Removing trapped and dissolved air from a sealed heating system is essential for maintaining efficiency, ensuring accurate heat meter readings, and prolonging the system’s lifespan by minimizing corrosion.
Ultrasonic heat meters e.g Kamstrup, Axioma, Sharky etc are unable to measure the flow rate if there’s air in the system. This will result in the flow rate being reported as zero, which then in turn results in the heat meter reported heat dropping to zero 0W. The most likely time for this to happen is towards the end of a DHW cycle when the flow temperature is highest e.g
Sontex heat meter use a different flow measurement principle, they won’t throw an error and stop reporting in the same way as ultrasonic meters, but they will quietly underreport if air is present. Sontex heat meters are also susceptible to dirt and can start quietly underreporting overtime if they get silted up with debris.
We’re interested to hear feedback on the effectiveness of these measures are at removing air, or if you have any other suggestions or methods which you have found effective?
We’re also working on a feature to flag any air issues reported by the heat meter in Emoncms to enable it to be resolved by the installer early on when the system is first installed.
Personally I specify (and use on my own system) a fill and flush valve to eliminate air from sealed systems and is the only effective way of getting rid of air on commissioning imho. If you have a buffer cylinder or hydraulic separation you would need one on the primary and one on the secondary side to be effective.
Thanks for posting this Richard - a great explanation of all the issues and specifically on page 16 why air vents where they are traditionally placed can miss a lot of what’s going through the system. The air vents fitted by our installer are both just above a bend…
We have corrugated coils in the tanks and the DHW one has always been an issue with noise which I’ve always thought was trapped air in the corrugations, so I think a fill and flush valve as you’ve referenced in the post above plus a microbubble separator is the minimum of what we need to do.
Yes, as noticed by @SianiAnni we’ve now setup error flagging which will highlight in shaded red on the MyHeatPump dashboard the period of time the heat meter is displaying an error when unable to read the flow rate due to air in the system e.g
This will be setup by default on all new systems. To add it to existing systems, you either ask us to set it up, or do it yourself by logging heatmeter_Record_error Input to a Feed with 10s interval and then selecting that Feed as the error feed in the MyHeatPump app config.
Error flagging is currently only supported with Axioma heat meters.
Looking at my heatpumpmonitor.org stats, the heatmeter error is only showing on DHW cycles. I’ve compared MyVaillant electricity and heat stats for August with heatpumpmonitor.org :
OEM Elec
MyVaillant Elec
OEM Heat
MyVaillant Heat
Heating
15.5
22.5
91.0
90.2
DHW
20.3
20.6
???
64.6
It’s clear that the electricity figures for heating aren’t comparing like for like, but the generated heat figures look very similar. And the heat meter error isn’t being reported during heating cycles.
I was going to ask whether that was because of higher flow temp for DHW, but just reread above and see that you’ve already explained that it is!
Now that the heating has been on more, I’ve started bleeding radiators a couple of times a week, and getting air out of one of the top floor radiator each time.
Displaying the extent of the error flagged by the Axioma heat meter is a great addition but can someone explain why, in the screenshots below, does it show errors for 11 minutes for the last 24 hours but errors for 18 minutes for a smaller window (of less than 1 hour) within the last 24 hours?
The article says that AAV should be closed after commissioning. Is that standard practise? My installer told me to leave them open, and I’m not sure how they’d be automatic if they’re closed.
Do they tend to admit air when open ?
Personally I think it’s good to leave them open, just in case there is any remaining air to be released. However, if they get clogged with dirt than can leak so installer like to close them to avoid call-backs. There is also some thinking that they could under some circumstances allow air back into the system, but I’ve never experienced this.
Interestingly, Panasonic are now stating that AAVs should not be used with their R290 units, due to the slim chance of the refrigerant entering the system due to a leak across the heat exchanger. Not sure what other manufactures are saying?
Really?! Where have you seen this? I’ve just looked through their service and installation guide and can’t see any mention of it. No other R290 manufactures have any issue with AAVs. Not being able to fit AAV would make filling a system and purging air very awkward.
See page 157 of that service manual and/or page 82 of the service manual for the Bi-bloc version…
*“ Do not install automatic air purge valves on indoor water pipes. In the unlikely event that the R290 refrigerant leaks into the water circuit, there is a risk that the refrigerant will leak indoors.”
It dose seem a little OTT and may just be arse covering by Panasonic, but I guess it dose reduce the risk of uncontrolled release of propane refrigerant into the house.
We use a fill & flush pump to purge UFH etc and AAVs were necessary during commissioning, then isolate/remove them and/or use manual air vents - AAVs often end up leaking and cause other problems if left open!
