ASHP/Plumbing Quote Help Please

[canalsiderenovation]

31 minutes ago, PeterW said:

 

... and ... 

 

For an ASHP system, minimum spec regardless I go for is 300 litre and then usually 400 litre if it will fit. The tank recovery time of an ASHP driven UVC is more than double that of a gas or oil boiler so I would just go with a bigger tank and insulate the tank cupboard and pipework to reduce losses. 

 

 

Cheers I'll ask him to price for 300 or 400 little tank. I like a big hot bath most nice so the larger one sounds better.

[Nickfromwales]

1 hour ago, canalsiderenovation said:

 

Cheers I'll ask him to price for 300 or 400 little tank. I like a big hot bath most nice so the larger one sounds better.

Higher volume tank = lower storage temperature too, so the ASHP won't have to work as hard = better SCoP. Capital uplift to go to the bigger tank shouldn't be more than a few hundred quid and worth the investment IMO. If you go for PV, you'll have loads more headroom to store visa PV diversion too ( subject to the size of the array and your surplus of course ). With you being an all-electric house I'd try and max out on PV, so get an application into the DNO now to see how far you can push them  

[canalsiderenovation]

Thanks I'm going to get some quotes for in roof solar - around a 4.4-4.8 GSE system. I just know I need to make sure whichever 300-400 litre tank I have it has an immersion element.

[Benjseb]

Our tank is 250l and we heat it to 47c. 
 

That’s for 2 adults and a 4 year old. We’ve never run out of hot water. Takes about 30 mins to heat from 18c to 48c
 

don’t go too big or youll just be paying for a large tank of water to lose heat 

[joe90]

10 minutes ago, Benjseb said:

don’t go too big or youll just be paying for a large tank of water to lose heat 

But less losses than a small tank at higher temps!!! My losses are minimal, well insulated in an insulated airing cupboard.

[Benjseb]

1 minute ago, joe90 said:

But less losses than a small tank at higher temps!!! My losses are minimal, well insulated in an insulated airing cupboard.

 

Very true. 400l sounds huge though unless it’s for a family of 6. 

[joe90]

5 minutes ago, Benjseb said:

 

Very true. 400l sounds huge though unless it’s for a family of 6. 

but not the whole tank gets heated unless the stat is at the very bottom. It’s only during summer months you can consider it a loss, during heating months it helps with the heating. On my 350 litre tank I have two stats, lower and higher, I switch stats depending on whether it’s just the two of us or having visitors .

[scottishjohn]

heating to 47c -- better make  sure the ASHP anti legionella function is working --which means  it will have to raise it to a high  regularly-so I see little advantage in an over large tank

 just more volume to have to put up to the high temp,unless you are using free PV  for it most of the time  and tank VERY well insulated

[PeterW]

40 minutes ago, scottishjohn said:

heating to 47c -- better make  sure the ASHP anti legionella function is working --which means  it will have to raise it to a high  regularly

Legionella in domestic systems is extremely unlikely as it needs air to breed - and a UVC is a sealed system. There are no known reported cases of it in a domestic water system. 
 

Even if it was required, it needs 8Kw to heat 400 litres from 48-65c. Using an immersion heater that is 2.5 hours, or about 18p on E7 twice a month. £5 per year. 

[Nickfromwales]

28 minutes ago, scottishjohn said:

heating to 47c -- better make  sure the ASHP anti legionella function is working --which means  it will have to raise it to a high  regularly-so I see little advantage in an over large tank

 just more volume to have to put up to the high temp,unless you are using free PV  for it most of the time  and tank VERY well insulated

You can set the lower immersion to do a purge once every 7 days, and that can be set to happen during off-peak times eg Octopus 5p/kWh / other similar tariff.

The OP mentions an intention to employ PV, so the extra volume in the larger tank will be a friend not an enemy. The routine temp can be the cutoff point of what the HP will economically deliver, say 50oC, and that can be set to recharge the cylinder once a night off Octopus with enough capacity to not need further input for the whole following day. I would suggest that for the winter so the PV ( roughly 25% gross kWp over winter so no excess will be available after the household base / vampire loads ), looks after the house only, so ~12.5p for DHW per 24hrs. In the summer, halve the nighttime recharge time and leave headroom for diverting any excess, with the caveat that the OP would have to learn when to manual boost ( via the HP only ) for when the DHW is used in duress. Living with the system will quickly give a pattern to follow.

1 hour ago, Benjseb said:

 

Very true. 400l sounds huge though unless it’s for a family of 6. 

Not at the lower temperature  Check the MI's and you'll read that the capacity is stated at the typical storage temp of north of 65oC. The difference in heat energy between 50oC and 65oC over the additional ~200L is 'huge', but is the margin of headroom that you have to store any excess. That excess will then offset the amount of overnight recharge, so if you're clever you can play the numbers to your advantage.

A smaller cylinder will have reduced scope for; 1) load-shifting, and 2) absorbing excess PV. In a time where you do NOT want to be exporting, even when getting Octopus's 5.2p/p/kWh rebate, this is a no brainer.

As mentioned elsewhere, the smaller cylinders will have to be kept super hot to be at their rated capacity / delivery, so will have significantly higher losses.    

[Nickfromwales]

Crossed with the old boy.

[ProDave]

The Anti legionela thing was discussed before. The conclusion was if you have treated mains water and a UVC it was not an issue.  It might be a different matter with a private water supply.

[joe90]

28 minutes ago, ProDave said:

The Anti legionela thing was discussed before. The conclusion was if you have treated mains water and a UVC it was not an issue.  It might be a different matter with a private water supply.

yes, I have not bothered with my system either.

[joth]

12 hours ago, PeterW said:

it needs 8Kw to heat 400 litres from 48-65c.

 

Nit: 8kWh

(I've not checked the calc, just corrected the units)

[Nickfromwales]

If it wasn’t you, it would have been @SteamyTea that jumped on it lol  

[canalsiderenovation]

Soooo, met plumber and he is going to sort out pricing comparison for 300/400 litre tanks.

 

I mentioned making sure tanks had immersion element as we are obtaining some pricing for solar and he said he will raise this with Alto energy. He was sceptical on how much solar would actually contribute to hot water of the ASHP and seemed to think we couldn't do this going down the RHI route.

 

I'll wait to see what he comes back with and in interim see what prices I get back for solar. 

[PeterW]

So the RHI can be done and then an Immersun added to any “spare” immersion. If it’s not wired in then it’s irrelevant when he does the calculations ....

[joth]

RHI is valid even if it's used for space heating only, there's no policy requirement it contributes to domestic hot water heating, let alone that it must provide 100% of it. In fact the rules around Legionnaires pretty much requires there's a secondary DHW heat source.

 

 

https://www.ofgem.gov.uk/environmental-programmes/domestic-rhi/applicants/eligible-heating-systems

Heat pumps don't have to provide domestic water heating to be eligible, but may do so

[canalsiderenovation]

Now we have finalised the solar materials quote we have had an updated plumbing quote. It's around £900 more and the changes seem to be from the initial heat pump and 210 cylinder (quoted as per the plumbing quote above £7749.08):

 

To this (£8690)

 

A Mitusubishi 11kw 1P air source heat pump, 400 litre Gledhill Heat Pump Pressurised cylinder, low loss header, 40litre expansion vessel, 4 x circulating pumps, 3 port zone valevs and all other required items for new design. 

 

As per the suggestions on here we asked for the larger tank, to 400 litre rather than the 210 one as I believe this will go in our favour for solar and hot water.

[canalsiderenovation]

I'm still really confused and then came across this thread on a similar matter by @gc100

 

OurPV controller we had earmarked is the Solic200 but we can look at alternatives.

 

I still can't work out if what the plumber is now saying we need to work with the solar is correct.

 

Along with the heat pump is my plumber correct in saying we also need a 400 litre Gledhill Heat Pump Pressurised cylinder, low loss header, 40litre expansion vessel, 4 x circulating pumps, 3 port zone valevs and all other required items for new design. 

 

@ProDave @Nickfromwales

 

Can you confirm if this makes sense or is far more complicated than what we need.

 

[canalsiderenovation]

@PeterW forgot to include you too as you provided some initial advice.

 

Just want to make sure this is all OK before giving him the go ahead and I'm not missing something or paying over the odds for something we don't need.

 

I think the previous 210litre tank was around £2500 but I believe the Gledhill 400litre is cheaper but then there is the additional parts and work so perhaps that accounts for the price difference. I'm so confused.

Edited September 15, 2020 by canalsiderenovation

[PeterW]

Tanks are a personal preference but assuming he is going with the Gledhill pre-plumb it seems ok. Is he integrating it with the heat pump and the Mitsubishi controller as I thought the quote was for the Mitsubishi pre-plumbed cylinder ..??

[canalsiderenovation]

4 minutes ago, PeterW said:

Tanks are a personal preference but assuming he is going with the Gledhill pre-plumb it seems ok. Is he integrating it with the heat pump and the Mitsubishi controller as I thought the quote was for the Mitsubishi pre-plumbed cylinder ..??

 

Initially he had quoted for the pre-plumbed Mitsubishi 210 but has now changed the quote completely and got rid of this because apparently we can't have it with the solar immersion controller thingy (and we wanted the bigger tank) and has replaced it with the 400litre Gledhill and all that other stuff.

[PeterW]

Ok - not sure why he’s got 4 pumps but worth checking. Has he provided a design schematic ..? Expansion vessel, low loss header would have been needed regardless as they are not built into the pre-plumbed tank. 
 

Also ask for brand and spec on the pumps - some are really noisy !!!

[canalsiderenovation]

5 minutes ago, PeterW said:

Ok - not sure why he’s got 4 pumps but worth checking. Has he provided a design schematic ..? Expansion vessel, low loss header would have been needed regardless as they are not built into the pre-plumbed tank. 
 

Also ask for brand and spec on the pumps - some are really noisy !!!

 

Nope just updated the quote. If they were all required before I'm not sure why it's quite a bit more expense.

 

I'll ask which brand the pumps are.