Thoughts on commissioning a Vaillant Arotherm Plus 12kW

[sharpener]

  

Finally got my new HP installation up and running last Friday.

 

Some issues on the DHW side which I will write up in due course but this morning I tested the behaviour of the radiator circuits starting with all the rad valves fully open.

 

OAT 21.5C. Target flow temp 47.5C, actual 49 - 50C (but see below).

 

11 rads in circuit: Flow rate 1670 l/h (nominal/max is 2040). Power input 4.0 kW. Compressor modulation 75.5%. No flow through automatic bypass. Some tonality in the noise from the outdoor unit.

 

7 rads: Flow still 1651 l/h. Power input 3.0 kW. Compressor modulation 53.1%. No flow through automatic bypass. No tonality any more.

 

2 rads: Flow now 1333 l/h. Power input 1.6 kW. Compressor modulation 27.2%. Some flow through automatic bypass.

 

1 rad: Flow still 1400 l/h. Power input 1.4 kW. Compressor modulation 27.2%. Some flow through automatic bypass.

 

Actual flow temp on VWZ AI Appliance Interface is 50.5C but on the VR720 SensoComfort controller only 42C. Both use the same single sensor.

 

0 rads: Honeywell wireless TRV system no longer calls for heat, HP shuts down.

 

Conclusion: the system is well behaved. Interface with legacy Honeywell control is operating correctly, it will mainly be used to zone off unused rooms depending on occupancy. Normal operation will rely on the WC in the HP. There is also underfloor heating to most of the ground floor which will provide an additional base heating load.

 

Dynamic range of modulation is 2.8 to 1 in summer temperatures which is quite good, it gets better as OAT falls as per the chart below. (Max compressor current is turned down from 25A to 20 to match output limit of Victron battery inverter in EPS mode. However output is limited ATM by the OAT of 21.5C):

 

 

CoP varies a bit with output but reaches 3.7 at current OAT

 

[JamesPa]

Congratulations!  It's been quite a long journey for you I'm pleased that you have reached this milestone.

[sharpener]

20 hours ago, JamesPa said:

It's been quite a long journey for you

 

Yes, thank you for your help over many months and I am only sorry you are still enmeshed in the noise dispute with yr LAPD.

 

Have been experimenting with the vexed small HW coil a bit now.

 

 

You might think that this statement defines the actual flow temp but it doesn't. It appears to set a minimum. It seems the Vaillant HW strategy is to push energy into the tank as hard and fast as poss, which is resulting in flow temps of over 70C.This makes sense in the winter when you want the CH to have the min downtime.

 

In summer it means the HP works unnecessarily hard and you do not get the optimal CoP. The Eco setting gives 45.4% compressor mod. But from the Czech performance tables this still means at today's OAT there is 9kW min thermal o/p to be dissipated somehow. Eventually when tank reaches 48C it turns down to 40.8%, and it ends up at 36.3%.

 

It would be nice to have had that option from the start. Or 27.2% which is the min mod level it can and does achieve for CH.

 

Charging both HW cyl and TS in parallel this morning maintained the nominal flow rate of >2000 l/hr and resulted in somewhat better behaviour, but the final outcome was still 5.15kWh electrical input to top up tank after two showers, which is about the same as using the immersion heater. As it tells me I am achieving a CoP of >2.0 this means there is another 5kWh thermal going somewhere which I can't account for, other than the standing losses for the thermal store which themselves are 1.49kWh/day.

 

So I may just save the wear and tear on the HP and go back to using the solar diverter + immersion during the summer. Advantage is that it will adapt to whatever free PV is available whereas the HP will take what power it wants, from battery if necessary. A dummy anti-legionnaires cycle once a week should keep it from seizing up.

 

Still some other things to try and some snagging to get them back for.

[JohnMo]

4 minutes ago, sharpener said:

Vaillant HW strategy is to push energy into the tank as hard and fast as poss

You can change that setting, think there are three settings you can use

[JohnMo]

6 minutes ago, sharpener said:

5.15kWh electrical input to top up tank after two showers,

You may as well use the immersion 

[sharpener]

8 minutes ago, JohnMo said:

You can change that setting, think there are three settings you can use

 

Do you have more details? From the manual there are

• Eco mode: "Compressor output control that is as efficient as possible (longer cylinder charging time)"
• Normal mode: "Balanced control [!] (short cylinder charging time/maximum compressor output)"
• Balance: "Rapid charging for a cooled cylinder in combination with efficient re-charging by controlling the compressor speed" [IIRC it also says somewhere that Balance uses max compressor up to a certain tank temp then Eco for the rest]

So one of the first things I did was to select Eco mode. But as upthread, at summertime OAT this gives 9kW thermal output, which is too much and gives un-necessarily high flow temps and correspondingly low CoPs. It makes more sense for the small HPs, but the 12kW ought IMO to be capable of being turned down a lot further.

 

There is also an independent Noise Reduction mode which sets a maximum of 45.4% compressor speed, so the same (they are not compounded!).

 

29 minutes ago, JohnMo said:

You may as well use the immersion

 

Bingo!

 

36 minutes ago, sharpener said:

So I may just save the wear and tear on the HP and go back to using the solar diverter + immersion during the summer.

 

[JohnMo]

1 minute ago, sharpener said:

Do you have more details

I saw it on a heat geek video about heating DHW cylinder efficiently. They tell you most of the setting in Vaillant speak.

[JohnMo]

3 minutes ago, sharpener said:

There is also an independent Noise Reduction mode

There may also be a min hertz setting, as well as the noise setting. On my ASHP it derates everything down a %.

[sharpener]

1 hour ago, JohnMo said:

There may also be a min hertz setting, as well as the noise setting. On my ASHP it derates everything down a %.

 

No, AFAICS the only other thing is the max compressor current, for the 12kW the normal limit is 25A and I have turned mine down to the minimum setting of 20A so there is hopefully some capacity in my 4.4kVA battery inverter for other stuff.

 

1 hour ago, JohnMo said:

I saw it on a heat geek video about heating DHW cylinder efficiently. They tell you most of the setting in Vaillant speak.

 

You might have in mind this one https://www.youtube.com/watch?v=tAoRH_WEt78.

 

At 4'45" Adam is under the same misapprehension as I was, that Vaillant's target DHW plus their offset (he calls it "differential") is the actual flow temp. But as I have discovered in the last 48 hours it is nothing of the kind, it is a minimum.

The reason he gets a much better CoP than I do (>4 vs 2) is that he has a small HP and a big coil, I have the opposite.

 

The HP set to 50 with zero offset is producing hotter water than the immersion did set to 55 (which was more than adequate). Maybe something to do with relative positions of heat source and sensors, also I have now added a de-stratification pump.

 

I will revert to the immersion tomorrow and see what temp the HP thinks the tank is, to cross-calibrate. Then will turn down the HP setting to match, bearing in mind legionella (which we have not knowingly had any problem with).

[sharpener]

Some musings on the hydronics side of things.

 

Installers included a power flush in their scope of work. It didn't produce much in the way of discolouration or debris but good to have it confirmed. When I added 3 rads a few years ago I did a de-scale with Fernox DS-1 (citric acid based), followed by 3 flushes, neutraliser and inhibitor so I was pleased to see it had all stayed clean thereafter.

Flushing was done with treated rainwater (free) but the final fill was with mains water as it is slightly alkaline, so I was able to meter the volume, 348 litres which includes the 270 l thermal store. Slightly surprised that te rest including 11 rads was only 78 l but it is possible it was not completely drained to begin with.

I would have preferred glycol (see this thread) but the cost for 20% of 348l would have been prohibitive. I asked Hydratech for progress on their cheaper alternative to Fernox HP-5C (which has a min conc of only 10%) but didn't get any meaningful response. So went along with installers' plan to fit 2 x Intatec AFVs which they did neatly and in strict accordance with the MFIs.

 

To treat up to 375 l they then added 1.5 l of Adey MC1+ inhibitor and 1.5 l of MC11+ biocide which they have found necessary in the past. They then tested water samples from the HP itself and the extremities of the system. All three confirmed by the Adey app as OK for pH, corrosion and inhibitor level.

 

 

Finally when the M.D. came to inspect two weeks later I got him to open the Magnaclean up, there was a small amount of deposit collected by the magnet but nothing on the knitted s/s filter. I was amused to see it was just like an enormous kettle fur collector, and a surprisingly coarse mesh. However its primary function is to trap particles big enough to block the passages in the HX so presumably adequate for that.

 

All in all I felt they had done a very diligent job on all this. Some of the plant room lagging was a bit ragged but they left me some spare lengths and different rolls of tape for inside and outside which I have been using as and when. The pipework external to the house is however lagged with Armaflex inside 2x black plastic ducts so looks very neat. The sparky has done a good job too, and hidden the mains wiring in one and the l.v. in the other to keep them apart.

 

The mild weather has meant that so far we have had no real opportunity to put the heating system to the test. As upthread the HW side is still a bit of a puzzle, I will write up the results as a separate exercise, meanwhile ATM there is mostly enough sun for the immersion heater to cope from the free PV generation. NGED have finally agreed I can increase the battery inverter max power setting to 4.4kW, which gives us a chance of now running the HP at 60% of full output entirely on battery power. This will give us 9kW thermal output down to 0C while leaving 600W to spare for other loads.

 

 

 

Edited September 10 by sharpener

[m0deller]

Good explanation here on HW

 

https://energy-stats.uk/arotherm-plus-hot-water-modes/

 

I use ECO over the summer to maximise solar PV consumption

[sharpener]

On 16/09/2024 at 21:36, m0deller said:

Good explanation here on HW

 

https://energy-stats.uk/arotherm-plus-hot-water-modes/

 

I use ECO over the summer to maximise solar PV consumption

 

Yes but the output from the 12kW unit is so much that it would be highly desirable to be able to run the compressor at less than the 50% setting that Eco mode gives you. Then there would be less delta T across the coil and even better CoP. Have been in correspondence with Vaillant tech about this but they have not been able to suggest anything useful.

Just back from hol and will post some more analysis when I have crunched the figures a bit further.

[davidh72]

Just wondering if you have ever sorted the  'heat build pump auto' auto setting or the one below that which is the dhw build pump setting on the main controller. I presume if the pump is slower it will use less energy running for a longer time, be quieter and will also improve scop? Could be wrong but I just reduced mine which was at auto for the to 60%. The manual says default is 65%. Last year scop annual was 3.3 on a 250l valiant cylinder with the 10kw arotherm ASHP. 

 

I was happy with that but my heating was only 3.6 running at 40deg min and 45max. Found less than 40 upstairs bathroom just don't heat as I didn't lay enough ufh pipe when I built the house. 

 

Wonder if lower build pump and run for longer at lower temp would improve the scop for heating

[davidh72]

Meant changed not sorted! Using predictive text on a new phone keeps altering words. These settings are within the vwz controller

[sharpener]

10 hours ago, davidh72 said:

the one below that which is the dhw build pump setting on the main controller

 

Will try it. But I think the HW algorithm maximises flow temp as it tries to minimise the HW heatup time to avoid disrupting the heating schedule too much. So it might not help, and may actually make it worse (power = flow rate x dT and all that).

[sharpener]

So a lot has happened since my previous post!

 

• 3/10/24 Octopus' subcontractor fitted a smart meter in place of the obsolescent Radio Teleswitch E7 meter.
• 4/10/24 smart meter operational, and import tariff changed to Octopus Cosy
• 8/10/24 the DNO agreed to unlimited exports (installed PV 6.9kW nom) and an increase in the inverter rating to 4.4kW
• 17/10/24 smart meter exports now operational on Octopus Outgoing Fixed tariff (though Good Energy have yet to discontinue their deemed exports)

All this has enabled me to change the way I use the HP/battery system.

The house is long and thin and unless we have guests we only use specific rooms at specific times. In addition to the HP there is also an AGA in the kitchen/dining room where we spend much of the day if we are not out or in the garden. Bedroom is over the kitchen so requires only a little additional heat.

So the time schedule is now as follows (cheap windows in bold😞

0000 - 0400 Cosy tariff 24.71p/kWh - house runs from battery, HP off
0400 - 0700 12.11p - forced charging of battery from grid, HP charges 270 litre thermal store
0700 - 0900 24.71p - thermal store supplies bedroom and bathroom radiators
0700 - 1300 24.71p - PV surplus (if any) charges battery. HP available for UFH (only needed for hall and dining area in cold weather).
1300 - 1600 12.11p - forced charging of battery from PV or grid, HP charges the thermal store
1600 - 1900 35.82p - thermal store supplies sitting room radiators, HP off, house runs from battery.
1900 - 2200 24.71p - HP runs from battery to heat livng room (and bedroom and bathroom from 2130)
2200 - 2359 12.11p - forced charging of battery, HP runs from grid as necessary to heat bedroom until 2230.

The battery charging is under the control of the Victron inverter's Dynamic ESS algorithm (in its more agressive Trade Mode) which is still learning. But I am not yet convinced it is doing any better than the standard Scheduled Charging regime would achieve.

 

Apart from this I think the routine is now fairly settled, but optimising the DHW is still a voyage of discovery.

[sharpener]

Edit: Forgot to include this pic. It shows that today the Victron algorithm has decided the optimal state of charge is 83%, and achieved this during the first two cheap windows so it can export most of the solar which was predicted for the afternoon. Whereas yesterday the plateau was at only 40%, was it expecting there to be more sun so left more headroom but it failed to appear?

 

There's not a lot in it anyway as the round-trip efficiency is around 80% so the cost of charging at 12p is almost exactly the same as the extra PV gained at 15p. And that is before the depreciation which has been put in at a token 5p/kWh/cycle.

 

 

 

 

Edited October 23 by sharpener

[sharpener]

Finally made a discovery which might explain some of the anomalies on the HW side of things. Water was too hot to touch but temperature measurement was only 30-ish degrees.

 

The temperature sensor had been stuffed into some random hole about 2/3 of the way up the tank, I think it is a cable strain relief for the (unused) upper terminal cover. Not a thermostat pocket at any rate, see pic:

 

 

There was no thermal contact with the tank at all bc the springiness of the cable pulled it back out a bit.

 

Removing it from there and pushing it a short way under the insulation on the outlet pipe at the top of the tank caused the reading to jump from 32.5 to 40.5 and running off some hot water raised it to 42.

 

Explains a lot. Will now have to re-do all the tests I did to find the optimal way of running the HW.

 

The original plan as upthread was to configure the TS as a second HW tank but that didn't work bc (contrary to what Vaillant Tech said) if there are two cylinders they are fed one after the other not simultaneously. Because of this I have now added a switch so that charging the thermal store automatically feeds the coil in the cylinder in parallel. And then the HP isn't working on its HW cycle, so doesn't run up to 70C trying to force 12kW into the cyl (or even 6 in Eco mode).

 

Every day a school day.

 

 

Edited October 29 by sharpener

[sharpener]

So to wrap up what I have learnt on this project

 

What worked out OK:

• Hard to be sure yet but so far the house is as warm as when we had the oil boiler
• The installers did a good, tidy job and the Vaillant stuff is well engineered and quiet
• We didn't need to replace the awkward-to-get-at HW cylinder
• The thermal store (which cost about the same) works as designed to time-shift energy from when it is cheapest to when I want to use it
• Integration with the battery inverter system and the legacy controls (UFH stats/manifold and Honeywell wireless TRVs) went well and the existing 3-core and earth wiring was sufficient to carry all the control signals (including the temperature sensors) satisfactorily

What has not worked out so well and how we got round it:

• HW operation is not as Vaillant portray it, and in particular you cannot control the maximum flow temperature in HW mode
• The perforated baffle near the bottom of the Thermal Store separating the 45 litre volumiser section from the main body of the tank (225 litres) has too many holes in it so the entire tank rapidly heats up to the highest DHW flow temp
• Hence I have had to modify things to force the cylinder coil to operate in parallel with the thermal store charging circuit. So there are no separate HW statistics, and the temp for the thermal store has to be at least 45C irrespective of OAT.
• As a result the standing losses mean it will probably be cheaper to revert to using the immersion heater in summer
• HPs with inverter drives must not be fed via Type A or AC RCDs so it needed a Type B RCD in a separate CU
• The numerous Vaillant manuals are very difficult to read and although all the information is there somewhere it is pretty cryptic even once you find it.
• This BuildHub forum and the Vaillant Arotherm plus FB group have been invaluable sources of help.

A big thankyou to everyone who contributed to the success of the project, you know who you are!

[JamesPa]

1 hour ago, sharpener said:

HW operation is not as Vaillant portray it, and in particular you cannot control the maximum flow temperature in HW mode

Thanks for posting this and I'm pleased to hear it mostly went well.  Do you have any control at all over dhw.

 

1 hour ago, sharpener said:

HPs with inverter drives must not be fed via Type A or AC RCDs so it needed a Type B RCD in a separate C

Is that regulation or technical.  My electrician (not connected to the hp installers, a separate bit of prep) has just provided an MCB and no RCD because he couldn't find an RCD to fit my cu (which is an older model where some of the circuits are just on mcbs not RCDs) and didn't consider it worth upgrading or necessary to do so.  My suspicion is that he may strictly be right but perhaps I would have preferred an RCD in a separate cu for maximum safety.  

Edited October 31 by JamesPa

[sharpener]

44 minutes ago, JamesPa said:

Thanks for posting this and I'm pleased to hear it mostly went well.  Do you have any control at all over dhw.

 

Not directly. TS charging is set up as Circuit 3 and configured (at present) with OAT threshold 25C (or the mid-day boost stops in mild weather), slope 1.5 (largely random choice), min 45C to ensure HW sufficiently H enough, max 50C (achieved at about 5C OAT) to avoid scalding/inefficiency. DHW temp is set indirectly by all this. As an example during this last cheap period the bottom of TS got up to 47C (don't know why, it's meant to be the control variable), top 48, HW 43 with the sensor now on outlet pipe.

 

Now we need some cold weather so I can fine tune this kind of thing. Considered having TS charging as a Fixed Temperature circuit but discovered that these are not displayed in or controllable from the app, only Heating and DHW circuits.

 

Why do Vaillant have a Circuit 3 but separately some of its properties are listed under Zone 3, there is a 1:1 correspondence and I can change the name of the zone to "Charge TS" but Circuit 3 stays the same, silly or what?

 

Annoyingly although there was an update to the app recentlly to add WC details, even in its expert mode not only can you not set the max temp but even if you have set it on the SensoComfort it does not show up on the app. So on there it looks like the flow temp will be 58 at 0 OAT and 84(!) at -20.

 

55 minutes ago, JamesPa said:

Is that regulation or technical.  My electrician (not connected to the hp installers, a separate bit of prep) has just provided an MCB and no RCD because he couldn't find an RCD to fit my cu

 

Nearly came to blows with installer about all this. See this thread for a full explanation. He was technically correct in all respects but I felt wanting to ring Electrium to ask permission to put their Loadstar breaker in their Crabtree CU was a bit excessive. Electrium are not bringing compatible Type B breakers out until next spring, what do they expect customers to do? On a purist view you could never put third-party devices in any CU, what about contactors, timers, meters, light-level sensors even PLCs, no-one makes everything.

 

Fortunately they did not notice that the supply first goes through the battery inverter which is fed via the original 1995 Type AC 100mA RCD anyway. So in theory that might be blinded by a DC fault in the HP, however the Victron is stuffed full of protection of its own.

 

Solution was a separate 6-way Fusebox CU for the HP, I was surprised that Fusebox have a Type B as I have always regarded it as a cheapo brand, wouldn't have been my first choice. It is very clunky looking and the corner projects slightly into a (little-used) doorway. Eventually I might replace it with the small plastic Crabtree 4-way DIN-rail box I originally bought to match the other two I have on the panel. But it is quite a lot of work and I still haven't finished the paperwork the BI is demanding.

[JamesPa]

1 hour ago, sharpener said:

Nearly came to blows with installer about all this.

Interesting

 

The two candidate installers have both said that so long as mine has been signed off by an electrician they are happy.  However I can easily see that changing when they get on site if their electrician (assuming they bring one - I dont think there is now anything to do for which an electrician is mandatory, circuits are all in place its just a case of making a connection) looks into it in that much detail.    

Edited October 31 by JamesPa

[sharpener]

16 minutes ago, JamesPa said:

I dont think there is now anything to do for which an electrician is mandatory

 

What about all the 230V stuff, diverter valve, zone valves, connections to existing controls etc.

Did he put in a meter for the HP circuit, that can be quite instructive. Or a 13A socket for the internet interface box? Stupidly Vaillaint have neither incorporated this into the SensoComfort nor made it powered off the e-bus (though the Appliance Interface is so they can clearly do it).

 

BTW I recall you too were trying to avoid replacing the HW cylinder. Should be easier for you with a smaller HP. How has that worked out?

[marshian]

On 29/10/2024 at 18:45, sharpener said:

Finally made a discovery which might explain some of the anomalies on the HW side of things. Water was too hot to touch but temperature measurement was only 30-ish degrees.

 

The temperature sensor had been stuffed into some random hole about 2/3 of the way up the tank, I think it is a cable strain relief for the (unused) upper terminal cover. Not a thermostat pocket at any rate, see pic:

 

 

There was no thermal contact with the tank at all bc the springiness of the cable pulled it back out a bit.

 

Removing it from there and pushing it a short way under the insulation on the outlet pipe at the top of the tank caused the reading to jump from 32.5 to 40.5 and running off some hot water raised it to 42.

 

Explains a lot. Will now have to re-do all the tests I did to find the optimal way of running the HW.

 

The original plan as upthread was to configure the TS as a second HW tank but that didn't work bc (contrary to what Vaillant Tech said) if there are two cylinders they are fed one after the other not simultaneously. Because of this I have now added a switch so that charging the thermal store automatically feeds the coil in the cylinder in parallel. And then the HP isn't working on its HW cycle, so doesn't run up to 70C trying to force 12kW into the cyl (or even 6 in Eco mode).

 

Every day a school day.

 

 

 

That is a little poor (understatement)

 

PS thanks for sharing the journey

[JamesPa]

3 hours ago, sharpener said:

3 hours ago, sharpener said:

 

BTW I recall you too were trying to avoid replacing the HW cylinder. Should be easier for you with a smaller HP. How has that worked out?

I could have avoided replacing the DHW cylinder (one installer, still in the frame, was willing to work with existing), but I eventually decided to replace.  TBH I'm fed up of the two pumps I have to boost the DHW pressure (particularly galling since my mains pressure is about 9bar) and the mess of pipework in the airing cupboard, plus I finally found a do-able way for the D2 vent (which is the key issue).  So it will go UVC.  Still TBD whether its a 'Heat pump' UVC or a 'direct' UVC with a PHE on the side - that depends who wins the job which I'm (hopefully) sorting out with final questions at present.  

 

3 hours ago, sharpener said:

What about all the 230V stuff, diverter valve, zone valves, connections to existing controls etc.

I'm pretty sure plumbers connect these up if they choose to, and I'm pretty sure there is no regulation that says it has to be an electrician, its just connecting to an existing circuit via the 'wiring box'. 

 

But then again that's why I still think an electrician may turn up and disagree with the signed-off installation.  However if the installer has in fact budgeted for a day of electrician time, its not going to take more than a couple of hours to splice a small CU into the current circuit that my electrician was perfectly happy with, so its hardly a disaster if that does happen.   

 

3 hours ago, sharpener said:

Did he put in a meter for the HP circuit, that can be quite instructive. Or a 13A socket for the internet interface box? Stupidly Vaillaint have neither incorporated this into the SensoComfort nor made it powered off the e-bus (though the Appliance Interface is so they can clearly do it).

 

No (because I didn't ask him to) and No.  There is a switched fused spur and typical heating wiring where all the electronics will be, and the one installer that specified what he wants didn't specify any sockets, because he presumably reckoned he could connect to what was there.

 

That said, thanks for the tip-off, I might just put a double socket on the end of the fused spur before anyone turns up😀

 

its a wonder anyone ever gets a heat pump installed given how difficult the industry manages to make it.

 

 

 

 

 

Edited October 31 by JamesPa