Posted by: @boycey

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@toodles hi, I think you may of mis understood my post, I'm happy with my temps atm, and I'm monitoring them as the oat getting nearer 0C and will tweak as needed. My post was, am I thinking right, aiming to keep the third party stats above the obtainable room temp so they are always calling for heat, ie so the loops are all open and flow temp is just right to keep rooms at, for example 20.5c or whatever the comfortable level is for any one using this thought process. If one can get the weather comp curve just right, the ufh will continually run just the right flow temp, ie low and slow.. is this the right way to try and run my heat pump.

principles are good. 
regarding DT3 this may or may not be issue.

May be issue- if flow rate is high (I believe the 5kw model has a low flow rate, less than 14 LPM.) or you have a low loss header with balance issues. Or WC curve is calling for too low a temperature for the HP to keep operating at (leading to cycling) 

May not be an issue- if HP is trying to minimise output (modulate) if your WCcurve is asking for a low flow temp and the heat pump can manage to run at that low output without cycling.

three questions- 1 what’s your flow rate compared to optimum in data book? 2 what’s your total emitter heat loss when running at 25c in an ambient of 20c? 3 is the answer to Q2 equal to or higher than the minimum output of the 5kw model? If the output capability is less than the min operating output then there may be short cycling.

questions easy but answers may be bit harder.

maybe try posting an hourly operation graph off MELCloud showing flow and return temps and cycling frequency.

also try moving flow temp up one degree at a time if you want to stop cycling… if that’s a problem.

When ambients are colder cycling should get less. So any problems may be less noticeable.

Also raise your room stat a bit higher incase you’re getting room stat cycling instead of output short cycling. If your WC curve is set accurately to your heat loss temperature gains in room should be very slow.

Hi @boycey

Optimum flow rate is 9 LPM for the PUZ WM50. Max/Min is 6 to 14.

@sunandair Hi thanks for the questions, im not sure i can answer then fully though but hes what i can say.

1. i have the MCs cert and under floor flow rates from commissioning, Design flow rate 7.2L/M (7 rooms all at 1l/m each) then Actual  adds up to 9.8L/M, 2 rooms at 1.5, and 2 at over 2L/M. The cert also say flow rate 45deg and SCOP of 3.65. but i can't see any where near that when i use the consumed and delivered figures on the FTC6.

my pump was set to speed 5 originally approx 14 L/M when we first moved in, ive got it down to speed 2 now =9L/M.

2, not sure where this info is

3, nor this 

so ive reduced the pump to what seems a better rate i think, should i be looking at the manifold rates and adjusting them to compliment the pump flow rates now, and bring them closer to 1 for each room?

ill see if i can get the melcloud hourly graphs

@sunandair Hi here's the hourly screen shots from 6am til now 3:30pm, DHW comes on at 11am

That’s great @boycey  

it might help to know how warm the room was at 14:00 and what was the outdoor ambient at the same time. It looks like the cycling increases once the floor has been heated for a few hours…. As though it reaches a certain saturation temperature.

your DHW cycle shows it’s keeping a steady DT OF 5c

reverting to space heating also good 

interesting that 14:00 graph shows heating after the ramp up. 
I think I see return water (black line) coming back a bit too warm so the line  curves upwards. forcing the flow temp (LWT) to also rise- until it reaches 30c which is presumably target flow temp so it shuts down for a while
That would suggest insufficient heat is being offloaded into the floors to allow the 30c flow temp to continue, for whatever reason. 

Others may have a view as to why. But it does seem to behave differently the next hour. 

I think your model heat pump has a minimum output of around 1.9 to 2.4kwh depending on outdoor temperatures.

Do you know the construction of you UF heating is there poured concrete or insulation under it? Spacing of pipes? Floor coverings… These things affect the performance of the heat emitting surface. 

@sunandair hi. So if the Delta T is OK when doing DHW that's good, but not so on ufh? Could this be the flow rates on manifold need adjusting, I've reduced the pump flow, not sure what the rates are on the manifold as its behind the washing machine, I'll have to pull it out whilst the system is calling for heat. Am I correct in thinking the flow rates on the manifold could be a bit high, as per the commission doc designed at 1 l/m per room but some were set up at 2 l/m? So maybe by reducing these the delta T for heating would be better?

Oat was around 4 deg at 14:00, rooms at about 20.5 deg stats at about the same or just calling 

I don't know the construction, but it's 2 years old, I assume poured concrete with insulation, LVT main living area kitchen/diner/lounge and hall, tiled baths, and carpeted bedrooms. Top floor in block, south facing front and east on one side 

hi @boycey I don’t have underfloor heating so can’t comment on what adjustment to the existing setup you might make. hopefully there may be others in this forum who know more about the specifics of Under Floor heating and about flow rates through the manifolds.

My thoughts are drawn, perhaps prematurely, to the carpeted areas and whether you have underlay which might prevent heat radiating. Or whether introducing towel radiators might raise the heat loss to a better level. But this may be far too early or complex to even think about doing at this stage. 

So perhaps someone who has UF Heating might offer some advice on how these graph outputs appear or may be adjusted.