My first week of getting Data from my Fujitsu heat pump. I have set a low 0.5 curve on my Weather compensation. Turned off all room stats by turning them to 30c and
Got it running 24/7.
The house is very warm maybe slightly too warm but I can get that right in the future.
What I’d like to know is How to interpret this graph. The first one is the whole day and the second one is a closer look at the second half. I’m happy with heat and happy with the COP but just want to know if this is normal or what is happening?
Any advice appreciated.
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Hello! Welcome to the heatpump club 
What you’re seeing here is known as “cycling”, where the heatpump cannot modulate low enough in mild weather. This is very common and not something to worry about; 3 cycles per hour is an acceptable level.
In detail, the heatpump is producing 5kW of heat, yet the radiators aren’t able to emit that heat at such a low temperature, which forces the heatpump to run for a bit and then turn off for a bit while that generated heat dissipates into the house. You’ll probably find the mean heating power to be around 3.5kW for the period you’ve shown. (Click on Show Detail in bottom right)
To reduce the cycling, ensure all radiator valves are open. You could also raise the WC curve a little, though you’ll need to rely on room thermostats to prevent the house from over heating. Basically, cycling on the room temperature instead of the flow temperature.
When the weather is colder, the curve will select a higher flow temperature, which will allow the radiators to shed the heat more quickly, and require less cycling of the heatpump.
Hope that helps.
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Thanks Tim!
I did wonder if it was cycling but I wasn’t sure because looking at the bottom of the cycle it still seems to never really stop, its still using about 83 watts!
One more question! in those cycles it seems that its dropping down to about 900watts before it stops so does that mean my system it can modulate down to 900watts ?
That seems very good to me as I thought it would be about 2KW.
Its a 10Kw fujitsu waterstage.The Builder wanted to install a 16KW heatpump but I persuaded him that was too big.
Thanks again.
Mike
That is the power for the circulation pump, which is kept going between cycles + background system power use (electronics etc.).
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Yeah, 16kW would have been massively oversized. Dodged a bullet there!
I did wonder if it was the pump, and yes I did dodge the bullet he was very insistent at first and refused to change it, said that he had put in dozens of them and never had a complaint ! But I had done a lot of research and was certain that was way too big , I wanted to go with an 8kW but he said the installation company wouldn’t do it, as they said I’d be freezing. He changed his mind when I pointed out he was going to save money 
We compromised with the 10kW. and to be fair he did give me an £800 discount. 
Thanks again.
Mike
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from your graphs it shows that your heat pump is still way too big and even on it’s lowest output is cycling a lot ( 3 per hour is still far too much ) would love to have seen the heat loss report for the install. my bet is a proper heatloss calculation would have come in around 4kw to 5 kw @-3.
you should be able to drop the flow temp a little more but with such an oversized heat pump you may benefit from timing the heating into some blocks of 4 hours on and 2 hours off in the milder months although it would be probably be fine all year round. this would increase the effeciency quite a bit. ( not the calculated COP but the actual electrical usage)
The problem I having at the moment is that the underfloor is working well and is happily plodding along at about 28c but they have sized the rads upstairs for 45c and it’s too cold upstairs now the temperatures are dropping. To be honest I’m not sure how to proceed from here? it’s going to be painful to have to replace all brand new rads and towel rails.
One solution is to install fans under the radiators, as this can significantly boost output. Another option would be to increase the flow temperature a bit but restrict flow to the UFH, this way the radiators can supply more heat and the UFH doesn’t overheat the rooms because of the reduced flow.
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Didn’t realise your system was a mix of rads and underfloor.
Makes it more difficult to setup. Ideally you will have a system that will allow you to run 2 different heating profiles. ( I doubt it though).
Use the under floor downstairs to heat upstairs by having the doors open upstairs. If you are already doing that then the only option if you have the rads on all,the time is to raise the flow temp. Most houses this only really applies when the temp drops below about 5 degrees. So if you change your heating curve to increase the flow temp more when it’s colder this may solve it. Rads probably need to be 38 to 40.
I am thinking of restricting the flow to the floors. I was going to wait till after christmas and ask for advice on that.
thanks
Yes the Rads are too small + 1 doesn’t work at all ! got to get them back to see to that.
Rads are constantly on. I tried raising the “Comfort SetPoint” to 22 and a very slight adjustment to the curve but downstairs got too hot, over 24c in 1 room !
The water temp was only at 31c at that point and the upstairs was still very cool.
So yesterday I reduced comfort setpoint to 21 and taking the curve back to the original setting but it is still staying quite hot! i think the outside temps have risen a lot today though.
It seems downstairs is going to be easy to run constantly but I can’t just turn the water temps up to heat upstairs. I’d have to reintroduce the thermostat controls which I didn’t want to do!
At the moment I’ll have to do that as the house is baking hot, (except upstairs of course)
Just found out that even with the thermostats in charge again there is a problem.
I was labelling the heatmiser control and I wanted to find out which cct was connected to which room. So I turned all of the thermostats off and then switched 1 on and checked which light lit up etc. but I noticed that when the kitchen was off the upstairs wont come on even if the stat upstairs is calling for heat.
So when the Kitchen is Hot it turns itself off and the upstairs!!
Looks like a wiring problem.
This won’t be what is causing me problems though as I had all the stats set to 30c so that the system runs continuously . Not a very good installation though 
Maybe you could repurpose some of the new radiators?
Bigger ones into the smallest rooms and just replace some?
Of course, I don’t know if that is possible.
The best outcome will be to get the radiators sized to match the flow temperature of the ufh.
Limiting the ufh to match the undersized radiators will just result in you having to run higher flow temperatures than you really need consuming more electricity (probably) and at a lower efficiency.
My opinion.
It’s really something the system designer should have thought of and taken into account.
Thanks I didn’t think that would be the case. I thought I would just get more flow upstairs and more flow = more heat ? But I think I get what you are saying . That reducing the flow in the floor will mean I have to increase the temps anyway. but to be honest I can’t get my head round it 
I am having a bit of Brain freeze I have just been checking about my supposed wiring fault but I got that all wrong and its not a problem 
It’s all a bit confusing and difficult to get your head around
To get you radiators to work upstairs you need a higher flow temperature.
A higher flow rate won’t cut it. You may get a slight improvement by increasing the mean flow temperature but by the sounds of it upstairs is cold.
You need more heat output, actually the correct heat output, upstairs at a flow temperature your ufh works well at.
It needs careful planning, ideally you want it all to work in harmony at the same flow temperature with no trvs or zoning.
Anything else will compromise efficiency and running costs.
Yes that’s what I set it up like at first , same flow temp no trvs no zones no thermostats.
It really ran quite well at first with very nice cops and nice temps downstairs. TBH i thought i’d cracked it but gradually the temps upstairs dropped whilst downstairs stayed the same. It doesn’t help that we had some mad swings in external temps here lately. The heat curve is set at 0.5 and the flow temp didn’t really change much which surprised me a bit!
Thanks that looks really interesting!
Mike