@trebor12345  The penny has finally dropped. I thought you were describing defrost sequences. If you say that this happens at 20C OAT, it is not normal defrost. Thermo-Off is an error condition I believe and it is forcing the compressor off due to, for example, over-temperature of the water flow. After a 3 minute period the compressor will reset. If you say it is going into defrost, maybe it is trying to cool it down. This is not normal operation! I have not looked into this but look at the Service Manual, it should have something on this.

It has taken me a while to get my head around it, plus the warmer temperatures to prove it. I have tried to explain the situation to Hitachi, but they say the unit is working and nothing appears to be unusual.

I have watched the Live View of the heat pump operation and was unable to identify anything that specifically caused the Thermal Off. I have attached a screenshot of what it displays (was going to attached a video, but file formate not supported).

I don't have access to a service manual.

@trebor12345  I can send you a service manual however it is very large (200MB) so exceeds the file size limit here. If you can send me an appropriate email I can Wetransfer it to you. You can PM me with it. It may not be specific on this (I haven't looked) but should be useful generally if nothing else. This Hitachi is quite complex. It will help you to get your head around it.

Your situation is interesting because of the parallel with mine. To try and get some handle on this, could you send the following information if you have it?

i) What is your UFH pipe spacing and is it laid in spiral form or up/down?

ii) What is the screed? 7 cm concrete or anhydride?

iii) What is the tog value of the floor covering? Do you have tiles, engineered hardwood or pile carpet?

iv) What is the model number of the secondary pump? Is it Grundfos? Is it switched on by the UFH control box?

v) Do you have thermostats in all rooms?

I do not think that open loop working is appropriate for you. There is no control and you will overheat. However, let's not get ahead of ourselves.

@trebor12345  There doesn't seem to be anything obvious on the refrigeration cycle as the temperature ups and downs look logical. However your DT is extremely low at 1C. If it drops below this, it could cause a Thermo-Off. What flow rate has been set for space heating? 100%?

@trebor12345  Re your question about changing setting to controlled DT, this may be worth trying if your current DT is 1C as the heat pump will automatically reduce flow to keep DT constant. The DT value it sets will probably be dependent on the flow temperature set, probably 5C for low flow temperature. However you also have a buffer tank in between. What speed setting has the secondary pump been set to? Is it constant speed setting?

Posted by: @heatgeek

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@trebor12345  I can send you a service manual however it is very large (200MB) so exceeds the file size limit here. If you can send me an appropriate email I can Wetransfer it to you. You can PM me with it. It may not be specific on this (I haven't looked) but should be useful generally if nothing else. This Hitachi is quite complex. It will help you to get your head around it.

Your situation is interesting because of the parallel with mine. To try and get some handle on this, could you send the following information if you have it?

i) What is your UFH pipe spacing and is it laid in spiral form or up/down?

ii) What is the screed? 7 cm concrete or anhydride?

iii) What is the tog value of the floor covering? Do you have tiles, engineered hardwood or pile carpet?

iv) What is the model number of the secondary pump? Is it Grundfos? Is it switched on by the UFH control box?

v) Do you have thermostats in all rooms?

I do not think that open loop working is appropriate for you. There is no control and you will overheat. However, let's not get ahead of ourselves.

UFH is mainly 200mm.  
Screed - 17mm Ambi Tak.  
Mainly engineered wood and carpet and tiles.
Grundfos UPM3 (K) in constant pressure mode.  Switched on by the UFH control box
Thermostats in all rooms and off, except one in the family room.
I have attached a copy of the floor design

Any help on how I private email you?

@trebor12345  Use the internal private messaging system on this forum.

Posted by: @heatgeek

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@trebor12345  Re your question about changing setting to controlled DT, this may be worth trying if your current DT is 1C as the heat pump will automatically reduce flow to keep DT constant. The DT value it sets will probably be dependent on the flow temperature set, probably 5C for low flow temperature. However you also have a buffer tank in between. What speed setting has the secondary pump been set to? Is it constant speed setting?

I have tried the DT mode and it does seem to be better with this setting.  The Gundfros UPM3 is current in constant pressure setting 3 (max).

When the video was taken it had just done a Thermal Off, so was starting up.  Typically it 4 or 5C between the Twin and Twout.

Posted by: @heatgeek

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@trebor12345  I can send you a service manual however it is very large (200MB) so exceeds the file size limit here. If you can send me an appropriate email I can Wetransfer it to you. 

File received thank you.

@trebor12345  Your house is remarkably similar to mine, layout included. I have 185 sqms with 4 beds and 2 baths, same size lounge with exactly the same open plan kitchen with island and 12 loops of UFH, except my heat load is 3.5kW with MVHR. Your calculations for UFH are not done correctly for practical implementation. The heat output of UFH is stated as 11kW which is crackers. Maybe that’s where the 11kW peak heat pump creeped in. As yours is similar to mine, I have done a spreadsheet for you to assess your heat output and flow.

I have used my own calculated ventilation figure from my house software model which is 1.5kW without MVHR to current defined standards. Therefore your total heat load should theoretically be 4kW with ventilation loss. Unfortunately, you do not have calculated individual room heat losses at design temperature so we will have to assume that the installed loops are correctly sized. You can enter the flow temperature (in blue) to see heat outputs. For 4kW it is 30C (32.5 flow, 27.5C return). Also, DT. You do not need WC. At 15C OAT, your loss will be 1kW. Hitachi quote a minimum output of 2.1kW, so a bit of cycling will be inevitable.

So, what’s to be done? What I am going to say runs against the normal grain so you will have to decide for yourself. With a UFH system and HP with DT control, open loop working is a load of bollocks. There is no control and your bedrooms overheat as you have found out. You need to go back to the original design with thermostats for control of each room (as you have them, together with a buffer tank). The design is not that bad. Set the HP to DT control 5C so that there is variable flow. Set output flow temp to 32C as first trial and set up loop flows (see below). I am not familiar with the screed used so it may be higher on emission, requiring flow temp to turn down a bit more. The secondary pump is correctly set to constant pressure. What this will do is maintain the set flow in each loop as actuators turn off i.e. reduce the overall flow more or less in line with the HP pump so that the buffer tank doesn’t go skew whiff. You will hit a limit when HP gets down to 2.1kW but the excess flow from the HP will bypass through the buffer e.g. when 1kW at 15C OAT. You could keep some loops open to mitigate this if you wish e.g. one of the loops in the lounge and the hall loop. Not critical.

To set up loop flows, I recommend putting cheap Caleffi plug-on thermometers on each return pipe. Set 5C on these rather than on the manifold flow meters as flows are very low. You could of course try 3C on the HP to increase flows but 5C is best IMHO. The HP will modulate from your peak 4kW output down to 2.1kW so you may suffer some inefficiency below this level where COP is anyhow high. The smaller Hitachi heat pumps only go down to 1.8kW so there is not much difference. No big deal. However you will have fine control everywhere and you will have perfect comfort and save money. You can see open loop systems on heatpumpmonitor.org where room temperatures in a season vary from 17C to 24C with no mention of bedroom temps. Not for me.

That’s the best I can do. The rest is up to you.

Posted by: @heatgeek

↑

@trebor12345  Your house is remarkably similar to mine, layout included. I have 185 sqms with 4 beds and 2 baths, same size lounge with exactly the same open plan kitchen with island and 12 loops of UFH, except my heat load is 3.5kW with MVHR. Your calculations for UFH are not done correctly for practical implementation. The heat output of UFH is stated as 11kW which is crackers. Maybe that’s where the 11kW peak heat pump creeped in. As yours is similar to mine, I have done a spreadsheet for you to assess your heat output and flow.

Trebor Heat Calc.xlsx

I have used my own calculated ventilation figure from my house software model which is 1.5kW without MVHR to current defined standards. Therefore your total heat load should theoretically be 4kW with ventilation loss. Unfortunately, you do not have calculated individual room heat losses at design temperature so we will have to assume that the installed loops are correctly sized. You can enter the flow temperature (in blue) to see heat outputs. For 4kW it is 30C (32.5 flow, 27.5C return). Also, DT. You do not need WC. At 15C OAT, your loss will be 1kW. Hitachi quote a minimum output of 2.1kW, so a bit of cycling will be inevitable.

So, what’s to be done? What I am going to say runs against the normal grain so you will have to decide for yourself. With a UFH system and HP with DT control, open loop working is a load of bollocks. There is no control and your bedrooms overheat as you have found out. You need to go back to the original design with thermostats for control of each room (as you have them, together with a buffer tank). The design is not that bad. Set the HP to DT control 5C so that there is variable flow. Set output flow temp to 32C as first trial and set up loop flows (see below). I am not familiar with the screed used so it may be higher on emission, requiring flow temp to turn down a bit more. The secondary pump is correctly set to constant pressure. What this will do is maintain the set flow in each loop as actuators turn off i.e. reduce the overall flow more or less in line with the HP pump so that the buffer tank doesn’t go skew whiff. You will hit a limit when HP gets down to 2.1kW but the excess flow from the HP will bypass through the buffer e.g. when 1kW at 15C OAT. You could keep some loops open to mitigate this if you wish e.g. one of the loops in the lounge and the hall loop. Not critical.

To set up loop flows, I recommend putting cheap Caleffi plug-on thermometers on each return pipe. Set 5C on these rather than on the manifold flow meters as flows are very low. You could of course try 3C on the HP to increase flows but 5C is best IMHO. The HP will modulate from your peak 4kW output down to 2.1kW so you may suffer some inefficiency below this level where COP is anyhow high. The smaller Hitachi heat pumps only go down to 1.8kW so there is not much difference. No big deal. However you will have fine control everywhere and you will have perfect comfort and save money. You can see open loop systems on heatpumpmonitor.org where room temperatures in a season vary from 17C to 24C with no mention of bedroom temps. Not for me.

Caleffi Thermometer 675900.pdf

That’s the best I can do. The rest is up to you.

Thank you this is very helpful.  There is a lot to take in.  I have the heating on today and have been doing videos of the Live View.

The funny thing I attempted the flow calculations for the floor this morning.  Not as good/detailed as yours.

I also have a MVHR.

One question, what pump setting should I run on a Grundfos UPM3 (K) Auto?  Currently 3 max, but I think 2 might be OK.

I will drop you a private email

@trebor12345  The Auto function is supposed to adapt automatically and select the right curve in constant pressure mode. By default the pump is set to middle curve and it adapts from there. See description. A kind of pump AI. 😊