Ground Source Heat Pump Installation - Metering Locations

Hardware Heatpump
1

Hello Everyone!

Brand new to the community, and recently became aware of OpenEnergyMonitor through the YouTube collaboration video with ‘Heat Geek’. Looks like a really powerful bit of kit for real-time monitoring but also the historic logging and potential fault finding is a great capability, awesome stuff!

I’m very much a novice at this point with plenty of reading left to do, but as I’m due to have a Ground Source Heat Pump installed in the next couple of weeks, and I’m sold on installing an EmonPi (or the dedicated Heat Pump Monitor), I thought it best to at least ask a couple questions now as there’s never going to be a better time to install the required metering aspects than during the installation phase!

Question 1
Our proposed system has been designed to incorporate the Heat Pump, a Buffer Tank, and connection to the existing Domestic Hot Water & Central Heating systems (I’ll call this ‘House Plumbing’ for simplicity). With real-time COP being the ‘highlight’ parameter, would the heat/flow metering be best positioned pre-Buffer, post-Buffer, or a combination of Heat Pump outlet and House Plumbing return?

My thoughts (assumptions) being that if the meters are positioned between the Heat Pump and The Buffer Tank I’ll get a very accurate COP reading, but positioning the meters post buffer would allow me to identify any issues/wastage within the ‘House Plumbing’ should I suddenly see a drop in performance when engaging a single zone/room/radiator for example.

Is treating the Heat Pump & Buffer Tank as a single entity a sensible way to go to obtain a realistic COP, or is this even the norm? (again, only an enthusiastic novice at this point, certainly not a heating engineer)

Question 2
Having quickly reviewed the ‘Selecting the right heat meter’ page, understanding that MBUS outputs are required, and seeing that there are a good list of existing compatible & tested models available. I’ll openly admit I’m not yet clever enough to fully understand John Cantor’s table of different brands and their performance at different flow/pressure rates. But the fact that the blog starts with the phrase “This topic is VERY IMPORTANT…” makes me a little nervous to go off and buy something myself that’s not fit for purpose.

Therefore, am I correct in thinking that this is something I’ll need to discuss with my Heat Pump installer and let them select the best brand/model/technology to suit the system they have designed (Obviously stipulating that MBUS is a solid requirement regardless of metering installed)?

Presumably, once I know where I need my metering to be installed to best suit the EmonPi readings, the installer should then select, source and install the best matched meter equipment before needing to check the actual performance of the system? ie. The potentially unknown ‘House Plumbing’ shouldn’t be a factor in choosing the right metering for the Heat Pump (chicken & egg situation)?

I think those are my most time sensitive questions anyway, I’m sure there’ll be more down the line as the GSHP is only the first step in our plans toward a net zero home/life.

Thanks in advance for any help, apologies for the lengthy first post, and I look forward to learning a bit more as I go!

Kind Regards,
Leon.

1 Like
2

Hi Leon,

we only fitted our ASHP a couple of months ago, so I’m no expert. But here’s my ha’porth

As regards question 2 - I would recommend talking to your installer right away. I ended up buying the heat meter, and my installer fitted it for £300 (I’m no good at haggling - so this is probably expensive). You need to ask your installer whether your system is going to use anti-freeze. Mine does use anti freeze - and according to John Cantor’s list, only the Sontex Superstatic is known to have a calibration for glycol. OE also recommend an AC power supply, which narrowed it down further to the Superstatic 440. To work out the optimum size, you need to find out the peak flow rate of your heat pump. Mine has a peak flow rate of 32.1 litres per minute (=1.93 cubic meters per hour). On the face of it, the Superstatic 440 with a max flow rate of 2.5 cubic meters per hour (Kv=5) looks like it would be OK for my system. But using John’s formula
pressure loss (in bars) = (flow rate (in cubic meters per hour) / Kv)^2, it would give a
pressure loss = (1.93/5)^2 = 0.386 x 0.386 = 0.15 bar which causes the pump to use significantly more electricity. John recommends choosing a larger meter to drop the loss through the heat meter. He reckons 0.04 bar is a reasonable loss, whilst 0.025 bar is a good level to aim for.
I ended up getting the Sontex Superstatic rated for 6.0 cubic meters per hour (Kv=13.4) which gave a pressure loss 0.021 bar for our system. If I had left the decision to my installer, or to the heat meter vendor, I would have ended up with a smaller meter, which would have been a bit cheaper. But John seems a very knowledgeable guy, so I went with the bigger size.

As regards question 1, I don’t have a buffer tank, so I’m even more out of my depth. I think I would put the heat meter pre-buffer. I am most interested in finding out how efficiently the heat pump gets heat into the house, to run the central heating and heat up the hot water tank.

PS This was the first time I have had a heat pump. In retrospect, when getting quotes for the system, I should have got the installer to specify the size of radiators they were going to fit in each room. Mine just said that 6 radiators needed changing. I was expecting them to fit the biggest radiators they could, so that the heat pump would run at minimum temperature, and hence more efficiently. But he said they just size the radiators to deliver the required heat assuming the heat pump exit temperature is 50 degC. In retrospect, I should have got them to drop this temperature down as much as possible. The radiators could have been considerably bigger, which would have cost a bit more, but would have been more efficient, and dropped the running costs significantly.

I hope this is helpful,

Regards
Richard Brooks