18 posts were split to a new topic: Vaillant Arotherm: excessive noise from compressor
Cycling with Vaillant is not an issue and doesn’t seem to affect efficiency. If I were still specifying Vaillant, I would go a size up, 10kW in place of 7kW. I don’t see a point for a 7kW unit - for me it would be 5 or 10 or 12.
3 Likes
Very interesting, thanks. Are you no longer specifying Vaillant units? If so, which units do you prefer now?
I have a 7kW Vaillant with a measured actual heat loss of just under 6kW, and it’s been fine during the recent cold snap, down to -4C. Although it looks like the internal flow/return temp sensors are not calibrated, resulting in overblown CoP readings via Vaillant monitoring…
The performance tables I’ve seen mention the EN14511:2018 standard.
This standard, as far as I understand, defines the exact outdoor test conditions (including humidity) that should be used for tests, and requires that the results include time and energy spent carry out defrosts. So it’s very disingenuous of Vaillant if they have ignored defrosts here, or calculated/extrapolated rather than tested. Maybe that’s why they hide this tables? That said the max output values in marketing material was also 8.8kW @ -3C, 9.5kW @ 0C, also ignoring defrost.
Luckily my 7kW is oversized, but must be a bummer to have intalled these assuming vaillant data was following the standard (and considering defrost) only to find out later that it doesn’t.
edit: yes, UK humidy levels might be worse than Germany, but they’ve ignored defrost compleleltly, this isn’t an UK vs Germany climate issue.
3 Likes
My sensors are off as well, pretty normal. You see some people posting with COP of 10, but it’s invariably their sensors off. Your need to get OEM installed 
This is not necessarily true, it also depends on what max. rem. head is set to. The lower that setting is, the lower the resulting auto pump speed.
I think it still targets 1200 l/h and likes to work at 1200l/h. Yes, if you lower max rem head this may impact pump speed which in turns means it can’t achieve 1200 l/h in auto, but that doesn’t mean it’s not targetting 1200l/h, just you are stopping it from getting there (pressure loss in circuit may also stop if getting there). A bit like noise reduction constrains compressor speed. That said, I haven’t experimented much with this, so may be wrong. I was just pointing out that in general all 7kW units target 1200 l/h with default settings. (i should have clarified default settings maybe )
I don’t have experience with the 7kW, only the 5kW. To reach their badge capacity when there are many defrosts, they need to be able to reach their peak capacity between the defrosts (almost 7kW for the 5kW a0/w35). When you try to design for very low temperatures, this can be a challenge, and imo impossible with the pump speeds on auto as that targets badge capacity at dt5. If you run the pump at fixed speed and target a flowrate for the peak capacity at dt5 it can do its badge capacity on average.
2 Likes
Thanks, your data is the 1st to make me believe there is a reallife practical issue for correctly deaigned/installed systems.
But is output being linited by flow rate?
1 Like
@UrbanPlumber What flow rates and dt are you getting on the problem units when they can’t cope?
Blockquote
But is output being linited by flow rate?
I don’t know enough to know how much of an impact this would have. Others have commented that the flow rate seems low and I will investigate further. I guess that the compressor would be working at a slightly lower temperature if it were at a faster flow rate and the heat transfer might be a bit more efficient, but the max flow temperature I was seeing was not too high (~41). Maybe others can comment more knowledgably.
I have a feeling heatpump output can increase with dt (eg lower return temperature) but that then will reduce radator/UFH output, so require higher flow temperature. (Unless indoor air temperature have dropped.)
But I never liked systems desinged so they can’t recover from a power cut at likely outdoor temperatures. I not convinced many heatpumps without backup headers could cope if the floor screed for a high thermalmass UFH drops close to 5c in a powercut at a time of near design temperature.
1 Like
All have good flow of 1200 and dt of 3k to 7k
By the way - every single unit underperforms- no exceptions. Some or just oversized so do not cause issues
5 Likes
Do you mean all Vaillant units underperform during constant defrost conditions, or mainly the 7kW units?
They don’t technically underperform / it’s just that Viallant data is wrong as they quote peak output and not mean output and they also tell installers to size to peak - which is wrong
5 Likes
Thanks. So, sizing based on the quoted badge output (mean output), rather than the figures in the datasheet tables (peak output), is a safe bet across the Arotherm Plus range?
You mentioned above that some of your 7kW units struggled to hit 7kW sustained output at design temperatures with constant defrosts… this would indicate that they are underperforming even against their nominal badge rating…
this is correct, I’ve been looking through as many 7kW Vaillants as I can for @UrbanPlumber , there are a large number of systems that appear to be maxed out and so the data should be a suitable reflection of their max outputs. The flow rates I’ve looked at so far are running at a fixed rate with expected DT during these periods so I don’t think it’s a flow rate issue.
Il post up a table of systems and links to max output periods for discussion…
6 Likes
Do they all underperform relative to “headline” output, eg 10kw giving less then 10kw at -3 or “just” relative to the detailed desigh tables? (We know 7kw is more of a problem.)
Is that partly why oversized Valiants work so well, eg they are not as oversized as it looks in the data?
What the true incremental cost of a 10kw variant over a 7kw variants if the installer make an identical profit in each case rather then putting a percentage market on what they pay for equipment? (Fit the 10kw with the pipework sizing that would normally be used for a good install of the 7kw.)
10kW needs planning, 7kW doesn’t. 10kW is marginally noiser too, however it’s also more efficient. 10kW needs more system volume than 7kW, also 7kW can sometimes get away with 25mm primaries, but 10kW can’t.
2 Likes
Here’s a list of all the 7 kW Vaillant units on HeatpumpMonitor.org with data over the last 30 days:
https://heatpumpmonitor.org/?filter=query:hp_model:Vaillant,hp_output:7&period=last30&minDays=24&add=combined_heat_kwh