Posted by: @iraknic

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When it cycled on it did not exceed 30% capacity

... which is probably its min output.  At 12C you would expect cycling even if the pump was right sized, it gets colder later this week so i suggest repeat the obs then and note.

Posted by: @iraknic

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If i force it to stay on for longer how it will be able to stay within water temp limits?

It won't, which is why forcing long cycling, which also increases the load (because the slab is cooler) might be good.

Posted by: @iraknic

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On the other hand if i force it to stay off for longer wouldn't it operate harder to get back to temp each time it cycles on?

Yes but if it is operating at a flow temp defined by the wc that won't materially affect efficiency.

Essentially what you need to find is a cost effective way to deliver the energy required to keep the house warm which, unfortunately, is less than the minimum output of the heat pump.  Additionally you have a buffer which further complicates the analysis.

As regards monitoring I did a search on the play store for the Hitachi app, there isn't one.  Hitachi don't really major in the domestic market in anything, so perhaps they haven't yet got round to this, because their major market will have a BMS (building management system).  So you are probably dependent on what you can get from the controller or something independent.

Your secondary pump is also well oversized  40l/min at 5C dt is 14kW.  My guess is your house needs 8kW max, more likely 6 ir less.  You could certainly turn it down which might increase the secondary dt, but possibly won't change the primary dt much given how oversized the heat pump is.  That said if you decide to try batch heating as suggested below you will (or at least may depending on the actual loss of your house) need the current throughput

If it's really the case that your house cools only a degree or less in 12hrs, i suspect your optimum strategy is batch heating aligned to cheap rates, like storage heaters.  Let's postulate a house demand of 6kW at the design temp.  Your heat pump can deliver roughly 18kW.  So it needs to be on one third of the time.  If you can buy electricity cheaply for 8 hrs per day or thereabouts, this will be low cost and will improve cycle times.  It's probably a textbook case for octopus cosy where the cheap rates are at intervals not all together.

You ideally do need some basic monitoring.  Would you be comfortable setting up something like home assistant on a raspberry pi?  

@jamespa i'm using an app named hi-kumo, which has no monitoring tools, only basic settings. There is an updated controller, released recently by Hitachi which provides more information and i plan on installing. I believe part of my problem is the low demand of the ground floor of which temp sits at 21c without heating. The ground floor circuit is off most of the times. I will increase the thermostat temp a bit to increase demand to see any changes in delta t

Posted by: @iraknic

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. The ground floor circuit is off most of the times. I will increase the thermostat temp a bit to increase demand to see any changes in delta t

It will, but it's heating more than you need assuming you are happy with the current downstairs temp and unlikely to fix the basic problem ie that the heat pump is (almost certainly) seriously oversized to the extent that it can't modulate down to anything like the required output.  The only way to fix this is time slicing (cycling).  You can either leave the heat pump to do this in its own way, or impose something for some defined purpose eg taking advantage of tarrifs.  Once that's roughly right you need to adjust the flow rate in the downstairs loop down so that it is balanced with respect to the upstairs loop (I'm assuming that they are on separate circuits)

There is a "nightshift" mode with which you can set the hp to operate at reduced fixed capacity (lowest setting is 40%) for a period. If i set it to work permanently at recuced capacity it will take longer to achieve the flow temps and thus reduce cycling? It will also reduce consumption and stress of the hp working at 100% to reach flow temps from cold. Just a thought

Posted by: @iraknic

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There is a "nightshift" mode with which you can set the hp to operate at reduced fixed capacity (lowest setting is 40%) for a period. If i set it to work permanently at recuced capacity it will take longer to achieve the flow temps and thus reduce cycling? It will also reduce consumption and stress of the hp working at 100% to reach flow temps from cold. Just a thought

Possibly not.  As I understand it this mode, which many heat pumps have, caps the compressor speed which reduces the maximum output but not the minimum.  However it's worth a try as your heat pump might start at maximum when switched on and then ramp down, in which case Nightshift might moderate the initial hit.

Unless you are worried about running cost, which you haven't mentioned, I wouldn't get too concerned about this.  Modern heat pumps are designed to turn on and off in a way that doesn't cause too much wear.  You do appear to have a bit of an extreme case judging by the info you have posted, but the simplest adjustment might be to increase the minimum cycle time parameter from the default (probably 10mins,) to 20 or 30 mins.  That will be buried somewhere in installer settings.  Balancing the upstairs and downstairs loops would also be good, just like radiators you need to try to get ufh adjusted hydraulically.  What do you know about the hydraulic layout?

@Jamespa There is a "minimum off" and "minimum on" setting. What do you think i should set the values at?

Posted by: @iraknic

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@Jamespa There is a "minimum off" and "minimum on" setting. What do you think i should set the values at?

No idea because not sure what they refer to.  What's the context and what are the units and factory defaults?

Mostly I would say leave things at factory defaults unless there is a good reason to change as part of an identified improvement strategy!

Another thing i noticed is the flow temp at the manifolds. While the heatpump shows a reading of lets say 35 out and 32 in, the temp reading at the manifold using infrared temp guns is only 27. What can cause such a drop?

@iraknic the buffer tank or pipe losses.  It sounds like a classic case of excess mixing in the tank.  That said not sure how accurate the or guns are, is there somewhere on the heat pump output you can take a measurement with the gun?

@jamespa i will try to have a reading as near to the hp as possible. So its possible that hot water enters the tank and is mixed with colder water that returns to the tank? Maybe this explains the low dt?

Posted by: @iraknic

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@jamespa i will try to have a reading as near to the hp as possible. I understand the whole mixing issue and pipe losses you ve mentioned, however why the return temp is still higher than the manifold temp?

I dont know, unless water is circulating in the UFH much faster than its coming out of the heat pump so basically its going round and round the UFH being topped up a bit by water from the heat pump and rather than top to bottom stratification you have two loops inside the buffer with a turbulant interface.  This is however pure speculation!

It could also be measurement error which would be an easier explanation!

@jamespa there is indeed a large noisy water pump placed after the buffer tank that circulates the water through the ufh and the fan coils. However flow rate is regulated at the manifolds and i wouldn't expect that there is a significantly faster water flow through the ufh. Nevertheless i will measure the temp at the hp exit and see