Is a 16kW HT ASHP really needed for my UFH with these heat loss figures?

[oranjeboom]

My ordered (2x)UNIQ eDual12 eHW12 should arrive in the next few weeks. Originally these were going to be used for DHW (occupancy of 4) as well as my UFH. It's a renovated/extended bungalow with 300mm slab insulation, 3G passive windows, 100mm EWI and 150mm spaced UFH. After getting  a potential Sunamp installer to talk to Sunamp, the recommendation is for me to now also get a 16kW HT ASHP that will purely heat the slab. I always knew that I would be reliant on grid electricity over the winter months when my 3.8kW PV would not get sufficient sun.

 

Using Jeremy's heat loss tool, I am looking at the following heat loss figures:

 

 

Main issue will be the ACH that I may have imputed on the high side of 2, but despite taping, siliconing and sealing as best I can, there will be some leaks that I will have missed. I may still be able to tackle those when I do an air leakage test.

 

Most winters don't achieve -5c here in Kent and when it does, it's for 2-3 days during which I would just switch on the 4.9kW LPG (balanced flue) gas fire. So a temp max  temp difference of 20c would be more realistic during the colder months when the average OAT is around 5c.

 

 

I know @TerryE has his willis heater set up with UFH, but he has a passivhaus set up (iirc) whereas mine won't be that close so I don't think a willis heater instead of an ASHP would work (though I lie the idea of it as a backup!). Not sure whether I want to go down the e7 route either just yet.

 

So looking at the figures above, would a 16kW HT ASHP be overkill?

 

Edited August 4, 2019 by oranjeboom
corrected sunamp units to eDual12  instead of eHW12

[Nickfromwales]

Are the Sunamps to be heated by the ASHP? 

[Jeremy Harris]

16 kW sounds pretty big for that sort of heating requirement to me.  The spreadsheet really gives a worst case result, as it doesn't account for incidental heating gains, from people, appliances, etc.  I would have said that a 10 kW unit should be more than enough, and should work with a fairly high efficiency even in pretty cold weather.

[TerryE]

The low hanging fruit here is your air leakage.  I you are going for Willis backup then it makes sense to use 2 in parallel; if your are using E7 then you can shift the bulk of your heating to overnight window.

 

But 10 kW should be fine, IMO.

[oranjeboom]

13 minutes ago, Nickfromwales said:

Are the Sunamps to be heated by the ASHP? 

 

Not actually clear from either Sunamp or the installer, but I thought DHW would be powered by PV/grid and then UFH solely by ASHP. I am speaking to installer on Monday so will find out. Sunamp did actually come back to me this year and say that they recommend  "16KW HT ASHP with 2x UNIQeDual 12 and 1x UNIQeHW9". No way can I afford a further outlay for another UNIQ unit for HW! And of course this can only be confirmed after a £500 energy assessment. Things were certainly different with Andy at the helm of customer servicing!

 

I did pick up a pool heat pump the other day so wondering whether that could be used to test a lower kW input requirement. Will need to check the spec on that.

 

 

 

 

[SteamyTea]

1 hour ago, oranjeboom said:

a 16kW HT ASHP that will purely heat the slab

Probably get away with half of that.

If you can get some local weather data, you can see how often it will not supply all your space heating needs.

The MCS rules is that a heat pump needs to be able to supply 99% of all heat load.  It i a reasonable rule to work to as it builds in oversizing, which improves the CoP.

Thing is about using an ASHP for space heating only, is that it may only be needed for 3 or 4 months of the year (though Kent has a cold wind), so may be worth considering using to to heat water during the other times of the year.

Just needs more detailed modeling.

 

Edited August 3, 2019 by SteamyTea

[PeterW]

2 hours ago, oranjeboom said:

So looking at the figures above, would a 16kW HT ASHP be overkill?

 

If this is UFH only, why is he speccing a high temperature heat pump ..??

 

You need flow of 35-38c tops, well within the realm of a standard heat pump. HT is only needed for a flow temp higher than 52c, and that’s only used on Sunamps where you want to regenerate the units. Is he thinking of using a 9Kw Sunamp as a buffer vessel..??!

 

Ask for a design and schematic and post it here. 

[MikeSharp01]

6 hours ago, oranjeboom said:

300mm slab insulation, 3G passive windows, 100mm EWI and 150mm spaced UFH.

How thick and what is the area of the concrete the UFH is heating up? As this will also need to be part of the bigger picture because of the decriment delay it introduces against the various energy inputs and outputs. Also have you factored in the potential ability of the ASHP to cool the slab in summer which might add value to it as an option. 

[oranjeboom]

22 hours ago, SteamyTea said:

Thing is about using an ASHP for space heating only, is that it may only be needed for 3 or 4 months of the year (though Kent has a cold wind), so may be worth considering using to to heat water during the other times of the year.

 

Yes, that makes sense. Then having the ASHP to also charge the sunamps during the winter months rather than relying on the grid.

 

17 hours ago, MikeSharp01 said:

How thick and what is the area of the concrete the UFH is heating up? As this will also need to be part of the bigger picture because of the decriment delay it introduces against the various energy inputs and outputs. Also have you factored in the potential ability of the ASHP to cool the slab in summer which might add value to it as an option. 

 

I don't think you came inside that time you were here Mike, but the house has a north and south wing, so setting up the ASHP to cool the southern slab would be good. I was also thinking to use the UFH to shift solar gained heat from south to north wing if required but not sure what additional items would have to be built in. All rooms will have their own stats and I have a temp sensor in the slab in the south side and one in the north side slab.

 

slab is 140sqm and is 100-110mm.

 

21 hours ago, PeterW said:

If this is UFH only, why is he speccing a high temperature heat pump ..??

 

You need flow of 35-38c tops, well within the realm of a standard heat pump. HT is only needed for a flow temp higher than 52c, and that’s only used on Sunamps where you want to regenerate the units. Is he thinking of using a 9Kw Sunamp as a buffer vessel..??!

 

Ask for a design and schematic and post it here. 

 

Presume high temp is needed to charge the sunamps rather than just the UFH. My presumption now is that it will do both, blending down the temps to the UFH and/or using the eHW sunamp as a buffer. I don't really want to add a further 9Kw eHW sunamp just as a buffer for the UFH. Think i read that getting an ASHP as a twin unit, one would heat temps for UFH and the other for the sunamps?

 

So looking at the sunamp manual, the eDuals should only be charged by electric means:

 

 

 

Hence their additional Sunamp eHW requirement now. So the eHW unit is purely to act as buffer for the UFH then. So the ASHP would not be charging the eDuals for my DHW in winter then and would be 100% reliant on grid (so e7 would need to be looked at again) unless there is a better setup?

 

In any case, will talk to the installer tomorrow to see how this is all meant to work efficiently.

[PeterW]

17 minutes ago, oranjeboom said:

Think i read that getting an ASHP as a twin unit, one would heat temps for UFH and the other for the sunamps?

 

Thats barking mad ..! And the eHW and eDual both use e-lectricity to heat up the cells. @Nickfromwales can probably comment better here. 

 

My view would be a small buffer tank of 80-100 litres with an “emergency” immersion in it in case of loss of ASHP and then use the eDuals on E7 for the DHW. Load shift to night time usage and it’s about the best you can do.

 

Don’t use the buffer as a pre-heat for the DHW as it will only use high rate grid energy to recharge via the ASHP assuming you’re using DHW in peak hours and even with a decent CoP you will be saving buttons a year. 

[MikeSharp01]

Hmmmm looks to me like the advice you are getting from the installers has conflated efficiency with complexity and although you can do most anything with the setup the things you really need to do are being compromised by having the bells and whistles plus, as you point out, the e versions don't use hot water to charge them so what's the point of the HT. It seems to me that you would best, as you say, to just use the ASHP for the UFH, you have a great mass of concrete, with a Willis or two in there if the ASHP goes down and then charge the sunamps on E7 / PV ( if allowed by their controllers) although I am not sure you need two of them.

[Nickfromwales]

[Nickfromwales]

That's one i did a while back.

14kW HT split, feeding 2x eHeat + 1x HW ( all size 9 ), load-shifting off E10 into high temp emitters ( standard convector radiators ) in a poor performance dwelling.

For this instance i totally understood the remit and the above system complimented the job perfectly. For a hose with low temp emitters I think it needs to be revisited. Without all of the details I cannot comment absolutely, so any other info would be good.

[oranjeboom]

20 hours ago, Nickfromwales said:

That's one i did a while back.

14kW HT split, feeding 2x eHeat + 1x HW ( all size 9 ), load-shifting off E10 into high temp emitters ( standard convector radiators ) in a poor performance dwelling.

For this instance i totally understood the remit and the above system complimented the job perfectly. For a hose with low temp emitters I think it needs to be revisited. Without all of the details I cannot comment absolutely, so any other info would be good.

 

Hi Nick, I am speaking to the installer tomorrow hopefully so any tips/advice you may have would be appreciated. Most of the info is on my introductory post. Supplementary info:

 

DHW requirement:

• 2 adults and two soon to be teenagers (do they wash?)
• 1 morning shower; 1 bath
• 1 evening shower; 1bath
• Hot water for washing up (though may get a boiler-type tap for most hot water needs in the kitchen) though dishwasher for most items.

Occupancy: Wife and kids out and I although I work from home, my office will be one of the sheds out the back so main house can either be set to 'off' or very low temps during the day.

 

UFH demands:

Groundfloor: Water volume: 129L; Estimated loading: 9.45Kw (as per Wunda calculations)
Upstairs on separate manifold: Water volume: 25L; Estimated loading: 2.03Kw (possibly won't have the upstairs UFH on as it's only 1 bedroom and one bathroom which will have an electrical rad).

 

 I decided on Sunamp as wanted to limit heat loss (so didn't go down the UVC/thermal store route) and wanted to maximise 3.8kW PV setup. I have limited space internally (the two 12kW Sunamp units pretty much fill up the 'plant room'). So originally Sunamp designed my setup so that the eDuals would cover DHW and UFH to some extent with the knowledge that I would have to supplement charging the sunamps with grid electricity during winter months. Both units were received this year but had to go back due to a production issue and now on the cusp of delivery they suggest going for an additional 16kW HT ASHP plus UNIQeHW9. Obviously these can't be charged by water (i.e. ASHP) so they would be reliant on PV and grid (e7/e10). The ASHP would be purely for the UFH then but 16kW HT seems overkill for just the UFH, and not sure why HT if the eDuals or eHW unit can't be charged by ASHP?

 

Indeed, can the eDuals be setup for the DHW as well as the UFH? I doubt we would be needing fully charged eDuals for DHW every day,  so possibly use some capacity for the UFH as well.

Winter months would see the DHW being reliant on e7/e10 grid and any sun during the day could be utilised to partly run a 8-10kW ASHP for the UFH. Obviously very  little output from PV in the winter so reliant on the grid, but the long term plan would be to expand my PV setup with a further 5kW DIY system.

[ProDave]

18 minutes ago, oranjeboom said:

 

UFH demands:

Groundfloor: Water volume: 129L; Estimated loading: 9.45Kw (as per Wunda calculations)
Upstairs on separate manifold: Water volume: 25L; Estimated loading: 2.03Kw (possibly won't have the upstairs UFH on as it's only 1 bedroom and one bathroom which will have an electrical rad).

 

I thought you worked out with Jeremy's spreadsheet that your max heating load was just under 6KW so why are you still thinking of a 9Kw or more HP?

[ProDave]

20 minutes ago, oranjeboom said:

 

, but the long term plan would be to expand my PV setup with a further 5kW DIY system.

In what way is the first 3.68Kw solar PV not "DIY" then?  Now the FIT has gone you are not surely thinking of an MCS install?

 

Remember to seek DNO permission before going above 3.68Kw

[oranjeboom]

28 minutes ago, ProDave said:

I thought you worked out with Jeremy's spreadsheet that your max heating load was just under 6KW so why are you still thinking of a 9Kw or more HP?

 

Just added that as worst case. Those UFH calcs were from Wunda, who base them on 'standard' build regs.

 

28 minutes ago, ProDave said:

In what way is the first 3.68Kw solar PV not "DIY" then?  Now the FIT has gone you are not surely thinking of an MCS install?

 

Remember to seek DNO permission before going above 3.68Kw

 

My existing PV was an MCS install. So really no point going for another MCS install without the FIT incentive, so just looking at spending 2k for a DIY install.

[oranjeboom]

@Nickfromwales Hi Nick, any more thoughts? ? https://forum.buildhub.org.uk/topic/10802-is-a-16kw-ht-ashp-really-needed-for-my-ufh-with-these-heat-loss-figures/?tab=comments#comment-183019

 

Alternatively, when are you next in Kent? ?????

[Nickfromwales]

11 hours ago, oranjeboom said:

@Nickfromwales Hi Nick, any more thoughts? ? https://forum.buildhub.org.uk/topic/10802-is-a-16kw-ht-ashp-really-needed-for-my-ufh-with-these-heat-loss-figures/?tab=comments#comment-183019

 

Alternatively, when are you next in Kent? ?????

Thoughts still are;

1) you don’t need this setup. 

2) see point 1. 

 

Get a cheap ASHP ( LOW TEMP ) off the ‘net to do space heating / cooling, and link your pv up to dump any excess into DHW. 

[puntloos]

Silly question perhaps, but is an overdimensioned ASHP (e.g. 15kW even though the calc says you only need 9..) going to be quieter since it doesn't have to break a sweat? Is that a good reason to go large?

 

I've never been 'near' an ASHP, so not sure how loud it is in best and worst cases, but I hate to be a bother so if I can go for 'quiet' I will..

 

[SteamyTea]

43 minutes ago, puntloos said:

Silly question perhaps, but is an overdimensioned ASHP (e.g. 15kW even though the calc says you only need 9..) going to be quieter since it doesn't have to break a sweat? Is that a good reason to go large?

It should be, though if the fan is out of balance, or the case not fitted correctly, then it could make more noise.

44 minutes ago, puntloos said:

I've never been 'near' an ASHP,

You probably have, there are thousands used as A/C units.  Usually a few feet up a wall.

Have a look around bars, small supermarkets, offices.

[Nickfromwales]

1 hour ago, puntloos said:

Silly question perhaps, but is an overdimensioned ASHP (e.g. 15kW even though the calc says you only need 9..) going to be quieter since it doesn't have to break a sweat? Is that a good reason to go large?

 

I've never been 'near' an ASHP, so not sure how loud it is in best and worst cases, but I hate to be a bother so if I can go for 'quiet' I will..

 

There are several manufacturers now offering ‘super silent’ units for areas that require it.

[oranjeboom]

Just resurrecting this thread as now looking to get my ASHP. If I go with pessimistic heat requirements, then that points to 10Kw input. Do I need to slightly oversize in any case and then run it slightly lower? 

 

ASHP will only be heating up the UFH (DHW will be via sunamps) so no cylinder needed. I presume also that I should be looking for an inverter controlled unit so that it's not simply turning on/off all time?

 

Anything else I should be looking for? I have an installer in mind but don't want to be sold something I don't need! And most likely won't be going the RHI route unless his install price is really good.

 

Haven't seen any Carrier units on ebay but did see this 10kW unit: https://www.ebay.co.uk/itm/Ex-Display-AIR-SOURCE-HEAT-PUMP-WATER-HEATER-10kW-EVI-Heat-Pump-Works-to-25/113863582069?hash=item1a82cc6175:g:S1kAAOSwSk5dLwgp

 

Anyone know the credentials of this unit?

[PeterW]

They have other units and they are Mitsubishi compressors inside. £2150 inc for their 11kw unit. 

[oranjeboom]

4 hours ago, PeterW said:

They have other units and they are Mitsubishi compressors inside. £2150 inc for their 11kw unit. 

 

Yes, saw that one too. Probably a case that you end up with a Copeland rather than a Mitsu:

 

 

 

 

 

Not that I am qualified to compare the two brands though! But for another £100 and the fact that you have a 5yr warranty...

 

Actually, I re-read the listing. You get a Copeland if you go over 11.6kW. And as far as i can make out, only the 18.7kW model has an inverter. As the Dragons say "and on that basis, I am out" (on these units).

 

Looks like people already reviewed the seller here: 

 

Will see what my installer comes up with, but will probably be a fair bit more ££££!