Thanks Brian, i’ll look at what my pressure is.
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Seems I spoke too soon… Whilst the pressure increase did make an improvement, it’s since dropped out a couple more times over the past few days.
I’ll have to investigate further when I have time. I still like the cavitation hypothesis because I’m seeing good flow readings at the start of the DHW cycle, then some time into the cycle it’s dropping out completely, and I’ve read that cavitation increases as the temperature of the liquid increases.
I’m also reasoning that this extends to any tiny air bubbles in the flow, potentially causing them to expand and cause issues (I’m no expert on this). In the left graph above, there’s a bit of a “wobble” in the flow reading right at the start - I’m guessing this is likely air?
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I’d say air.
Air and dirt get entrained in the flow at certain pipe velocities and will move around the system.
They settle upwards when flowrate drops or stops. They can persist for an age I’d you’ve no way of flushing them out into radiators or purging from the DHW loop.
Cavitation is indeed a bigger issue at higher temperatures.
I’ll try running the automatic de-aeration cycle for a few more hours when I get a chance.
There are 2 high points in the system: top of the DHW cylinder coil (in pictures previously) and the top port of the volumiser in the loft. Both have automatic air vents.
I have a feeling that the arrangement of the filling loop could be causing issues though
Any air trapped there will get flushed back into the system if I need to top up the pressure. Seems overkill to add another automatic vent, or re-plumb it, so I guess I’ll crack the flexi joints loose and manually bleed them when filling is required.
AAV is well positioned and ought to eventually purge air in that DHW loop even if entrained. Assuming there aren’t high points elsewhere.
Flipping the fill loop to point down would perhaps have been nicer such that it fills “upwards”
Any luck with the Packom Pi Hat? Am toiling with getting it set up.
New to all of this.
Just seen your other thread. I’ll head over there and reply!
I have a new ASHP installation together with level 3 emonHP solution using the Kamstrup Multical 403 heat meter. This works well except when the ASHP switches to Domestic Hot Water (DHW) mode . After a few mins the flow readings go haywire - see picture
I am wondering whether this turbulent flow is the same as described in this thread?
I suspect the heat meter has been installed too close to the tap (it’s about 10cm away):
Should I ask the installer to move the heat meter?
Any thoughts/advice would be welcomed.
Here are a couple of other threads that discuss similar issues:
Kamstrup Multical 403 Erratic flow readings - Hardware / Heatpump - OpenEnergyMonitor Community
New emonHP install with strange readings - Hardware / Heatpump - OpenEnergyMonitor Community
In my case it eventually resolved itself, especially after space heating started to run more often as we went into Autumn so it was probably dissolved air that was being released at higher temperatures when doing DHW runs. Hasn’t been a problem since.
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Same here - I have a Sharky (another ultrasonic flow sensor) and it settled down after a little while once the air worked its way out of the system.
Dissolved air in your system.
Raise the fill pressure; get it good and hot; bleed the radiators; switch back and forth from DHW to purge the water with disoolved air from the DHW loop; bleed the radiators etc.
Once there isn’t air in the flow sensor it will work correctly.
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I ended up adding a Spirovent deaerator/air separator just after the heat pump primary flow comes inside - I got bored of waiting for the air to work it’s way out via the radiators or existing automatic vents. After a while the issue went away for me too.
Is the flow going vertical, upwards through the meter? From the emonHP user guide (taken from Kamstrup install guide)
Position B (upwards flow) is fine, but position D (downwards flow) is suboptimal. Either should be fine once all the water is purged from the system.
The flow meter is in position D, 30cm down from the T bringing the feeds back together for the return to the heat pump, and 20cm above a manual isolator valve. The pipework is 22mm OD copper, so should be just about good enough. It’s running at a pressure of 1.75bar.
There is a deaerator in the system and I have bleed all the radiators over the last few days. Initially some air did come out but now nothing.
The net result has been a slightly improvement in the flow measurement during the DHW cycle (the flow measurement doesn’t crash straight away), but it is still far from fixed.
Any further ideas or do I need to get the installer to move?
Could you post photos of the installation? Try increasing pressure to 2 bar and keep bleeding radiators and ensure automatic air valves are open. It usually takes a few weeks for all the air to be purged from a system. Small pockets of air gets trapped inside the DHW coil.
Here’s another photo showing the complete indoor installation (yes, it’s a tight squeeze and the cabling is a bit of a mess right now as I have added lots of digital thermometers to emon on the radiator side of the buffer tank and elsewhere in order to better understand what is going on!).
I’ve now increased to pressure to 2bar, and have bleed the radiators again (no air is now coming out).
Here’s hoping I can get a clean flow measurement.
Mixergy tank?
Using a coil or a plate? Air loves to hide in plates. Any means of bleeding it other than hoping to flush into the rads over time?
I’d try bleeding from that pressure relief valve. That’ll trap some air given th orientation. Also from the magnaclean whilst it’s in hot water mode and stinking hot. What’s the lump of brass to the right?
Is that an auto air vent on a buffer in the foreground? Working correctly?
I’d have fitted the heat meter flowrate sensor on the supply not the return myself. Higher dynamic pressure there and less likely to cavitate.
Using a coil or a plate? Air loves to hide in plates. Any means of bleeding it other than hoping to flush into the rads over time?
It’s the Mixergy plate heat exchanger. I can’t see any way of bleeding in but the installer is back later in the week and I’ll get him to check.
I’d try bleeding from that pressure relief valve. That’ll trap some air given th orientation. Also from the magnaclean whilst it’s in hot water mode and stinking hot. What’s the lump of brass to the right?
I’ll try these as well. The lump of brass is a Spirovent deaerator. Not sure how to tell if it’s working.
Is that an auto air vent on a buffer in the foreground? Working correctly?
Yes, according to the manual that came with the buffer tank, it’s an auto air vent on the top. Interestingly, I hadn’t looked at the buffer tank manual before and I cans see that it has a holder for a temperature sensor. As I have a spare 1 on my EmonPi I’ll install it. As a separate exercise I’m trying to understand the heat flows involved with the buffer tank.
I guess the installer fitted in the return loop because of space constraints. I am thinking of asking them to move it to my loft space the other side of the wall where the pipes are easily accessible and straight. I’ll see what progress I make before they come.
Ask the installer to show you the little cabps and fibre washers on the top of the spiro / air vents and how to use those
Thanks for everyone’s help. My flow readings have much improved during the DHW heating cycle. As you can see below, I am now getting readings throughout the whole period although there is still some turbulence at the higher feed temperatures. This was achieved by further bleeding of the system, especially the Mixergy heat exchanger and other “high points”. I’ll monitor it to see if there is further improvement.
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