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