Hi all, trying to decide between the Vaillant Arotherm plus 10kW or the Altherma 3 mono 11kW. I’ve been offered the altherma for about £1k less than the arotherm and I’m also familiar with daikin controls as we have them for a smaller ASHP in an outbuilding. Most of the high performing systems on OEM are the vaillants but I know both are not without their issues. Does anyone have any real world insight as to which one to go for? Feels like 6 of one half a dozen the other at the moment. I’m also pretty clued up and technical with heat pumps so feel free to be as detailed as you wish!
What’s your heat loss, design temp, design flow temp etc? Both suits are big units with hardware to match and min modulation is around 5kw heat produced around 10C so cycling will be a thing. The dakin is R32 not R290 of Vaillent so can’t heat water so high.
All else not considered for 1k extra I’d out in a Vaillent. But maybe you could get away with a smaller Vaillent unit and use immersion on design days. And or consider a grant r290 unit which supposedly can modulate lower.
Don’t rush a decision either way.
Fyi I was in a similar place, and I stumped up extra for a Vaillent and very glad I did. It works. It cycles well. There support has been great after commissioning too.
Heat loss is just over 8.2kW (measured so that’s very accurate). Design outdoor -2, design indoor 21. Design flow 35. I’ve done quite a bit of digging (and experience with the altherma in the outbuilding) that all heat pumps produce significantly less than the rated output, anywhere around 20% so both units would be right on the limit at design temp when considering the heat loss. I’m erring on the side of the vaillant for the very reasons you gave.
They don’t generally produce 20% less than the rated output, it really depends on flow temperature and ambient conditions. But at your design temperature you’re right in the defrost dip region which can eat up 20%, so you’re right to oversize.
At 35°C design temperature and -2°C outdoor temperature, the Vaillant is rated for around 11 kW but can modulate down to around 4 kW so you’re comfortably in the operating range even taking defrosts into account.
Yes sorry, should have specified that the drop is really seen around defrost conditions and the high humidity in the UK.
The Grant 9kW modulates to 2.5kW - if it were me i’d research into this model, it’s been discussed here.
Shame the 8kW Vaillant isn’t available in the uk as that modulates down to around 3kW.
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Wow that looks like I great bit of kit. My main gripe with the Daikin over anything else is that it has a very aggressive startup which causes it to overshoot its target flow temp and cause horrific short cycling and poor efficiency. The Grant looks very interesting.
And the Madoka’s fixed 2c hysteresis (and other issues) is potentially a problem (it is for me). I’d never install Daikin again.
Yes I was mainly put off with the issues mentioned by @matt-drummer being seen myself in our other system.
Thanks for asking this question - answers are all great to read: my contribution is that refrigerant is a consideration in that R290 is future proof and R-32 will ultimately be phased out as an HFC. I’ve read that in engineering terms R-290 is a more efficient refrigerant but that gets lost in the overall appliance efficiency I would think. Perhaps the Grant or Vaillant would suit and the other issues cited here tilt that way?
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The 10kW Vaillant unit can sustain ~10kW output, as per its nameplate, during constant defrost conditions. There is a thread on here with a list of ASHPs and their real world maximum power outputs under defrost.
It really can’t, output drops to around 8.5kW under defrost at design temp. That’s a massive drop comparatively. I think currently I’m looking at the 12kW Grant Aerona as it looks like a top bit of kit.
~9.5kW mean sustained during defrost conditions for the 10kW Vaillant, as per actual monitored data.
Edit: same data presented here also: HeatpumpMonitor.org
You’re missing my point, if you look at the loss over rated power on that table for temperatures between upper defrost and design, they’re almost 20%. Therefore, per the charts produced by Vaillant, it is significantly below what you may have picked as the right size unit, actually ends up being undersized.
I had a Vaillant 5kW Arotherm+ installed at the end October. One thing I would say about the Vaillant is that it is very easy to tune and can be done with a couple of clicks in the MyVaillant APP. Also there seems to be a lot more support and experience available online from both owners and installers for Vaillant. For examle Mick Wall’s excellent blog, i85: Heat Pumps & Controls YT channel, Urban Plumbers etc etc.
Nick
This! I would never fit an R32 unit.
Vaillant are the Volkswagen of heat pumps. They’re not perfect, but you’re not going to go wrong with one. That said, if a Grant is an option, that’s what I’d get.
Ah, we have a case of crossed wires, apologies for any confusion!
I think we both mean the same thing; I’m well aware that the Vaillant output charts do not factor in defrost conditions, and none of the Vaillant units can sustain their data sheet chart output figures under defrost conditions.
However; as per my original post, all of the Vaillant models sold in the UK do achieve their ‘nameplate’ outputs (5kW, 7kW, 10kW etc) under sustained continuous defrost conditions, as per the OEM data linked to above.
So yes, if an installer uses just the Vaillant output graphs to size a unit, and the actual heat loss of the dwelling is marginal according to those charts, then you’re likely to have a bad time in winter. But if you take the ‘nameplate’ rating to be the actual maximum output at design conditions, then the Vaillant units will be able to sustain this.
As in my previous post: the ‘10kW’ Arotherm+ can sustain its nameplate output in defrost conditions (~9.5kW mean as per the OEM data above).
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Running my Altherma 3 (11kW) for 2.5 years now, apart from fine tune it (took me about 3 months) I have a very positive experience. I only use it for heating (200sm, two level no zoning), so DHW max isn’t an issue for me. Also I’m in a mild climate. Annual electricity consumption is below 2000kWh, most of the time it runs on 7-800W. I like it very much but I cannot compare it to Valliant.