PAU L OCKENDEN
Paul begins a two-part series about how to use tech – such as aircons, boilers and meters – to save energy in the home
Paul begins a two-part series about how to use technology – such as aircons, boilers and meters – to save energy in the home.
Ioften write about how I use automation to switch things on and off automatically to reduce fuel costs and save energy. I’ve had quite a few requests asking to provide more detail of the setup that I use, so that’s what I’m going to do over the next couple of months. Not just what works well, but also the mistakes I’ve made along the way. Oh, and before I start I should probably admit that I’ve spent far more on the kit to save energy than I’m likely to actually save in the short to medium term. For me it’s partly fun, and also an attempt at doing my bit to save the planet.
Let’s start with a descriptive picture of my setup. My house has mains gas and electricity, with a smart meter on each – more about that in a moment. I have solar panels on the roof with microinverters on the panels. This means that the feed from the roof is 240V AC, and I can just connect it into my house wiring.
My house has conventional gas central heating from a combi boiler. The boiler also delivers instantaneous hot water. I chose to fit a boiler from the Dutch company Intergas for two reasons: firstly, it’s a clever design that has far fewer moving parts than a conventional combi, so there’s less to go wrong. None of that diverter valve nonsense that you get with a traditional combi boiler. Secondly, it’s one of the few boilers you can feed with already heated water on the supply side (I’ll come on to why w that’s important in a while). The high reliability aspect with Intergas boilers is, I suspect, why you won’t find a lot of heating engineers recommending them. They realise there won’t be as many callouts. When I was looking for quotes, one told me “I don’t see many of those”. He thought that was a bad thing, I thought the exact opposite!
The heating is controlled by Evohome from Resideo.
“It’s one of the few boilers you can feed with already heated water on the supply side”
I’ve written about this in several previous columns, so won’t bore you with too much detail, other than to say that what’s great about Evohome is that you can set individual temperature profiles for every room in your house. For example, I only heat the bedrooms from early evening until the morning. There’s no point in paying to heat them during the day (although I can override the schedule if I fancy a day in bed). Likewise my living rooms aren’t heated at night, while my office is set to only get warm Monday to Friday. It all works smoothly and has a noticeable effect on the gas bill.
Evohome connects to the boiler via an OpenTherm interface. In the old days a boiler would either be off or on full blast, and it would cycle between the two to maintain some semblance of stability once the house was up to temperature. Your radiators would either be red hot or stone cold, often pulsing between the two every half hour or so. OpenTherm allows the heating controls to request a lower flow temperature rather than pulsing the boiler on and off. As a result, my radiators usually just feel warm, and if I look at the requested temperature on the boiler it will usually be somewhere between 30°C and 35°C. Just enough to compensate for the heat losses in the house. By the way, OpenTherm isn’t exclusive to Evohome – other heating controllers offer it too these days. The great thing is that because the radiators don’t oscillate between hot and cold, the room temperatures are more stable and so the comfort levels are increased. A nice side effect is that you’ll find you end up setting ng the room temperature setpoints to be somewhere between one and two degrees cooler than you would with a conventional heating system, and this of course saves money. Although in my case I’ve appreciated the increased
comfort level far more than I have the financial savings.
I also have aircon fitted: a big box in the garden and six wall-mounted units dotted around the house. It’s nice in the summer, keeping the house cool during our increasingly frequent baking hot days. Being able to sleep properly on hot nights is another bonus. And it’s pretty much free to run during the day because when it’s hot outside the sun is inevitably shining and so my solar panels are generating full blast.
As with most modern aircon systems, you can use the system in reverse for heating. It’s surprising ly efficient to do so too because of the gains that you get with heat-pump technology. It’s essentially pulling warmth from outside (even on a cold day), concentrating the extracted warmth so that it’s more than the temperature inside, and then using this to heat the air in the rooms. With a normal electric heater (think of something like a traditional bar heater), and simplifying things by ignoring losses, it takes 1kWh of electricity to dump 1kWh of heat into the room. The coefficient of performance (COP) is one. With an aircon unit running in heating mode, the COP will be somewhere between five and six. So to add 1kWh of heat to a room takes just 200Wh of electricity, the rest being extracted from the air.
Of course, you need to factor in that gas is currently cheaper than electricity by a factor of four; gas costs around 4p per kWh, electricity 16p. On purely economic grounds, ripping out your gas boiler and replacing it with aircon units doesn’t make any sense at all. But if you heat your home using LPG or oil from a tank in your garden, the electricity options start to make more sense, because these fuels cost more than mains gas. In my case, because I ca n maximise the us e of free as well as time-shifted cheaper electricity, using the aircon units for heating makes good economic sense. Plus it’s better for the environment – gas is a carbon-laden fossil fuel whereas more and more electricity comes from renewable sources, especially the electricity that I generate on my roof!
It’s a different type of heat to radiators, though. Blown hot air will quickly take the chill off a room, but it’s more of a “dry” heat. It warms your skin rather than your bones. So what I’ll do is have a blast from the aircon units to help the radiators to bring a room up to temperature, but once the room is heated up I’ll switch the aircon heating off. Luckily my Daikin units are Wi-Fi equipped so it’s easy to do this via automation.
Many people expect aircon to be expensive but my system cost just over five grand, and I’m pretty sure that it’s added more than that to the value of the property. When I had my system fitted it attracted a VAT rate of just 5%, but the government has scrapped the reduced rate for energy-saving materials now, so you’ll need to pay the full standard 20% (unless it’s for a new build, in which case there’s no VAT to pay).
Not so smart
I mentioned that I have smart meters earlier, and I know that some of you flinch at the idea of installing them. There are many arguments against th e m, some more rational than others. The press has been full of scare stories about the devices being unreliable, and people ending up with bo gus bills for thou sands of pounds. The first generation of smart meters was indeed a bit dodgy, but modern SMETS2 installations usually go without a hitch.
Some people are worried about data implications, with smart meters potentially allowing third parties to know when their house is unoccupied, for example. I’ve found that these are often the same people that will post photos on social media showing them and their family on holiday! Others seem to be obsessed with the fact that smart meters contain a remote kill switch. This is because the same meter supports both monthly payment type contracts and pay as you go – the latter needs to be able to disconnect if you don’t pay for your fuel, just as would happen with an old-fashioned prepayment meter.
I did a search and found a couple of stories where there had been mistaken disconnections, but both were a while ago and were genuine errors that were quickly corrected. And two out of the 20 million smart meters that have been installed in the UK (as of March 2021) is, I think, vanishingly small odds, so I’m happy. But feel free to contribute to the letters page if you disagree!
One interesting aspect of smart meters in the UK is that they work differently in the north and south of the country. In both instances your meter connects to the mesh-based Smart Metering Wide Area Network (SMWAN). The SMWAN is responsible for passing the readings to Data Communications Company (DCC), a government-funded project set up by Capita and overseen by Ofgem.
In the south and the Midlands, as well as Wales, the system uses 2G/3G mobile data provided by O2/ Telefonica. Whereas in the north of England and in Scotland the system
“Smart meters in the UK work differently in the north and south of the country”
uses long range radio communications, similar to the kind of stuff that I’ve written about previously in this column. The latter runs on 423MHz – unless you live near RAF Fylingdales where, for “national security” reasons, the system uses 454MHz instead. The official reason is that the kit at Fylingdales interferes with the smart meter transmission, but some believe it’s the other way round, and that nearby smart meter transmissions would impede the UK’s early warning technology. Whichever frequency a meter uses, the network is run by Arqiva, the company that also runs the UK’s terrestrial TV transmission infrastructure. Oh, and bad luck if you live in Northern Ireland because you can’t get smart meters at all if you live there.
For me, smart meters give two advantages, one relatively small and the other much more important. The minor plus point is that I don’t have to read the meters once a month and upload them using my supplier’s app or website. But much more important is that smart metering opens up previously unavailable tariffs from innovative energy suppliers, particularly on the electricity side.
Old-fashioned meters were usually single rate or dual rate. Dual rate was either Economy 7 or the rarer Economy 10, where you got either seven or ten hours of cheaper electricity overnight. But the whole thing was inflexible. Smart meters being able to deliver a reading every half an hour has opened up many more possibilities. Take Octopus Energy, which offers Go Fast and Go Faster tariffs: the former offers 5p per unit electricity for four hours overnight, while the newer Go Faster offers three, four or five-hour periods (with configurable start times) at
4.5p, 5p and 5.5p respectively. Outside these cheaper hours the day rate is competitive, although it will vary by region.
Then there’s Octopus Agile, where the price you pay for electricity varies throughout the day. Most of the time it will be significantly cheaper than the big energy suppliers, and very occasionally it will go below zero for an hour or so overnight. But during the early evening (between around 4pm and 7.30pm), when there’s more demand on the grid, the cost shoots right up to around 35p per unit, well over double the industry average. The tariff follows the wholesale energy price, which fluctuates throughout the day based on both demand and weather conditions. So Agile makes sense if you can minimise your usage during these periods, but for most families the early evening is when the kettle goes on, the dinner is cooked, the washing machine starts, the kids have their baths and so on.
The only thing I don’t like about Octopus is that it makes extensive use of referral bonuses. I flinch at reviews that include a referral link because you can never be sure whether the person genuinely likes the company or is just looking for a quick bung. As you might have noticed, there’s no referrer code in this column!
Octopus isn’t alone in offering time of use (TOU) tariffs – even the “big six” suppliers are starting to dip their toes into this area. I expect it will get quite competitive over the next year or two.
I mentioned earlier that my boiler will accept hot water. The reason for this is that I have a stainless-steel tank with an immersion heater in it on the water feed just before the boiler (this is for the domestic hot water and has nothing to do with the central heating loop). If I have excess generation from my solar panels – in other words if the house is generating more than it’s actually using – then rather than exporting the excess to the grid I use it to heat the water.
The tank will heat up to around 75°C, but I have a blending valve on the top so that the feed hitting the boiler will be at a maximum of 60°C, which is also the temperature that the boiler is set to when delivering hot water. I could set my tank to have a maximum temperature hotter than 75°C; after all, it’s at mains pressure so even at 100°C it wouldn’t boil. But I worry about what would happen if there’s a sudden loss of mains pressure – I don’t want my pre-heat tank turning into a bomb!
If my tank is up to full temperature the hot water simply passes straight through the boiler and it doesn’t need to fire, so no gas used. But if the tank is only at, say, 50°C then the boiler only needs to add a further 10°C, rather than the extra 40°C that would be required if you assume the mains water comes in at 20°C. This ends up saving me quite a lot from my gas bill.
Next month I’ll explain how I divert my excess solar generation into the pre-heat tank, as well as the other pieces of my energy jigsaw such as the car charger, and a bank of batteries. More important than the kit is how it all works together: if you get the energy flows wrong you can easily end up using more energy than you otherwise would. Especially if you have several different technologies all fighting each other to mop up the excess solar generation. That was a very expensive month!
“Smart metering opens up tariffs from innovative energy suppliers”