Very low COP?

Having just managed to get data via MBUS from my Sontex 789, Im a bit surprised by the results. The 5kW Samsung gen 6 is heating my home (a 2 bed bungalow) perfectly adequately with a flow temperature of about 38 degrees and return temperature of about 35. Its 10 degrees outside, flow rate is 15 lpm. From CT clamps on my outside unit and inside control unit and pump Im using about 700W combined. What is surprising me is that according to the heatmeter, the heat pump is only producing about 900W of heat which cant be right?? I know delta T should be a bit more and Im thinking maybe slowing the pump might help but what is going on?
The heatmeter and its return probe pocket are about 4m away from the ASHP which I guess means the the flow temperature reading is lower than it actually is and the return higher, is this an issue?
Thanks for any advice. Mark

Ive just put some figures into an online calculator and a 3 deg Delta T at 15 lpm comes out at 3.14kW which divided by 0.7 gives a COP of 4.48 which is much more what I would expect?

Yes that’s correct 4187 J/kg.K x 3K x (15 lpm/60) = 3.14 kW

Was it a transitory effect or is the heat meter reading 900W steadily? Can you graph flow, return temperature, flow rate and heat output over a period?

Hi Trystan, very sustained, which makes me wonder if I have matched the wrong value in the inputs. I used Heatmeter_Power as the HP Heat Output in Watts, is that correct?

thanks! I assume flow rate is steady enough at 15 Lpm?

Can you share a screenshots of the inputs you are seeing? and perhaps a part of emonhub.log?

Yes, the Samsung reports it as the same although I took the heatmeter input called Heatmeter_Volume to be the flow rate which might have been a mistake. However the heatmeter_Flowrate input is nothing like it. Thanks

emonhublog.txt (607.5 KB)

Thanks @bontwoody ok that clears up that the heat meter thinks the flow rate is 0.27 m3/hr = 0.075 L/s. Hence (37.88-35.47) x 4150 x 0.075 = ~750W

The volume should keep increasing.

A 5kW Samsung has a minimum heat output around 2kW so 800W is still unlikely to be correct. Sounds like there some kind of flow rate measurement issue 0.27 m3/hr, 4.5L/min is very low… you would expect that to be around 10-15 L/min as you suggest…

So does the heatmeter measure the flow rate internally Trystan? If so is it likely to be an equipment failure? thanks

It does, what does the heat meter report the flow rate to be on the heat meter LCD display itself?

Can you hear any air in the system?

Is the flow meter on the primary pipework of the heat pump or after a low loss header / buffer?

There is only one button Trystan so ive videod me pressing it lots :slight_smile: I couldnt see flow rate.

No air in the system is audible

The meter is located on the return pipe to the ASHP there are no buffers or headers.

I will attach a picture of the install in another reply as the video seems to have mucked up the upload

Here’s a video showing how to view the flow rate on the LCD of a Sontex 789/749

Did you just record that gyln :laughing: The LCD shows the same reading as the MBUS data 0.285

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Mmm that flow rate is only 4.75 lpm. That’s lower than it should be. Can you check the flow rate that the Samsung flow mater is reporting, can you view the in the service mode settings on the controller:

This sounds like some kind of fault with the heat meter. Neither Glyn and I have experienced issues with Sontex heat meters, generally found them reliable but there is a thread on here where the flow rate measured dropped over time so perhaps there’s some debris or an other issue?

Hi Glyn, thats what Ive been doing, its consistently 15.5 lt/min +/

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Do you mean something blocking the flowmeter mechanism in the heatmeter without restricting flow Trystan?

yes, something like that, Im guessing? who installed the heat meter?

Twas I :slight_smile: I installed it all

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ok great, worth draining down cleaning out the heat meter and trying again?

Its a bit of a pain if I dont find anything wrong with it Trystan. Unfortunately I didnt put isolation valves either side of it. Could you send a replacement that I could pop it, if its the meter itself thats faulty? It seems a bit of a stretch imagining something that could slow the flow mechanism without stopping it altogether.