Vaillant Arotherm Owners Thread

Before we start, we have to remind ourselves of the following

Heat Output = Specific heat capacity x flow rate (l/s) x (flow temperature - return temperature)

Specific heat capacity (SHC) of water is 4.2 and it’s 3.8 for Gylcol.

Flow Rate conversion m3/h to l/s = (m3h * 0.277)
Flow Rate conversion: l/hr to l/s = (l/hr / 3600)

So 860l/hr = 860 / 3600 = 0.238 l/s

3.8 x 0.238 x 5DT = 4.5kW

No if we go back to our ‘gold’ tech document, whilst it doesn’t list the 3.5kW model, it lists a 3kW one.
Which suggests that even that model can kick out between 4kW and 6kW of heat depending on outside temp and flow temp combinations.

During my hot water run, i’ve got my flow rate fixed at 550l/hr and I still output almost 8kW of heat cos my DT is around 10 on hot water runs.

So yes, I have much to play with there too.

But that makes me wondering why your installer has put a secondary pump in.
Is the cylinder a long way away from the outdoor unit? Are they trying to extend the distance?

Because as shown, you don’t need super high flow rates to get high output.

Do you track your flow and return temps? During heating and hot water?

VWL 35/6 (ASHP) and VIH QW 190/6 (uniTower) are the units. The ASHP has rated output of 3.4kW in UK spec sheets (as in Czech), and you are right it is the 3kW output curves in your golden find. My sloppyness stems from the 35 in the device name: sorry.

I mirrored your calcs yesterday but included density as it is not 1g/cc for a glycol mix, and got same (ish) results. Currently monitoring dT is a PITA as I only have the installer test outputs to go by. There is a limit to how often I’m going to push buttons during a heating cycle! At the end of a heating cycle dT is about 3C. I have ordered EmonTx4 which I hope will turn up soon so I can get the temperature monitoring sorted. It really bugs me that Vaillant don’t allow access to all this data via their access point!

I’m struggling to answer re the additional pump: I knew nothing about ASHP when the installer put it in and he was an experienced Mitsubihsi installer with all the right paperwork. However, this was the first Vaillant he had done (and it showed). I have been trying to learn about heat pump optimisation since then because I have never been happy with the install. Initial wiring and controller setup issues were sorted out by getting an accredited Vaillant ASHP installer in, but there are plenty more issues to deal with. System noise has always been one such issue, due to excessive flow rates through the emitters: it seems worse this heating season and, given the need to spend time at home with COVID, I’ve been digging further.

I don’t think there is any need for the second pump in order to get the flow rates @ dT5 I calculated to be necessary to meet the design loads in individual rooms. All loads are distributed via 20mm MCLP from a 10 way manifold which is 1m away from the internal unit (28mm copper). My ability to determine the total head loss across that lot is not there (yet?). However, at 860l/hr rated maximum, the ASHP pump has residual head of 5.7m, which the uniTower reduces by 0.6m in heating mode. This leaves a bunch of head for the rest of the system!

So I’m guessing that the installer played safe.

Once I can monitor the dT I am going to test with and without the additional pump. As it is in the flow, it may cause a big head loss if the impeller is not powered. If not needed, there is a great opportunity to replace with an 1-1/4" heat meter I guess!

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Perfect!!

Yeah, all the pipework sizing sounds more than adequate for the heat pump, which is a good sign.

I’ve played a lot with my install since it was put in, most of the changes driven by monitoring data.
I know a heat meter and associated kit is expensive, but i’m not sure how you could determine things are all working without it.

If you look at my data
https://emoncms.org/energystatsuk

You’ll see during heating that it hasn’t really hit DT5, same with Adam Heat Geek install.
It seems to prefer to max out the flow rate and squeeze the DT. Most of the time my DT is 2 or 3.

Perhaps when it’s -3 and it needs to output 5.5kW it might get closer to DT5?

I was worried about this DT2 / DT3 at first having read ‘heat pumps work at DT5’, but it doesn’t seem the case. Even Glyn and Trystans seem the same.

When you think about it, if you’re sticking with a fixed pump speed / flow rate, it’s only DT in the 'heat output = ’ equation that you can modify?

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:face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth: :face_with_hand_over_mouth: I’ll get my :tophat:

Your data is fascinating, for me at least! The power curve is all but identical in shape, cycle duration and cycle frequency to what I see. Not really what I would have expected in two different installs with differently rated units. My design load is only 1500w at -3C external. Do you know yours?

Is this the “default” 65%PWM pump setting? Looks very close. Will be interested to see what dT on the DHW cycle is here with 1186l/hr.

1.5kW at -3C? Almost passivhaus?

My heat loss survey was 5.4kW at -2.5C

You can read all about my design and how we sized it here:

and a shorter summary here:

I will be very interested to see the heat meter trace from the 3.5kW unit. Just to see ‘how low’ it can go, in terms of electric in and heat out.

The 3.5kW is the smallest unit on the market I think. but I have heard it’s just a downrated 5kW unit. The ‘golden’ doc suggests there isn’t much difference in the ‘floor’ of both 3kW and 5kW units. It’s more than that the smaller unit can’t reach as high.

Yeah, it’s on 65%
I had to leave it here as I had issues with my heat meter when I ramped the flow rate up.

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I have at last worked out what controls the Vaillant heat pump cycle timing; this may have been obvious to all but, just in case, here is my understanding in the hope it might help others. Thanks for contributors on What is Energy Integral - Air Source Heat Pumps (ASHP) - BuildHub.org.uk for the penny dropping moment, which I followed up with an hour watching the energy integral in Live Monitor on the Vaillant lcd and the pump power draw feed in Emoncms.

On the VWL35/6 at least, this is what happens:
Compressor starts at Energy integral of -60degmins (default setting, can be changed).

Every 30 seconds the difference:
(Flow temp) - (calculated target flow temp)
is calculated and added to the previous degmin value. So, if flow temp is 2C lower than target, -60degmin changes to -62degmin after 30secs.

The degmin value continues to get smaller (more negative) at an ever decreasing rate until the flow temp exceeds the target temp. At this point, the compressor modulates back to 25% (which appears a hard coded minimum) and, because the sign of the temperature difference has changed, the energy integral begins to increase.

Once the energy integral reaches 0degmin, the compressor goes into standby mode, with the energy integral continuing to drop every 30 secs.

Once the energy integral reaches -60degmin, the cycle starts again.

So the absolute value of the increment to the energy integral is clearly dependent on the balance between the rate of heat energy added by the compressor and the rate of heat loss in the emitter system. The balance of heat loss versus the modulated heat input controls how long the “on cycle” lasts, while the heat loss alone controls the length of the off cycle. Intuitively obvious once written!

Looks like the “heating start from” value may be an interesting tuning parameter, but that is a thought to follow up once my monitoring is more automated!

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@AndyS
Hi Andrew, I was using stock ebusd config files … which are auto loaded as ebusd discovers devices on the bus. A few weeks ago I decided to try and get the necessary feeds working to populate the emon ASHP application (I needed a live Yield value) and as a result now have the config files locally (using a modified GitHub branch from mwildbolz) .
Good luck with Vaillant - but I suspect the reason ebusd exists is because they wouldn’t make the data accessible

All data from emontx3 and ebusd. A wishful 30min CoP!

@modeller
Thanks Steve. When I eventually get an Adapter 3 I should like to call on your experience!
EEBus specification files are corrupt on download, so making no progress there either.

@AndyS yes, NP

Me too, we’ll perhaps create another thread for that? Unless you wanna create that now so insights can be shared?

I’m using EEBus from Loxone. Works but is fairly basic what you can do with it. The main issue I have is that it doesn’t support cooling.

Vaillant appeared to promise a Modbus gateway in a press release 18 months ago but nothing is available to the public yet. Although a Vaillant UK rep suggested they are using it in some instances in the U.K, but wouldn’t give me any further details.

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@dfeist: Many thanks for contributing this lead to Loxone. Looks like they have a reasonable product line, but at a cost. At least their solution allows for everything to be monitored and controlled within the local lan/wlan. The case example at https://www.loxone.com/enen/kb/eebus/ suggests that, as you say, there is very limited data exposed via EEBus, yet Vaillant suggest their SMA EEbus integration allows full optimisation. Seems a bit of a mismatch there, to me.

Not sure what this is, but what is available via Loxone is the same as what is shown on that page you linked to. When I first ordered AroTHERM I was working on the assumption that the “Modbus Gateway” that was announced in 2020 would be available at some point.

See: New control units for more convenience – A new gateway for more control

There is some sort of Modbus gateway being used in some installations, but I can’t get Vaillant to give me any information on this, and my installer has also been successful in getting any details.

See Mark’s comment here: Vaillant AroTHERM heat pump group uk | I control heating from my Loxone home automation system (using the internet gateway and EEBUS) | Facebook

I should probably give up asking/waiting for Vaillant to provide something and go down the ebus route, but I didn’t get on the waiting list for the ebus hardware yet.

When I was looking, there was a gshp solution from ISE  SMART CONNECT Modbus Vaillant - ise Individuelle Software und Elektronik GmbH . They also had a KNX + ebus adapter solution for older Vaillant controllers. Didn’t work with VR720 at the time.

Ebus adaptor 3 reservations are suggesting Q1 23 at the moment.

I’m sorry you are finding Vaillant difficult to deal with: this has been exactly my experience too. I can’t see any reason why Vaillant will not expose as much of their internal data as do their competitors. What have they got to hide I wonder :wink:

Amazing set of information, i have been looking for this for a while. I unfortunately don’t have independent heat monitoring on our 7kw arotherm. I do have independent electrical monitoring and can see Vaillant control unit under reposts by between 50 and 100w. so when i work out the COP i use my measurement of electricity consumption with Vaillants heat out put. have you compared the Vaillant’s claimed heat out put vs your open energy measurement? it would be really useful to know if their figures are of a meaningful accuracy.

Hello All,

I’m chancing my luck as a fellow Vaillant Arotherm owner as I’m having a nightmare that our installer is not able to troubleshoot.

Installation is an Arotherm Plus Monoblock 155/6. It was installed in the summer and has been working well ever since.

Two weeks ago, we had a power cut just after we left the house for the Christmas break. The neighbour restored the power, and within an hour of the power going back on I got an F.788 error through the Vaillant app. This indicates a problem with the high efficiency water pump for the heating circuit.

The installer took a look and said it had completely seized, and has done something to get it working again and the system is now displaying no error messages.

But the compressor will not start even when there are obvious calls for heat (13 degree house temperature, 15 degree domestic hot water cylinder).

He gave up for the evening and is going to have another go tomorrow. Is there anything obvious that could cause the compressor to not start. Is is possible that a day without power during the cold weather could kill it through frost?

Thanks for any suggestions. We go back in two days and are not relishing a house with no heating and hot water with our 3 year old kid.

I’m afraid i’m not technical to that extent regrading compressors.

All I do know is that there’s two ways of protecting the outdoor unit against frost.

  1. You have Glycol in your system, which acts like anti-freeze. So if the outdoor unit stops working, the working fluid won’t freeze. Things should hopefully start up again once power returns.

  2. Anti-Freeze valves on the outside pipe work at the lowest part of the run. You have these if you have only water in your system. In the event of the power going off, the valves drain before the water freezes. You would then need to refill the lost water in the system before switching the power back on.

Do you know which protection method the installer chose for you?

Alternatively, you could try the Arotherm Facebook page?

Thanks that’s very helpful. From looking at the manual Vaillant recommends glycol as the frost protection mechanism. I don’t know if the installers used this or just used water plus rust inhibiters. I would hope they followed the Vaillant recommendation which is repeated in several places with the warning ‘If you don’t do this there is no frost protection in the event of a power cut’.

Not sure if there are also anti-freeze valves that would have let water out. I’ll ask the installers to confirm.

I also don’t know what frost damage would look like. If the expansion of the water/ice has burst a pipe then there should be a leak now everything is above freezing. But is it possible that there is internal and invisible frost damage that could have killed components without causing a leak?

The installer is due back today to continue troubleshooting.