Bit more detail: this is mine today with 4-min dropouts. Definitely not defrosts: the flow temp never drops below return and I've watched it happen, there's no frost.
The heat pump is being stopped because the thermal energy output being produced, is greater than the minimum value possible under the present operating conditions. It is not timed, but due to changes in LWT. If the heat did not stop the LWT would continue to increases, which in turn would cause the IAT to increase, and hence the building heat loss would increase to the point where the system balances.
At lower ambient temperatures the loading on the heat pump is greater, which causes the cycling to stop.
@rod what is the difference between your flow and return before the drop outs?
I find mine will run continuously if the dT is no closer than 2C to 3C (2 hours from yesterday afternoon below with no cycling) once you get to <2C then it wants to cycle, that's will all my UHF circuits open and rads upstairs open if I restrict any of those then it will start to cycle. If I try and run it any cooler than 32C then it will also cycle.
Just like a car engine has a minimum 'tick-over' speed, a heat pump has a minimum thermal energy output, below which it cannot modulate down any further.
The DT reduces because the heat pump is producing more thermal energy than the heat emitters can emit, so the RWT starts to increase, which in turn probably pushes up the LWT.
As described above, the heat pump therefore needs to stop periodically to prevent the temperatures rising too high.
As you state, lowering the LWT or reducing the heat emitter capacity will probably cause cycling to happen more frequently.
@derek-m I think that you are correctly interpreting the algorithm that is being executed, my surprise is that the pump can run at lower power consumption rates - it can go down to 750W which must mean the compressor can run at lower speeds, being the main thing that's doing work. If it were down to the lowest power consumption, I'd be happily accepting that it is just cycling, but the fact that I know it can go lower power but chooses not to is why I think there's some other algorithmic component that I can't explain away.
@rod I don't have monitoring on the Heatpump itself but the house load with my heat pump running is about 1KW and my background is around 200W so at 32C my heat pump is pulling about 800W so at its miniumum. Mine is an 8.5KW unit
@derek-m I think that you are correctly interpreting the algorithm that is being executed, my surprise is that the pump can run at lower power consumption rates - it can go down to 750W which must mean the compressor can run at lower speeds, being the main thing that's doing work. If it were down to the lowest power consumption, I'd be happily accepting that it is just cycling, but the fact that I know it can go lower power but chooses not to is why I think there's some other algorithmic component that I can't explain away.
Because of the way a heat pump works, lower Energy In does not always equate to lower Energy Out.
A heat pump 'harvests' most of the thermal energy from the ambient air, with the remainder being obtained from the electricity supply, so the more it can get from the air, the less it requires from the electric.
The compressor will be running at the speed and power required to maintain the pressure and temperature of the refrigerant gas going into the Condenser, at the required level for the present operating conditions. When the heating demand is increased, more thermal energy is being extracted from the refrigerant gas inside the condenser, so it condenses at a faster rate. As the refrigerant changes from a gas to a liquid, its volume is reduced dramatically, which in turn tends to lower the pressure within the condenser. To counteract this reduction in pressure, the compressor will run faster and work harder, and hence use more electrical energy.
In the real World, the controller will be continually monitoring the required pressure and temperature, and varying the compressor speed to try to keep it reasonably constant.
Bit more detail: this is mine today with 4-min dropouts. Definitely not defrosts: the flow temp never drops below return and I've watched it happen, there's no frost.
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Very curious, this Rod
Ive always understood from heat geek video that the poorest efficiency stage is at the beginning of a HP Operation cycle and gradually gets more efficient with continued operation. However your graph shows higher energy consumption as the cycle progresses and peaking right at the end before it closes down. This suggests a double whammy in that the start may still be inefficient but what’s causing the strain and energy rise towards the end of the cycle?
i also note the DT is gradually rising during the cycle and not regulating downwards. I’m not sure what’s your set up is so there may be a logical explanation perhaps UFH etc.
@rod This pattern is very familiar to me as it just how my heat pump chooses to operate. Under WC it would cycle more frequently but using AA it is around an hour between each break. The overall shape of the power draw cycle too, a bumpy lower stretch followed by a sustained rise and then off for a period of time that depends entirely on the OAT. As it is running in AA mode the algorithm has control over the LWT it wants to achieve, and there is no obvious reason why it could not choose to run for longer with a more even power input and maintain a constant lower LWT. Very occasionally it does somewhat, but it is almost odd when that happens. The image of the consumption from this afternoon shows one of these odd times when it is flat in the middle for 45mins, but the three cycles on the right are more typical of the pattern of power usage, and so similar it surely indicates a decision by the software to run this way, however much I might form an idea of how the pump 'should' function.
Mitsubishi EcoDan 8.5 kW ASHP - radiators on a single loop 210l Mitsubishi solar tank Solar thermal 3.94kW of PV
@rod This pattern is very familiar to me as it just how my heat pump chooses to operate. Under WC it would cycle more frequently but using AA it is around an hour between each break. The overall shape of the power draw cycle too, a bumpy lower stretch followed by a sustained rise and then off for a period of time that depends entirely on the OAT. As it is running in AA mode the algorithm has control over the LWT it wants to achieve, and there is no obvious reason why it could not choose to run for longer with a more even power input and maintain a constant lower LWT. Very occasionally it does somewhat, but it is almost odd when that happens. The image of the consumption from this afternoon shows one of these odd times when it is flat in the middle for 45mins, but the three cycles on the right are more typical of the pattern of power usage, and so similar it surely indicates a decision by the software to run this way, however much I might form an idea of how the pump 'should' function.
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harryup
it looks, to me, like a clever way to modulate when the HP Can’t operate at a low enough flow temp. It’s clearly shortened the cycle to 30 mins on-time. That’s after the wide cycle.
Perhaps there was a change because your set temp was reached? Or a new target was set?
I note you are operating rads and an ecodan8.5 which is the same situation as ours.
We are not getting cycling like this so wondering what’s different. We have 180m floor area and 21kw of rad capacity (at DT50 rating) how does yours equate? If you know? We are also operating at 35c. To 38 mostly when in Auto Adapt at the moment. I noticed @rod was operating his UFH at30C Andy he has a ecodan 11.2kw in 130sqm.
regarding the rise in power output before the pause - we get that rise on our cycles just before a brief shutdown. Ive explained this away to myself that the HP is preparing to shut down so putting a slight boost in before a programmed pause period. It’s just a theory.
Here, perhaps you can see the slight rise in flow temp before the pause.
I've remembered something that may explain it; some FTC6s were supplied without the energy delivered functionality. I don't know if it was hardware or software or if anything can be done retrospectively.
This was my experience too, and our installers removed the FTC6 and replaced it with an FTC5. Otherwise, I believe, you have to invest in the dedicated energy monitoring kit.
On our system this morning, set temp has been passed by 0.5c and the current cycle is continuing. It is about 90 minutes long and still running at the moment this image was taken.
It will probably shut down for an hour when it stops to allow the room temp to drop 1 degree.
There’s was a bit of an increase to the flow temp at about 12.28pm But the room temperature has remained constant between 19 and 19.5 so I guess our heat loss more or less matches our Auto adapt settings at these outside temperatures. 7C.
Mine has cycled quite steadily twice an hour today in these warmer temps. I’ve lowered one end of the curve to 30 now (so now at 42/-4, 30/15). A couple of questions on this - I think it could probably go a bit lower still, but the 42 end was right for the colder temps. Is there any issue with a steeper WC curve? And (this one is probably obvious to those in the know) are lower flow temps likely to make the cycling more frequent?
overall since I started using WC comfort has improved dramatically though. Although I don’t think I’m using much less energy overall (30-40kwh a day this week for the whole house, so inc. appliances etc. I feel this is probably still quite high relative to others?), it is being used to much greater effect
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