Vaillant Arotherm Owners Thread

Fortune7 · 31 July 2023 09:37

Hi Mick,

Many thanks for the excellent analysis and commentary; it’s of massive interest to me having just had my Arotherm Plus 5kW heat pump fitted to my 1930’s house! Like you, my ‘low carbon’ journey has stepped through:

2014 Combi gas boiler with kitchen extension
Improved loft insulation
Improved windows and external doors
Loxone smart lighting to renovated rooms

2015 3.6kWP roof-top Solar PV
Hybrid petrol/EV with self-built OpenEVSE wall box for home charging

2017 OpenEnergy Monitoring (Saw most of my summer solar was being exported)
Octopus ‘Go’ tariff
Added Loxone wireless radiator valves for individual room temperature and boiler control

2018 Sunamp 6kWh heat battery to use excess solar via ‘Eddi’ diverter and cheaper overnight elec.

2022 Givenergy AC coupled 3kW inverter / 8.2kW battery

2023 Detailed DIY home heat loss calculation using Heat Engineer software and CIBSE guide
Suspended floor insulated using Q-Bot (robotic foam application)
Vaillant Arotherm Plus 5kW heatpump fitted, plus 2 radiators upgraded
OpenEnergy Monitor level 3 heat pump monitoring fitted

I’ve tried to follow (within reason) all the best practices that my old home will allow and it’ll be interesting to tune the heating through the winter. Like you, I plan a completely open system but will use my existing (Loxone) room control to limit max room temps. The Vaillant system will use advanced weather comp for heat pump control.

I had the Sunamp unit installed for DHW ‘storage’ as I don’t have convenient space for a cylinder. The downside for the heat pump is it apparently needs 70C water to charge it, despite the phase-change at 58C. My understanding is the heat input after the 58C point is largely ‘latent’ which needs the higher DT to make it happen. However, I’ll try dropping the DHW flow temp incrementally to see what I can get away with, but keen to get winter-time (low solar) DHW heating done within my 4 hour ‘Go’ window! Juggling with tariffs might open-up improvements.

I agree that it’s easy to get obsessed with COP (having just completed the Heat Geek Mastery etc. course online), but ultimately, comfort is key. The disadvantages of single living can be offset by my plan to start the cold-season with a falsely-low heat curve (0.6??), get as-good a balance of radiator temps as I can, then gradually raise the heat curve while shedding the extra 4th clothing layer. OK, probably too far!

The questions / issues / dilemmas I now face are:

Gotta get rid of my cooker gas hob and (never used) flueless gas fire, then the gas meter!
Now my home battery won’t be big enough to run the heat pump all day in winter - do I upsize the battery and (maybe) inverter, or tough-it-out until my next EV has Vehicle-To-Home?
Improving insulation is a good way to achieve lower flow temperatures (and COP) so I’ll do a second-round to see what’s possible. Maybe a ‘door-fan’ test to improve ventilation losses but not at the expense of air quality.

It’s like herding cats, this.

Again, thanks so much for your report and analysis - I’m sure it took a great deal of time to prepare. I’ve read it once; by the time I’ve read it another ten times I’ll have taken almost as much as I need to improve my knowledge, through your experience.

Cheers, Andy

Zarch · 31 July 2023 09:51

Proper reply to your details later, but a quicky.

Unless you’ve got unlimited funds (and space for batteries) this is always going to be a compromise.

As you saw from my article, my heat pump alone can consume 30kWh on the coldest days, then you’ve got general house stuff on top.
But in the summer you’re gonna use next to nothing when there’s tons of PV.

I think the sweetspot is somewhere around your normal summer daytime?
Could be 8kWh to 16kWh? Depending whether you wanna include DHW runs too?

Or even what you’d use during the shoulder months, including heat pump use?

I did this chart where I looked at ASHP only usage (kWh) depending on average outside temp.

Avg Outside	Elec In
-3	34.6
-2	31.7
-1	29.1
0	26.8
1	23.7
2	21
3	18.6
4	15.6
5	14.3
6	13.1
7	11.6
8	10.8
9	9.9
10	8.9
11	7.9
12	7.1
13	6.2
14	5.2
15	4.1
16	3.3

Once you get below 4C outside the heat pump usage really ramps up.

So enough battery to cover 7C and warmer (by filling batteries overnight and using solar) is a good place to be most days?

Fortune7 · 31 July 2023 09:58

Brilliant - thanks, Mick!

My plan is to monitor through the winter and ‘shoulder’ months and then assess next year for the battery. I agree that it’s pretty impossible to cover the heat pump + other loads during the coldest weather so your suggestion and ‘real’ data is very helpful. I know there are Octopus specific tariff offerings for heat pumps (Cozy?) but like all things, it’ll need careful analysis to balance it all out.

Thanks again, Andy

Zarch · 1 August 2023 08:25

I’ve written up a new article on my Energy Stats site.

All trying to explain about the Arotherm weather curves.
It was all a bit of a mystery to me initially and I put some of the early learnings stuff up at the top of this thread.

But thought it needed a more permanent and public home.

Hope you find it useful.
Any comments or corrections please let me know.

jamespa · 13 August 2023 08:48

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.

Robert.Wall · 14 August 2023 14:03

6 posts were merged into an existing topic: DHW storage and Legionella Risk

AndyS · 13 August 2023 08:56

@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?

jamespa · 13 August 2023 08:58

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.

Robert.Wall · 13 August 2023 10:43

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.]

Zarch · 14 August 2023 12:29

Right, here we go, a dedicated eBUS adapter thread to keep things from clogging up this more generic Arotherm thread.

tommyt · 14 August 2023 19:22

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

Zarch · 15 August 2023 07:45

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.

Zarch · 15 August 2023 07:57

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?

tommyt · 15 August 2023 09:34

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)

AndyS · 15 August 2023 20:43

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!

Zarch · 16 August 2023 07:51

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%.

tommyt · 30 August 2023 08:38

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

AndyS · 31 August 2023 19:44

@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!

tommyt · 31 August 2023 20:10

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!

AndyS · 31 August 2023 21:16

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?