Vaillant Arotherm Owners Thread

[Fortune7 (Andy Silvester)]

I’m about to have my gas boiler swapped for a Vaillant Arotherm Plus 5kW ASHP and have been keenly absorbing as much info. here and elsewhere as I can. I’ll be adding the ‘level 3’ heat pump monitoring package to add to my existing Solar / Battery monitoring platform. I’ve agreed to my installer’s inclusion of a 45 litre buffer tank and, while I originally wanted to run an ‘open’ system, for my particular application I can see the sense in it, despite the extra complexity and (some) losses. To some questions:

1. Can I assume that the heat meter in the monitoring setup goes in the return pipework of the ‘house’ circuit rather than the heat pump side of the buffer? This way, if I can extract COP info. from the Vaillant’s integral controls (VRC720), I’ll expect it to be different than on the ‘house’ side of the buffer, as the flow temp. into the buffer will always exceed that of the outlet, if not by much.
2. Currently my existing radiators are controlled on a room-by-room basis from my Loxone miniserver and associated wireless radiator valves. With the ASHP, I propose to apply room set points a bit higher than required temperature (as upper temp limits), then let the Vaillant controls run the system purely on weather compensation and flow temp. I’ll need to tune this to achieve some night set back in the bedroom(s) but expect the Vaillant controls will do this. Bearing this in mind, does anyone have experience of post-ASHP installation and integration (or otherwise) of third-party room controls? Also, where do you generally locate the Vaillant ‘thermostat’ controller? I realise it’s wireless and can be moved, but (again, without experience) assume it’s placed in a ‘living’ space.

I’ll be adding my setup to the HeatpumpMonitor.org site as soon as possible and will continue to learn from others’ experiences here. Some other info. in case it’s useful:

1930s end-of-terrace 3 bed house with (early) cavity-foam insulation, 300mm loft insulation, Roof re-battened/tiled 2022 with TLX Gold quilted membrane (felt replacement). Lounge suspended floor foam-insulated 2023 with Q-Bot underfloor robot application - very effective and minimal disruption. Modern kitchen extension 2015. I live alone, so heating system tweaking can be done with impunity - unless visitors!

Radiators throughout, 2 replaced with ASHP install; others might need updating after monitoring system temps, COP and responsiveness. Heat loss calcs. including radiator sizing using Heat Engineer software. Overall heat loss around 45W/m2 from calcs and historic gas consumption. Last winter boiler range-rated to minimum (7kW) and run at 40-50 deg. flow temps which seemed acceptable.

Domestic hot water is provided by a 7kWh Sunamp ‘Thermino’ heat battery which will be fed from the ASHP as well as excess solar / off-peak grid top-up via MyEnergi ‘Eddi’ diverter. Sunamp was chosen as no convenient room for HW cylinder. I’ll be interested to see what the cost-difference is between charging the Sunamp with the ASHP (COP about 3??) or using 12p/kWh (Octopus GO) cheap rate 4 hrs overnight in winter. DHW load is covered May - Sept with excess solar.

3.5kWp rooftop solar and Givenergy 3kW inverter and 8.2 KwH attic-mounted battery.

EmonTX3 and EmonPi monitoring solar/home/divert etc.

[Zarch (Mick Wall)]

@Fortune7

I’ve agreed to my installer’s inclusion of a 45 litre buffer tank and, while I originally wanted to run an ‘open’ system, for my particular application I can see the sense in it, despite the extra complexity and (some) losses

Unless you need this for ‘separation’ (gycol in heat pump, water in rads for example). I really don’t know why they are putting this in?

You only need a minimum of 15 Litres volume in the system for the defrost cycle. That’s only a couple of open radiators.

I’d be very interested to hear the rational / design reasons for the buffer, especially as it looks to be £670? Are the suggesting glycol? And are you having extra pumps on the house side?

I’ve just got a full water install with anti freeze valves. Leaving rads open mean I don’t need a buffer!

Glycol, pumps and buffers cost money, affect COP and in most cases aren’t needed.

This will be my system going into this winter.

If my 1930’s semi doesn’t any ‘bumf’ I doubt yours does too?

@Fortune7

Can I assume that the heat meter in the monitoring setup goes in the return pipework of the ‘house’ circuit rather than the heat pump side of the buffer? This way, if I can extract COP info. from the Vaillant’s integral controls (VRC720), I’ll expect it to be different than on the ‘house’ side of the buffer, as the flow temp. into the buffer will always exceed that of the outlet, if not by much.

Most heat meters certainly go on the return (they can be configured on the flow, but better on the return).

But I think it needs to on the pipework back to the heat pump, after any buffer.

@Fortune7

Currently my existing radiators are controlled on a room-by-room basis from my Loxone miniserver and associated wireless radiator valves. With the ASHP, I propose to apply room set points a bit higher than required temperature (as upper temp limits), then let the Vaillant controls run the system purely on weather compensation and flow temp. I’ll need to tune this to achieve some night set back in the bedroom(s) but expect the Vaillant controls will do this. Bearing this in mind, does anyone have experience of post-ASHP installation and integration (or otherwise) of third-party room controls? Also, where do you generally locate the Vaillant ‘thermostat’ controller? I realise it’s wireless and can be moved, but (again, without experience) assume it’s placed in a ‘living’ space.

On pure WC, it doesn’t matter where the indoor controls go. It just uses the outside temp and the heat curve to choose the flow temp.

There are ‘room influence’ modes that you can choose. So you could use those and move the controller around. Probably best starting with WC and see how it goes.

I use Tado smart TRV to close bedroom rads off around 7pm. Tado only closes the rads and sends no on/off signals to the Vailllant.

You’re right. Run it on vaillant controls ALWAYS. Don’t be having any other controls interfering.

@Fortune7

Domestic hot water is provided by a 7kWh Sunamp ‘Thermino’ heat battery which will be fed from the ASHP as well as excess solar / off-peak grid top-up via MyEnergi ‘Eddi’ diverter. Sunamp was chosen as no convenient room for HW cylinder. I’ll be interested to see what the cost-difference is between charging the Sunamp with the ASHP (COP about 3??) or using 12p/kWh (Octopus GO) cheap rate 4 hrs overnight in winter. DHW load is covered May - Sept with excess solar.

What temp do you have to get the water to, to charge the Thermino? Earlier Sunamp models needed very hot water? Either way, shouldn’t be an issue with the Vaillant. For a laugh I chucked the target temp upto 65/70 and it worked fine. Although the COP took a bit of a hit!!

Hope some of that helps.

[Fortune7 (Andy Silvester)]

Hi Mick,

Yes, that’s all very helpful - thanks.

@Zarch

I’d be very interested to hear the rational / design reasons for the buffer, especially as it looks to be £670? Are the suggesting glycol? And are you having extra pumps on the house side?

Like you, I resisted having a buffer (i.e. a 45-litre low-loss-header - there’s no physical separation of primary and secondary fluids), but the installer’s view is that, for systems with radiators which will (probably) be turned down or off, the buffer will help to prevent the heatpump cycling on low-load conditions, i.e when heat loss is lower. I appreciate the heatpump will probably modulate down to around 2kW, but I see the point you make; theoretically I don’t need it if the system is ‘open’. Also, I live alone, and while I’m keen on keeping the system ‘open’ as much as poss, there’s really little point in heating un-used rooms, so the effective system volume will reduce. I also accept that adjacent rooms will lose heat to these unheated spaces, and I’m happy to experiment with rads on/off/setback to see the effect on COP and overall comfort / responsiveness. I also have a couple of ‘uninhabited’ spaces which have rads. and need to be heated to anti-condensation levels, one’s a utility room and the other a small engineering workshop with expensive machines to keep rust-free! These 2 spaces will be heated to around 10 deg. C., so the existing emitters will be throttled. Finally on this point, I purposely didn’t change all the rads. to match my heat loss calcs, which I think despite being carefully calculated, use CIBSE and other industry standard factors which tend to over-estimate the end result. I’m looking at my metered annual gas usage and making a judgement between actual consumption and heat loss calcs. Overall, I’m seeing the inclusion of a buffer as possibly frivolous (!) but I want to monitor the system closely to prove its worth, or otherwise. Later, if I can bypass it and lose the secondary pump too (yes it needs one with a buffer/LLH), I’ll do so with more confidence. Happy to discuss further! I note that the Vaillant heatpump controls both modulating pumps (primary and secondary) so I’m confident the two will play together well. The installer originally included for gycol, but I soon got him off that in favour of antifreeze valves!

@Zarch

But I think it needs to on the pipework back to the heat pump, after any buffer.

Thanks - seems sensible.

@Zarch

What temp do you have to get the water to, to charge the Thermino? Earlier Sunamp models needed very hot water? Either way, shouldn’t be an issue with the Vaillant. For a laugh I chucked the target temp upto 65/70 and it worked fine. Although the COP took a bit of a hit!!

Apparently, the heatpump needs to produce a flow temp of around 70C for the Thermino; I queried this on the basis of the ‘58C temperature for phase-change’ but of course the material takes more energy as it changes state without temperature change, so the higher DT is necessary to force that input. Either way, on my setup I see the heatpump as a secondary heat source for DHW, with the excess solar being primary and in the winter as I said before, I’ll experiment with the costs and relative efficiencies of using off-peak (e.g. Octopus Go) electricity which is 100% efficient compared with the cost/efficiency of the heatpump banging away at 70C+

Thanks again - very helpful feedback!

Cheers, Andy

[Zarch (Mick Wall)]

@Fortune7

Like you, I resisted having a buffer (i.e. a 45-litre low-loss-header - there’s no physical separation of primary and secondary fluids), but the installer’s view is that, for systems with radiators which will (probably) be turned down or off, the buffer will help to prevent the heatpump cycling on low-load conditions, i.e when heat loss is lower. I appreciate the heatpump will probably modulate down to around 2kW, but I see the point you make; theoretically I don’t need it if the system is ‘open’

Lowest I can get mine to steady state is around 450W in and 2220W out, so around 4.8 COP

Anything above 8C outside and mine starts cycling. But cycling isn’t bad in this instance, it’s just I can’t shed 2.2kW of heat in the house when it starts to warm outside.

Your usage may vary.

Extra pumps take electric (hurts COP).

Turning bedroom rads off at night makes sense, like I do.
But there will still be lots of volume in the system to heat.

Surely better to open some of these available rads and heat those than heating a £700 vessel of water?

The heat pump is gonna have to work to heat 45L of water in the buffer, so why not heat the water in the rads instead? 45L is more than half my total house volume.

The other way to consider, which is something i’ve seen is to just stick the buffer on the return and it be just a volumiser. So lose the secondary pump and it provide just a whopping amount of additional volume to your system. Ie, more open space to work in.

Either way, it will be interesting to see the outcome.

[Fortune7 (Andy Silvester)]

@Zarch

Lowest I can get mine to steady state is around 450W in and 2220W out, so around 4.8 COP

That’s impressive!

@Zarch

The other way to consider, which is something i’ve seen is to just stick the buffer on the return and it be just a volumiser. So lose the secondary pump and it provide just a whopping amount of additional volume to your system. Ie, more open space to work in.

Good idea - I’ll certainly look into that; thanks!

@Zarch

Either way, it will be interesting to see the outcome.

Agreed - I’ll try to report some objective results after the winter. Thanks again!

Cheers, Andy

[BristolJoe (Joe Wentworth)]

Hi Arotherm owners.

I saw the video by Glyn here Air Source Heat Pump 1st Winter Performance Update - YouTube

Really interesting look at a samsung instal.

A point that stood out to me was minimum flow temp. My arotherm is set to 20 degrees.

The theory goes lowest temp possible will give best COP. But in the real world i can see there could well be COP peak that falls above the minimum achievable flow temp. As Glyn found.

Do any arotherm owners have and experience of the most efficent min flow temprature to use?

Interested to hear your thoughts.

[Zarch (Mick Wall)]

@BristolJoe

Do any arotherm owners have and experience of the most efficent min flow temprature to use?

Hi Joe,

@glyn.hudson and I have been having some conversations about this.

Obviously, the lowest possible flow rate is very much dependant on the curve setting.
What are you set at?

The ‘lowest’ option in the sensocomfort (ie 20C in your case) may never get that low if the curve is higher.
Look at the top of this thread for curve charts.

Here’s the chat Glyn and I were having where he observed my unit cycling at 30C whilst not at 33C flow. All controlled by weather comp and the curve.

Here’s my daily monitoring stats: Emoncms - app view dashboard

My argument in this example is that the outside temp rises from 3C to 10C in the space of 2 hours.
The house when 10C outside cannot shift the minimum 2kW output when it gets that warm outside.

I’ve observed the tipping point to be about 7/8C outside when it starts cycling. Remember, some cycling is fine and in warmer weather it has to.

[Zarch (Mick Wall)]

For any anyone interested, i’ve published a very detailed write up with stats, cop and observations about my first winter with my 5kW Arotherm.

First winter with my air source heat pump - Energy Stats UK

Hope folk find this useful and/or interesting.

[BristolJoe (Joe Wentworth)]

Hi @Zarch
Thanks for your extensive response. I have been running at 0.4 weather compensation curve. So there is potential to be in the bottom temprature zone during 5 to 15 out door temps…

It is interesting that you point out that we are rarely at a steady state.

I apreciate cycling is necessary. I just wonder if the peak COP is at say 33 degree flow. Would a 15 min burst at this more efficient and higher output with a longer standby be more efficent than a longer less efficient on time and a shorter standy time. If it has to cycle it feels the longer the lull time the better, presuming that is not at the expense of a lower efficency during the heating phase .

I guess instantaious cops from real instals probably dificult to read meaningfully. Unless there are good periods of stable tempratures. And try different flow temps.

What would be great would be a lab graph like those at the start of the thread of cop vs flow temp to see if there is a low point in the graph.

[Fortune7 (Andy Silvester)]

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:

1. Gotta get rid of my cooker gas hob and (never used) flueless gas fire, then the gas meter!

2. 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?

3. 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 (Mick Wall)]

@Fortune7

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?

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 (Andy Silvester)]

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 (Mick Wall)]

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.

Vaillant Arotherm Weather Curve Information - Energy Stats UK

[jamespa (James Parker)]

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.

[AndyS (Andrew Sims)]

@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 (James Parker)]

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]

@jamespa

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.]

[Zarch (Mick Wall)]

@AndyS

@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?

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

eBUS hardware adapter (and ebusd software) Thread

This thread is talk about the eBUS adapter and ebusd software used to talk to eBUS enabled heating systems. This is primarily Vaillant heat pumps and combi boilers. But Atag boilers also allow connectivity. You can purchase the hardware adapter from here (it ships from Germany) https://ebusd.eu/myadapter/ With documentation to the latest software here:

[tommyt (Tom Thomas)]

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