Im just about to acquire a Vaillant heat pump and have a morbid desire to monitor it. Would you be prepared to share how you stitched your ebusd monitoring system together? I am moderately software literate but sadly not a linux expert so a bit of guidance (not step by step instructions unless you have already written them up) from someone who has done it would be much appreciated.
@modeller @Zarch
My ebus adapter just arrived, so I shall be playing soon too. Is the new thread that Mick suggested up the thread a good idea now?
I would be in support of that.
Replies on this forum dont seem to quote the post to which they are a reply which is confusing me at present, hopefully I will shortly get the hang of it.
It depends on where you click to reply - “Reply” against the post or the blue “Reply” at the bottom of the thread. It never quotes the post, but links to it (with the up-pointing arrow).
You can quote a section of a post (not the complete post) by highlighting it and clicking the “Quote” that pops up.
[Search for 'Discourse` - the name of the software - for more.]
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Right, here we go, a dedicated eBUS adapter thread to keep things from clogging up this more generic Arotherm thread.
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Hi all,
Has anyone seen a power signature like this for their Arotherm? At first I wondered if the heatmater had gone offline, however this 90W is less power than I ever see during a genuine ‘firing’. Not just the ‘90W with spikes’ between 0930 and 1200, but the 42W constant since the last firing finished at 2100 last night (normally quiescent power is 10W).
You can dig further at Emoncms - app view if interested!
Thanks,
Tom
I was interested in the max/min flow rates of the various Arotherm models from the spec sheets, so I translated this across to Excel.
Taken from (https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-plus/arotherm-plus-spec-sheet-1892564.pdf)
Might be of use to someone. 
In Pure WC mode, the pump seems to overrun after heating, ie continues to circulate the heating circuit water. But only about 20-40W depending on the heat required. If no further heat required, the pump/controller drops back off to 10W
What Room Temp Mod setting do you have? ie, any room influence?
What is the ‘OT switch off threshold’ set at. ie, at what outside temp does your heat pump not bother firing up? Mine is 15C
Not sure what those 600W spikes are?
How are you collecting electrical data? SDM120? CT clamp? No chance of any other devices being those spikes?
Pure WC, no room influence (I think but will check, in any case the room shouldn’t have been calling), OT switch off at 17, electrical data from SDM120. Yes the spikes are the weirdest thing, but last night again from about 2030 right through to 0900 there was 42W constant, which suggests to me that the pump was circulating (but not following a heating cycle, which is weird)
I asked Vaillant about those specs for the 3.5kW because my Vaillant trained installer set the pump speed for DHW to 100%PWM rather than the default 65%PWM. This results in 1160l/min pump rate during DHW cycle, which is outside those specs. Never got a response!
Yep, If I stick the pump on my 5kW to 100% (for heating) I did observe it going past 1000l/h too last winter. I may have another play with that.
But i’m not sure if 100% pump is the best approach, for heating or DHW?
For the moment, i’m sort of settling on leaving both DHW and Heating to Auto speed now.
Let the unit find the best it flow rate to get the job done. I’m assuming it finds the more efficient flow rate?
DHW (on Auto) last night was around 680l/h last night… If I set DHW to 100% I get 820l/h
I need to do more comparison testing, but I do seem to get better COP (and carnot) when running Auto versus 100%.
Hi all,
Can anyone shed some light on this please. I have my HP all open zoned, desired room temp at 20.5 in the day. Room influence inactive. I’m seeing modest cycling but am unsure whether this is due to a modulation limit on minimum power delivery, or an over-conservative approach by the controller to avoid overshoot. Notice that HP comes on with gusto at 0600 which is when I switch from overnight 18 setback to 20.5 day, but then stops at 0710 then cycles somewhat. Current room temp on HP controller (I don’t have the emonPi internal sensor up yet) at time of writing (0935) is 19, so we are some way off 20.5 target. I would’ve expected the HP to run in the steady power delivery state as seen up to 0710 until we get close to target?
Thanks,
Tom
https://emoncms.org/app/view?name=MyHeatpump&readkey=1548bb92f8413211bb7c36cfa154ac94
@tommyt I wish I understood this better too. It looks like this is the energy integral at play (post further up thread on this), but your data might not follow how I think my Arotherm+ behaves. EI controls the compressor on/off and is dependent on the dT between target and actual flow temps. Target temp should in theory be determined by heat curve, so varies according to set temperature and outside temperature. When your set temp rises in the morning, the target temp rises and the EI decreases rapidly. When target temp is reached, on my system the compressor modulates to 25% and, presumably, attempts to maintain that TT. As a result EI stays constant or begins to increase if the TT is exceeded. At some point, the heat loss in the emitters is less than the 25% modulation output and EI then begins dropping. When it gets to zero the pump turns off and flowrate drops. EI becomes more negative due to the FT dropping and, at EI of -60 (default), pump turns on again.
Looking at your data I would guess you are on a low heat curve. The energy use is proxying the pump modulating and, excluding what look like defrost cycles, suggests modulation down is happening. As your FT is rising throughout the first two periods, this suggests to me that the modulated output is greater than your emitters are emitting because, otherwise the EI would not change to cause the compressor to stop. Note that the outside temp change would also drop the target temp, so there may be a balance of effects here. The rapid drop in flow temps between runs then drops EI back to the start point.
I’m pretty sure that Vaillant have lots of fancy stuff going on in their algorithms, but we know little about them. The above is my guess based on what I have worked out (with lots of contributions from all on this thread). I may be way off in my reasoning, and hope others will correct me if that is the case!
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That’s pretty comprehensive! To answer your question, yes I was on a curve of 0.35 but have pushed up to 0.4 since original writing to see what happens.
Your comment ‘ the heat loss in the emitters is less than the 25% modulation output and EI then begins dropping. When it gets to zero the pump turns off and flowrate drops’ might be what I’m seeing. I notice that my dT is around 3. It is not a ‘problem’ as such as the house is comfortable, but I want to understand what is going on here. Am I simply hitting up on modulation limit? Note that half the house is shutdown as it is not habited yet, and we are still in August!
I’ve been trying to understand how Vaillant work for two years, but the devil is in the details, and the details are proprietary it seems. My instrumentation does not include heat meter, so I can’t yet test the output kWh versus the house design energy usage, which is very low as we are in passive house. However, dT (flow-return) is always +/-2.5C on heating cycles and our emitters can never dump the 25% heat output fast, because output is higher than House heat loss by a large margin. So we get lots of short cycles triggered by EI as described. Makes for a poor COP as the pump circulates for a lot of the time with out the hp generating. But the room temp rarely gets to the set point, which I think is Vaillant algorithm backing off to not exceed the set point, but I’m guessing on that.
I’m extrapolating from my experience to your data, so take with appropriate pinches of salt. May be worth comparing your 25% heat output from your data with the heat loss for the rooms you currently have live?
We should share some more data on this. I’m not passivehouae level but not far off. Heating is currently constrained to a 75m2 basement living area which is insulated to above current regs standard. I may try opening up the upper floor manifolds which, although not habited, are in a habitable state (weather sealed, no draughts). I think I’m trying to jump the gun a bit by analysing too early in the heating season, but I’m a nerd so then you go 
Sounds like you need to disconnect the direct link between the HP and the output by adding in a tank. Mine is boiler based currently, but I have a large tank that the boiler charges which I then pull from as and when needed at what ever rate is needed. The UFH manifold is blended so only pulls in heat from the tank when the return temp in the UFH drops below target. It often then pulls the heat very slowly.
Hi Mick,
I’m trying to work out what units my (Sontex 789) heat meter is showing on EmonCMS graphs. From your work above, the max. flowrate my Arotherm plus 5kw heatpump should output is 860l/h or 0.86m3/h. Converting to l/min it’s 14.3. However, my flowrate at 100% is showing as around 23 ‘units’ which (for the life of me) I can’t seem to equate to the Vaillant figures. See pic below, which is one of my early DHW runs into my Sunamp heat battery (hence the high flow temps). My pump was set by the installer to 100% hence the constant ‘23’ flowrate. I’ve now set it to 65% which now has a better DT (about 5-7) and the pump modulates to accomplish this. The heat meter is as-supplied as part of the EmonHP level 3 kit, so I’m assuming the meter’s calibration is OK.
I’m probably missing a simple maths conversion but can’t see it!
Cheers, Andy
Edit a day later: Got it (!) and I should have just read other posts above. The 23 seems to be litres/min and is correct if the pump is set to 100%, instead of the factory 65% figure. 65% of 23 is around 14, agreeing with @Zarch and @AndyS for the Vaillant specs.
Vaillant settings question
As a heat pump newbie I’m eagerly awaiting the colder weather to ‘tune’ my month-old setup (yes, yes, I need serious help). The recent few days have produced cool-ish nights which have triggered heating but with my room temps maintaining around 21C, the heating’s not yet needed.
I have my system currently set-up for ‘pure’ weather compensation with no room influence, so it’s just outside temp, and my present 0.6 curve triggering the heating.
Clearly, the heat required is minimal so the heat pump ‘pulses’ the heat in 15-minute cycles every 1.5 hours or so. I don’t think this is classed as ‘cycling’ but I appreciate it looks that way. Ultimately, I suppose the heat pump is doing its job, reacting to the outside temp but it’s not necessary for the current conditions. Clearly I didn’t need heating so I looked at settings and found the ‘OT switch-off threshold’ set at 21C, so lowered it to 15C and inhibited the heating accordingly. I’ll have to experiment with this but can appreciate the controls were working correctly, but in these ‘cooler nights/warmer days’ where internal temps don’t change much, I don’t see much point in the system trying to supply very minimal heating.
Does the assembled brains-trust think it best to alter the ‘OT switchoff threshold’ or perhaps temporarily lower the curve even further? In the coldest weather I doubt the 0.6 curve will be sufficient (my design was for -2C outside / 45C flow so about 0.8). I don’t think setting minimum flow temps has much effect, but I’m happy to try. There may well be other Vaillant settings (VRC720) that I can use.
Cheers, Andy
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