Monthly Archives: September 2023

Heating makeover – step by step into the heat pump era

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There is a hard push under way to make us abandon fossil fuel boilers and adopt heat pumps instead. The trouble is they don’t seem to work for everybody and they are expensive too. So, in many cases that’s a lot of money for something we don’t even want. Don’t despair though, there’s a way through this maze and the outcome could be cheaper heating for less initial outlay. The trick, in a nutshell, is to have more than one heat pump; the one they pay you £7,500 to install and then a smaller one to back it up.

Learn to love heat pumps

Typically consuming not much more power than an electric kettle the heat pump will deliver about 3 times as much energy to your heating, often more. The power is increasingly produced by renewables so the heat pump is an essential multiplier of green energy. That’s why we love them and that’s why we should have them.

Overcome the issues

Heat pumps work well at lower temperatures but that drastically reduces the effectiveness of your existing pipes and radiators. The pipes are the first bottleneck and probably only transmit around 12kW. If you are resisting a total pipes overhaul there is no point in pushing heat pump power beyond 4kW to deliver the 12kW. 6kW delivered is very common and suits well insulated modern houses. With extra back up power that might be the one for you too.

Down the line the radiators will need an overhaul though; either some unsightly bigger ones or, preferably, fan-coil units with smart radiator valves on them to make heat distribution more selective and locally more effective. I prefer my own design for a DIY fan-coil unit (obvs). With a smaller heat pump in the mix the chances are you can cover most of the cost with the £7,500 grant. A good start but now we need more power to back up a system living on the edge.

First things last

Before you start the big overhaul it’s best to install the back-up elements. These will be mini-split heat pumps – those aircon units often found in a hot foreign rental. You probably only need one or two and they are so effective that they should be low power units. The 1.71kW Mitsubishi SRK60ZSX-WF Heat Pump for example bangs out a healthy 6kW. Expect to spend about £2,000 for each one fully installed.

With the heat pump makeover done the running costs will still be the same as oil or gas but now the fun begins as we can move to the cost reduction phase. First off, solar panels. Fitted with Enphase micro inverters you can fit odd numbers in odd places without any problems and they should give 20 years of trouble-free power. Because your heat pumps are low powered you will often find you can run one for free even when panel output is reduced. Include a solar diverter (like the Eddi) and the panels can send their surplus power to the immersion heater. This fixes the problem of poor hot water delivery associated with low temperature heat pumps and is the reason you might get away with not changing the tank in the first place. Keep your old tank, spend the money on panels. Now the heating and electricity bills are usefully reduced and maybe servicing costs too. Do you service your fridge every year? No; same for heat pumps.

What about batteries? They used to be expensive and they wore out too quickly to justify the cost. But now they are cheaper (check out the Fogstar site) there is a good case for storing cheap off-peak electricity and running your (low powered) heat pump on it later. This can literally halve your energy bills – see graph below.

There’s a useful tactic to be considered when you are finally persuaded into owning an electric car.

Some EVs can offer 240v vehicle to load (V2L) with around 3kW available from a socket behind the back seat. They imagine you might plug in a toaster when you go camping. So, never mind the toaster, you could plug in a mini-split and use cheap off-peak electricity to heat the house. If you are looking for a box of tricks to make this work check out the Victron Quattro-II which has an extra 240v input. The idea here is to go for a domestic battery first but be ready for the EV when it comes.

This all gets you connected to super cheap heating and air-conditioning too.

As you can see, cheap off-peak electricity, time shifted then multiplied with a heat pump gives astonishing results. Vehicle to Grid charging is another way although not yet mainstream but V2L gets us there now without installing the expensive V2G charger and you can choose from a bigger range of cars. So not a Nissan Leaf now, more likely a Kia or Hyundai. The result; half price for a lot of your heating if not all of it.

Of course, all houses are different but hopefully there are some ideas here to help make a complex topic simpler. Small heat pump + mini-split + solar – the way to go – then batteries.

Heat pump conversion – the successful way

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How much is a heat pump – £15,000?       Actually, they start at £1.200

so let’s get going.

It’s easy to ruin a perfectly good house by doing a heat pump conversion. Thousands of people have already done so and yet the pressure is on to keep doing it. So, here’s how to do it logically and successfully. The measure of success here being better comfort with lower running costs and the satisfaction of lowering emissions too, but most of all, a system that actually works.

First of all, don’t rush in until you know how much power you have already and whether that is too much or too little. You might not know the answer to that until after you have done a big purge on insulation, and tested the result. All installers have to err on the side of caution so your boiler will certainly be bigger than it needs to be.

Stage 1/:

Insulate, insulate, insulate, floors, walls, loft windows, all of that. Start here because, compared to your old boiler a heat pump is relatively weedy and anyway very different. It’s a low temperature high flow device and it will need all the help you can give it.

Stage2/:

How much power?

After insulating take a look at how much energy you are currently using and hoping to replace. There are a couple of ways of doing this and it is best to do them both. First check the nominal power of your boiler then see how often it cycles on and off on a cold day. This might involve half an hour standing by the boiler with a stop watch. You might have a 30kW boiler but the chances are it will be short cycling, especially if it runs on oil. When you have the time to running ratio you can see the average power your boiler is delivering.

Secondly, check your total oil or gas bill and use this chart to calculate how many kilowatt hours of energy you have been buying.

There are about 200 days of winter so dividing the energy total by 200 will give you an idea of the average daily power requirement. There is no such thing as an average winter day so this is only going to give a rough idea. The peak requirement could be double the average. If you can get the data for shorter periods that would be even better.

Unfortunately, we are not there yet because there are transmission issues to consider. The pipe that runs from your boiler to the radiators is likely to be 22mm copper which with typical heat pump temperatures will transmit between 10 to 15 kW and more likely towards the lower end of that. On a COP of 3 that means the maximum heat pump power will be around 5kW (delivering 15kW), any more cannot be used. That almost certainly leaves a large hole in the requirement and is the reason why so many installations are a disaster. The solution is pretty obvious though; just add a mini-split air to air heat pump or even two. They will plug the gap and leave your existing pipework untouched. A mini-split has no connection to your existing system and all the pipes and radiators etc. It’s a stand-alone heat pump and that’s why it is so cheap to install.

Stage 3/:

Transmission

It’s not just the limitations of the pipework to consider, now the heat has to come out. Assuming there is no underfloor heating in place that leaves replacing existing radiators with really huge ones (not an inviting prospect) or fan coil units. The latter can be inexpensive and effective – see DIY fan-coil units. Again, the mini-splits make up for transmission shortfalls.

Hot water

Quite often you will be quoted for a new hot water cylinder to go with the heat pump. The reason being that the coil needs to be bigger to accommodate the low temperature heat pump. I’d ignore that suggestion and spend the money on solar panels and an energy diverter like the Eddi. Cheap night time electricity might be in your mix and that too can drive the immersion heater.

Looking back at that chart it appears that there are no savings to be made by running a heat pump. You can press on happily though because further tweaks will lead to the cheapest heating available. Heat pumps can run on renewable electricity too so they really will help you to save the planet.

If you have solar panels, they can make a free contribution and the low power mini-split(s) will often run for free on the first glimmer of sunlight.

In the long run you might have an electric car that allows the use of its battery to power the house. In one stroke that will easily halve your energy bill as you time-shift cheap night time electricity and amplify it with a heat pump.

For bigger houses with unusually high heating demands the answers are still the same although the transmission limitations can be bypassed with the aid of a heat bank with its multiple pumped outlets. That’s a longer discussion for another day.

So that’s it. Just sidestep the limitations and embrace the advantages. Easy really.

P.S. Some EVs can offer 240v vehicle to load with around 3kW available. They imagine you might plug in a toaster when you go camping. So you could plug in, for example, a Mitsubishi SRK60ZSX-WF Heat Pump System along with a changeover switch to pull in the mains when the car is not connected. This unit consumes 1.71kW (a lot less than a toaster) and delivers 6kW which is pretty punchy when it comes to making up any system shortfalls. Expect to pay £2,000 fully installed. This all gets you connected to super cheap heating without installing the expensive V2H charger and you can choose from a much bigger range of cars.

If I was building a house I’d be thinking about an extra ring main for EV powered devices.

Heating News – Free or Freeze

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Energy price comparison

Well, the Ofgem cap for October is out and also, over the last few months. various energy prices have changed quite significantly. So, allowing for the likely efficiencies of the boilers, stoves etc here is the latest chart showing how much energy you get for £1,000. Most houses will need 15 – 20,000kW.hrs over the winter so you can guess the level on (or off) the chart where your house is.

Electricity

Still the most expensive energy you can buy by miles despite a slight fall. Solar panels are still the best way forward and payback is quick if you don’t have too many.

Heat pumps

Now slightly worse than natural gas so there is little incentive to go along with the Government push on boiler replacement. Of course, if you have access to solar power then the picture gets a bit better but remember that in the winter it’s dark and cold by tea time.

Natural gas

As this is what most homes have, and it works very well, there is no great rush to change. An upgrade to a condensing boiler might be timely if you are still nursing an old boiler. (insert predictable joke here)

LPG

The price has risen about 16% to put LPG on a par with oil but a lot depends on the efficiency and running costs of the boilers in question. I once had an LPG gas boiler that was never serviced for 9 years so I could have replaced it on the money saved – that’s not a recommendation, just making a point.

Oil

There have been some big swings over the last year but it looks OK for the time being although boiler efficiency could make the picture worse. Old oil boilers can be very inefficient and servicing and sludge cleaning costs can add up. If an upgrade is needed then LPG should be the top consideration.

See https://www.boilerjuice.com/heating-oil-prices/ for an oil price chart.

Wood

I just bought a huge load of about 6 cubic metres for £500 and the result looks good on the chart although there will be significant variation depending on weight and moisture content and type of wood. I used 70% efficiency for a stove but of course an open fire would slay the calculations, maybe even down to zero gain.

Solar panels

Still worth it? Depends on what you pay of course but a rough estimate goes like this. 3 panels cost £1,200 and make 1,200kW.hrs a year worth 27p x 1,200 or £324. So, your money back in 4 years then. In practice it’s hard to consume all you make, even with a solar diverter driving your immersion heater, and self-consumption falls off with even more panels. Even so it looks like a good plan and the gas boiler will get negligible use in the summer months. You can, however, bump up self-consumption to 100% with batteries, whether car or domestic.

Batteries

They are simply wonderful but the trouble is the cost. Once your electricity bills have been eased by solar panels the remaining savings produced by batteries give rather extended payback periods in line with the life expectancy of the batteries themselves. Cheap energy deals from Octopus and others make for some interesting calculations though. If say you paid 9.5p/kW.hr overnight and used it later driving a mini-split heat pump then the resultant heat would have cost you under 4p/kW.hr. That’s astonishing but you’d need a very big and expensive battery to make it work for a reasonable length of time. Hold on though – electric cars have huge batteries!

This is all very exciting and as soon as your electric car battery can be utilised in the home a new era will arrive. A Nissan Leaf battery is about the same as 4 Tesla Power Walls! If this piques your interest then check out the car battery maths below.

Car battery maths – halve your bills

Your 7kW car charger charges your Nissan Leaf for 6 hours every night on Eon’s 7 hour offer (Octopus only offer 4 hours). The other hour is for the car itself and the 6 are for use back in the house.

Each day we can use 40kW.hrs in the battery to run a small 5kW heat pump for 8 hours and on a COP of 3 that’s 120kW.hrs a day. Totalling 24,000kW.hrs over the 200 day winter that will be more than enough for most homes.

24,000kW.hrs would have cost you just £760 but the chances are you could get under that.

Without any further key bashing the outcome is that your heating bill will be more than halved.

This is such a game changer that it must be part of your future heating strategy and that means you must have a heat pump of some sort even if it’s a mini-split or two. A regular heat pump with a mini-split added as a gap filler would be perfect.

And let’s not forget

Mini-split heat pumps

Mini-splits are just small air to air heat pumps which are easy to install and you could get one fully installed for about £1,200. Yes, a proper heat pump for £1,200.

I’ve said this before but it bears repeating.

My mini-split has been running for over a year so I can tell you how it’s been.

In the shoulder months the PV panels (4kW) run it free a lot of the time

It often draws well under a kilowatt so we run it when needed without worrying about the cost too much

Low power means the solar panels have it covered very often

It often provides enough background heat to enable the main heating to be left off

It blows hot air so makes a great laundry drying machine.

Summer air conditioning is really good, cooling the whole ground floor

It actually cost under £1,000 installed and that took just 4 hours

It was bought from Saturn Sales who gave good advice and delivered on time

Conclusions

It’s still a good idea to go solar. Check out micro-inverters on the panels, a concept that makes sense – ‘Gary does solar’ on YouTube will explain all and get you £50 off if you change to Octopus.

After solar get a mini-split or two. Your bills will plummet and your comfort levels will rise.

Start thinking about an electric car with V2H charging. That is still only a Nissan Leaf as far as I know.

It’s early days but with some solar exports and a bit of insulation, might that car battery get you close to ZERO-COST heating?

While I hope my figures are accurate, please do your own research before making any commitments.

Comment on electric cars.

We’ve seen a massive depreciation hit as electric cars transition from very expensive to near parity with normal cars. A series of price cuts from Tesla, to the chagrin of current owners, and now a wave of reasonably priced EVs such as the MG4 and the rather fabulous Volvo EX30 are setting the tone. The high cost of batteries will halt the slide for a while, and the car makers will have to try to settle into profitability, so it is probably safe to enter the market now. Vehicle to home charging capability should be high on the options list when you do. Before you dive in perhaps consider locking in a nice old-school classic for the potential appreciation when it becomes clear that they are the last that will ever be made.

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