OpenEnergyMonitor Community

Heat Pump Monitor & emonPi advice


Thanks. The external emonTH sensors are placed just before the last radiators in each zone (our plumber was good enough to put thermowells into the 21mm flow pipe under floorboards) with the emonTH’s hidden in cupboards nearby. Would you recommend also placing sensors on the radiators themselves somehow?

Thank you, I will do that - and I appreciate the advice on putting the lower tank sensor at the same point as the ASHP probe - I had not considered the potential benefit of matching these.

I wondered if there was any advice or experience on how to create semi-permanent seal for the DS18B20 probes within the larger thermostat pockets of a typical water tank? The pocket diameters are significantly wider than the sensors which I’m conscious might skew readings.

Imagined I might use following in order:

  • thermal paste on sensor
  • alu foil ‘plug’ to help reflect heat back inside the pocket
  • final bubble wrap wad for insulation

Any more professional methods that have been tried/tested? Apologies if I missed previous articles on this. Tku

I think I might have confused you (and myself) with my final comment. You already have a sensor right by the heat exchanger. ignore my suggestion of temporarily using an EmonTH for anything

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Sounds sensible to me. I’d be tempted to fill the pocket with the grease and push the sensor into that. Then cover with your alu foil and whatever insulation takes your fancy.

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Happy New Year everyone.

By way of an update, the system is largely installed now and providing excellent visibility of the ASHP performance generally. Still, some things to fix, namely some unexplained dropouts from the SDM120 meter and work to integrate the Sontex heat meter which I’ll address separately.

While not directly related to the emonpi setup, I’d greatly appreciate your thoughts on the data being obtained by it in the meantime given the heat pump experience within the forum…

We’re seeing a consistent 7-8 °C loss between the primary and secondary flow temperature within the plate heat exchanger. Our radiators are unable to break 38-39 C as a result - a long way off the 50 C max design temp. The two flow sensors are in close proximity to one another and am confident they are reading fluid temps accurately (all genuine, tested DS18B20s from OEM with each one plumbed into a brass sensor pocket).

While the ASHP itself is working very well, the data points to a significant temperature loss at the source. I am told the heat exchanger is there to maintain hydraulic separation but wondering what value this is adding besides some protection for the ASHP.

Is this normal for other ASHP installations across the group and data others may have obtained? Any insight is hugely appreciated…

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There will obviously be some loss across the heat exchanger. How much depends on the flowrate and the design of the heat exchanger. A greater flowrate gives less time for heat to move from the primary to the secondary. An exchanger with less area provides less capacity to move heat, and there are other design paramters that affect the exchange. The simplest way to reduce the difference would be to reduce the pump speed but that affects the mass of water delivered and so the total heat transferred. It all depends what’s most important to you. Changing the heat exchanger would offer a greater range of possible performance combinations. Your temperature difference is normal, but on the high side, AIUI.

A quick google shows lots of hits on the subject of which one is Heat Exchanger Selection and Sizing Guide

Thanks for sharing @thedawnbefore wow that’s really interesting and quite a temperature drop across the heat exchanger! Do you have the spec/model number of the installed heat exchanger, it would be interesting to understand what the options might be for reducing that temperature drop as @djh mentioned. @johncantor would be interested in your latest update as well.

Do you know if they decided on a heat exchanger rather than low loss header or just direct connection because of the wish to have glycol in the heat pump loop but not the rads? or was it just for hydrolic separation?

Can you take a pic of the heat exchanger for interest? Is that a normal cylinder with coil for DHW?
Anyhow, plate heat exchangers are not common (I dont know of any), and 7-8decrees is what you might expect. one advantage is you don’t need much glycol in the system.
So, the dt across the HP flow and return looks like 7 deg to me. can you try increasing the heat pump flow a little to see what happens? would 4deg between heat pump flow and heat pump return help a bit?

Thanks all for the very helpful feedback and queries and apologies for the slight delay in responding while travelling. I have attached photos and details of the heat exchanger, which seems to be the following model,113,845.html

Thank you @djh, i have a meeting with the installer later today to run through the OEM data and this guide will provide some helpful talking points. I could imagine a ~2-3C temperature drop but have difficulty with the current loss.

Thanks @TrystanLea , i’m told the heat exchanger is there to protect the ASHP (a Midea 16kw) and reduce the need for glycol in the radiators. For further context, it’s a fairly conventional well-insulated 1970 4-bed brick-built detached house, 15 rads and ~2k sqft of heated space in total.

I’m thinking any glycol saving may quickly prove false economy however and my private research suggests most ASHP’s work fine without full separation or a low-loss header instead.

Thanks @johncantor , photos attached of the Heat Exchanger specs. I will do as you suggested and run at 50 degrees today and report back. My slight fear is that due to the power consumption of the Midea ASHP, higher flow temps may not be a long-term solution for me.

And forgive the temporary OEM setup and spaghetti wiring while we test it all, still to be plumbed in! More than can be said for the pipe lagging…

I think I misled you… sorry, I meant increase the flow-rate so that the temperature difference between HP flow and return temperatures reduces a bit. It seemed to be at least 7degrees. it would be interesting to see your graphs with say 4 or 5degrees td. e.g. your 47c/39c might become 45c/40c
The plate HE looks a good type, it is a very common design. You might find selection software, but not sure that would help a lot. Hard to say if your best plan is to simply make the best of what you have, or make some changes. proceed with caution I would say