Samsung ASHP (Joule) poor performance - help needed!

Hardware Heatpump
1

Hi,

Although I’ve had a heat pump of nearly two years for a whole variety of reasons I‘m only now digging into the why my lifetime COP is only 2.36! I’m gathering information but am struggling to know what to expected and what/how to optimise, so I’d really appraicfte you help and expertise!

So, our environment is:

  • Well insulated 2y old detached house
  • Samsung Gen6 AE120RXYDEG
  • Pre-plumbed system provided by Joule, UHF downstairs, radiators upstairs
  • Heating runs as single zone
  • Wilo para pumps on ASHP - Joule advocate running all the pumps at maximum speed

I don’t have any of the design documentation for the system - I’m chasing the developer for it with little success so far!

I’ve just installed monitoring using ESPHome Samsung HVAC Integration and so can finally look at the system in some detail. I also forward the data from Homeassistant to emoncms: Dashboard (ignore Friday 24/1 14:00 - Saturday 25/1 12:00)

What do I see:

  • UFH performs better than rads, maintains good difference between flow and return
  • When the rads are heating up, performance is OK, but as the they get warmer the difference between flow and return narrows to only 1-2 degrees
  • DWH COP is terrible usually less than 2, but lower priority at the moment
  • Primary and secondary pumps on ASHp are fixed speed, typically pushing around 24l/m
  • Monitoring shows that compressor frequency and fan speed are reduced as the system approaches target flow
  • PWM signal also reduces significantly to 40% or less

Key variables:

  • WL 2011/2012: -2 to 15
  • WL1/WL1 (2021,2022,2031,2032): 35-45
  • FSV 2091/2902 set to 3 (joule default is 1)

I don’t know if these settings are remotely close to being optimal!

So key questions:

  • Delta T: I’m becoming fixed on the low delta T when the radiators are warm. I read conflicting views on whether this is an important factor in the efficiency of the system, what do you recommend? I’m not sure if I can achieve a different delta T for HFW and Rads, but if I can should I?
  • PWM pump or not: Should I replace the primary pump with a PWM pump? Would that allow the system to use Water Law/Weather compensation more efficiently?
  • Balancing radiators: I’ve currently balanced the rads to have roughly the same return temp. I read in some places that it is best to have maximum flow through the radiators Including keeping all TRVs fully open. What is recommendation?

Any help gratefully received!

2

You’re sure to get lots of replies…
I’m not a Samsung, Joule, or UFH person but 2 immediate observations, focussing on the space heating:

  1. Your flow temp (Dashboard) a bit high. [edited as I hadn’t spotted it was on DHW when I looked!]. Unless you have too few radiators, a house like you describe should be able to cope with 35C except for very cold weather. Try running for longer periods.
  2. You will get poor COP with return water to the HP being so close to leaving water. Assuming there are no other causes (such as a faulty automatic bypass valve leaking lots of hot water back into the return before it does anything useful), I suggest you get your pumps slowed down a bit. You could also restrict flow to all the radiators so that their dTs are all increased. In practice, I have found that a dT of between 3C and 4C is quite enough to improve my COP to as good as what the data book says, but at 1-2 the COP is WELL below.
3

I have a 16kW AE160RXYDEG, similar to yours but we are all radiators and much older house.

What kills my CoP is the starts, so this year I have gone to full time running, 27@15c, 35@-2c. Getting CoP around 4.5 at 8-10c. It’s also nice to have the home warms at all times.

Flow is about 24l/min, sometimes a bit more.

Radiators - about 1c between flow/return (we have a 50l buffer tank). I’ve tried balancing and fully open, not sure there’s any difference although flow rate seems to go up to 27l/min if I balance rather than fully open.

I don’t use it for heating DHW, I don’t like the power consumption although it gives CoP of about 2. I use PV diverted from solar or overnight cheap elec, this heats the right amount of water for us.

You didn’t mention if you have an external thermostat or use the Samsung control unit?
I have a Tado thermostat which isn’t really fit for purpose (heating via ASHP) but I’m reluctant to move the Samsung control unit as it would have to have a longer cable than Samsung recommend.

Edited to correct 25 to 27@15c

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Thanks Christian, that’s very interesting. Your performance is significantly better than mine, though I thought I’d read somewhere that radiators need a flow of 33 or more for convection to work. Clearly it’s working for you at much lower flow temps. Your anecdotal experience about balancing is also food for thought.

We don’t have an immersion heater so don’t have a choice atm about DWH. We don’t have a separate external thermostat, I just take the reading off the control unit.

There are 4 thermostats controlling the downstairs UFH and one for the upstairs radiators.

5

Thanks Adam - I assume you have a PWM pump?

I did discuss flowing down the flow rate with Joule and they said the minimum recommended flow for my system was 20 l/m, lower than that would most like cause the unit to raise errors.

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Do these call for heat, or just open/close the circuits?

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As far as I understand, Joule keep the heating circuit open all the time (that’s what the remote controller seems to show) and then the individual thermostats call for heat.

8

I have a UPM3 which has 3 speeds and a PWM input for which I built my own controller. I run at about 50% of the lowest crude speed setting (dramatically reduces flow noise and reduces power consumption to 1/4 of what it was).

I definately endorse Christian’s run at lower temp for longer periods recommendation. As to the efficiency of convection, I believe this also depends on the room temperature. So 25C probably won’t cut it with a desired room temp of 23C, which some folk seem to think is a good design temp (I consider 18C quite toasty FWIW).

9

I’ve had an interesting response from my query to Samsung technical support on this matter:

After reading your email and looking at the data available on Emoncms following your link, the main thing that sticks out is the flow rate. From the Emoncms data we can see a flow rate of 25.7lpm whils an 12 kW heat pump requires 35lpm to efficiently transfer the heat it have the potential to generate in to the building. (25.7 lpm can transfer approximate 9kW with a delta T of 5 degrees, 5K Delta T being what the heat pump is controlling the compressor to achieve)

It is also worth checking what the free circulating volume is in your system, this being the minimum volume of water circulating through the heat pump at any one time.

Your 12kw unit will have a minimum compressor output of around 2.9kW giving that the unit will need about 83 liters of free circulating volume to operate at peak efficiency.

With my pumps set to constant speed, maximum, it looks like I can’t much above 25lpm? I’m trying to find out what this means.

10

The book said we needed 30l/min minimum but it seems to work okay with 24.

I’ve also tried changing my pumps’ speeds but the end result was to run both as fast as possible. That said I did those tests last year running it more like a boiler rather than this year with low flow temps.

Edit: i just checked and I’m running 27/35 not 25/35 as stated in my first reply above.

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It means that you have restricted your maximum output to 9kW according to the Samsung tech. response. I also have a 12kW Gen6 which is about 1.3 times over-size that has a flow rate of 27.6lpm at 100% pump speed. I have recently reduced the pump speed to 70% using FSV 4051 giving a flow rate of 19.7lpm as an experiment prompted by Optimizing flow rate for ideal COP
This seems to have had the benefit of curbing the aggressive startups that often caused overshoots and it means the compressor will spend less time at 100% output so should improve lifetime of the equipment. It doesn’t seem to have had a detrimental effect on COP, it might even have improved it, but early days yet.
Emoncms - app view

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12

Thanks - very interesting. You are achieving better performance than me at higher flow temperatures! I don’t think 4051 will do anything for me as I don’t have a PWM pump.

From this thread Oversized ASHP (Samsung), flow rates, LWT and dT, it looks like the way Joule systems are plumbed with some 22m pipework means they are restricted in the flow rates they can achieve.

I’m coming to the conclusion that I need to prioritise balancing the radiators to get the dT to 5, and see where I go from there.

13

Hi Gary,

I also have the 12kW gen6 Samsung with a pre-plumbed Joule tank (with two Wilo pumps).

My system has all radiators and a 50L buffer tank. My system volume is around 190L.

Some measurements from the two Wilo pumps - with both operating at full speed (setting III), I get max flow rates of around 27.5L/min, 26L/min with one pump turned down to II, 24L/min with both pumps on II, and 21L/min with one pump on I and one on II. I’ve not taken a reading with both pumps on minimum setting (I). Flow rates are a little higher on the DHW cycle than heating, presumably due to less resistance. I am currently running with both pumps on (II) giving flow rates of 24.1L/min for heating and 25L/min for DHW.

I have FSV #2091/2092 set to 1 so that the compressor can be turned ON/OFF only by the thermostat, and I have a separate 3rd party room stat that I use to turn the system ON/OFF. I refer to this as ‘always on’ mode, and I find it useful to run like this for taking COP measurements and seeing what’s happening as the heat pump cannot cycle, and I’m in control of turning ON/OFF (via the room stat).

I typically run flow temps in the range of 32-35C during the day, and set back to 30C overnight. As the system heats up from a cold start, I see a wide dT of around 5-6C on the Samsung controller (I have no external monitoring, so all my readings are taken from the Samsung controller). As the LWT approaches the set temp, the system throttles back and the dT narrows. Once at temp and ticking over, my system settles at a dT of ~3C (note the Samsung controller reports whole numbers so this could be within quite a large range of +/-1).

From my thread above, I was initially quite concerned about the ‘low’ dT, but have since come to realise that it does not appear to be detrimental to my system performance. I don’t have a heat meter, but I do have a MID meter for electrical usage, and combined with the Samsung controller data, my COPs are near identical to Samsung’s published book values for my unit. So I wouldn’t be overly concerned with a low dT if the COP values are otherwise where they should be.

What I do notice when running in ‘always on’ mode (FSV #2091/2092 = 1) is that the LWT will continue to rise is the system cannot dissipate the heat generated. I have calculated that my radiators can only emit 2875kW of heat when de-rated for a flow temp of 30C (at room temp of 20C). In the summer, when COPs are high, this means the minimum heat output of the heat pump is more than my radiators can emit. Normally, if running with FSV #2091/2092 of 2-4, the heat pump would cycle, but in my case it’s ‘always on’, the heat being produced has to go somewhere, so the flow temp rises until the system reaches equilibrium. In the milder months, the lowest flow temp (LWT) I can achieve is around 32-33C. The dT is dictated by the flow rate, and for me this settles out at around dT=3C (as per above). In winter, as the ambient temps, and hence COP, are lower, so is the minimum amount of heat produced and when it’s 2C or below outside, I can achieve an overnight setback LWT of 30C. All the time, the COPs are in line with Samsung’s published book values for my unit.

Have you worked out how much heat your system can emit, and is that in line with the amount of heat your system is producing. A quick back of an envelope calculation for our Samsung unit might be to assume a minimum electrical input of 8-900W, so with a book COP value of 3.27 for a flow temp of 35C at 2C outside, we’d expect the system to produce around 0.9W*3.27=2.9kW of heat as a minimum. Can your system emit that heat efficiently? As above, you can answer that by running in ‘always on’ mode and see if the system is able to equilibrate at 35C (+/-0.5C), or if the flow temp keeps rising.

Have a look at the Samsung reported values for dT (from Master Indoor Zone Information, under Connection Information in the installers menu). Tw1 is the water temp going back into the PHE (i.e, the ‘return’ flow) and Tw2 is the water temp out of the PHE (i.e, the LWT). My system shows a dT of 5-6C as the system heats up to temperature from a cold start, and then eventually settles at 3C once the set temperature has been reached.

In summary, with the same heat pump unit and pre-plumbed cylinder (and pumps) as you, I am able to achieve near book COP values with flow rates of ~24L/min, and a dT of ~3C (with radiators only, no UFH). Hope that helps?

1 Like
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Thanks, this is both helpful and encouraging. Hopefully I can tune my system as well!

I’ll change my 2091/2092 settings back to default and reduce the flow temps and see what happens.

Do you run with WL and, if so, what are your settings for 2011,12,21,22,31,32?

Have you balanced your radiators and if so what process did you follow? As I said, at the moment my are set such that the return temps are similar on each radiator, but I’m struggling to work out whether to open the, completely or restrict them to achieve dT 5

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Yes, I run with WL, but I use a ‘flat’ curve of 32C for both high and low temps. I then manually adjust the flow temp up and down on the front screen of the controller which allows you to manually adjust +/-5C. This is my first winter, so at the moment I’m doing it this way to give me complete control so I can gather some data and have compete control over the flow temps rather than them automatically adjust to the outside temps.

No I haven’t balanced my radiators and I run with all TRVs fully open. The house temp is controlled by adjusting the flow temp and/or the master room thermostat to turn heating on/off.

To be fair, my radiators were all replaced during the install, and were sized to match the heat loss for the room, so assuming uniform flow rates, they shouldn’t need adjusting for output as they should be outputting the correct amount of heat for the room by design.

Whilst you are troubleshooting, I would recommend you fully open all radiators and UFH valves to ensure you have maximum flow and maximum system volume, so you can identify or eliminate that as the cause of your poor COP. Start with your system fully open and pumps on maximum, turn the flow temps (LWT) down to around 35C or whatever is appropriate for your house (you can set a flat WL curve of 35C at both ends to achieve this), run the system constantly (no cycling) for a few hours (or longer) and observe the COP, ambient outside temps and dT once the system has settled. Compare data if you have data available from more than one source (I have an MID electric meter and compare against the Samsung electrical usage data). Just let the system run in an unconstrained state and observe how it is performing.

Do you know what your system volume is? The minimum system volume stated by Samsung is 50L, but this should be seen as an absolute minimum. A more reasonable system volume would be 3-4 times that at around 150-200L. I have around 190L (~95L in rads, ~45L in system pipework and a 50L buffer tank) in my system. A low system volume can cause the system to cycle giving poor COPs

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Experimenting this afternoon with open values, always on etc, with a fixed WL temp of 35 I was able to achieve equilibrium when only the UFH was operating. When repeating the experiment with only the upstairs rads on the temperature rose above the fixed WL and kept rising slowly.

I don’t have any design documentation for my system (I know!) and so don’t know my system volume. I (think I) know that I don’t have a buffer tank.

I also don’t know if the system has been installed as per the design eg are the radiators the correct size etc. I’m still trying to get hold of the design documentation and will do more experiments over the weekend.

I’m becoming convinced the issue lies with just the radiators but don’t know how to prove that nor how to fix it! Thanks for all your help so far!

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Why do you need to use the upstairs radators without the downstairs UFH?

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I don’t necessarily need to use the radiators without the UFH. My system has 5 thermostats controlling room temperature, 4 on the UFH and 1 upstairs on the radiators. I’ve noticed that the COP is much better when only the UFH is operating but is much worse when the radiators are operating.

19

I’ve had another look at your dashboard, Saturday 25/1 afternoon/evening.

This is my interpretation of your data, I’m not a heating engineer but I have had a Samsung Gen 6 16kW for over 3 years.

After presumably a DHW cycle, you got pretty nice performance until it switched off just after 6pm.

It comes back on a couple of hours later. The water in your system is cold and it’s colder outside so a lot of power is needed to bring it back to the desired flow temp. It was just getting back into the efficient zone at 22.40 but then switched off soon after.

The 26th has a similar story, using loads of power to heat cold water then switched off just as it doesn’t need so much power to keep it all warm.
It looks like at 09.00 one of your zones opened up, putting cold water back into circulation.

Look at the power consumption on both days as it reduces approaching 18.00. This is what you should be aiming for; wouldn’t it be nice if it always ran at that level or lower?

I think it should, if you:

  1. aim for constant running (or at least, much longer periods of running)
  2. open all zones, all the time
  3. get your weather compensation right for your house
  4. deal with any areas that get too hot after you have got your key areas right

To set my weather compensation, I set the targets as low as I thought they could reasonably be (25@15, 35@-2). The weather was mild.
The living room only got to 2c cooler than we wanted so I apologised to Mrs D, got her a hot water bottle and increased both by 2c to 27/37.
It got a bit too warm so reduced to 26/36.
It went sub-zero outside so changed to 27/36.
Mild again, too warm, 27/35,
When it was really windy recently I added a degree to both.
Then the winds died down so returned to 27/35.
There was quite a bit more tweaking but I kept a log of what I changed, when & why.

I have compared my power consumption for 2 similar days.
Last year 30/Jan with average temperature 8.6c the system consumed 29.1kWh running like yours, on for a total of 10 hours out of 24. Simulated CoP 4.0.
This year 24/Jan, same average temperature, 25.4kWh, running for all 24 hours. The house was always comfortable and the simulated CoP from the heat pump app is 4.94, the Samsung figures are 22.3kWh used, 114.4kWh generated.

I hope this helps and that you find a way of running you are happy with.

20

I was just thinking; you’ve got 4 thermostats on the UFH and 1 on the upstairs radiator.

What exactly is turning the heat pump on/off?