The eddi sensors seem to be a little inaccurate reporting higher than the actual temperature. I didn’t realise until we had the Vaillant installed and tested them in different cylinder pockets and against ambient temperature. They are two wire PT1000 sensors I bought from Amazon.
I will check the Vaillant sensor, thanks for the suggestion. I am happy for the Vaillant sensor to be lower down the tank and targeting a lower temperature.
Tank just has a slightly larger coil, a relatively low immersion and slightly thicker insulation than the standard spec.
First overnight DHW cycle since adjusting the offset to 2K (as our eddi’s been keeping it hot).
The Vaillant tank temp readings are a little less jumpy than the previous graph I shared but there’s still the curious plateau around half-way through.
The flow temp still peaked at almost 60C though which suggests, as others have previously mentioned, that the offset isn’t doing what we would wish.
Sort of related to the previous post, does anyone know what the setting: ‘Conf. DHW build.pump’ actually does?
I have an issue in that, when the hot water heating cycle ends, the 2-port value switches to the heating circuit and the pumps overuns for a few minutes (even though the heating is off) which causes a hot bolus of water to hit the radiators sometimes causing a lot of noise. Well at night it seems noisy. This isn’t helped by the fact that my HW offset value is ignored and the water gets to around 62 C.
The ‘Conf. DHW build.pump’ value was set to 100. Last night I changed this to the factory setting of 65 and there was no pump overrun at all. I’m going to see if this is reproducible, but I’m a little unclear as to what this setting actually does. I thought it was the pump speed(?).
Thanks for any feedback
Edit:
So I’ve just run a HW cycle again with Conf. DHW build.pump value at 65. When the HW gets to temperature, first the power draw drops to background levels, next the flow rate drops from 1120 l/h to around 820 l/h and this rate is held for a minute or so. Finally, the 2-port value swiches to heating and the flow rate quickly drops to zero. So, no significant overrun after the switch and no noisy rads.
This is the pump speed setting for the DHW cycle (in % of max). For me it is at 100%. By dropping it to 65% the bolus probably doesn’t travel as far after the switchover because you have a lower flow rate for the DHW cycle. Note that while this helps with your problem, you will see a slightly lower DHW energy efficiency because you now have to utilize a higher flow temperature to compensate the reduction in flow speed.
Thanks, that may be the case, but I don’t remember seeing flow rates significantly higher than 1120 l/h. I’ll play with a few settings to get a better idea of what’s going on.
I am running the occasional manual Legionella cycle by increasing the DHW temperature to 65° (I have a couple of essentially unused hot water pipes that I am flushing to prevent any bacterial growth that might spread to the “used” parts). In Eco mode I cannot reach temperatures above 60°C of the hot water (flow temperature around 70°C then). Is that expected? In normal mode I quite easily reached the 65°C target purely with the compressor.
I’d like to know that as well, however it depends on a few more factors:
charging hysteresis (how much you allow the water in your storage to cool before reheating, higher hysteresis= increased COP)
charging offset (how much hotter the flow temperature is than the target DHW temperature. Seems this is fixed somehow and changing it in the controller doesn’t do anything)
type of storage cylinder (location of temperature sensor, efficiency of heat exchanger)
So unfortunately we won’t get as simple an answer as for the heating COP.
Sorry for butting in as a newbie, and I’m not sure how to use this community forum correctly yet, so apologies if I’m in the wrong place with this post, but I’ve just had a play with the conf.heat.build.pump setting, and it is (or at least I’m pretty confident it is) the pump speed during the compressor off period - so it determines sort of how quickly the flow temp drops to the target temp.
Thanks for the reply. That may explain what I have observed if the setting also influences how quickly the flow rate ramps down when the compessor turns off at the end of the HW heating run.
I hope I’m adding a post to the main topic, so here goes. (I’m a newbie!!)
I’ve for some reason got a quite noisy bedroom radiator which really hisses at the full 900 flow rate, so I had a play this morning with the conf.build.heat.pump setting. What I discovered was that it only applied once the compressor had switched off. SO setting it at 60 caused the flow rate to drop to 600’ish; This was after first trying 75%, which had the flow at around 740, so proof to my mind. I thus thought the setting only applies to when the compressor isn;t running. But, once my integral returned to -60, the compressor kicked back in again, and I expected the pump to return to 100%, 900’ish - but no, it has stayed down at about 750.
It’s almost as if the original change didn’t happen until it worked out a new desired flow rate - at compressor switch off point - but now it has changed it, the full flow rate is an offset to the setting one, rather than the 100% 900’ish rate.
Three points: Don’t worry about being new, we were all new once; all the people here are a pretty decent bunch, and you’ll find your way around, how to operate the forum and then how to use the forum, if in doubt, just ask - it’ll have sent you a link automatically giving some basic details, the software is “Discourse” if you need to know more, and finally; if you’ve posted in the wrong place, just ask again and one of the moderators will move it for you. And I almost forgot, there’s the “Sandpit” where you can play and test out features etc. Nobody pays any attention to it. https://community.openenergymonitor.org/t/about-the-sandpit-category/95
I’m having a rather frustrating time trying to mimic and understand my noisy radiator issue.
Previously, running a hot water cycle at night resulted in a bolus of hot water hitting the radiators at the end of the HW cycle. This was caused by the 2-port valve switching to the heating circuit before the pump overrun had finished at the end of the HW cycle so water at 60C hits the cool rads. And, this happened when the heating was set to ‘off’ after the HW cycle had finished.
I’ve tried to reproduce this by running a HW cycle using various setting of the ‘Conf. DHW build.pump’ value but in all case the following happens:
the compressor switches off
the flow rate drops to about 50% and is held at that rate for a few minutes
the flow rate drops to zero and then the valve switched back to the heating circuit
no hot water hitting the rads as no flow.
I’ve reproduced this result four times. I know as soon as I switch back to a night HW run it will start playing up again. I give up.
Yeah, I kind of figured that might be the response.
The position of the temperature sensor is crucial. Mine is quite low down so is not representative of temperature of water from the taps.
I think I am going to have build a curve, I have direct power monitoring and have a PCB I need to plug into the interface to start pulling the stats from it. Other than that I just have the data from myVaillant directly or via Home Assistant. I’ve been playing around tonight and its obvious the lag in reporting screws the data on an hourly/daily basis.
Yes, that is expected. Eco gives up at around 60 degrees (bit above). If the target is higher (like 65), even the Eco increases the compressor RPM from 41.6% to higher (5kW version), trying to cope. I saw it at around at around 60% with 65 degree target (EDIT: what I mean by this is that it defines power by target, but it never gets there anyway). I would guess that this is dependent on the inlet temperature to some extent. The Carnot cycle simply can not take it further without more pressure from the compressor. It also makes no sense to run Eco so high, IMO. This comes from the COP graphs. It becomes less efficient than the Normal mode at higher flow temperatures (or low inlet temperatures).
My solution for this thing is to have a morning water run to 45 degrees, afternoon to 55, both in Eco. The afternoon run target is changed to 65 degrees once a week, mode set to Normal (via cron on home server). The pre-programmed Legionella cycle starts ± directly after the 65 degrees run. This switches the internal heater and circulation pump on and takes the flow to some 72-75 degrees. Funny thing is that the legio cycle ignores many settings (like circulation, heater, …), but it observes the eco/normal mode (running the legio cycle with Eco mode compressor = COP killer).
Very cool. This is exactly the way I would like to set up my system. Can you share the commands you use to set the temperatures and eco/normal mode? Via ebus I guess?
I would say the Legionella risk for water heated to 55 C is negligible. Personally, I would only run a higher temperature cycle after a period of absence. In domestic settings the only place Legionella has been isolated from is shower heads. It’s therefore more important to flush infrequently used showers on a regular basis.
