My latest DHW run today 21st August OT 22.9ºC for some reason the temp blue line stopped showing on the graph after 14:00pm.
Reduced DHW programme duration to 30mins; 14:10pm - 14:40pm
Target DHW temp 45ºC
Starting temp for DHW 26.5ºC
Pump speed set to 100%.
As you can see after 8 minutes flow rate starts to wildly fluctuate. Flow and return temps maintain a steady D6 which is perfect. Electricity input is stable too.
Hi John,
Sorry to hear you’re still having issues. I think the issue for your system is likely to be air in the system since the heat meter is located in the loft which is the highest point in the system. I notice you have an automatic air valve on the flow but not on the return where the heat meter is located.
There’s also a chance that the double bend and the valve before the meter could be causing turbulence, but I think this is likely to be less of an issue.
Thanks Glynn, appreciate your thoughts and suggestions. It’s frustrating as it’s impacting my stats badly on the open energy page. 
Mark from JMR Heating and Energy is with me on 20th Sept to see what we can do. I will chat to him beforehand about adding another air valve on the return flow and see if he can bleed the system.
There’s a potential to straighten out that double bend and remove the value which is downstream of the meter. They were put in to accommodate the buffer tank which has since been removed.
Having researched a little more I too am not sure the double bends are causing an issue. Looking at the specs quoted in Kamstrup’s document: The challenge of correct flow sensor installation with respect to flow disturbances.pdf I don’t believe there’s an issue. It states for out of plane double bends (mine are in plane, so presumably less of an issue);
Min. pipe distance from out-of-plane double bends mounted downstream 0 x DN (diameter of the pipe)
I guess it’s a bit of trial and error fault finding to see what works and what doesn’t. I shall report back mid September. In the meantime I’ll carry on collecting data.
Whilst not ideal John, I was able to swerve my Sharky issues by dropping the DHW pump speed to the 50% setting.
Hot water runs still work fine.
But what was baffling is that I could run the pump on heating at 100% with no heat meter issues. Obviously, not much call for heating this time of year to test that. 
Be interesting to see all these symptoms.
I shall give that a go at 50% pump speed and see where we land. 
Glyn and I have been going through the data here from the system we have access to to try and work out how prevalent this issue is. It does seem that it’s affecting a larger number of kamstrup units than we thought.
50% of kamstrup systems are not showing the issue, 22% of systems did show the issue early on but the issue has now resolved and 28% of systems still appear to show the issue to varying degrees.
The Sontex systems do not appear to have this particular issue, at least not visibly, though the DECC report below suggests that air issues can manifest as an error in the readings rather than no readings. There is another thread on here about potential issues for Sontex meters if there is dirt in the system, see Sontex heat meter accuracy over time.
We think that most of the issue is likely caused by remaining trapped air in the system and this might explain why 22% of systems improved as air is removed over time. There’s probably linked issue with turbulence caused by flow disruptions here as well, perhaps if there is air, other disruptions may have greater effect?
The systems that improved suggest that there is hope for resolving this issue. We will update our guidance to highlight that special care is needed here.
This DECC report is interesting and discusses the issue of air (gas entrainment) and highlights some of the other challenges with ensuring accurate heat measurement
An_Investigation_into_Heat_Meter_Measurement_Errors_Final_Report_AECOM.pdf (5.1 MB)
Laboratory Tests
To provide an indication of the effect of free gases on the test meters, air was deliberately introduced into the test rig and the reaction of the meter noted.
Little effect was observed with the turbine meter, but more significant effects were seen with the ultrasonic and vortex meters.
The ultrasonic meter stopped reading and showed an error code. The error code is a standard feature of
the meter and is intended to alert the user to a problem rather than attempt to give spurious readings.The vortex meter showed a relatively small error at low air volumes, increasing as the volume of air
increased, eventually causing the reading error to exceed the MPE for a Class 2 meter.
I would add that these issues seem very similar to the ones I experienced with my Sharky 775 heat meter as detailed in this thread.
https://community.openenergymonitor.org/t/sharky-775-heat-meter-questions/
Not sure what help that is, but just corroborates the positive numbers of the Sontex.
When I swapped out the Sharky and replaced it with a Sontex, all my flow rate recording issues went away overnight.
I would say a bit anecdotally that when I tried the Sharky on a test setup it took me a bit more time to purge the air sufficiently than with the Kamstrup, though I may have just got better at purging the air…
I know from my own heat pump it took quite a while for me to get rid of all the air, especially in the hot water cylinder coil. I have a sontex and even audible air noise didnt seem to affect the readings… though perhaps as the DECC report notes it likely manifested as an small error rather than no flow readings…
Thanks for looking into things.
I have now run 2 hot water heat ups on the lowest setting on our pump and these completed without an issue. Is the actual flow rates are within the capabilities of the heat meter I assume the difference will just be that there is more turbulence caused by the air the faster it is moving through the meter.
I also assume that reason the problem doesn’t happen until later in the hot water heat up as at higher temps that’s when more air bubbles are forming?
Any tips for venting the system? Apart from running the pump and switching between hot water and rads?
Yes that’s my understanding as well.
Does the return pipe go down before going up to the unit? or is it horizontal and then straight up?, the air bleed there is a bit strange … would be better at the top… do you have any way to bleed the air out at the top of your system? have you bled the radiators?
Yes I’ve been bleeding rads, there was quite a bit at the start but not much recently. There is one rad in particular in the attic where a lot of the air ends up.
I guess my system has 2 high points as the ASHP is higher than the pipework shown in the photo and my cylinder. The horizontal flow and returns where the pump and heat meter are are horizontal till they get to a 90 degree upward bend to ceiling level. The flow and return connections on the outdoor unit would be a little higher again. These have take offs just lower than the heat pump connections and I’ve turned them and only water comes out.
Thanks @ajdunlop just re-read your original thread as well. Sounds like you managed to get an improvement before further air dislodged again and so back to square one? What are your options to get the installer to look at this / add further air vents say up at the unit itself? or to re-orient the heat meter with a good length of straight pipe before it?
@marko made lots of great replies in my Sharky thread about cavitation and air bubbles etc.
Might be worth taking a look back through that?
Yes when I first had the heat pump going I had it cutting out readings. After a bit or radiator bleeding and bringing up the pressure things improved (was still always a bit spiky later in the cycle) but looks to have gone backwards.
I believe my installer still has to come back to commission (after a few other electrical bits are done) so I’ll see if they are happy to move it then. There aren’t many good long sections without bends but a straight length that would probably be better than where it is now.
Thank you for investigating this further and drawing some sensible conclusions. Just out of interested what numbers of heat meters are we talking about here? e.g. 50% of how many? I plan to ask Mark, our heating engineer, to bleed the system on his next visit, so will report back.
50% of kamstrup systems are not showing the issue, 22% of systems did show the issue early on but the issue has now resolved and 28% of systems still appear to show the issue to varying degrees.
Hello @JohnT 34 working fine, 15 resolved and 19 still showing the issue (dont think most of these have tried to resolve the issue actively). Hope that helps
Been a few days since I bled all radiators upstairs and downstairs. There was some air in one of the upstairs radiator. I’ve been round and done this twice now with a couple of days gap in between and DHW runs. Second time no air escaping just water. System at 1.9bar. Pump at 50% speed.
Attached a 2 runs for the DHW; 25th and 30th August respectively. Seems to be much better if I’m interpreting the data correctly. Seems rather erratic on the flow rates still.
Yes, that looks much better. There are still some erratic readings but at least this will have less impact on the energy reported rather than completely missing heat data! It will be interesting to see if over the coming weeks if you keep bleeding the radiators and keep the pressure high at around 2bar to see if the trapped air will dissipate.
Thanks Glynn. I’ve marked the Solution option in this thread. I will keep bleeding the system. Once the heating season kicks in that should make it easier to get out the remaining air.
Sorry but I can’t help it.
