. It is reproducable, on the basis that ebusd gives relative pressures, add 1 bar to get absolute pressure.
a different working point is: compressor inlet 5.7C/4.6 bar, compressor outlet 33.2 C/10.3Bar, Condensor outlet 31.4C, EEV outlet 10.9 C, Air intake temp 7.3C.
low relative pressure of 4.6 bar, 5.6 absolute, should give 6-7C boiling temperature, which could be consistent with compressor inlet and air intake temperatures. However, I do not understand the EEV outlet temperature to be so high. After expansion it would be impossible to have a temperature above boiling temperature I would think.
I hope somebody knows what I am missing, should the EEV outlet temperature not be lower?
For sure the EEV outlet will be mixed phase, as you show on your PH diagram. I’d expect the pressure drop in the evaporator to be only a fraction of a bar (not the ~2bar suggested by the EEV outlet temperature), so at least one of your instruments (compressor suction pressure and/or EEV outlet temperature) must be misreading (or else there’s something in your R290 that’s affecting its vapour pressure, like oil carryover if your compressor is continuously lubricated).
One word of caution when analysing the refrigerant circuit - the evaporator exit (i.e. compressor suction) may be superheated by a few degC, so you can’t guarantee that it will lie on the saturation curve on the PH diagram.
In this very mild weather my newly installed 7kW Vaillant is cycling, not surprisingly. Its a straightforward system, no buffer, phe etc, just heat pump to diverter valve to rads/cylinder.
There are two features of the behaviour I wasn’t expecting:
The off times of the cycles are very long, often more than an hour, its almost like the heat pump waiting until the room starts to cool.
When it ‘starts up’ after a cycle it seems to run at max compressor speed for several mins before calming down.
The latter in particular is a bit annoying as it gets noisy at this point. I have enabled quiet mode to cap the compressor speed for now, but since it doesnt need to run at full speed in these conditions, that seems a bit silly.
Do others experience either or both of these behaviours?
Your symptoms sound similar to those I would expect with one of the controller settings available on Samsung controllers. I can elect to switch the compressor on and off only from the roomstat (though LWT is maintained if possible through speed control according to the weather compensator target).
Under this option, after startup the compressor runs at full speed until the weather compensator target is approached, then successively reduces speed to minimum and sits there (minimum speed) until the roomstat is satisfied, when the compressor switches off. Once the roomstat hysteresis has occurred (which could easily be an hour later), the compressor starts again and the cycle is repeated, with the compressor at full speed initially.
You will almost certainly have the option to start and stop your compressor if either weather compensation target or roomstat are satisfied.
Vaillant have a fair few options but sone of them arent entirety transparent in terms of what they do. I may try their tech support and, armed with your observation, will also read the manual again.
I fear there’s not really a way around the initial high-power ramp-up period, at least for me it happens with full silent mode as well. The controller wants to reach the target temperature as quickly as possible and then ramps down to keep the steady state, if possible, or it starts to cycle. This initial period is not even full power typically.
Regarding the timing of the cycles, check what was written about the energy integral settings on the forum. If the cycles are too long and confort suffers, you can drop the compressor start heating setting down to -30°min, which will give you shorter cycles.
Thanks. The manual does refer but its not obvious what it means. Combining whats been written here and the discussion of energy integral on buildhub, I think its now clear. I just need to check my firmware version to see if I have the bug (not currently at home!)
The problem of over-long cycling (>1 hr and the house noticeably cools) seems to have persisted. I just checked my ‘Software Version’ in the appliance interface and its reading 301.02.02. Is this the same software as the ‘firmware version’ about which a bug was discussed, in which case mine appears to be even earlier than the buggy one (even though its a supposedly new pump).
The reported energy integral is -146 degree minutes, and the heat pump hasn’t turned back on. The target energy integral was set to the default -60mins.
Can anyone give me some pointers. My installer is back on friday and I would like to have some information if anyone can help.
Is the firmware field updatable?
Any information would be welcome thanks. This is a detail about the heat pump I havent yet understood.
I have a problem that my SensoComfort shows the expected target flow temperature related to the outside temperature but Interface unit (VWZ) has a higher target temperature (which is what is being driven to).
The discrepancy between the two temperatures changes and can be anything from 3°C to 9°C. To compensate for this error I run with an unrealistic low heat curve of 0.35.
I have looked at my VWZ and it has the VF1 connected, with the temperature monitoring probe installed on the Flow pipework nearby (I have no buffer tank).
I am reticent to disconnect the VF1 because I’m not sure what consequences there may be from this. Hence I’m seeking a Vaillant advice note.
I had a similar problem with too low energy integral values once when playing with some setting I can’t for the life of me remember now. I think it could have been the pump speed that I set to the lowest value (50%?) instead of Auto which caused it to not properly start as the EnergyIntegral reached the target. It’s worth a shot to look at the setting I think.
You can’t update the firmware unfortunately, only way to do that is to get a PCB exchanged. The device will show multiple version numbers of different subcomponents - did you look through the whole list?
Zero consequences other than it will start working as expected! I’ve not seen anything written down from Vaillant, but it is supposedly no longer used in their updated schematics and if you call them they will confirm this. If you don’t like how it behaves (correctly) with the sensor disconnected, it’s just a case of reconnecting it anyway! Hit the reset button on the controller after disconnecting/reconnecting, and ignore the missing sensor warning for a couple of days until it goes away.
When I was retesting, I accidentally turned the knob for setting the gas boiler flow water temperature, and it started up. It reacted to the knob even when I set the bivalence or Trivai back to values that reactivated the heat pump heating mode, the heating mode on generator 2 remained active, which meant that I could run the 2 together…
So I tried again, changing the tariff so that TriVAI was under 1, generator 1 (heat pump) went to standby, generator 2 to heating mode, and although the knob was at minimum, it finally started S 1 > 2 > 3 > 4 to rise to the temperature required by the heating curve.
Thanks for this Daniel.
I pulled the VF1 probe and the discrepancy between the Sensocomfort and Interface target temperatures has disappeared (as you predicted it would).
I can now control the ASHP as per manual rather than having to introduce a bodge (which I have been for the last year). Also hopefully I can get a bit closer control.
Grateful for your shared knowledge.
Does anyone have any experience with adjusting the hysteresis value of the compressor of the arotherm heat pump? The default is 7K. I assume this works the same as with DHW: The higher the hysteresis, the longer the pump will wait to fire, potentially leading to less cycling, longer but fewer runs. Is this assumption correct? Or am I mistaken? Any experience of the impact on COP if you switch from 7 to 10 for example?
Second question:
My plumber installed a 10KW Arotherm during the installation in winter 2022. After using the pump for 1 winter and spring and going into the second winter now, it appears this pump is way too powerful for our needs. Are there any tweaks to make the pump behave more like a 5 or 7 KW version?
For example, I see in my Ebusd sensors something that is called Compressor modulation type which has the possible values “hard” or “soft”. I can’t find a setting on the display of the unit that matches this and also can’t find anything in the (Dutch) manual. Any idea what this setting does and which setting is adviced?
Welcome to the forum. We’re in exactly the same boat - I also have an oversized 10 kW Vaillant unit.
The hysteresis value for heating is a secondary mechanism. Normally, cycling is managed with the Compr. Start Heating and associated Energy Integral setting. If you reduce this value (say from -60°min to -100°min), you’ll get less cycling and longer cycles at the expense of potentially stronger indoor temperature swings. COP is barely affected by this setting, though I have the impression that the higher values (-30°min) have worse COP. There are lots of posts on the forum regarding the energy integral, e.g. here or here.
Normally, this mechanism will start/shut down a cycle before the default hysteresis kicks in. If you’re aiming for the longest cycles possible, set the Compr. Start Heating to -100°min and hysteresis to 10K to be safe, but even 7 should not have an impact.
Apart from that there’s nothing you can really do to tame an oversized unit. If you go through my post history you’ll find a number of posts with more background on this. I haven’t looked at those compressor modulation settings you mention, but my heat pump never goes above the minimum modulation anyways, except from a few minutes at the beginning of a cycle. We just have to live with it and be happy that the Vaillant heat pumps have a relatively smart way to prevent short cycling.
I’ve been scratching my head about this too. You would have to insert some kind of manual control element. For example, as a cycle begins, the target flow temperature should be adjusted down and then gradually raised along with the flow temperature until the desired value is reached. My reasoning why this might work is that we only see higher power when the current flow temperature is far from the target, so gradually increasing the target would keep the compressor in its lowest state. This is all speculation but should be somewhat easily testable once I find the time.
I have done this approach with a Mitsubishi heatpump, and it does kinda work okay. Walk the target flow temperature up gradually, at some offset above return temperature to get a desired dT. See this post for summary.
Quiet mode might be another option to try, which might limit the power at the start of each cycle, with less interfering with the controller.
