Dave C

And yet, my ASHP was installed with a maximum flow temperature of 50c, and it doesn't need to run 24/7 even in the winter, and it doesn't cost a fortune to run either... Much like the OP, the installer set it up to run at 50C, but (a) that was indeed a bit pessimistic - after the first winter it became clear that I could drop the max down to 47 or even a bit lower, and it was fine; and (b) that's only when it's below freezing. Does that happen? Sure, every winter. Does it happen on that many days? In particular, are there that many days when it stays below freezing throughout the day (i.e. during peak electricity rates)? No, not really. A few days every year. That answer might be different if you live in the North of Scotland! I don't, and it sounds like the OP doesn't either. Nothing wrong with suggesting investing in insulation where possible, and being careful not to let an MCS installer flog an inappropriate heat pump, but the idea that (maximum, worst case!) flow temperatures >40C absolutely guarantee it'll cost a fortune isn't true.

All true, but if nobody's home after 8am, and no hot water being used, you wouldn't expect the tank temperature to drop any significant amount between 12:00 and 12:30. Particularly if everybody left at 8am and the tank was heated back up to full temperature just before 9am. Are you sure you don't have a leaking tap or similar anywhere? Only time my ASHP came on unexpectedly in the middle of the day last year it was because my daughter had left a hot water tap not quite fully turned off and there was a tiny trickle running out constantly - as explained above, it doesn't have to be much water drawn off before the sensor starts to see a drop. It would be consistent with the graphs - from 11:00 there's a slow but steady drop in tank temperature as the water trickles out, then the 'hot zone' in the tank is approaching the sensor so the temperature loss appears to speed up as the water continues to be used; then the heat pump kicks in to reheat the tank.

Depends how your pump(s) have been configured. If your pump(s) are set for the heat pump to control the pump speed - or if you have two pumps, but only one is coming on for DHW - then you might need to change the settings on the Ecodan; not sure what's involved in that. If the Ecodan is just telling the pump(s) to turn on, but not controlling the speed, then you'll be able to change the pump speed by turning a dial or pressing a button on the pump to switch it to a different mode. You'll probably need to find the user manual for your pumps; it should tell you how to find out whether the pump speed is manually set or not, and how to change it if it is. Regardless, you'll probably need to observe what the pump(s) are doing when the Ecodan starts trying to heat the DHW.

Certainly isn't what should happen! Some thing happened on my Ecodan after it was installed - heat pump would come on to heat up hot water cylinder, it would start heating OK, then in under half an hour would give up and switch over to the immersion, which I guess is the fall back behaviour for "we need hot water and the heat pump can't run for some reason". Turned out it was insufficient flow rate causing the heat pump to shut down - installer needed to reconfigure the water pumps. Could try turning the water pump speed up, if it's a separate pump plumbed in and it's just got a simple dial or push button to switch between different pump speeds.

Yes, absolutely - ASHP is set to heat my tank to 48c, and the mixer shower is plenty hot enough even after the tank has had most of the day to cool a bit. Don't know the exact water pressure, just it's "very good" according to the plumber and I'd agree. As mentioned above, some mixers might not be happy with the incoming hot being 42-48c, but mine certainly is. Feels unlikely you'd lose much temperature on your long pipe run if the pipes were insulated - just you've got the annoying long lead time to deal with.

I have an unvented cylinder heated via heat pump. Not Samsung or Joules, but the principle is the same... Setting the target cylinder temperature to 48c it works fine via a mixer shower (no pump in my case; mains pressure is plenty). Works fine when the tank has cooled a bit, too - I set the target temperature to 48c because then, even after 20 hours, it's still well over 40c and hot enough for a bath or shower, so I can just top up the hot water overnight on off peak rates. Mixer showers do tend to say the incoming hot must be a certain temperature e.g. 50c+. Mine says that but thankfully it turns out that's rubbish. I suppose maybe it's possible some mixers actually do always mix in a fair amount of cold and in that case you really do need 50c+ hot supply; I guess my example just proves that mixers do exist where 42-48c hot supply works absolutely fine (but unfortunately you won't necessarily find it out by reading the shower instructions/specs...) Maybe an expert can confirm whether all mixers are basically identical internally, and so they'd all work fine, or whether it's plausible that some will work fine and some not?

Might be worth bearing in mind that Freesat is a thing - I'm using Freesat currently because there was already a dish on the wall from the previous residents and Freeview reception isn't great for me. Also my (fairly new) TV has a satellite decoder built in, so no separate box required - plug dish into TV, done. Definitely don't watch enough TV to justify paying for cable or Sky By no means always the easiest option, but if Freeview reception is marginal it can sometimes be a good workaround.

Agreed. So many potential sources of inaccuracies here! If the electric meter didn't change reading when the immersion was on, then does that mean it only 'ticks over' when a whole number of kWh is used? In which case your heat pump used perhaps 1.01-2.99kWh of electricity, you can't be sure exactly how much. If the temperature sensor measures to the nearest degree, a 3 degree increase could be anywhere from just over 2 to just under 4 degree increase in reality. Except it's worse - the hot water tank is almost never the same temperature throughout. The water next to the sensor might have increased by 2 degrees, but that doesn't tell you how much energy has gone into the tank, because you haven't raised the entire tank's temperature by the same amount. If you have the entire tank at room temperature, then let the heat pump heat it up to full target temperature, you'll have a better estimation of how much energy has gone in, because at least then you know the starting temperature of the whole volume, and your rounded electricity usage will be off by a smaller percentage. Still won't know exactly - depending on where the sensor is, if it reads 45 degrees, might be a bit of the tank below the sensor at a lower temperature, and possibly the majority of the tank at over 45 degrees.

Thanks, that's good info - COP of 4.8 at below freezing temperatures is really encouraging! At the very least it shows there's some A2A options out there which keep a good COP at low temperatures. Still interested to see how well the electriQ holds up - that note about performance dropping off below 5C is still a bit suspicious...

That looked interesting until I saw the note in the documentation about it switching to purely resistance heating at 2C and below! Same question applies to the electriQ - it has a note about heating performance dropping off below 5C. But by how much?! I don't really care so much what the heating COP is when it's 10C outside, don't need much heat input then, the COP when temperatures are approaching freezing is much more interesting...

It was this scheme which I see has just finished, so nobody will be getting it after this month alas!

Also a Lux, with 7.2kWh of Pylontech batteries. No solar - just making use of Octopus Go off-peak cheap rates (although if off peak rates become less favourable in the future, installing solar is a possible next step). Since I also have a Lux... -Yes, you can set multiple charging timeslots, although I only use one of them (00:30-04:30 Octopus Go). Well, except on the one day per month that Octopus gives me an extra hour of free electricity then I use the second timeslot for that day. -It then defaults to being primary power source until empty (or until a certain charge level, so you can choose how much power to always hold back for a possible power cut) -The default offering is that you get a double plug socket hanging off the inverter that's continually powered including during a power cut - it doesn't feed the whole house. When I had mine installed they did offer the whole house switchover at additional cost, but I didn't bother to go for that (and I can't see it's on offer on the website now). Cost wise, prices have increased in the 8 months since I had mine installed so you're best just checking the website! https://homeenergygroup.co.uk/lux-ac-battery-storage-greenlinx/ I was pleasantly surprised that the cost on their site was indeed exactly what I paid, no hidden extras. (Shouldn't really be surprising, Yes, in my case - since I have the same system as Alshamal, my calculations were very similar The system and batteries have a 10 year warranty, and the expected cycle lifetime of the battery means they should still be usable at ~12 years. Since the entire system will have broken even at 7 years (hopefully!) that means a good few years of banking savings before the batteries start degrading to the point of needing replacement, or the inverter fails and incurs costs. In principle...

That's probably fair - I have a battery, but initially made the mistake of comparing the Cosy price to my current Octopus Go prices; of course prices have gone up since my last renewal! So you get two shots per day at charging your battery, and the price is higher than Go, but less than double. Working the figures out, for my battery I reckon Cosy is cheaper than Go on days where I'd use ~20kWh or more. That's essentially never during the no-heating part of the year, but during the winter ... eh. Probably a bit of a toss up: in January, that's the majority of days for me, probably about half the time in December/February - so for those three months, it's better than Go. The other 9 months of the year (especially when there's no heating going on!) it's worse. If you were willing to switch to it just for the winter months ... yeah, it could work.

My mixer shower says the same, but echoing the other feedback - it works fine with the hot water coming in at 48C (or realistically a bit less, given it's only 48 when the heat pump has just finished). Did have to tweak the temperature adjustment on the mixer up to its maximum, though.

Well, it's a 5kW heat pump (so probably not too big!), and I'm not shutting any radiators down so full system flow available all the time. That only leaves "I need a buffer" - but does that actually improve things that much? If the heat pump's coming on for 3 hours, then shutting off for 3 hours, am I actually losing that much efficiency? It's not short cycling, after all...

That might be the ideal, but in practice neither I nor the other two heat pump owners I know have ever managed to get things arranged so the heat pump just runs constantly at a low power. Perhaps that's because it's annoyingly uncommon to get load compensation (rather than weather compensation), or because on a-bit-cold-but-not-freezing days the heat pump just can't modulate low enough to do anything else, but the end result is that except on the coldest days (and even after all the tweaking I've made to reduce short cycling), my heat pump comes on for 2-6 hours, then the house is up to temperature and it shuts off for a while. It's not ideal but it's what's happening - so I guess you could regard this plan as a pragmatic acceptance of that pattern, saying "if you're going to have the heat pump running for 2-6 hours on 1-4 hours off anyway, why not play with your thermostat to get those hours to line up with not-peak-time". Having to pay those peak time rates during the summer, though ... it's more like 7 months of the year for me, that I don't need any heating, so while in principle this plan isn't a terrible idea during winter, having to switch onto and off it every winter (and hoping you don't get stung by a more expensive rate every time you do) isn't appealing.

You might not be missing something! I did the same calculation this year and ended up with similar results: -Solar panels on their own: I couldn't self-use very much, so the payback period was not great -Solar panels with batteries: Could then use vast majority of solar generation, but at additional cost, so payback period still not great -Batteries on their own: Octopus Go meant I could still make good use of the batteries, and lower up front cost meant payback period was noticeably better ...so I went with batteries only (and if Octopus kicks me off/discontinues the Go plan, can always fit solar later). Solar could make sense if you had different usage patterns to me - but yes, definitely worth doing the calculations as it can go either way.

The idea would be: -Off peak rates are 1/4 of peak time on Octopus Go (or maybe even less - more like 1/5 for me) -If your heat pump has a COP of <4, it's cheaper to use the immersion off peak than to use the heat pump during peak time -Obviously during a time of year when you don't need heating, you just run the heat pump to heat up the hot water tank. But when it's cold enough the heat pump is working a significant portion of the day to keep the house warm, you could be better off running the heat pump on space heating for the entire off peak period, and simultaneously running the immersion to deliver hot water. The immersion is less efficient - but it's cheaper than running the heat pump for 2 off peak hours on hot water and then having to run the heat pump for 2 hours more during peak time. Only makes sense on Octopus Go like plans, though, where the off peak rate is so cheap it outweights the COP advantage of the heat pump. As you said, on a non-variable rate, you wouldn't use the immersion at all.

Just to back that up ... I've had no real problems with my system: the only tweaking I've been doing is seeing how much I can adjust the WC curve down, because the installer set everything up with a default certainly-hotter-than-required curve. Which I suppose at least ensures your house gets warm enough so isn't the worst possible issue, even if ideally they'd have spent the time to get things better.

This is exactly what I do. But I paid <£5K for my 7kWh battery system, and pay a lot less than 15p on the night rates, so I make my savings out to be £700-750/year ... which is perfectly acceptable given the <£500/year cost of the system. Personally I didn't think a larger inverter was worthwhile - it turns out that in practice a 3.6kW inverter covers the vast majority of my usage, which is fine, the goal was never "must run house entirely on batteries absolutely 100% of the time" ... and keeping to 3.6kW makes the inverter cheaper and sidesteps the more complicated process to get permission to install it. Battery prices have gone up since I bought my system at the start of the year, mind. Certainly true that you want to work out how much it'll cost you and how much you'll save before making a decision. And yes, it's always possible the night rates you'll get in future years won't be as generous as they are now - do you know what you'd do if that happened? Isn't 2088 kWh day rate and 280 kWh night rate nearly 90% on the day rate?

Not sure why you say that ... at the current energy cap prices, a heat pump that manages a COP of ~3x is going to work out a bit cheaper than a gas boiler to run. If you can manage a COP of more than that, like the 3.4 COP figure Green Power quotes above, it'll be a bigger saving. (And if you can get off-peak electricity to run the heat pump, that'll help too, of course - but the heat pump works out cheaper even without such a plan, it's by no means required.) Well, all the figures above lay out why your running cost can quite plausibly be lower!

Mm, I think your calculations are correct - a 60dBA heat pump that's only 6m away from the assessment point attracts a -20 adjustment, so 40dBA, which then gets a +3 correction pushing it over the 42dBA allowed level, i.e. you need to be further than 6m away, and the next level is 8m distance. Something that might help is the rule on barriers: if you have a 2m fence on your garden, it entirely blocks line of sight to all neighbouring ground floor rooms (they don't count anyway if they're kitchens, but the fence gives a large adjustment that makes it trivial to come in under the limit). If the heat pump is just over 1m from the fence, the fence is far enough away it doesn't increase the Q factor, but it may still block line of sight enough to their first-floor bedrooms to get you the -5dBA adjustment for obscured line of sight ... now you only need to be 5m away, which considering you're measuring to a first floor room so you have the added height, is probably quite plausible. That may be how my installation skated in under the rules (assuming the installers actually ran the calculation correctly in the first place, which I suppose is not guaranteed!).

It can be done a lot cheaper - I had 7kWh of battery storage installed for <£5K earlier this year (not a DIY install or anything). That makes the payback period come quite a bit sooner...

That's an awful lot of energy usage even if it 100% of the DHW heating was on an immersion! Are you sure there's not a dripping tap or leaky pipe somewhere? Few months ago I had my heat pump firing up unexpectedly in the middle of the day, when no large amounts of hot water [should have been] used, and it turned out my daughter had left a hot tap trickling water - over a few hours it drew off enough hot water from the tank that the tank needed topping up again.

Not the original poster, but I've also got the luxpower 3.6+pylontechs, and yeah - 3.6kW is fine. Obviously it's not hard to exceed if you try - kettle + oven would do it - but in practice even when I'm cooking it doesn't tend to go much over 3.6kW, when you've got multiple hobs plus the oven on it tends to be with the hobs on well under maximum power. Putting the kettle on can easily push usage over, but that's only for a couple of minutes each time, so not really significant. I suppose it does require a bit of thought if you're trying to optimise your usage ... e.g. hold off running the washing machine until after you've finished cooking ... but it's not hard to stay under 3.6kW of draw the vast majority of the time. I guess in mid winter when the heat pump is drawing 1-2kW a lot of the time it'd be harder to stay under 3.6kW, but that's also going to drain the batteries down fairly quickly so there's less need to care - I expect to have to draw on the grid for a substantial amount of power each day anyway once the heating is running and the batteries will get fully used regardless, so no real point in trying to avoid the grid at that point.