@jamespa Oh, so ill just lower cold end again so as i think house is warming up too quick and im having to stop the pump.

Posted by: @newhouse87

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@jamespa No DHW cycle is 2-3pm, this was much later. Judging on my curve, @7.2deg, what should flow temp be? Maybe its ok. Using lot less KWH last few days which is good as i have been lowering flow temp since and slab is probably warmed up.

Based upon the setting of your WC curve, the calculated flow temperature should be 29.6C.

@derek-m Thanks, was calculating it as average between cold and warm end and was getting near that@30 but wasn't sure if that was correct. Luckily i think i should be further able to reduce flow rate and get to continuous flow at few degrees even lower. I will re calculate cop then but seems a lot better then last winter. only oddity at moment is that flow rate modulates down at times, is that due to delta t maybe?

Posted by: @newhouse87

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@derek-m Thanks, was calculating it as average between cold and warm end and was getting near that@30 but wasn't sure if that was correct. Luckily i think i should be further able to reduce flow rate and get to continuous flow at few degrees even lower. I will re calculate cop then but seems a lot better then last winter. only oddity at moment is that flow rate modulates down at times, is that due to delta t maybe?

If you have a modulating pump and a heat pump that modulates it then yes (and if they have been correctly connected which isn't always the case where the water pump is external), the flow rate will be varied by the heat pump to achieve a target deltaT.  

@jamespa mine is daikin altherma low temp split, its all enclosed, no external pump, but prob has to have internal modualting ump i suppose.

So if delta t is reducing, the flow rates reduce, that indicates house is after taking enough heat?

Today for example temp was 29.6 and return 24.6@10deg. The pump was circulating water at 14l/min, usually it starts off at 34l/min. It then shut off totally.

IM wondering, is there a lowest lwt that the pump will operate at. My flow temperature has never gone below 29 i think no matter outside temp. finding it hard to get to lower lwt to run continuously. I set offset minus 2 on main screen when it was operating at 29 and then shut off, indicating that maybe 29 is lowest lwt i can run at, is that possible that pumps cant below certain lwt. If thats the case i wont be able to get to flow temp that will warrant running continuously.

Just an addendum, leaving for the night shift an hour ago, lwt was at 27 and rwt 24.1, flowing approx half of capability then shut off again. Essentially is it that since i have been using higher lwt, i need to wait for floor to cool down as rwt still too high to run at new lower lwt as dleta t of 5 not possible. Apologies all the questions but if i don't ask i will never know. 

Posted by: @newhouse87

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Just an addendum, leaving for the night shift an hour ago, lwt was at 27 and rwt 24.1, flowing approx half of capability then shut off again. Essentially is it that since i have been using higher lwt, i need to wait for floor to cool down as rwt still too high to run at new lower lwt as dleta t of 5 not possible. Apologies all the questions but if i don't ask i will never know. 

As I explained previously, correctly adjusting the WC curve is a slow process that cannot be rushed.

Gas boilers and oil boilers cycle, so why not heat pumps?

Heat pump cycling is to be expected in the shoulder months, when the OAT can go from 5C to 15C over a few hours some days. As Kev has suggested, one way to reduce cycling frequency could be by increasing the warm end of the WC curve or alternatively increasing the Offset value, and then setting the thermostat say 1C above desired temperature.

The probable cause of cycling is that the heat pump is producing more thermal energy than can be absorbed and distributed by the heat emitters with the present level of heat loss. This causes the RWT to increase, which in turn will cause the LWT to rise above the required level. The heat pump controller should reduce the compressor speed so as to produce less thermal energy, but of course there is a limit to how low the compressor can go.

The problem may be reduced if the heat pump controller can also reduce the water pump speed.

No easy solution, other than to buy one of the heat pumps containing a large and small compressor, when one of the manufacturers takes up my idea and designs one.

@derek-m hmm, was hoping for an easy solution, cant say i have had this issue running at higher lwt or at least i dont know i had. House is warm and it doesn't appear to be using much energy so maybe i should worry about it less. I was just trying to  get to lowest lwt i could to run continuously. Not as easy as i have hoped as i never took into account the heat pump cycling. Should cycle less in colder i suppose.

"The problem may be reduced if the heat pump controller can also reduce the water pump speed." Do you mean the flowrate?

Posted by: @newhouse87

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@derek-m hmm, was hoping for an easy solution, cant say i have had this issue running at higher lwt or at least i dont know i had. House is warm and it doesn't appear to be using much energy so maybe i should worry about it less. I was just trying to  get to lowest lwt i could to run continuously. Not as easy as i have hoped as i never took into account the heat pump cycling. Should cycle less in colder i suppose.

It is probably just a matter of gradually adjusting the WC curve until you get the correct values for your home.

@derek-m Looks like i have gone too low so with the wc curve @32-5 and 25@20 so. Seems to keep house warm at that curve though just have introduced cycling.

No logic to letting floors cool down with no heat and then start heating again as RWT wont be as high this time around allowing a lower lwt long term.

Posted by: @newhouse87

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@derek-m Looks like i have gone too low so with the wc curve @32-5 and 25@20 so. Seems to keep house warm at that curve though just have introduced cycling.

Slow cycling at this time of year is not a bad thing, provided it keeps your home warm and does not use loads of energy. Short cycling (more than 6 times per hour) is to be avoided if at all possible.

Gradual adjustment of the WC curve is the preferred method, otherwise you could be just chasing your tail.

@derek-m Essentially its the delta t causing my pump cycling, so i need to alter curve so rwt isnt getting so close to lwt. That indicates to me that lowering my weather curve has caused this. as i dont recall it happening before. The pump does slow flow rate which should increase delta t but when it doesn't get to the 5deg it shuts off for a while. As you said the milder weather today doesn't help but it seems trying to achieve the lowest lwt is also causing cycling. I will bring back up the curve and see how it acts as i presume its not possible to lower curve anymore as it would only increase cycling.