Hi, newly installed 7kW unit, installed through OVO and HeatGeek in Northumberland. Happy with the install, at least as far as my limited knowledge gained from this forum and other sources, my only concerns are I’ve got an unreasonably high reported efficiency (temp probes?) and the limited data output. I’ve read through this and the Vaillant eBUSd threads and expect I’ll learn much more from you.
A shame. It seems to hurt itself by doing this - though I can appreciate it being needed in some cases. It seems vaillant could make an improvement to the algorithm to allow it to creep back up to desired temp when operating at lower heat outputs of total capacity. As it can eat up the energy integral allowance quite quickly with overshoot.
There might be some reason to why they’re doing it that way, related to getting the compressor going properly. If it’s any consolation, the gain in cycle length would be really low. Let’s take an example:
Here we have a single cycle at 16°C outdoor temperature with the typical overshoot. It lasts for around 23 minutes (13:31-13:54) and provides 2.6 kWh of heat. The steady-state power after the initial overshoot is 6300 W. So if we didn’t have that overshoot and instead had a constant 6300 W, that cycle would have lasted 2.6 kWh / (6300 W) = 24 minutes and 45 seconds. That’s less than a 2 minute extension of the cycle (<10%) - and that number is further reduced for lower outdoor temperatures as the overshoot takes up a smaller portion of the longer cycles when it’s colder.
COP is also only minimally impacted, if at all - so I think there’s really not a lot of potential for improvement.
Thanks for the detailed and considered reply, with that good information I’ll forget about this one (as you show it’s not really a deal), and find something else to mull and obsess over!
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Havenwise does a better job of choosing a lower target flow temp if required for me, rather than the Vaillant controller picking the default target flow temp off the WC tables.
And then it modulates the target flow temp during the cycle.
Might be worth looking into that?
Thanks that’s interesting, I guess havenwise has pretty deep control over how the machine is running. I can really see the benefit of this for installers and customers who don’t or won’t care about running it right.
Actually I am not sure its a curve or flow temp issue, just felt that if it hits desired flow temp quickly (by ramping power hard to get there) then it can overshoot, and with a powerful heatpump it can eat through the energy integral quickly.
I am not really interested in paying HW, actually very quickly I’ve been able to find a curve and ajustament of other settings that keeps the house at 21C all the time.
DHW.
Does a defrost show as DHW? I’m confused as my DHW is time constraint 1400-1600. However when looking at the app this morning I see it generated ‘dhw’ late last night - I doubt it did as the DHW tank temp is not high enough to reflect this.
Edit: it did add heat to the DHW tank as it’s 31.5C. I forgot my wife had a bath at around 8pm. It didn’t do a full cycle though as target is 53C and it’s at 31C and mains water is 12C here. But there should be no mechanism open by which it could have called for DHW at this time of day - is anyone aware of a setting which might have allowed it?
Anyone seen this?
Defrosts don’t show up at all in the Vaillant App, so that can’t be it. Are you sure your schedule is correctly set up for all days, maybe some extra time window slipped in for that day?
There is a DHW frost protection mechanism; if the DHW tank temp drops below a certain value, the ASHP will reheat briefly to bump it up to a ‘safe’ temp, regardless of DHW schedule/settings.
I’ve had this happen after kids having a bath along with it being cold outside.
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Thanks, this must be it then. Though it seems the limit is a bit high, especially given the tank is highly insulated and internal.
Do you remember where you saw the documentation on it, to understand what the rules are?
This document says something about 12C. Our mains water can arrive at less than that in winter, I guess evening baths might turn this protection on a lot. Which isn’t ideal with high electricity prices then. I need to see if I can turn it off or reduce the number lower.
Ah, I had suspected something like that. I wonder if it’s frost protection for the DHW (which would make little sense, as the cyliders are indoors), or if DHW is an emergency defrost energy source in case theres not enough energy in the heating loop.
it would be good if there was real documentation about it, then i could add into my hot water guide doc.
I’ve seen it mentioned anecdotally online a few times, and asked Vaillant about it at this year’s Installer Show… they confirmed it, but didn’t have an engineer on their booth who knew the specifics though.
I’ve only had this happen twice, when our entire 250-litre tank was fully depleted in the middle of winter, and likely completely filled with <10C mains water.
@Andre_K I’m pretty sure that there is no mechanism to use the DHW store as a defrost energy source. I’ve read plenty of accounts of Arotherms ending up in defrost death-spirals due to lack of space-heating water volume, without ever dipping into the DHW store.
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I have an email for someone at renewables UK. I have emailed them to see if they can help. They helped me before on another non related issue.
I doubt very much that there’s any way to modify the frost protection behaviour. There are certainly no related settings to change on the VWZ AI or Sensocomfort.
On the weird issues list.
The ASHP didn’t cycle on at a period of expect, so I went to look.
There was a long list of faults that made no sense and also it said heating compressor: blocked, anti cycle time: 63705, energy integral -180.
F703 low pressure sensor fault
F585 SF capac outlet temp
F529 SF builging circuit flow temp
F513 SF BC return temo
F73 water pressure
Has anyone seen this. I’ve had it twice now. Once yesterday and once today, a reset fixed it.
Yikes doesn’t sound good… https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/has-anyone-seen-this-problem-before-huge-anticycling-times/
Have these errors coincided with you monitoring via ebusd? Some on here were experiencing funky issues which turned out to be caused by polling the ebus too frequently…
No. This happened yesterday also. When ebusd wasn’t plugged in.
I was wondering last night if it’s just an air bubble going through the HP causing it to get all confused.
New Energy Stats article drop:
Vaillant Arotherm Performance Tables & Interactive Widget
So I’ve taken the Czech Gold Dust Tables PDF tables, thrown them at ChatGPT and had it create me a HTML widget where you can view them in tables and a wee little chart.
Hope this one is useful.
If you have any suggestions how this could be made better let me know.
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