another €8,000 for your 3 kW PV array, you’re around €13,000 down in total. But you have no gas bill and almost no electricity bill for the next ten years! Clearly this is variable, in terms of how much money that means, but according to Ofgem in the UK, that’s worth more than £12,500 over 10 years for the average household. Suddenly the air source heat pump / solar panel combination makes sense for any family, regardless of income, as long as you have a roof to put the solar panels on.

Concluding the sums

OK, I’ve done the maths to death. The TL;DR is if you have fuel delivered or you heat with electrical resistance, a heat pump solution is a no-brainer. If you heat with mains gas, you’ll want to combine the solution with a solar panel array, but if you do you’ll still be quids in. Really. No matter what your income is, even if you have to borrow the money to do it.

A note to landlords

I should note at this point the idea is to demonstrate this tech works for people of all incomes. I cannot do this without acknowledging that having the enormous privilege of being a home owner in the first instance excludes many low income families. Obviously tenants cannot force property owners to make changes like this, but if you’re reading this and you’re a property owner, I have a proposal for you:

It’s not beyond the realms of possibility to discuss this with your tenants and do them, yourself and the environment a favour, by figuring out a way to implement a green solution. Even if you’re totally self-serving, this is a good thing to do. And I hope many of you are normal people, like me, who would like to do the right thing when the opportunity presents itself. Well, here’s an awesome opportunity!

If you can figure out a way to get your tenants to help you with the installation costs, perhaps a supplement on their rent for a specific period, offset by the huge reduction in their energy bills going forward, this is win-win. You’ll increase the value of your property, your tenants will save money and you’ll all save the planet just a little bit.

Living with a heat pump

So on with the practicalities. We’ve been living with our heat pump for about 6 weeks now. How’s it working out in reality? In terms of cost of energy, it’s a bit too early to tell. I will follow up again next spring with real costs, however the heat pump was fitted on 17th March, the weather for a couple of weeks either side was very similar, and I’m a hopeless geek so I’ve been tracking our gas consumption for years. I can tell you this:

In the two weeks prior to the heat pump installation our total energy cost was €238 and varied between €11 and €24 per day, depending on what we were doing and what the outside temperature was like. The outside temperature ranged between 3°C at night and 22°C on the warmest day. In the two weeks proceeding the installation our total energy cost was €101, varying between €4 and €11 per day, with an outside temperature of between 4°C at night and 19°C on the warmest day.

So it’s fair to say our overall energy bill more than halved quite literally overnight. The nights were probably a little warmer on average in the second period, I haven’t checked, but there isn’t much difference. Ultimately we’ll have to see how this plays out over the year, but it’s an impressive start.

There are two important additional points that make this even more impressive. Firstly, these costs include powering the electric car, so our “petrol” budget is in there too. Secondly, since the heat pump was installed we have been keeping the house at 21 degrees all the time, whereas before we only heated the house first thing in the morning and from about 5pm onward, except at weekends.

In terms of warming the house, the space heating function of the heat pump is impressive, in so far as it’s made absolutely no difference! The house is just as warm as before, the radiators are, if anything, running a little hotter, you wouldn’t know there isn’t a gas boiler any more.

Because we had on demand hot water via a combi boiler, we’ve moved to a hot water tank which is heated by the heat pump directly. At night this gets super hot, up to its “storage temperate”, so we have to be really careful in the morning as the hot water is really hot. Much hotter than it used to be! The tank is huge, so we typically have enough hot water for the entire day. If we run it out, it automatically reheats itself on demand. It doesn’t get as hot when it goes up to “reheat temperature” — it deliberately avoids using too much energy at peak times and it also tries to keep this cycle short — but it still gives you enough hot water for a hot bath, so it’s more than fine.

The reason it keeps the cycle short is it can’t heat your water and your radiators at the same time, so it switches to water heating for about half an hour, to get the water hot enough, before switching back to space heating. We’ve not experienced this switch on a cold day, but I can’t imagine it will be noticeable. The radiators take a while to cool off, so they’re still warm by the time it’s finished heating the water and turned it’s attention back to the central heating loop.

So while it’s early days, we’re not finding any issues at all in terms of comfort of operation — there’s really no difference, if anything our hot water supply is better. And the energy costs to date are really impressive, although we won’t be able to make a final judgement until we’ve had 12 months of operation.

That’s it for now, I’ll report back in time on how it’s going. I’ll also go into more detail on the solar panel side of things, once they’re installed and have been running for a few months. Watch this space!