@derek-m thanks Derek

@bontwoody 

I think what you have posted/said is very good. 
 
The Pron-N will produce 6KW @ -5.2˚C  with house temp of 21˚C (that's with a buffer as well)

The property this Pro-N is installed in @ -3˚C has a heat loss of 6.53kW. Temperature this morning outside was -6˚C, house was @ 21.1˚C flow temp was 32.7˚C

Did they mention air changes at all as these are normally over estimated. They could have also done an airtightness test to get a more accurate heat loss calc. 

The Pro-N unit would have been fine especially as Helen doesn't like the house warm and only wants 19˚C. For the number of days @ -3˚C with the possibility to add a layer (though unlikely required) vs the increased running costs the rest of the time, with the larger unit in milder weather and cycling. 

Not that I'm particularly any expert when it comes to ASHP, still learning.  

Posted by: @bontwoody

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@derek-m

@kev-m 

@iancalderbank

if you have time could you please look at my reply in the post above and give me your opinions. Either I've got this totally wrong or they have or they are being deceitful. Thank you Mark

@bontwoody

I agree with most of your comments and I especially agree the installer is either making things up or is really incompetent.  On the sizing issue the 16kW model seems too big on the info you have.  However, I'm not sure the smaller one would be enough, even with the numbers you quote. With the extension, the smaller unit seems borderline. Last night my ASHP was defrosting regularly even at -4 deg and that (IMO) cuts output 15-20%.  A borderline ASHP would not have been able to heat my house last night.  And don't forget about DHW; that can cause the heating to be off for quite a long time (30-60 mins) depending on usage. 

I know your neighbour likes the house cool but if she has received any funding the design will have to comply with MCS, which won't allow for 18 deg living areas. 

I think the installer has concluded the smaller unit is too small and just gone for the next size they supply/have in stock rather than use a different manufacturer and are now trying to wriggle out of it. Maybe they should have gone for a different manufacturer or turned the job down. 

@deano Thanks Andy. Nice to have you in the forum. It’s really useful to have some real world data I can include in my response to disprove his assertion.

@kev-m Thanks Kev. I take your point about the sizing of the smaller unit. I am reassured however by the fact that Helen at the last minute decided to fit underfloor heating in her lounge area which should allow lower flow temperature and access the upper end of the output range. She also has mentioned a desire to have a wood burning stove in the lounge so I doubt she will suffer In a cold winter 😂

@bontwoody can't see anything wrong with your reasoning.  As per @kev-m, there is potentially a case that the smaller unit isn't quite enough - but in that situation the installer should have initiated a conversation about whether supplementary heating was going to be available for the worst case days (sounds like it is), or whether there was tolerance for running cooler (again sounds like there is) . At the very least , they should have proposed a design using a different manufacturer's unit, one that has a "medium sized" unit in the range, that better meets the specs needed.

The jump to the "large", just because "that's who they use" is what makes this not an acceptable piece of practice to me. But I've posted about this before - its common for two businesses to have preferred supplier relationships which are commercially favourable to both, and that negatively affects "what is right technically" decision making . So , making an informed guess that  installer's sole preferred supplier is Acond, then I would assume they would have just gone with that because cheaper and easier (for them). Moving to a different brand would have cost them time and money, they might not be trained on any other brand, they might have had to back out of the project.

@iancalderbank 

they also fit Ariston and Mastertherm, Mastertherm would have suited much better with a Boxair 26l which is up to heat loss of 8.5kWh

@iancalderbank Thanks Ian, I totally agree with your assessment. It would, in hindsight, been a lot easier if she had not mentioned the possible extension and then if it went ahead heated it with an air to air heat pump (if necessary). I have one in my kitchen, its great 🙂 Ive responded now to Thermal Earth so the ball is in their court. At the minimum my intervention has caused them to make contact with Helen and arrange a handover date!

Just an update. Following my response, the company have stated that the design flow temperature is 45C which puts the output smack in the middle of my ranges and proves their statement of outputs at -3C  demonstrably wrong. They are coming for a site visit/handover on Monday.

The moment of truth approacheth then!

@editor @toodles @deano @iancalderbank @derek-m @kev-m

So we had the meeting today with an Andrew Lloyd and whilst we didnt agree on everything it was a useful meeting. Access to the heat pump settings via a local website page was achieved and changes made to the settings to allow a reduction in running costs. Agreement was made to sort out the snagging issues with insulation etc.

Where we couldnt agree was over the size of the heat pump with Andrew insisting the the larger model would be able to successfully modulate low enough to avoid cycling in the shoulder seasons. In the end I asked for a written commitment from them to this effect and what they would do about it if it did. We shall see what I get!

Out of interest Andrew insisted that that it was the norm for heatpumps to heat DHW all through the day using a setpoint. say a drop of 5C. This isnt my experience, what is the experience out there please? I would have thought this arrangement would increase thermal losses from the cylinder and be more expensive to implement due to always heating water at the highest temperature

Sounds like an OK meeting overall. 

I'd be surprised if the larger pump would modulate that low, the small one (which I have) wont go any lower than 480w and 2200w of heat on a mild day, eg today. Flow temp 28˚C

Mine was setup to constantly heat hot water 🤣 

DHW run from the lowest possible temp is far more efficient. I have mine set 12 hours apart, reheats overnight after the dishwasher and washing machine have used any hot water if they're going to. 

On the clock icon top left, then down the bottom, select DHW TimeTable, dont forget it runs in CET so it's an hour out.