Heat pump thread

Molgrips: Our quote is crazy good, just under £2000 for a Daikin, 4 radiator upgrades (3 layer) and a 180l water tank inc installation and all electricals.

Wow.

Our condensing boiler is on its way out, the heat exchanger has gone apparently. 1910 semi w cavity wall insulation, double glazing and loft conversion in last 10 years, so thinking we might be ashp possibles

Anyone have any experience of this outfit ?
https://www.airahome.com/en-gb

Swedish apparently, with a mission to make ashp affordable

Always use a local company who will want to service and repair breakdowns in the future.

Wasn’t sure where else to post this but for the energy conscious minded, good deal on well reviewed budget thermal camera
https://www.hotukdeals.com/4275911

Tempting compared to £50 to hire an inferior Flir One for a week.

Hi team!

So we are investigating ASHP and have had a survey, to replace our oil boiler (fairly new, 2 years old Worcester Bosch which is adding to the conundrum).  House is mid-00’s build stone detached 4 bed, with a cavity then insulated breeze blocks.  Decent loft insulation and double glazed wooden windows.  No underfloor heating.

As part of the survey we’re looking at a 12kwh Samsung HT Quiet, with the aim of running it at a flow temp of 45 ish.  Listed specs show COP of 4.2 @ 45 degrees.

We’ve calculated then the output of the rads, and modelled it against a 55 degree flow temp, the first chart, and then a 45 degree flow temp, the second chart.  Both with -2.2 degrees external temperature and assuming worst case insulation.

55 degree:

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45 Degree:

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Our rad types are in there, and they’re wondering if we could switch to K3’s in some rooms. What are the general thoughts?  It goes from being ok in the 55 degree to definitely not in the 45 in some key rooms.  We have a wood burner which we can use to boost things when it’s very cold (rural area, we lose power supply quite frequently).  Is it sufficiently borderline that it would be worth going ahead with the ASHP and seeing what the performance is like?  Or stick in a modern K2 radiator?  Part of the reason I’m asking is the K3’s are so deep (18cm) it would be a bit of a nightmare.  Having looked at BTU outputs I think we could achieve similar outputs with modern K2/Type 22 rads.  Or am I being overly optimistic?  I think it’s fair to say we’re willing on this topic but generally a bit nervous.  Minus any radiators, we’re looking at about £4k after the grant, including a new 300L hot water tank and some 28mm pipe run.  I’d really welcome any advice or insight!!

We had single panel rads throughout, I’ve been fitting T21s that are 800mm wide instead of 600mm, it’s about double the output. I didn’t fancy T22, because of the size, and I think triple would be out for us.

We did fit a massive 1800mm T21 in the hallway instead of the original 600mm single panel which helps heat the core of the house. But then, the house is relatively well insulated so the rest of the rooms keep their warmth.

BUT we’ve done a lot of work reducing cold spots.  Ours was built in 2007 and the builders were slap-dash as you’d expect.  For example anywhere that the inner block wall was cut through – extractor fans, the French doors on the first floor – the cavity wasn’t blocked off, so there’s a great draught coming in via the soffits and the vent bricks.  Sealing these off where I can has made a big difference to keeping the heat in which means less heat from a smaller rad can still heat a room.

Yeah –  a bit of me thinks we could just put it in and see, and see how the flow temp works in the room.  If we had to have a flow temp curve that went up to 50/55 degrees when its sub-zero outside, I don’t think that would be the worst thing, given the frequency.  My thinking is we could then upgrade rads as necessary, once we see how it feels.  But this also seems a little contrary to advice.

Those heat loss numbers look huge.  How did you arrive at those?

That adds up to 9.5kW or so.  Our boiler runs at a minimum of 9kW, and even in this weather it’s running for no more than about 30% of the time – usually much less – which would put our heat loss at 3kW. It’s a smaller house though – 3 bed semi.

So the heat loss numbers were calculated by the company, they took worst case insulation values and higher design temperatures.  Do you think they’ve overdone it?  They’re estimating our energy use annually on a heat pump as being around 5163 kwh

replace our oil boiler (fairly new, 2 years old Worcester Bosch which is adding to the conundrum)

Why would you replace this before it is dead or oil prices are so utterly silly it is not economic? Surely £4k plus grant and a hugely wasteful environmental cost outweigh any benefits?

Do you know how they calculated the heat loss and what internal temperature they have assumed? Ball park figure for your house would be around 75W/m2 at a guess. It is also worth noting that the output of a lot of R32 ASHPs drop off at lower temperatures so worth checking the performance charts. You need to factor in the hot water too.

A new wave of Propane (R290) heat pumps are coming out now which will go up to higher temperatures and have slightly better performance at these higher temperatures so worth checking them out although most of the ones I have seen are lower capacity at the moment so you may need two units.

We have an oil boiler and I don’t think I’d rip out our system for an ASHP unless if completely failed, even with the grant money available. I certainly wouldn’t rip out a 2 year old boiler.

HI Matt, well firstly we’d look to sell the boiler so it wouldn’t be wasteful. Secondly heating oil prices are rising quite heavily over the last few years, to the point where the cost would be neutral right now when we’re paying circa 65p.  It’s not uncommon to have to pay up to double that, and that’s not going to get better over the coming years. In terms of environmental cost oil heating is far from brilliant!  

There’s also some secondary impacts, so we would be able to change the layout of the kitchen to significant benefit, which we’re thinking of re-doing this year, the boiler location is fairly intrinsic.

You’re right however, the kitchen component has got us thinking about it sooner than we might have, which is is making it a tricky decision!

Do you think they’ve overdone it?

Well I don’t know, I mean I’m not a heat engineer. But I think there are ways to calculate it.  I know that our boiler is over-powered even on minimum setting, so I could figure it out from that if I had a means to measure exactly how long it was running for, or even a smart gas meter – but if you had a decent modulating boiler then I don’t know how you’d know how much heat is going in.

I don’t think I’d rip out our system for an ASHP unless if completely failed

Our boiler is both old and crap, and it has gone wrong plenty of times. I’ve managed to fix it on many occasions, but I think there’s a pinprick leak in the heat exchanger so I think it’s only a matter of time.

Thanks Mranger156 – as I say I think they’ve overcooked the calculation on heat loss to be pessimistic – I’d asked us to calculate it erring very much on the safe side.  re the Propane 290 yes, been looking at that.  As mentioned part of the reason we were considering it was the ability to free up the boiler space in the kitchen and future proof etc.

HI Matt,

👍

Oh yeah, the boiler cupboard – we have a tiny kitchen, I’d love to get that back!

Yeah @molgrips!!  🙂

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.

[Bear]

Bear

Free Member

You can take into account MVHR in heat loss calculations.

I didnt know that, and I’ve asked the same question at numerous training centres, they’ve all told me you cannot downrate due to the MVHR. Thanks.

You can take into account MVHR in heat loss calculations.

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.