You are right to be cautious about the AI analysis, definitely contains some BS.  Once you have a preliminary decision feel free to post it and the rationale for final comment (by several members I suspect). 

Please check you aren't going to be saddled with a 4 port device (buffer tank, PHE, LLH) between emitters and heat pump, you will regret this for many years and remember that the 3.5kW Vaillant is just a 5kW software limited, so there is no reason to suppose the 5kW will cycle more.

@jamespa this is Sustain's reply to my queries

Posted by: @eliuccio

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@jamespa this is Sustain's reply to my queries

 

I have specified the 3.5kW unit as this provides more than enough heat for your requirements. The 5kW unit is essentially just a software upgrade but would cost more with no benefit for your system.

 

We would connect the vessel as a volumizer to increase the defrost capacity of the system.

 

We do include the Vaillant Connect interface as standard to give you the greater control you desire.

All good IMHO.  Others may have a different view of course.

Just an update on the responses received by Smart Heating.

Here are my questions:

Dear All,

I am coming to terms with accepting that I am not knowledgeable enough to make an expert decision, nor I can dedicate enough time to study the matter.

I therefore tried to put things together and come to a practical choice on the basis of the info collected. Synthetic analysis file attached.

The new Smart Heating offer is coming with 5 new radiators (I have also researched floor heating as an option but found it impractical and way more expensive).

I have put together a few tables to summarise what the two companies propose and narrow down on the important differences.

As you will see, I still have some question marks in my takeaways, which reflect in the final quandary.

I think I will accept the level of uncertainty and move on with my final decision, which is (rolling drums)

Smart Heating!

This is clearly more expensive, but it may translate into better long term performance.

I am of course happy to change my mind if you have strong counterarguments.

Thanks for all the advice and support!

E

@eliuccio 

Thorough analysis and, tbh, it looks like you have two viable quotes (a good position even if it makes the choice difficult!)

Here are some comments:

• Smart Heating’s higher SCOP could yield better savings *if accurate*, but oversizing may negate gains during milder weather?
• Smart Heating’s longer warranty

The 3.5kW Vaillant is just the 5kW one software limited so, with the same radiators, they will almost certainly achieve the same SCOP.  However as Smart heating are proposing to upgrade more radiators it may well be you will achieve a lower FT with their proposal than with Sustain

Warranty difference is presumably real.  7 years is offered by Vaillant provided the installer is Vaillant approved so it suggests Sustain may not be.  Its normally a condition that it is serviced annually to get the 7 years though.

Radiator Design

If you multiply the output at 50C deltaT by 2.8 you get the output at 45C FT, so you could do a direct comparison.  Personally I would make a list for each of room, proposed radiator type and size, claimed loss (5 columns in total) and do a stare and compare.

3. System Components - agree no difference

5. Installation & Compliance  Since they are effectively using the same heat pump the actual noise will most likely be the same.  If there is any difference it will be in favour of sustain because the software capping of output will also cap noise.  However this can be achieved by applying noise reduction mode anyway.  Basically no material difference in this section.

Final decision quandary:

See above as this affects some of your final summary.  However your final comment Considering the customer service promised by Heat Geek I am inclined to believe they would improve the system without further expenses on my part may well be true and, together with the difference in warranty, you may well think should be the decider.

If I were you I really would do the table of rads, feel free to post here if you do.  It may confirm the choice of smart heating unequivocally, may push you in the direction of going with Smart heating on the ground of likely better service, but challenge some of their rad choices.  Alternatively it may push you in the direction of concluding that they are overestimating their capabilities but you will then be prepared.  Either way you will be better informed.  The good news is that its a difficult decision so you have two viable quotes. 

I dont have strong counterarguments to your conclusion, cheapest is certainly not always (perhaps rarely) best and peace of mind and a longer warranty is worth paying for, as is a better radiator upgrade if that is in fact what Smart Heating are offering which, giving they are proposing 5 is very likely the case.

@jamespa there are some important differences in the estimates but I am not able to tell why that is the case.

There may be different software assumptions because I'm noticing that even the bathroom radiator heat loss (that won't be changed) is already quite different!

Any suggestion?

Thanks,

E

@eliuccio 

I think what you are seeing is the variation is loss estimates.  It happens, they are estimates, making different assumptions any of which may be more or less accurate.

The reality is that the loss is what the loss is and the radiator emissions are what they are, both are completely independent of the estimates.  Notwithstanding any of the estimates, the more rad area you have the lower the flow temperature and thus the higher the COP.  That's why I would concentrate on the actual deliverables.  

My initial reaction is that, in all cases except L2, SH are proposing larger radiators and so will achieve a lower FT = higher COP.  The sustain proposal for L2 is smaller but is 22 rather than 21, so I guess may have a higher or similar output (I can check, but not this evening!).  If you are happy with the physical sizes that SH are proposing that is unequivocally going to achieve a better COP (subject to checking L2)

Here is an analysis of the rads proposed excluding the bathroom where Im not sure what is actually being suggested.  The big differences, in favour of Smart Heating, are the kitchen and the totals.  I cant remember what your total loss estimate was but if its ~ 3kW both look a bit marginal at 45C but Sustain is nowhere near!  Of course they may have used more generous estimates of rad output than the Stelrad figures I have used - I found when I was doing this for myself that the Stelrad figures were lower than some others for any given rad type (I doubt this difference between rad specs is reflected in the actual output - probably just slightly different test methods).

Based on this I would expect the FT that you will need to operate at with the Sustain proposal to be ~5C higher than with SH, adding perhaps 15%-20% to the running cost.  By the time you add in heat lost from people and electrical appliances I would guess that the SH system should run at 45C or maybe a degree or so below (ie as they have specced) assuming your total loss is 3kW.  I am not sure that the Sustain proposal would run at the specced flow temp.

Please note that Im not a heating engineer, just an enthusiastic amateur with a background in physics and engineering who has spend 2 years studying this stuff in order to inform his own installation.  Thus I may be wrong!

Here are the performance curves for the 3 and 5kW machines.  Sorry they are in Czech, these tables dont seem to appear on the UK website.  Note that

the 3kW max compressor frequency is 85rps whereas the 5kW is 120 rps

the performance figures at any given compressor frequency/OAT combination are the same

showing that the 3kW is in fact just a software limited 5kW.  The separate spec sheet shows they have the same compressors with the same refrigerant charge, further confirmation they are the same beast.

There is no reason therefore to prefer the 3kW over the 5kW, if anything the opposite applies (again in favour of SH).

Both models maintain a good COP down to low compressor frequencies, which is important for you because you will often be running towards the low end.  At these frequencies my 7kW Vaillant is very nearly silent.

Hope that and the above gives you more confidence.

Dear @jamespa yes, this is very useful input overall, and I think I made a reasonable negotiating pull with SH which made the price not raising despite the upgraded design.

It is a lot of money, but I feel I have to do this for ethical reasons, and it also makes sense to spend money in this way rather than having them in a saving account (debatable I know!).

I really appreciated your advice and time you have spent on my case (as well as all the others who contributed to the thread).

You really helped a lot, and I am very grateful!

Hopefully the job will be done by the end of July and start enjoying my new system perks from next winter 🤩 

Have a lovely weekend,

E

Good luck.  For what it is worth my system was very definitely an upgrade to my heating.  Both DHW and space heating are now far superior to what I had previously.  I hope you have a similar experience.  Please post back if you have any more questions and as you get into the winter season.

You will likely need to adjust the weather compensation settings and maybe balance the radiators (but quite possibly not the latter) once it gets into the heating season.  Hopefully the installer will tell you how to do this - the Vaillant makes it especially easy.  In fact I would say the Vaillant controller is generally pretty good.  Like all modern controllers there are lots of options, but the main ones are pretty easy to work out.