Vaillant maximum output capacity testing

Hardware Heatpump
42

In the case of my 7kW Panasonic at -7.1C, this was the only recent example I could find with it running at, or near 100% (without having to raise the flow temperature :hot_face:) - unfortunately Panasonic only indicate compressor Hz in their controls and provide no cross reference to actual compressor duty % and max Hz varies with model depending on compressor mapping etc, so in this case (~77Hz) it’s an educated guess it’s maxed out, but there may be a little left in the tank? But its peak output is actually higher than their data sheet at around 7.4kW

Note, this is the standard/older R32 J series - the R290 L series have a similar mapping to the J, but the output is a little less at times. The M series T-Cap models maintain their output capacity down to -20C (need to test one), without back-up heaters and work down to -28C, unfortunately the smallest they offer at the moment is 9kW.

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43

Agreed. I’d love to see a schematic diagram for each system on HPM, to help clarify the usage of e.g. buffer tanks and the placement of heat meter(s). The ability to add multiple photos of the physical installation too would be really good.

Ideally these would be on HPM rather than the Forums, perhaps as part of the existing Summary page (system/view?id=nnn) for each installation.

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For example if you take air that was at 2c and high humidity and cool it to 0c (due to sun setting etc) you will likely get a different result then taking air that was at -2c and worming it to 0c.

In real life unlike test chambers the air have not been at the same temperature for many hours, and humidity is unstable when near 0c.

45

Late to this tread, but just to add that Samsung do publish two tables of maximum heating capacity data for their heat pumps, one for peak value and a second for integrated value. The peak values are without defrost operation in accordance with EN14511 and the integrated values represent actual capacities in an installed environment.

So the integrated values have allowances for defrost cycles, and this is confirmed by identical data for ambient temps of 7C and above, but the integrated maximum heating capacity values are lower at 2C, -2C, -7C. As temps fall below -10C, the data converges again, as presumably the air is too cold (and thus dry) to cause frosting.

For reference, the Samsung quoted integrated maximum heating capacity values are 86% at 2C, 88% at -2C, and 96% at -7C of the peak maximum heating capacities, respectively. These data seem reasonable given the experimental data presented above.

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46

I would add to @Old_Scientist’s observation that the tabulated Samsung data appear to correspond to a compressor motor inverter frequency of 50Hz. Data from a recent test run on my 8kW nameplate HP (at ambient temp +2degC, LWT 50degC) indeed showed 8kW heat output at 50Hz (the same as the Samsung data) but ~10kW at 57Hz (the maximum during the run), and ~4.5kW at 20Hz (the minimum during the run).

So the phrase “peak value” may need to be qualified when comparing between HP makes.

47

Hello,

I tested my Arotherm+ 55/6 at full blast at 0°C today, maximum power reached at 2500 W and maximum output power at 7500 W but only 4.6 kW average during these 2.5 hours. 99% humidity outside.
It could not even reach the desired maximum temperature of 40°, maybe because the usual temperature is low (heat curve 0.25)

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https://emoncms.org/app/view?name=Arotherm55&readkey=cf5de42a808d52683599b86327293092&mode=power&start=1735481920&end=1735491260

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48

Do you have high thermal mass UFH stopping the flow temperature increasing quickly.

99% humidity at 0c is likely near the worce possible case. Have you every seen over two defrost per hour for heating?

49

House is 230sqm
. 144sqm UFH with 9 loops
. 5 1sqm radiators for the rest

It’s my first winter and each time ext temp went under 1C, it’s been foggy… Worce case scenario indeed. I’ve never seen higher defrost frequency than those 2 per hour for this test luckily

1 Like
50

I little bit out of topic but I think your heatpump is underpowered. Is it a hybrid sustem? What is your walls insulation thickness, and what type of windows and doors you have installed?

51

I am glad I found this thread. I think I have some interesting additional information on maximum power output of Vaillant Arotherm Plus 7kW in real-world (and challenging) conditions. @glyn.hudson I think I have exactly the case where the installer, in good faith was interpreting the figures in the Vaillant specifications, but not considering that this does not take into account defrost cycles. I have heard that other manufacturers do publish “integrated” power outputs which take into account typical defrost cycles and this seems like it would be very useful.

In my case, the system was designed knowing that it would be somewhat close to the limit, but should not be undersized - we know that we have some opportunities to improve insulation which we plan to do and we do have some backup heating, in the extreme cases.

We had temperatures of -6 overnight recently followed by a foggy day where temperatures only increased to -0.5 max. For the period in the graph below, the pump was running at full capacity for the whole period (120 rps compressor speed whenever not in defrost and no hot water heating). What I am showing is temperature and instantaneous heat power (I cropped the power axis to see details better). I am also showing with the orange area, the average power between the end of one defrost cycle and the end of the next which seemed like a reasonable fair way of representing it, given the changing conditions (ignore the last period as not all of the defrost cycle is included). I have not shown all the data, but for context, the maximum flow temperatures were peaking at about 40-42 and return temperatures 33-35. The flow rate was stable at 912 L/h

At -2 in foggy conditions the output was only averaging about 5.5kW. Overall, it could be roughly summarsed as ~6.5kW during the colder/lower humidity half of the day and ~6kW during the warmer/higher humidity half when defrost cycles were more frequent.

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7 Likes
52

Couple of comments/questions:

  • That flow rate is a bit low for 7kW. should be closer to 1200L/hr when compressor is running. I don’t know if this is constraining output in any way, but it is worth highlighting.
  • Water of glycol? I would assume Vaillant performance data is based on use of water.
  • Out of interest, do you know what max compressor speed is used fo defrost? I’ve only seen mine go up to 80rps, but I don’t know if that is by design… or it is just fully defrosted by the time is ramps up to 80rps.
1 Like
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Thanks for the thoughts.

  • I will look into the flow rate when I get the chance - not sure what the water pump power is set to, but my guess is that it is set to “auto”. EDIT: confirmed it is set to “auto”. I see about 915 l/h for heating and 1050 l/h for DHW.
  • It does not have glycol in the system.
  • When in defrost, it seems to start at 40rps, then go to 80rps, then drop to 60rps
54

Auto targets 1200 l/h. Pump power will be 100%, trying to achieve this. When was last time strainer was cleaner, this can often restore flow rate.

Same here, thanks for sharing your observsations.

1 Like
55

Blockquote
Auto targets 1200 l/h. Pump power will be 100%, trying to achieve this. When was last time strainer was cleaner, this can often restore flow rate.

The system has only been in 8 months. The pipework is not ideal, so probably can’t achieve the 1200 l/h (though looking at the specs it says minimum of 550, max of 1200, so hopefully this is not having too much of an impact). I did have one radiator on a TRV and when I opened this it increased to 930 l/h, but the rest of the radiators are fully on.

56

Give strainer a clean, this might generally insreases flow rate a bit. If you don’t achieve the full 1200l/h I don’t think this is a major concern though.

Yes, datasheet says min 550 l/h but its very unlikely you’l get full output at that flow rate. Full output at 1200 l/h is almost dT 8K. So at 550 l/h that would imply a dT of over 16K which I would assume just isn’t going to happen (there must be a dT limit, not sure what it is though).

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Definitely take a look at your strainer, ~900l/min is way too low for a 7kW unit.

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Hi Guys. My first post here. I thought I would join in with my observations. I have installed over 40 Vaillant units so far and have around 10 of them on OEM. All my OEM units give around 20%-40% lower outputs than Vaillant sizing guidelines and Vaillant sizing tools suggest.

I think Vaillant quoted peak output, and no one ever noticed. It is not a problem for most, as most installers don’t do the heat loss right, so even when sized according to the guidelines, units are usually fine. However, when you do get your heat loss spot on and size to Vaillant guidelines, then well, you are in trouble.

I have noticed the biggest problems with 7kW units. I have around 15 of those installed and 5 of them are now undersized. The gap between Vaillant’s quoted ‘peak’ outputs and actual mean outputs is dramatic with 7kW units. Designed to 35c they should give 9kW output, and some of them struggle to give more than 5kW. The average I see is around 5.5kW.

The variable that changes the output, in my view, is the ratio of actual heat demand vs heat pump output. The higher the heat loss, the more time the compressor spends in full output, and the more defrosts happen because of that. In short - the bigger your heat loss the less output you get from the units at the design conditions - so opposite of what we would want to happen.

So far, we have had to install no.2 backup heaters on our 7kW units, which are also OEM. This resolved undersizing at the cost of slightly lower system efficiency. However, this is not all the issues we are seeing with 7kW units. They also become very noisy—noisy to a level that is definitely unacceptable.

In short, all Vaillant figures seem to be peak and not mean, and Vaillant still publishes data that will make your unit undersized, with the 7kW being the most underpowered. Hopefully, they will publish a correction soon and replace underpowered and noisy units.

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59

Oh, and I totally agree with @glyn.hudson - Those units almost never reach over 40c at design, so designing to above 40c with correct heat loss is not an option. It would simply not work. Again, most get heat loss over by some 20-40%, so that is why people get away with higher design temps, as on-site, it turns out that a 5c lower flow actually works fine.

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Thank you Szymon, great to see you here and thanks for the valuable insight!

Do Vaillant themselves use their ‘peak’ output values for sizing recommendations to their installers, rather than the nameplate rated outputs?

I’m very interested in your experience of the 7kW units being noisy at full blast; have you investigated the cause of the noise? Is it fan/compressor related, or vibration resulting in internal components resonating/contacting against each other, which could be solved by applying ties and foam tape?

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Have you found that the 10kW units behave better at design conditions? How then is the tradeoff between being able to cope with continuous defrosts, and efficiency when cycling during warmer periods?