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Hitachi Yutaki M efficient operation

iraknic · 2024-12-29T18:03:10Z

Hi everyone. I recently found this forum and i wanted to share my case and ask for input of you knowledgeable people. As the title suggests i have a Hitachi Yutaki m RASM-6NE that is used to heat a two floor 230 sqm house with two separate zones of underfloor heating. I use weather compensation with flow temps ranging from 33 to 41 degrees. Thermostats are set to 20 degrees for both zones. Two water pumps are used for the water flow, one that is integrated in the heat pump unit and a larger one with an output of 40l/m. I have a buffer tank of 200l. The ground floor is more warm in general so the ground demand is often off. I have noticed that the delta t between inflow and outflow is at most times between 1 and zero degrees. I have also noticed the heat pump turning off a few minutes when the set water temp is reached and then back on (i am not able to see the frequency of the cycling) until the room temp is reached. In general the heat pump works for an average of 8 hours day before reaching room temp and going off completely. Since the delta-t is so low i suspect that the number of on/off cycles is high. A reason i believe is causing a low delta-t is the waterflow that is too high. I tried to set the water pump speed to be controlled by the delta-t parameter without much of a difference since i think only the integrated water pump is affected as the external water pump speed is believe is fixed. Is there a way to see the number of on/off cycles?

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iraknic

(@iraknic)

Eminent Member Member

Joined: 1 year ago

Posts: 24

Topic starter 10/01/2025 8:28 am

So i think i have narrowed it down without however knowing the solution. Buffer creates a loop. Hp provides the required water temp to the buffer but somehow the energy is not diverted to the ufh but returns to the hp, hence the low dt and the reduced temp at the manifolds compared to the outlet reading of the hp. Does this means that there is unbalanced flow between the primary circuit (hp and buffer) and secondary circuit (buffer and manifolds)? The circulating pump in the first circuit is adjustable but the second is not

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4634

10/01/2025 9:35 am

Posted by: @iraknic

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Does this means that there is unbalanced flow between the primary circuit (hp and buffer) and secondary circuit (buffer and manifolds)? The circulating pump in the first circuit is adjustable but the second is not

Yes, almost certainly.

I dont know if the HP can control the buffer, some can. If the buffer has two temperature sensors at different heights then its possible in principle to use this information modulate the speed of one or other pump so that on average the rates are the same (which is ideally what you want). It would be worth looking at the HP manual and the buffer in case it can do this.

Otherwise you are down to adjusting the pump rates. The HP might adjust the primary pump to suit its needs. If it does so and unless the HP does feature buffer management, Id be loathe to touch this. That said there is generally no harm in turning the primary up, HPs complain about low flow (because its not enough to take the heat away) more than about high flow.

Im surprised that there is no adjustment on the secondary pump, many have three settings.

Having the primary a bit faster than the secondary will tend to force the thermocline (barrier between 'hot' and cold' water, assuming its stratified) down the tank, which means that the feed to the emitters should be at the same temperature as the feed from the heat pump, thus minimising the sacrifice in efficiency which would occur if the feet to emitters is lower temp than the feed from the heat pump. Obviously this will cause a little bit of recycling through the heat pump, but its better so far as I understand these matters than pushing the thermocline to the top which is what happens if the primary is slower than the secondary.

Do you know why the buffer is fitted? Generally they are a bad idea in heat pump systems, albeit that many installers put them in because its pretty much guaranteed to reduce callouts (by masking problems).

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

👍

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Mars

(@editor)

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Joined: 5 years ago

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10/01/2025 9:42 am

@iraknic how are you monitoring your UFH delta T?

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iraknic

(@iraknic)

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Joined: 1 year ago

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Topic starter 10/01/2025 10:14 am

@jamespa the buffer was fitted to increase water in the system due to the existence of zones. @editor
I am measuring the temps at the manifold using an IR thermometer. In my case it seems that the primary water pump is slower than the secondary (after the buffer) one? Can the secondary flow be reduced by manually decreasing ufh flow at the manifolds?

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JamesPa

(@jamespa)

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Joined: 3 years ago

Posts: 4634

10/01/2025 10:49 am

Posted by: @iraknic

↑

Can the secondary flow be reduced by manually decreasing ufh flow at the manifolds?

Yes. Its the same as turning down the lockshield on a radiator

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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iraknic

(@iraknic)

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Joined: 1 year ago

Posts: 24

Topic starter 10/01/2025 4:50 pm

i attach the setup of the buffer, highlighting the return lines and the specs of the water pump that is placed after the buffer. I thought of closing a bit of the outlet and return valves of the left side of the buffer (to and from) the manifolds and increase the flow of the primary pump (from hp to the buffer) to see what happens

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Toodles

(@toodles)

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10/01/2025 5:14 pm

@iraknic Please note, I don’t have any experience at all (diddly squat) of UFH plumbing but if a circuit has both send and return valves, it is probably only necessary and better to just constrict the flow to the circuit and leave the return without any restriction. I may be talking through the wrong orifice of course! Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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renewyfiend

(@renewyfiend)

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15/01/2025 3:47 am

Posted by: @iraknic

↑

A reason i believe is causing a low delta-t is the waterflow that is too high

I also tried lowering the internal waterpump speed but have not found yet how to do that. The setting in the installer section of the controller did have a deltaT setting and a HP ON deltaT setting I changed both to the same increase but the waterpump speed still is 100%

How did you try changing the deltaT?

I have a modbus gateway from which I can extract most relevant information. No real cycle information to be found though. Once can monitor and deduce it sure.

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