@ashp-bobba Good advice - thank you. My desire to spec the system for the house as it will be in ~12 months time and then retrospectively optimise the setup will end up being an important factor in helping decide who we choose. You points re. temp heat distribution during works are really helpful.

@transparent Thanks for the info and encouragement to document our UFH work. It's a little way off, but I'll be sure to do this, especially with regard to any retrospective work on the ASHP side of things to commission and optimise the new UFH.

I thought I'd post an update regarding the process of choosing a system and installer. I'm now in contact with 4 different organisations, and honestly I think this is more than enough to get a sense of the differing approaches and any outliers on e.g. heat loss calcs.

The first of these to visit was Aira. They sent a rep out very quickly and yesterday he spent around 1.5 hours with me looking around the property and discussing the likely setup etc. This first call is more of a sales pitch than a technical survey and discussion, but it did allow me to ask Qs and for them to supply a price. One quite nice part of the Aira approach is that they provide a fixed cost ceiling on this first appointment - basically if you need a larger HP or more rads, they foot the cost of that beyond what you are quoted. Anything that you do not need, is removed from the quote. 

Interestingly, the whole house heat loss calc that the rep did was quite a bit lower than my heatpunk estimate, coming out at 8.4 kW to my 10.3 kW. This meant that he specified the 8 kW HP in the quote. Until they undertake a detailed room by room heat loss survey, I've no way to know how this has been calculated, but of course, in the same way I don't want too large a HP, I do not want one that can't keep up (as an aside, an initial quote from an independent local installer, based on floor area and old epc, is suggesting 12 kW HP).

HP size aside, there were two main concerns I had regarding the technical detail of the Aira system: 1) the buffer tank that ALL of their systems use and 2) whether/how they use weather compensation. Regarding 1), I'll relay what he told me, which is that the system is designed bottom up to include this additional warm water and it is used cleverly to supply small amounts of additional heat to the system without calling on the HP. In the same way, it is also used to help with defrost cycles apparently. The argument is that this is slightly more efficient and avoids additional HP cycles, thereby avoiding additional wear. Given how the Aira system is built around quite careful (albeit remote and rather 'black box') system optimisation, I'm cautiously sold that this is a plausible explanation. Regarding 2), the system very much does use WCCs, in fact in the hard copy brochure I received, this is a key part of the blurb around optimisation by their algorithm. The more data and customers they supply, the better this system will become I assume. I'm thinking that this is essentially akin to Havenwise. For example, if they have a setup down the road, it would make sense to commission my system with the WCC from that setup. I do not know if this is the case, but one would assume so based on the quite incredible SCOPs that they guarantee (>4). Clearly their systems are much more closed book than e.g. those using OpenTherm, but if they work, then I suppose that is OK for many.

On the point of retrospectively fitting UFH, he said that they can absolutely accommodate that. I'd want to discuss that in much more detail with somebody more technical, but the very long warranty and support period perhaps provides some reassurance that they'll continue to want to keep the system running well. On the warranty, which I believe used to be 15 years blanket for all, this is now a subscription service. Interestingly, they've partnered with a third party to sell the carbon credits from installations, using them to offer 8-10 years of subscription up front, so I think most would still get a long warranty, including two yearly visits etc.

You'll get the sense from the above that I was actually very pleasantly surprised by the Aira 'pitch'. I'll be very interested to see how the other visits stack up and to compare the systems, costs, heat loss calcs etc. More in due course and happy to hear any initial thoughts...

Posted by: @jleyland

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happy to hear any initial thoughts...

Some orange if not red flags for me here. 

(1) a 'ceiling' cost sounds attractive but they give one without doing a full survey. Does that really make any sense? I suspect they just set the ceiling rather high...and then you may (or may not) get discounts for items removed (as long as you sign up today). Sounds like marketing BS to me.

(2) 'the system is designed from the bottom up'. So it should be. Or from the top down. Or possibly sideways, to get an alternative perspective. More marketing BS.

(3) 'and it is used cleverly to supply small amounts of additional heat to the system without calling on the HP. In the same way, it is also used to help with defrost cycles apparently. The argument is that this is slightly more efficient and avoids additional HP cycles, thereby avoiding additional wear'. This just plays on the all cycling is bad myth, that it wears you and your system out. Additional (free?) heat without calling on the HP? I don't think so. This smells of blinding with the clever science marketing, using a black box that has nothing inside.

(4) For example, if they have a setup down the road, it would make sense to commission my system with the WCC from that setup. I don't think so. The WCC is specific to the property, not the local weather. The idea of being in some sort of Aira cloud thingy which tuned my WCC based on what Joe Bloggs down the road does would fill me with dread.  

(5) 'the quite incredible SCOPs that they guarantee (>4)' this sort of claim requires scrutiny. Or maybe it doesn't, because I think guaranteeing a SCOP greater than four is well nigh impossible, unless there is some numerology behind the scenes. Compressorgate perhaps?

(6) 'On the warranty, which I believe used to be 15 years blanket for all, this is now a subscription service.' It seems 15 years blanket went the way I suspect SCOP > 4 for all will go. Call me old fashioned, but for me 'warranty' and 'subscription' next door to each other is an oxymoron. It's either one or the other.

More generally, heat pumps are not complicated. They use very well established technology that has been around for a hundred years. Using circulating hot water to provide heating is even more basic, and has been around for even longer. What they don't need is black boxes and 'clever' design, what they do need is basic design that follows the well established principles. Any attempt to sell a system based on the idea that it is somehow smarter and cleverer than the others reeks of marketing BS to me.        

@cathoderay Thanks for the reply and a useful sense check! I suppose the real evidence base for performance comes from users. I've been trying to do a bit of trawling around to find use case evidence from their systems and have found one or two detailed posts. I agree that much of the interaction yesterday fell into the 'polished pitch' category, and I'm not getting carried away. Equally the setup and results (looking objectively at feedback and how many are happy with the installs) looks to set this lot apart from the other 'larger' companies. I 100% agree that it is all about the careful design. That's what makes it difficult to really compare quotes - most (including Heat Geek for example) require a payment to proceed to a detailed HL and design stage.

Posted by: @jleyland

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most (including Heat Geek for example) require a payment to proceed

This is always a tricky one. Someone has to pay for the work and time. Personally I prefer the approach that the cost is absorbed into the overall cost, others prefer the more itemised approach ie you pay for the survey and design work even if you don't proceed with that particular installer. At the moment we have the worst possible situation, installers use both approaches, making it a very uneven playing field. But at the end of the day it is for installers to decide how to run there businesses, and us to decide how we want to spread our custom. Sometimes a free 'introductory' visit from an installer can be enough to tell you whether they seem sound, and just as importantly whether they are someone you can work with.

Heat loss - how detailed is your gas usage? If you have daily or better data, and you can get daily or better outside air temperatures for where you are, and your property is normally heated to much the same level, then you can plot energy use against OAT and get an empirical heat loss that way. It will almost always be more accurate than any spreadsheet based assessment or rule of thumb method.