Hi @hydros 

Because your Daikin controller has been configured to expect an enable signal from a thermostat, it will respond to this signal as the primary on - off instruction. Basically, the heat pump will not operate unless the thermostat gives it permission. So if the thermostat reaches the specified temperature, and removes its permission then the heat pump will stop.

Once permission to run has been granted by the thermostat, the Daikin controller will then decide whether the heat pump needs to run or not. It will check to see if the leaving water temperature has achieved the calculated value, and if not it will start the compressor and water pump. Without access to the actual control logic it is difficult to state definitively, but I would assume that the follow may occur. As the leaving water temperature increases towards the desired value, the compressor speed will start to reduce, the fan speed may also be lowered. When the desired leaving water temperature has been achieved, the compressor will continue to run at this lower speed, and supply heat energy into the home. Initially the warm water coming from the heat pump will push the colder water from the heat emitters back to the heat pump, where it in turn will be heated. Soon there will be only warm water being circulated around the system, but because some of the heat energy is being extracted from the water by the heat emitters, the return water temperature will always be lower than the leaving water temperature. As the temperature within the home starts to increase, the heat transfer rate from the heat emitters will reduce, so the return water temperature will start to increase. This in turn will cause the leaving water temperature to increase above the calculated value, so the controller will lower the compressor speed to try to prevent the temperature increase. When the compressor reaches its minimum operating speed, the controller will probably have already reduced the water pump speed to its minimum, so the leaving water temperature will continue to increase until the leaving water temperature reaches the upper limit and the heat pump is stopped.

So to try to discover what is happening within your system, you may have spend a little time monitoring its operation. Ensure that the thermostat and wireless adaptor are not removing the permissive signal prematurely. Observe the operation of the heat pump, noting changes in leaving water and return water temperatures, along with flow rate. Listen to the speed variations of the compressor and fan and try to estimate how hard it is working. 

@derek-m thanks again for the info.

So I sat with the heat pump controller for two hours this evening recording data every five minutes, I can post the data if you like (?!), what a way to live! It would initially appear the remote thermostat wasn't close enough. There is interference I think, maybe smart lightbulbs or the wifi. I moved the thermostat in to the same room and it didn't switch off once. The heat pump had an hour of running, then the defrost cycle kicked in, it did only then restart for a few minutes before switching off, but it restarted again soon after and ran for another hour. The house is toasty and its 1C outside. 

I am away for a few days from tomorrow but will continue to keep an eye on it over the next week, and feedback if you are interested.

PS - I'm also feeding back to my installer who are paying attention but due to some fairly unique circumstances are not local and can't drop by easily.

Hi @hydros 

It is always highly useful to get feedback, not only for my own benefit but for the other site users who may be experiencing similar problems.

Hi @hydros 

I forgot to mention, if your home is going to be unoccupied whilst you are away for a few days, you may wish to turn down the heating a little. The easiest way would be to use the offset on the Daikin controller to lower the setting by 2C to 3C, which could possibly reduce the energy consumption by up to 20%.

I've got a query about my heat pump

It seems to come on say every 20-30mins (maybe longer not actually timed it, maybe only once per hour) at night for say 5-10mins and then turns off again

No heat is being called or dhw etc and I don't think it is defrosting 

What I have noticed is it seems to do this more when it is colder (eg last night)

Any ideas? Is this normal behaviour? 

@hr_3 

To be able to provide meaningful answers I would need more information about your system, its controls and how you want it to operate.

@derek-m 

Still good news I think. I've had about a week of running using the weather compensation curve. The house is definitely warmer, almost too warm overnight. COP has crept up from ~2.9 to ~3.1. It seems that when the desired running temperature is higher the heat pump runs well, but when it's running cooler, for example yesterday during the day when it was 10-11C outside the desired leaving water temperature was 30C-29C, the heat pump would stop quite often. The current compressors cycles show 6.2 starts per hour of running, whereas before Christmas when it was colder this value was just 3.4. The house is still warm enough at this lower running temperature, in fact slightly too warm, but the compressor cycling does worry me a little for early failure of that component. 

I'm wondering if it could be something to do with the radiators not bring able to give off enough heat when the system is running at a lower temperature, or should they always have a temperature difference regardless of water temperature flowing through them, in which case something isn't running correctly?  

Is this something I should be highlighting with my installer or just accept that this is how the pump operates now? I still need them to come back and replace the thermostat because having it sat next to the heat pump controller in the utility room is not right. 

Posted by: @hydros

@derek-m 

Still good news I think. I've had about a week of running using the weather compensation curve. The house is definitely warmer, almost too warm overnight. COP has crept up from ~2.9 to ~3.1. It seems that when the desired running temperature is higher the heat pump runs well, but when it's running cooler, for example yesterday during the day when it was 10-11C outside the desired leaving water temperature was 30C-29C, the heat pump would stop quite often. The current compressors cycles show 6.2 starts per hour of running, whereas before Christmas when it was colder this value was just 3.4. The house is still warm enough at this lower running temperature, in fact slightly too warm, but the compressor cycling does worry me a little for early failure of that component. 

I'm wondering if it could be something to do with the radiators not bring able to give off enough heat when the system is running at a lower temperature, or should they always have a temperature difference regardless of water temperature flowing through them, in which case something isn't running correctly?  

Is this something I should be highlighting with my installer or just accept that this is how the pump operates now? I still need them to come back and replace the thermostat because having it sat next to the heat pump controller in the utility room is not right. 

Hi Hydros,

If the indoor temperature is being maintained, then the radiators are emitting sufficient heat energy, even at lower water flow temperatures. If you are still getting some cycling at outside air temperatures below +5C, then it is possible that the weather compensation curve is still too high. Try lowering each end of the curve by 1C. I can't remember the settings on your system, but if it is presently set for a water flow temperature of 45C at an outside air temperature of -10C, then lower the 45C to 44C. If the setting at the other end is 25C @ 18C, then reduce the 25C to 24C. Monitor the system operation for a day or so, to see if there is any change in the frequency of the cycling. If you are still getting cycling at low outside air temperatures, then lower the compensation curve by a further 1C.

Cycling will probably occur at outside air temperatures above 7C to 8C, because the heat pump is probably running at its lowest speed, but is still producing more heat energy than is required to meet the heat demand.

Is it a thermostat that you would like your installer to move, or the Daikin controller?

@derek-m 

The cycling is only occurring at outside temperatures above about 8C so probably nothing to worry about. COP for yesterday was 3.18, not bad but I was hoping for a little better. Not sure what else I can do to improve this?

Regarding thermostat. It is a remote thermostat that the installer fitted, which gets interfered with by something in the house, so this needs replacing with a different model. I like the idea of a smart version to be able to see some stats on the house temperature but from the experience over the last week, I think it's something that will mostly be forgotten above once weather compensation curve is fully optimised, so a basic wired version is probably sufficient. 

Posted by: @hydros

@derek-m 

The cycling is only occurring at outside temperatures above about 8C so probably nothing to worry about. COP for yesterday was 3.18, not bad but I was hoping for a little better. Not sure what else I can do to improve this?

Regarding thermostat. It is a remote thermostat that the installer fitted, which gets interfered with by something in the house, so this needs replacing with a different model. I like the idea of a smart version to be able to see some stats on the house temperature but from the experience over the last week, I think it's something that will mostly be forgotten above once weather compensation curve is fully optimised, so a basic wired version is probably sufficient. 

@hydros,

is the COP you quote for everything, i.e. heating  + HW? When your heating demand is low, the overall COP is influenced more  by HW, which will normaly have a lower COP because of its higher temp. 

@kev-m 

Yes, the COP is for both. I didn't use much hot water yesterday, so most of the demand was on the heating. See screenshot below for the last week. The legionella cycle dropped the COP for obvious reasons. I'm not able to split out the COP between heating and hot water with the info I can collect. COP for hot water is pretty rubbish on my system, I could tell this during the warmer months, when the heat was off, it was about 1.5 on average, I don't know if that's typical. A way to improve this would be awesome but I think that will involve a better tank setup.

@hydros Is the pump using more electricity now you're heating 24 hours a day ?