Heat Pump control options

@TrystanLea I’ve been looking into heat pump control options and haven’t found any particularly good solutions yet (I imagine that a decent controller would have eco and fast heat selectable user modes and in the eco mode would use the lowest possible flow temperatures it could to obtain the desired temperature target over a much longer period of time (either in the DHW tank or in the rooms).

I notice that you say you have a set up with the flow temperature controlled by a RPi? (see quote below). Is this because there aren’t any off the shelf controllers that do a particularly good job of controlling the flow temperature or because you wanted to do it yourself for interests sake?

“I have a 5kW Mitsubushi EcoDan with a 3m2 coil in a newark cylinder, I’ve got the FTC2b flow temperature controller for the EcoDan which lets me control the flow temperature using a voltage signal created using a digital to analog converter connected to a RaspberryPi…”

Hi @Henry_Fletcher welcome.

Better to start a new conversation that open up a very old one.

Hi Brian, thanks for the welcome.
I’ll start a new thread!


oh, I see you seem to have pulled it out into a new thread in any case…

For anyone looking for the original thread I posted in, it is here: Guardian questionnaire: have you installed an electric heat pump in your home? - #6 by MyForest

Actually, Henry, “the system” has already done that - it’s in grey at the bottom of your original post at the top of this thread - and if you go back there, there’s also a corresponding note where your post came from.

Ah yes, I didn’t notice that early, thanks for pointing it out @Robert.Wall

Hello @Henry_Fletcher and welcome!

I think I’m able to get some slight improvements with my custom controls but perhaps not that substantial. It might be more trouble than it’s worth. I get some nice benefits such as a scheduler built into emoncms that I can use for remote control but the code for that is very much a personal project (GitHub - TrystanLea/heatpump_control: heatpump_control) not something I can support or recommend others use my code… at least for the time being.

@glyn.hudson’s results Emoncms - app view dashboard are testament to the manufacturers own controller, he gets slightly better results than I do but with a different heat pump and careful setup of course.

Are you speccing up a heat pump for yourself at the moment? or already have a system and are wondering how to improve the controls?

Hi all
curious as to why you would want different flow tempreatures on a heatpump unless you were on a fixed flow temp setting as your weather comp should do this for you resulting in higher efficency and better scop. Trystanlea probably does it because he can but for us mere mortals then i would stick to the manufactures controls and learn as much as you can about the setup of heat pumps, it will serve you better.

There are plenty of examples on this forum that demonstrate the manufacturers controls are often pretty useless. The whole point of the forum is to explore better ways than just what is supplied.

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Im inclined to agree to some extent with you both, some systems may benefit from custom controls e.g @MyForest’s success in improving his system performance. Others e.g @glyn.hudson is getting better performance from his samsung with manufacturer controls than I get with my EcoDan with custom controls. I think my COP would be lower with standard Ecodan controls due to the way the central heating pump is kept running between cycles, though perhaps only a minor difference. One benefit that I do get with flow temperature control for the DHW cycle is the ability to perform a slower heat up during the night which reduces compressor noise, but better rubber vibration isolation on the wall mount would probably do a better job… Im also able to better optimise a legionella cycle so that the immersion heater is minimised.

These are all things that could be relatively easy for a manufacturer to implement and Im sure it will improve… There’s a significant difference between each manufacturer on the control options and I can understand the difficulty in designing controls given that large range of different radiator, under floor, buffers, low loss headers etc configurations that a heat pump can be connected too, alongside different expectations and preferences from users…


I agree with you entirely but unless you are confident and are able to reverse engineer I think it is beyond the average enthusiast. I would love to be able to break into the code of my controller and play around with the settings. Sometime times we have to just accept that there is a personal limit on what we can do. Sometimes people forget we are not all experts and there are no hard questions if you know the answers.
We all know that manufacturers will always base their settings on the side of safe so I’m sure there is plenty of scope for manoeuvre if you know what you are doing.
Like I said it’s not a slur or moan in fact I’m quite in awe of you all when you are able to do such things.

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Heya Trystan, thanks for the reply, I am currently specifying a heat pump and all the ancillary equipment to enable the changes I intend to make (currently on an old gas combi, so will be putting in a storage tank as well).

I’m aiming to use the manufactures controls if they meet my needs but before purchasing, I’m keen to ensure I have the options to control things more precisely myself if I want to…without ideally too much reverse engineering effort!

Are you aware of products like the “FTC2b flow temperature controller for the EcoDan” being made by other manufacturers e.g. Daikin?

Are there any bill of materials type lists anywhere that individuals with successful set ups/ maybe those sharing data publicly via Emoncms have posted to help inform purchasing decisions for other installers/ individuals? I’d be happy to contribute my current bill of materials and any subsequent results/ monitoring that occurs!

Is comparing COPs particularly useful? I’d imagine that usage patterns and environmental factors limit the maximum COP that can be obtained perhaps even to an equal or greater level when compared to technical optimisation? (e.g. if one person has their DHW at 50 degrees because they have an iron bath and love insanely hot bathing plus their house is in North Scotland and that day it’s -4degreesC then they are going to find it very hard to get as good a COP as someone who heats their water with a wood burner and whose house is in Cornwall where it is 4degreesC that day). I feel that an absolute energy usage per person is a more appropriate measure, and includes the important aspects of reducing absolute consumption, via household insulation, wearing appropriate clothing, living in spaces that are a sensible/ modest size etc etc.

Mike, I’m pretty happy coding, plumbing, wiring etc, I’m a robotics engineer by profession so this stuff is all relatively straightforward for me. The stuff that isn’t straightforward is faffing around with the limitations imposed by closed source manufacturers hardware and trying to figure out what each manufacturer supports and doesn’t support from a hardware and software perspective without buying every manufacturers products and testing them all myself! The typical installer is not blessed with the level of technical understanding I’m fortunate to have so is not well placed to answer my questions on such topics. I’ve also found technical support in the UK for products designed in places like Japan (e.g. Daikin) to be very limited as well.


Spot on, manufacturers are really loathe to share any of their coding and nothing is open source, so installers like myself are only able to optimise a system by what and how we install. Then really have to use their controls as best we can. So good luck and I will follow your journey with interest to see what you can achieve.

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Make sure you have the right kit so that you can extract the data locally. There are various wheezes to scrape data from the propriety online systems, but if it was me, I’d install heat meter and Energy meters I can read locally (like the OEM bundle).

Other than that, a flow meter and install plenty of pockets for temperature sensors, not just on flow and return but in other locations too. You can’t have too many pockets or too many sensors IMHO.

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Thanks both for the comments and advice.

On the heat sensor front, I had already been heading towards the Sontex Superstatic range, I note that the emonhp level 3 bundle ships with the M-Bus Sontex Superstatic 789 2.5m3/hour option: Level 3 Heat Pump Monitoring Bundle (emonHP) - Shop | OpenEnergyMonitor

Can anyone advise on the pros and cons of the following options:

M-Bus vs Pulsed?

  1. Does the M-Bus provide power to the meter unit so it doesn’t run out of battery after 6-years? I don’t like the idea of buying a product that costs this much with a 6 year battery life (I can’t find any obvious information on replacing the battery/ cost of replacement etc).
  2. I’m guessing the M-Bus allows for an external device to receive both temperatures and the flow rate as well as the calculated heat transfer? (whereas the heat transfer is the only thing you can get from the pulsed version?)

789 vs 749?
The 749 seems to be a brass/ metal body whereas the 789 is a composite body which is lighter? Does this just make it easier to mount or does the lower thermal mass also make it more responsive to temperature fluctuations and so more accurate?

Choice of flow rate?
Is it worth always going for the highest flow rate (2.5m^3 I think?) I guess one loses some measurement resolution but potentially useful to be able to measure higher flow rates if the heat pump system pumps at a high flow rate?

Choice of pipe diameter?
Just match to existing pipework? I guess the bigger the better in most cases? e.g. go for the DN (20)/ G1" rather than the DN(15) G3/4" ?

Yes, comparing COPs on the heat pump monitor site is very useful.There is enough information there to make an educated guess as to why any particular COP is as it is, high or low water temperature, make of heat pump, etc. It also gives an indication of the level of performance that is achievable with correct system design and implementation; that’s very valuable given the woeful performance that some ASHP systems give and the large amount of ill informed anti-ASHP opinions that there seem to be.

Absolute energy consumption per person is what you are ultimately interested in, but there are way to many variations in circumstances for that to be a meaningful metric.


I have the M-bus 749. I don’t believe the bus provides any power but the battery is replaceable AFAIK despite some sites stating not.

There’s lots and lots of data readable from the Sontex over M-bus. I’m currently logging flow & return temps, flow rate, active power and total power but there’s more available.

I went for the largest flow and largest connection size as it matches the maximum flow rate for my ASHP and I’m using 28mm pipes.

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I believe that the m-bus is self powering and has no drain on the battery, however i think the read times are every 30 seconds when on battery power. I have the sontex449 fitted and reads flow temp, return temp, flow rate, temp differential, power, energy over m-bus to emonhub

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I’m getting my boiler pipework altered in the summer and I am strongly considering putting in a heat meter just for interest purposes. :rofl: