Saunier-Duval (Vaillant group): nominal power vs maximal power vs name of the thing

[Garald]

Current state of the saga: I'm now trying to estimate heat loss as accurately as possible - and also making small changes that seem obvious in retrospect and, according to the spreadsheet, make a large difference. (For instance, the stairwell going to the attic is small and narrow and will have to remain uninsulated for now; I will try to deal with this issue (which costs me 0.4kW, apparently - more than the loss from the largest room) by insulating the door at the bottom of the stairwell - convection should be enough that not much heat is lost from the attic through the stairwell, no?) My aim was to get safely under 6kW, so that, allowing a margin for the production of DHW, I could consider getting a GeniaSet Split 7 rather than a GeniaSet Split 10 (there's nothing in between - and the Split 7 is 6dB quieter than the Split 10, which, in turn, is just 4dB quieter than a Yutaki S Combi 8kW).

 

Except - 

https://files.izi-by-edf-renov.fr/files/catalogue/produits/fiche-technique-pompe-a-chaleur-saunier-duval-geniaset-split.pdf

shows that the power of the GeniaSet Split 7's power is not 7kW, ad I was expecting - rather, it is under 6kW in most circumstances, with the maximal power often not being that much higher (6kW at 45C when it is -7 outside).

 

Is the number "7" in the name just a fantasy?

 

It might be best to get the Split 10 unit, then, and choose the "silent" mode when possible. The technical information list gives no information on efficiency while on silent mode, however - it states that power is then cut by 60%, but it's unclear whether that means power consumed or heating power produced. I'm starting to think that Saunier Duval's publicity department is a little too talented...

 

(Or am I misreading things?)

 

PS. A comparison of figures confirms that this is the same as the aroTHERM Split 7kW and 10kW. Again, I don't really see how the "7kW" label is earned (whereas the 10kW generally produces more than 10kW, i.e., quite a bit more than I need). https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-split-1/vaillant-arotherm-split-1-0-lr-1454128.pdf 

It's interesting that the brochures in French emphasise much more the unit's relatively low noise levels (to the point of overselling them, I'd say).

Edited December 9, 2022 by Garald

[akjos]

If I remember correctly, manufacturers need to publish data at 7’C outdoor temp and 35’C flow temp. That’s where the unit produces the label output…

 

Quite stupid tbh, as nobody designs at those numbers.

So always check the detailed tech spec. Also keep in mind that during defrost situations (~4’C outdoor temp) the unit looses an additional 10%. It kinda has a dip in its capacity curve, which they rarely document.

[Garald]

2 hours ago, akjos said:

If I remember correctly, manufacturers need to publish data at 7’C outdoor temp and 35’C flow temp. That’s where the unit produces the label output…

 

 

But the unit doesn't produce the label output even then! At 7C/35C, it gives 5.8 nominal, 9.8 maximal, whatever that means. At -7 C/35C, it gives 6.7 nominal, 6.7 maximal.

 

(45C will probably be more typical for me when it's -7C outside; I don't have UFH, and I need most of my wall space (because books), though it's true I also have PIV with pre-heating. Then it's 5.8/6.0.)