How do you judge ASHPs?

[SuperJohnG]

I need to buy and install an ASHP to do my UFH and DHW in the next 4 weeks.

 

Single zone, high level of airtightness (0.8) and lelevs in insulation. 

 

I had my mind set of coolenergy unit, but the return to base warranty has put me off, its madness to think I need to take it off a resend it a unit at 100kg.

 

I'm currently looking at a valliant unit (Arotherm plus) but massively struggling with valliant selecting the unit which they said someone would come back to me in 5 days but valliant is now saying an installer will select the unit and give the price .its been over 2 weeks and no contact from a supplier/installer. 

 

City plumbing have given me a price for a 17 kW Grant Aerona unit, which I told them was oversized  and then gave them the SAP calcs and they have now quoted a 6 kW unit (with strong recommendations UFH on the gf only wouldnt work - even though the SAP  calcs show it) which I think is likely OK for the UFH but I'd like a slightly bigger unit for the DHW for the recharge times. It's clear city plumbing renewable team don't understand near passive houses. 

 

So likely I'll need to select the unit and manufacturer myself so what criteria shall I stick on my excel sheet? 

 

1) Price

2) SCOP

3) Warranty

4) minimum size required? Based on UFH requirements and DHW reheat times. How do you check the reheat times?  

5) what else? 

 

I have an installer lined up who is valliant approved to get the warranty but they have no preference on the manufacturer really. 

 

 

 

[SteamyTea]

I think in reality they are all much of a muchness.

The technology should not be confused with the sales department.

Problem best to get one with the easiest to use controller.

[SuperJohnG]

59 minutes ago, SteamyTea said:

The technology should not be confused with the sales department

For sure

[Iceverge]

Willing to take a punt on ebay? 

 

Vaillant Arotherm Heat Pump 10.6kw Rrp 5k. Pos Del. Never Used Display Only | eBay

 

 

[ProDave]

Many on here including myself will confirm a near passive house building will work perfectly well just with UFH downstairs and a small ASHP.  My 5kW ASHP works fine even over here on the east where I am sure it is colder than Ayrshire.

[SuperJohnG]

2 hours ago, Iceverge said:

Willing to take a punt on ebay? 

I don't mind ebay, but I would like local new unit. 

 

34 minutes ago, ProDave said:

Many on here including myself will confirm a near passive house building will work perfectly well. 

Unfortunately we are in the minority. 

What are you DHW reheat times? 

[ProDave]

54 minutes ago, SuperJohnG said:

What are you DHW reheat times? 

A bit slow.  I can't accurately define how slow but I am sure someone will do the sums and tell us how long it should take to heat 300L of water from 6 degrees (yes that is the mains water temperature at this time of year here) up to 48 degrees at 5kW heat input.

 

Most (if not all?) heat pumps set time limits on how long it will spend heating DHW before reverting to space heating (they never do both at the same time)  I have mine set at the moment for 30 minutes heating DHW then 30 minutes heating the house.  So whatever is the theoretical heat up time, double it with my present set up.  I could set it to spend much longer heating the DHW, with a near passive house you don't have to worry about the house going cold if the heating input to the house stops while it is heating the DHW.

[DanDee]

33 minutes ago, ProDave said:

A bit slow.  I can't accurately define how slow but I am sure someone will do the sums and tell us how long it should take to heat 300L of water from 6 degrees (yes that is the mains water temperature at this time of year here) up to 48 degrees at 5kW heat input.

 

 

Q = m * c * ΔT = 300 kg * 4.184 J/g°C * 42°C = 52,718.4 kJ

 

52,718.4 kJ/3600=14.644kW=3Hours

[DanDee]

47 minutes ago, ProDave said:

A bit slow.  I can't accurately define how slow but I am sure someone will do the sums and tell us how long it should take to heat 300L of water from 6 degrees (yes that is the mains water temperature at this time of year here) up to 48 degrees at 5kW heat input.

 

Most (if not all?) heat pumps set time limits on how long it will spend heating DHW before reverting to space heating (they never do both at the same time)  I have mine set at the moment for 30 minutes heating DHW then 30 minutes heating the house.  So whatever is the theoretical heat up time, double it with my present set up.  I could set it to spend much longer heating the DHW, with a near passive house you don't have to worry about the house going cold if the heating input to the house stops while it is heating the DHW.

 

In your situation with a start temp of 6, I would try to divert part of the heating residual so it commutes less when it's usually commuting. I would even have a second DHW buffer with 50% space for water and 50% taken by a big coil for heating diversion for the same purpose, less commuting. With the benefits of pre heating the 6 degrees water to LWT for heating. Now in a passive house might not be that drastic the commuting. But a general idea for the one case that it would fit their needs.

[SuperJohnG]

54 minutes ago, DanDee said:

 

Q = m * c * ΔT = 300 kg * 4.184 J/g°C * 42°C = 52,718.4 kJ

 

52,718.4 kJ/3600=14.644kW=3Hours

 

It'll be the 5kW x the COP for that temp won't it? So pessimistically says its 2.5 that'll be around 1.5hrs? 

[SteamyTea]

6 hours ago, DanDee said:

Q = m * c * ΔT = 300 kg * 4.184 J/g°C * 42°C = 52,718.4 kJ

 

While that looks right, I doubt the whole 300 kg starts at 6°C.

DHW below 30°C is of little use, that is a pretty cold shower.

So less mass DHW is probably heated i.e. @ProDave washes less than he thinks.

5 hours ago, SuperJohnG said:

52,718.4 kJ/3600=14.644kW=3Hours

That like does not make sense.

52,718.4 kJ/3600 s = 14.644 kWh

[ProDave]

Yes in normal use DHW would start re heating when it goes a few degrees below it's set temperature.  So a normal reheat is easily done in it's half hour window.

 

But Daughter likes to shower until the water goes cold.  I just can't get through to her you are not going to come out any cleaner after a half hour shower than you would after a 15 minute shower.  So when she is done, most of the 300L in the tank will have been displaced by 6 degree incoming mains.  Allowing for mixing with the small residual tepid water that was left in the tank, I have seen the temperature sensor starting at 9 degrees when starting a re heat from that.

 

[SteamyTea]

17 minutes ago, ProDave said:

most of the 300L in the tank will have been displaced by 6 degree incoming mains

She does not end her shower in 6°C water.

Humour me, next time she finished showering, run the hot kitchen tap and see what the temperature is.

Edited March 23, 2023 by SteamyTea

[andyj007]

From my post in another thread.. may be usefull 

"I  heated my 300l DHw that was down to 22degres to 54.7deg  in 90 mins  , The energy delivered to the heat pump was 2.6kwh . total , with peak draw hitting 2.5kw  twice during the 90min session. it was heated in about  . outside temp was 11-12 degrees .. " 

 i can heat the same volume  in about 50 mins to a higher  63 degrees ,, if light my wood burner with back boiler , about 1.5-2kg 

of wood 

 

 

Edited March 26, 2023 by andyj007

[SteamyTea]

12 hours ago, andyj007 said:

I  heated my 300l DHw that was down to 22degres to 54.7deg

That is about 11 kWh.

12 hours ago, andyj007 said:

i can heat the same volume  in about 50 mins to a higher  63 degrees ,, if light my wood burner with back boiler , about 1.5-2kg 

of wood 

Say timber has an energy content of 4.5 kWh/kg.

2 kg is 9 kWh.

 

I suspect your cylinder was not at 22°C.

[andyj007]

On 27/03/2023 at 08:23, SteamyTea said:

That is about 11 kWh.

Say timber has an energy content of 4.5 kWh/kg.

2 kg is 9 kWh.

 

I suspect your cylinder was not at 22°C.

 

 

If you say so..

 

 

 

 

 

 

 

Edited March 28, 2023 by andyj007

[markocosic]

Choose based on stock. I wouldn't touch something that wasn't commonly stocked 

 

Choose based on heating controls. You probably need load and weather compensation. Cheapo units don't have load compensation etc.

 

That leaves Vaillant, Nibe, Daikin in the UK I think. (the latter only if you pay for upgraded controls and don't mind r32)

 

Samsung don't have heating controls that work. Also all days units still. Ditto the other Asian manufacturers and indeed Stiebel.

 

300 litre unvented with a big coil. "5" or "7" kW models will give more than this in a mild UK climate and with lowe space heating temperatures.

 

Business partner just did a 7kW vaillant and that's actually 9 kW output at -2 air 45)40c water for example.

 

sCOP for UFHed max 35C unit will be in the 4-4.5 range.

 

Similar effects at occur at higher ambient even at the temperatures.

 

Biggest thing affecting performance will be getting heating controls right. Open zones, balanced, weather compensated etc.

[JamesPa]

10 hours ago, markocosic said:

Choose based on stock. I wouldn't touch something that wasn't commonly stocked 

 

Choose based on heating controls. You probably need load and weather compensation. Cheapo units don't have load compensation etc.

 

That leaves Vaillant, Nibe, Daikin in the UK I think. (the latter only if you pay for upgraded controls and don't mind r32)

Surprised you didn't include Mitsubishi in this list, any particular reason why (it's on my short list for very similar reasons).

[JohnMo]

10 hours ago, markocosic said:

Choose based on heating controls. You probably need load and weather compensation

If you're on UFH only, load compensation is of no use to you. So not really an essential feature.

Edited April 1, 2023 by JohnMo
Spelling

[sharpener]

Grant (Chofu) seem to have versatile units where you can interface external controls to many useful functions with a simple contact closure, plus weather comp. Cool Energy much the same. Are there drawbacks with either of these brands?

[JamesPa]

1 hour ago, sharpener said:

Grant (Chofu) seem to have versatile units where you can interface external controls to many useful functions with a simple contact closure, plus weather comp. Cool Energy much the same. Are there drawbacks with either of these brands?

From my research, but not yet experience, (and thus based on specs only), they all seem quite similar.  The differences are in detail, but in any particular application the detail may matter.  Form factor for the required output, the availability or not of load compensation, the availability (or not) of a setback function as well as physical appearance and sound power all vary and, in any particular case, including my own, are determinants.  I have personally come to the conclusion that it's horses for courses rather than a case of there being a universal 'best'. 

 

Having said that I have to agree with the view that stock is a significant factor, if only to minimise the risk that service and spares become unavailable.  These units should last for decades if maintained, it would be frustrating in the extreme if, in say 10-15 years time, most of the unit was still in good condition but it has to be thrown away because spares are unobtainable.  Obviously there are no guarantees of spares availability, but it's perhaps more likely for a brand that is popular in this country than for an outlier.

[markocosic]

13 hours ago, JamesPa said:

Surprised you didn't include Mitsubishi in this list, any particular reason why (it's on my short list for very similar reasons).

 

- I guess I think they're a little immoral for continuing to push FGas units. I wouldn't take the first years production of R290 units either. Let somebody else test drive. Therefore unsaleable until 2025.

 

- I've yet to see a performant Mitsi monobloc install beyond the opnenergymonitor folk f**king about a lot to get the things to work well. Probably as much down to their bad design advice (mixing buffers etc) as anything to do with the unit

 

They're robust though; and plenty of them about.

 

Comparing with the "plug and go" of the vaillant setup it seems like only true enthusiasts get the best out of these; and given that they and nine both have well sussed R290 units now why roll the dice?

 

Dad has Mitsi air to air chosen by me FWIW. (as they had a small ceiling cassette to fit between trusses in the upstairs landing) They're all R32 though. And the controls are dog excrement from a usability perspective. Probably wouldn't buy again for the controls alone.

[markocosic]

13 hours ago, JohnMo said:

If you're on UFH only, load compensation is of no use to you. So not really an essential feature.

 

Fair point!

[markocosic]

3 hours ago, sharpener said:

Cool Energy much the same. Are there drawbacks with either of these brands?

 

Stock stock stock with cool energy. Most of the website is out of stock.

 

Return to base warranty is a joke too.

 

They are a Meccano kit of off the shelf bits so in 10 years they ought to be eminently repairable but it's the timescales that matter.

 

But repairable Vs throwing in a new one off the shelf then fixing/flogging the old one is a different matter.

 

Little monoblocs are like £3k. Most of the cost is installation and cylinder etc. If they go boom in a way that isn't a 5 second fix (e.g. frozen/bust plate, shredded gears in reversing valve or expansion valve) you unbolt and pop a new one on then flog the leftovers for somebody to resurrect at leisure.

 

OTOH if there are skilled fridge people available then even tricky rides can be quick. Friend of mine over here had a noname Chinese split unit (outdoor unit, fridge lines to a hydrobloc thing the size of a fridge that does the gas to water part and has cylinder etc) shred it's expansion valve gears this winter. "No worries, yes it's that widget, we'll vacuum it out, swap it, new dryer and regas, €250" or similar. You don't get that in the UK though hence nervousness about actually fixing something.

[bungledlow]

On 31/03/2023 at 22:29, markocosic said:

Samsung don't have heating controls that work. Also all days units still.

 

@markocosic can you elaborate on both of these points? What do you mean by "all days units"?

 

These were on my shortlist, but now you have me concerned.