In general lower FT = higher efficiency.  

These are only 1C apart however and with different outdoor temps, but perhaps more importantly both have an indoor temp of ~15.  Is that your target indoor temp?

In general (in most cases) start by setting your FT as low as you can (with the heating operated 24x7 and all zone valves/TRVs fully open), consistent with the house being warm enough. 

You can tweak starting from that point, but thats the starting point for max efficiency and usually lowest cost, unless you have a heat pump which is well oversized and a strong ToU tarrif.

The exact waveform does matter too much it’s the average  that matters. I can’t read the scale too well but both shapes look reasonable. There’s no need to stress about tiny details.
Do you have a smart meter to compare with?

I find the graphs somewhat hard to reconcile against the references to 31 or 32 @ 3° ambient as in both the flow temperature seems to be targeted at the mid/high 30s and the ambient is a few degrees above 3. Surely the 11.3 noted against the power line can't mean its drawing 11.3kW?

I like the look of the second graph, fewer cycles and more periods of even output, but as JamesPa states the ambient temp (known round these parts as the OAT - Outside Air Temperature) is slightly higher and that alone will be enough to change the operational choices of the pump's software.

I suspect a 12kW sized unit is larger than you need for a medium-sized house that appears to be well insulated, and a target temperature of 15 or 16°C is on the low side requiring less heat to be generated. You may well be operating at the lower end of the capacity range of the pump already.

Posted by: @ivanhoew

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My question is , if  i set the heat curve at 32c @ 3c ambient , i get one waveform , and if i set it at 31c ,i get a  diferent one .and different cycling rates 

which one is most desirable?

The second lower one is marginally among purists perhaps more desirable, but as @judith says, you don't need to stress about this.

I'm pretty sure the two charts straddle the point at which your heat pump changes from mostly steady state running to cycling. The upper chart (LWT 31 degrees) is at the point where the heat pump has to cycle to modulate, the lower one (LWT 32 degrees is just into the range where it can manage at least some steady state running. Typically, heat pumps have three operations modes depending on LWT/OAT: a mid range where it can modulate parameters enough to achieve steady state, a higher OAT/lower LWT range where it has to cycle to reduce output sufficiently, and a lower OAT/higher LWT range where it uses defrost cycles. 

If, as @harriup suggests, tour heat pump output is on the high side for the demand, the you will be more likely to get cycling, because there will be more times when the heat pump can't lower output enough without cycling. In general, the larger the heat pump, the higher it minimum as well as maximum output. This is one of the reasons why it is a good idea to match the heat pump output to the heat loss as closely as possible, just banging in large one makes it much more likely you will get cycling.

The cycling you have is relatively low frequency, maybe every 30 mins in the upper chart. Nil desperandum.  

Gosh !  thank you for all the replies , i'll quote each one and try to anser the questions in them ..

Posted by: @jamespa

↑

In general lower FT = higher efficiency.  

These are only 1C apart however and with different outdoor temps, but perhaps more importantly both have an indoor temp of ~15.  Is that your target indoor temp?

In general (in most cases) start by setting your FT as low as you can (with the heating operated 24x7 and all zone valves/TRVs fully open), consistent with the house being warm enough. 

You can tweak starting from that point, but thats the starting point for max efficiency and usually lowest cost, unless you have a heat pump which is well oversized and a strong ToU tarrif.

Thank you James , 15c is my indoor temp at night, 16c during theday .working outside on the banrs meanswhen i come in that feels quitewarm , then i use my tiny wood burner in the sitting room at tv supper time .

ihave been trying not using the thermostat in the hall , and setting the flow temp to keep the hs at 16 ,but i am concerned about the rapid cycling phenomenon , i can see the ashp is switching on and off more rapidly with the 31c , but from comments i can see here , it appears to be within acceptable parameters, and not about to hit a freqency of operation likely to damage itselt or the ears of the local dog population .

i have a  suspicion than my heat pump is oversize .

regards

robert

Posted by: @judith

↑

The exact waveform does matter too much it’s the average  that matters. I can’t read the scale too well but both shapes look reasonable. There’s no need to stress about tiny details.
Do you have a smart meter to compare with?

Thank you Judith ,

i do have a smart meter ,and also the foxcloud and energy stats apps , however i find it a little hard to compare the exact power usage for each setting ,,,must try harder!  keeping everything ,ext temp , internal temps, the same ,while varying the flow temps , and trying to compare energy used over a set time , is hard , i can see the amps used seemshigher on average wit hthe higher flow temps, but ,,,its cycling less times an hour too .....

i dont find this stress , just an interesting  problem ,which uses less energy for the same hs heat .

regards

robert

Posted by: @harriup

↑

I find the graphs somewhat hard to reconcile against the references to 31 or 32 @ 3° ambient as in both the flow temperature seems to be targeted at the mid/high 30s and the ambient is a few degrees above 3. Surely the 11.3 noted against the power line can't mean its drawing 11.3kW?

I like the look of the second graph, fewer cycles and more periods of even output, but as JamesPa states the ambient temp (known round these parts as the OAT - Outside Air Temperature) is slightly higher and that alone will be enough to change the operational choices of the pump's software.

I suspect a 12kW sized unit is larger than you need for a medium-sized house that appears to be well insulated, and a target temperature of 15 or 16°C is on the low side requiring less heat to be generated. You may well be operating at the lower end of the capacity range of the pump already.

thank you HarriUp ,

I can see what you mean , and my guess is the flow temps are being measured at the pump , and ,by the time its got into the hs its dropped a touch , and then also its creating an average of 31, by exceeding then dropping beloww ,whcih over time creates that average temp .

yes! that is 11.3 kw !! ...scary,and depressing ,i just assumed thats how they all work .

i will admit , going from my old electricity usage , of 6 kw a day , to 20-30kw over the -9c days lately is a hell of a shock , especially at a house temp of 16c

but hey i must remember i am not burning 50-60 litres of heating oil a week .

Re the second graph , that is how i had been running it up to now . i am just starting to get into the system and whether its at its best ,due to the fact i can now data log and graph the design.

with this pump ,  i can program in 5 ambient temps , and 5 flow temps , so i have good control over the graph of amb/FT.

Yes , i think youre right re lower areas of this pumps capacity , a12 kw may well be too big . at ambient of 10c i can use 28-29 as my flow temps .

regards

robert

Posted by: @cathoderay

↑

Posted by: @ivanhoew

↑

My question is , if  i set the heat curve at 32c @ 3c ambient , i get one waveform , and if i set it at 31c ,i get a  diferent one .and different cycling rates 

which one is most desirable?

The second lower one is marginally among purists perhaps more desirable, but as @judith says, you don't need to stress about this.

I'm pretty sure the two charts straddle the point at which your heat pump changes from mostly steady state running to cycling. The upper chart (LWT 31 degrees) is at the point where the heat pump has to cycle to modulate, the lower one (LWT 32 degrees is just into the range where it can manage at least some steady state running. Typically, heat pumps have three operations modes depending on LWT/OAT: a mid range where it can modulate parameters enough to achieve steady state, a higher OAT/lower LWT range where it has to cycle to reduce output sufficiently, and a lower OAT/higher LWT range where it uses defrost cycles. 

If, as @harriup suggests, tour heat pump output is on the high side for the demand, the you will be more likely to get cycling, because there will be more times when the heat pump can't lower output enough without cycling. In general, the larger the heat pump, the higher it minimum as well as maximum output. This is one of the reasons why it is a good idea to match the heat pump output to the heat loss as closely as possible, just banging in large one makes it much more likely you will get cycling.

The cycling you have is relatively low frequency, maybe every 30 mins in the upper chart. Nil desperandum.  

Thank you cathodeRay,

 It looks like neither flow temp graph is horrific , thats very reassuring , and i think the conversational  trend is that my pump is a little on the big size .

I wonder if there's anything i can do to encourage steady state running to use less overall kw , would it be worth me running at say 33 or 34 c FT, and casuing a longer session of steady state , and fewer cycles per hr  ?

by the way , i should point out the time scale on the bottom line is 8hrs advanced from uk time .

regards

robert

just in case it helps , here is my graph for the last three days on the ashp , and also the energy usage for january day by day to today ..

regards

robert

@ivanhoew - most if not all of what you need to understand your heat pump's behaviour is on the second chart. Here's an annotated version: