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HI Matt,
👍
Oh yeah, the boiler cupboard - we have a tiny kitchen, I'd love to get that back!
The heat loss figures are not too far off. What I’m looking at is the flow temperature of 45, and, they’ve put a delta T of 20 degrees.
Thats the radiator mean water temperature to air temperature DT, (mean water, ~40 degrees minus desired room temp, 20 degrees = 20 Mean Water to Air temperature differential / DT). That would give a HP flow/return DT of 10 degrees (MW-AT of 40, so flow is at 45, return at 35), which is a little high for my liking.
45 degrees flow is the max I’d even look at if fitting an ASHP, I’d design it for 35 degrees, with a return of 30 degrees, Delta T of 5. That will be far more efficient than running at 45 or higher. I read a figure of something like a 2% increase in electric use for each 1 degree rise in flow temperature, so 45 degrees flow would be 20% more than 35 degree flow.
Could you add another radiator into the rooms needing K2/K3 rads? I’ve got the same thing in my bathroom, the OH wants a towel rail, it wont give out enough heat, so I’ve got to fit another rad.
Also, be aware, the quoted BTU/KW outputs of radiators is at a MW-AT of 50, or 60 degrees (all makes differ slightly), yours will be ~20 MW-AT, so a rule of thumb (it can be calculated more accurately) is you need a rad 3 times bigger,e.g. if 100 kw is required, you need a radiator with an output of ~300kw at MW-AT of 20 degrees.
R290 heat pumps are around now and have been for a number of years, but just because they can do higher temps I wouldn't recommend it. Lower the flow the more efficient it will be.
Do the rads now and it will be zero rated for VAT.
heat loss calcs should be to MCS standard.
the OH wants a towel rail, it wont give out enough heat, so I’ve got to fit another rad.
I would like a decent rad in our bathroom but there's no space other than where the towel rail is. I could replace the rail with a rad and just hang towels above it - but can you get some kind of rail/rad combo for central heating usage rather than electric?
I may try our house on 35C tomorrow and see what happens
The MCS heat loss calcs generally already have quite a bit of margin for error so no need for the installer to add an even bigger factor on top. That is how you end up massively over specified. You can get a door blower test done on your house and manually add that figure into the mcs calcs to make the heat loss more accurate
@alanl that is super useful, thank you!! I’ll get them to model the 35 flow temp and delta of 5, and see what that shows in terms of rad volumes.
what external temperature would you use for the calculation?
grateful again for the brains on singletrackworld!
Typical is -3 to 21 degrees in the middle of the Country, if you are in the Highlands, then -5 or -8 to 21, in the sub tropical South coast, you could probably get away with 0 to 21. It can be adjusted for the location and personal requirements, if you never have it above 20 degrees, then use that as your target room temp. If you only get 5 frosts a year, then put it at 1 or 2 degrees. This heat loss figure is used to size the heating system required, in a perfect world, you’d get exactly the right size heating source as your heat loss, but in the real world, if you get within 10%, thats good enough for most.
‘ajc' makes a good point, most heat loss surveys over estimate the heat required. They do not take account of people in the house (people give out 100 watts of heat), hot water use - the heat from the water exits into the house, cooking, when your oven/hob is on, that heat warms the house too, of course, any clear sunny days heat the house,and my favourite gripe with them, MVHR systems.
MVHR cannot be used to downsize the heat requirement, which is stupid, as that is what they are designed to do. The ‘ventilation’ heat loss is typical given as one change of air per hour, in many houses, the ventilation losses are bigger than the fabric losses (through the walls/windows/roof), adding a MVHR should drop the ventilation figures from 1 to 0.2, so a house that has a 2000w ventilation loss would only have a 400 watt loss with MVHR, yet the heating system has to be designed for the 2000w loss. Totally messed up.
Thanks @alanl that’s very useful. We are rural North Yorkshire so somewhere in the middle probably. We are also a 19 degree house tops. 19.5 on very special occasions 🙂 you’re right about the bodies. It’s quite noticeable how warm it gets when we have people round We do however do quite well with the sun. The length of the front of the house is south facing and it’s amazing how it heats the house. We have got solar panels going on next week!
You can take into account MVHR in heat loss calculations.
Providing you can justify why you have dine so then it is fine.
If you heat loss a passive house you have to do so accordingly. You adjust the losses through the fabric depending on how it is constructed, you can do the same for the air losses.
the heat from the water exits into the house, cooking, when your oven/hob is on, that heat warms the house too, of course
If we had a heat pump I'd have the gas turned off and get an induction hob. But that would result in much less heat from cooking!
So I've spotted some errors in the sheet, so I'm going to get those fixed. I then realised my logic was a bit flawed, so I'm going to get them to model every P+ rad being upgraded to K2, then with the lower flow temp and delta t.
One question, probably fairly silly, how is delta t adjusted? What determines it being 5 degrees, not 10 degrees?
I would like a decent rad in our bathroom but there’s no space other than where the towel rail is. I could replace the rail with a rad and just hang towels above it – but can you get some kind of rail/rad combo for central heating usage rather than electric?
@molgrips yes, we have exactly that, a ladder rad with no electric connection. Works as long as you don't cover it completely in towels.
Alan, I’ll talk to my boss who is involved with MCS so he will know exactly. But when you think about it as I said you adjust them for passive houses, you adjust the losses through the fabric accordingly. Air losses are no different and often way to high for most buildings as people are getting rid of draughts
Including mvhr in retrofit heat losses through MCs came up yesterday at an aecb certifiers meeting I was at. From memory they were told by MCS that they could not include mvhr and were in discussions about changing the rules.
Does anybody in the South East have a recommendation for someone to design and supply (maybe also install and commission) a heat pump, hot water system, underfloor heating and MVHR? Ideally one company to do it all as a complete balanced and designed system, and somebody that will offer a reasonable level of post install support.
This is for a new build. Approx 300sqm.
I've had quotes from Omnie and Green Building Store, but see that Screwfix and a few other places sell the ASHP and hot water tanks as a package for what seems like a good price. Would rather source from someone who can offer some design and advice though.
My sister's new ASHP install was costing her a tenner a day this last week.
Is that the heat pump or all her electrics? She should have a kW/hr meter installed to check the actual heat pump usage. We are spending £9 on all our energy per day at the moment. This is why SCOP is more important as when it is milder it will be cheaper than other fuels if it has been designed and installed well. But high COP are achievable even in cold weather.
There are too many generalisations on here, but also there are too many companies who aren't doing a proper job too.
Is that the heat pump or all her electrics?
All, I think. Of course it drops right down when it gets milder and is generally cheap to run. It seems to get disproportionately worse when it's particularly cold though as not only do you lose more heat from the house but the pump becomes much less efficient. Of course we need to consider the whole winter not just one cold snap.
@Peekay You could try cvc systems. I have used them for mvhr and they are also doing heat pump for a job I have on site at the moment. I don’t have a completed heat pump install from them to give a rating, generally a little cheaper than green building store.
Does anyone actually have experience of a propane base ASHP? I really think this is what I need based on a low temperature ow test in the house a couple of weeks ago. I can't see a downside apart from having to site it away from the back door of the house (but not too far).
All the Vaillants are R290. Decent unit, good support.
This is a great thread. Finally got around to asking our installer how to adjust the flow temp on our Daikin ASHP. Seems we were set to 55 degrees!! No wonder it was so expensive to run. Today I did an experiment and set it to 45 degrees - house is still nice and warm and is costing about 80p per hour while heating the house to around 19-20 degrees.
Think I can go further and try 35 degrees flow temperature tomorrow and see what temperature the house settles at.
My sister’s new ASHP install was costing her a tenner a day this last week.
Easily done! I turned ours on during the cold spell last week and it was closer to £13 for a days electric.
Don't make such big changes, go for a couple of degrees and leave it for a few days, ideally in cold weather.
For those of you who've had an ASHP fitted, did they make much mess? Also how many fitters were on the job?
Sorry I haven't read the whole thread.
We had 4 fitters (4 vans) on site for 4 days then 2 for 2 days. They had messed up during their survey day so basically replumbed the whole house. They expected 5 days max. Weren't too messy although I had to take up carpets later to improve the way they had refitted the boards and I have to patch some walls where they channeled out to fit additional rads, that was expected so no complaints. Our house was almost all 8mm microbore so had to be ripped out, we expected the inconvenience so no problem. If you have larger bore piping it may not be necessary but you may need additional radiators after the heat loss calcs are done.
It all depends on who is fitting it. If I was doing it, there’d be little mess, and what there was would be cleaned up every day. I work on my own, so take longer fitting it, changing from a gas boiler to a ASHP would take me, typically, 5 days, with a few rads changed too. If its a full pipework change, easily 10 days work.
I’ve read reports of others doing it in 2 days.
Octopus are now offering in our area. It gave me a flat rate of £3000 after the grant, regardless of what extra work needs doing.
On the one hand this is great, but I am planning to change the rads myself and I'm fairly sure I won't need anything else. I'd that's the case I don't want to pay the flat rate. I think I'll contact some local installers. I want to get it to come in under the £7500.
Just starting my third winter with an ASHP, still like it 🙂
I've been planning to replace rads, I did the central areas of the house last year, now I want to do the living spaces. I've been working on making them slightly wider and double panel which will roughly double the area. This will make the current boiler much more effective and efficient. However the rule of thumb seems to be that for a heat pump you want 2.5x the area.
However, I think that the original rads were oversized when run at 80C, because the house was really warm. Even as they are I can run the boiler at 55C or even 50C when it's mild and 60C when it's cold. That's a dT of around 40C. If I halved that, that would mean a flow temp of 40C in the coldest conditions we see would be enough to heat the house - therefore suitable for a heat pump. However there's a couple of caveats to that calculation. The radiator isn't the same temperature all the way across, so by doubling the area you're not really doubling the heat output. However I'm more than doubling the area, but how much heat is output depends on the flow rate, so I'm not really sure how much extra heat I'll be able to get.
The other thing to consider is that even at 55C in mild conditions the heating warms the house in say, 30 mins, and then stops for an hour or so. So in theory a heat pump could run at even lower temps for longer or even continuously, and still heat the house. And at the lower temps it could be very efficient and therefore cost less than gas (which is what I want).
I don't want to replace these rads and then have to do it again for a heat pump install in the future. But the rads I am choosing now are the biggest I think I can fit in the spaces we have so.. dunno.
Coincidentally Octopus just called me back to follow up on the quote I requested. She said that they would come and do a survey to verify what you actually need, and if rads didn't need changing that would knock the price down. She also said I could send photos of possible locations for it.
This is great service from Octopus, they have an actual knowledgable person contact you and provide follow-up through the process rather than a call centre drone. You don't have to commit after the survey which is great.
Octopus have come back with £2,400 after the grant, given that we don't need any radiators.
My sister’s new ASHP install was costing her a tenner a day this last week.
I visited my dad on Sunday and that was the cost per hour showing on the IHD for his electric panel radiators! He pooh-poohed the ASHP suggestion saying it was too expensive! It wasn't that cold in Peterborough on Sunday hopefully there won't be a fierce winter this year.
Hmm, that quote does not include £800 worth of scaffolding 🙁
Hmm, that quote does not include £800 worth of scaffolding ?
Weird, it was included in mine.
They just called me back to say that they'd waive it...
We had a heat geek survey on Monday and tomorrow have the octopus one. Fairly certain we won't be using octopus as I don't want the rads they will supply (unless I did these first). HG losses were calculated at just over 10kW at -1 (south coast, 21deg room temp). That needed 2 rad changes as apparently the modern column radiators we have are quite beefy.
Hmmm Octopus came up with a massively different 15kW loss (though the surveyor could not tell me at what internal/external temps that value is for)! Definitely no HP from octopus as they don't offer a model with a large enough output.
got a lass at work who's just bought a 3 bed semi and needs a full new GCH instal.
shes been quoted £10,000 for the boiler and rads.
shes also been quoted £9,500 for heat source instal (after the grant).
she doesnt know anything at all about them, efficiency, longevity, reliability etc, so is there a rule of thumb to work to here?
if its a total new instal would she always be better going for heat source over GCH?
are the monthly running costs going to be slightly better for the heat source pump?
another consideration is that if she had this done then she could cap her gas off which would save monthly standing charges.
she has had the loft done with decent insulation and is having new windows and doors so the insulation should be pretty decent.
cheers
If she needs a whole new system seems like an ideal time to look at a heat pump.
End of our first winter with an ASHP. 4 bed detached. Really happy. Run the house at 18c and allow up to a 2c drop overnight. House is always warm (assuming you feel warm at 18c, which we do) loads of hot water and bills over the winter lower than last winter (of course every winter is not the same) our boiler was very old so probably less efficient than a modern one.We also have PV and a battery so use Octopus Cosy tariff.