Can I just check / ask
Is the way to reduce the internal water temperature by reducing the heat curve value ?
I am currently installing external wall insulation (EWI) and there is a huge difference in the heat retention. I am down to 0.30 now and still have lots of cycling, so I’ve just reduced it further to 0.20
I have a 5kW unit
Yes it is
But on shoulder periods it’s common to have more cycling.
Perhaps you have the energy integral issue
Very likely the shoulder months. But the addition of the insulation is looking hugely beneficial. I’ve added 100mm
I saw this question the other day and I’ve always wanted to write an article on the subject of cycling. So this, coupled with a similar post elsewhere it was just the kick I needed to make it.
So here it is “Heat Pump Cycling and Minimum Modulation”
Hope it makes sense. There’s some examples and charts for all the various Arotherm models, but the same principles apply to all heat pumps.
Any questions or feedback (typos) please let me know.
And for info, I’ve been recently going through and updating some of the Arotherm guides.
The following sections have had big refreshes this past week.
Another older article has had a refresh on the site. 
I have the same unit, which in my case is freestanding on the ground next to the kitchen wall, and it is very quiet. Running at low power, the compressor could easily be described as silent; even when operating at full capacity, it’s not much more than a domestic fridge. You do get some fan noise at high speeds, such as during a hot water run, but it’s not audible in the house.
There are settings on the heat pump, like ECO mode, that reduce even those low noise levels.
Vibration levels are very low, probably not enough to vibrate a solid brick wall, especially if you have a good anti-vibration mount.
The air brick that ventilates the downstairs room is probably a hangover from when they had a gas fire. A gas fire needs a very good air supply, hence the ventilator. If they no longer have the gas fire, it’s probably now surplus to requirements and a source of unwanted draughts.
The refrigerant in a modern heat pump is a flammable gas, so there are regulations regarding the distance between the heat pump and a window or ventilator, in case of a refrigerant leak.
Hi guys
I’m not getting great COPs on DHW.
I strongly suspect its because the flow temperature is getting very hot; upto around 75C. Is this a typical system temperature when charging DHW? A quick look at heat pump monitor shows DHW charge temperatures in the mid 40s or 50s, but not mid 70s
Has anyone had this issue?
3.5kW Arotherm R290
Vaillant cylinder; 150 litre
DHW set point 48C
DHW mode Eco
Hysterisis 3K
Offset 5K
3 hour window scheduled; although it only heats water for 1hour, 1hr 30 max.
The temperature sensor sits between the flow & return ports for the coil, so the top of the cylinder will be hotter than the set point. But 30K hotter? seems mad.
When swapping between DHW & HTG, the 3 port valve lever doesn’t seem to move from ‘Auto’; should it move?
I was getting heat bypass into the heating manifolds when in DHW mode, so I asked the installer to look at it, he said it was fine. So the 3PV is possibly the cause, but unlikely. (We also put in a non return valve to prevent short circuit into htg circuit.)
Could be an undersized coil but its a vaillant cylinder.
Could be constrained flow rate on DHW branch?
Grateful for any pointers.
Hi,
Its sounds like the tempreture sensor is not making proper contact with the tank?
R.
The miniscule difference between your flow and return temperatures (maybe 1degC?) suggests to me that you have poor heat transfer between the circulating fluid and the tank contents. If the tank coil is large enough (normal recommendation is 1.0 - 1.5m2 per 5kW heat pump nameplate duty) then it may have become fouled. (If you live in a hard water area, then regular heating to 70degC or more could induce calcium deposits to form on the coil outer surface, so reducing the heat transfer coefficient.)
What flow rate are you getting?
What DHW pump speed are you set at (auto or a %)
Is this trace coming from a heat meter?
Can you provide the emoncms url so we can look at the data
Standout issue for me (as well as the tight DT) is that the starting flow is showing ~50C, rising to 70+C.
So you’re never going to get the good COP early in the hot water run where the incoming cold is around 15C this time of the year.
PS. you need to be careful with Eco mode, especially on a lowly 3.5kW unit. It will take a LONG time to re-heat as the heat output is so low.
Below a plot with flow rate; upto about 1.2 m3/hr. I think that’s quite good, right?
I don’t know how to read DHW pump speed
This trace is from Emoncms heat meter; can you open this link? HeatpumpMonitor.org
The starting temperature must be whatever temp the cylinder drops to after a day of use, which varies. I wonder if its just topping up the top half of the cylinder to ~70C each day, i draw that down to about 35-50C over the day, then it tops up again.
I just measured the DHW at the tap its 52C; system says cylinder temp is 46C. Today weve had a bath and a little washing up. I’ll repeat this after the next DHW charge.
What governs the flow T? why woudl it go to 70C- it must think its struggling to achieve teh set point - as Arbie noted maybe cylinder temp sensor is not properly connected (it looks fine from a visual inspection).
Eco mode - OK, thanks for the article. it seems to run for no longer than 1hr20m. No issue with cold house its well insulated.
Please do take a look at my data feed and give me your thoughts.
Cylinder temp sensor. Ive stuffed it in further. The wiring has a junction on it but that shouldn’t cause an issue, right?
I suggest dropping the pump speed to try and achieve closer DT5 than DT2 that you’re seeing now.
VZW AI controller, double press both buttons, installer menu (code 17), then look for DHW build conf or something like that.
Options are Auto or any manual setting between 50% and 100%
By dropping the flow rate, the DT will open up (mass flow calc: DT x flow rate x SHC = heat output)
Although I still think the bad COP is cos you’re heating water from 40C to 65C.
Maybe you’re just doing little top-up reheats? Increase the hystereris? 3K means you’re only dropping 3C before it kicks in to re-heat.
Why is it going to 70C?
Have you got legionella scheduled everyday?
Something must be overriding the 48C target you’ve got set.
Thanks, I’ll adjust the pump speed. But as you say it’s still going to 70c
You might be onto something with the little top ups. I reheat cylinder daily.
I will change schedule to 3x a week and see if that helps. It will still try to get to 70c though at the end of every run.
Legionnaire run is only 1/week.
It’s not hysteresis I’ve played with that already.
Yes something must be overriding but I don’t know what.
Hi all, currently having a 15kw plus installed. I live in the Pyrenees and design temp is -7C. No UFU, just pipe and radiators in a big stone house. Having a volumiser (100L) installed (help with defrost cycles) and all open system - hoping the machine pump is enough.
Looking forward to getting it commissioned and trying to get it running well. I will likely try havenwise, if I can integrate their app with online spot prices (electricity is set price by government and cheap).
This place is a great resource, thank you!
Ok we’ve made some progress.
Off Arbie’s comment I stuffed the sensor deeper into the sensor pocket. That’s shaved 20k off the final flow temperature!
or hot
Great! Vaillant’s DHW mode is more or less dumb - they run at a fixed power level determined by the mode (Eco or Normal) until either the DHW target is met or the flow temperature reaches the heatpump’s max value at around 70°C. The charging offset value is ignored and there is no control mechanism to somehow bind flow temperature to current tank temperature.
Thanks André useful to know the control. This is exactly what we were seeing, the sensor wasn’t reading cylinder temp hence it was ramping up until it hit max.
Hi all. I’m interested in monitoring my vaillant 15kw. Please can someone point me to a guide/article explaining my options and what id need - the lower the hardware cost the better.
Thanks
