I have a Samsung Split HP with Hydro unit also but a much older model (Gen 4) which works well. From your description you are not too dissimilar to my original installation, except I had a buffer tank. The first thing you should know is that you have a variable flow PWM pump in the hydro unit which is capable of driving your whole system efficiently. You have a UFH only system with all loops in parallel, therefore there is no reason whatsoever to have an LLH and secondary pump. Its lunacy. The Samsung diagrams specify this when there is a mixture of UFH and radiators, but even then it is not necessary, as I had this daft arrangement before I changed it. The PWM pump should drive the manifold directly (no mixer) and then set the flows accordingly. You have over 6m pump head to play with. UFH loss should be nowhere near that. There are cheap Caleffi clip-on thermometers that you can buy for the 16mm return loop pipes to measure the return pipe temperatures. Set your dT’s with the help of these if you do not know the lengths.

Your pipe spacing is very close which is good as it will provide quicker heat up. I believe that the Samsung flow switch operates at 7 l/min which is the minimum switch on flow (check your documentation). That means you have 25 l/min to play with over and above this if your heat pump is not too over-sized. Instead of full open loop, what I did was this. Open enough secondary loops (scullery, etc) to provide minimum flow to avoid dreaded E911 flow alarm. For the primary loops, use thermostats (as you have them apparently) to provide full control of temperature. For example, if you have a wood burner, kitchen cookathon, lot of people around or sudden increase in OAT with good solar gain, the thermostats will turn zones off automatically. Thermostats also allow you to program switch off zones for Time of Use tariffs and provide night setbacks. I do not believe in uncontrolled open loop systems but it is your choice, of course. The Samsung PWM will control the change in flows (at least mine does).

Note that there is no need for an LLH/secondary pump for warranty purpose in your case as there is no danger of malfunction. Quite the contrary. Talk to your installer. Hope this helps.

First, a disclaimer. I am not associated with the Heat Geek podcaster of the same name. I chose the name before I knew of the existence of the other. One is not allowed to change it. Unfortunate coincidence.

I have attached information for the thermometers. They come in a box of 10 with a syringe full of thermal grease. You have 11 pipes which is a bit awkward but I would get 2 boxes as they are cheap enough and donate the excess to a friend. You should put one on a flow pipe and ignore the Samsung reading. There is a small coupling loss when connected to a pipe so this will be cancelled by reading the difference between flow and return thermometers. You can put one on each zone flow. It will not add any extra information but it looks good. 😊 

For setting up you should identify the lowest flow of the controlled zones. Subtract this from 8 which will give you the flow for the open loop(s). This should be a non-essential one. You can cheat by increasing the open loop flow for a 3C dT to make it a sacrificial loop. This will reduce the maximum heat output but, if it is a secondary area, it will not matter. You will find that the zones will switch off randomly and, with good thermal mass and insulation, will stay off a while. Use 1C hysteresis. Therefore the HP will run at partial load frequently with hopefully long cycles like mine and you have full room control. It depends on the heat loss profile of the house, of course, if not too lossy. The setting of the WC temperatures will depend on this.

To estimate pipe length, you need 10m of pipe per sqm for 10cm spacing. So, it sounds like the property is around 90 sqms and quite lossy. You can estimate each room’s pipe length from the area and add a bit for flow and return from manifold. It would help if you can explain where the loops go.

Otherwise it looks like you shouldn’t have too much of a problem. Just keep it simple.

One more thing. Do Samsung explain how defrost works on your Hydro unit? Does it use heat from the hot water tank which would make sense? If not, you may need to add a volumizer for safety. I guess the LLH is small on content for a 2 pipe connection. The UFH has 0.12l per metre of water so you have >100l water content. Some loops would probably always be open at low temperature but maybe an extra 30l would not go amiss.

Just found out that flow limit for 12kW HP is 12 l/min. 9kW HP is 7 l/min. Shame. Less flexibility.

Posted by: @heatgeek

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First, a disclaimer. I am not associated with the Heat Geek podcaster of the same name.

So you’re not Adam Chapman? 🤣 

@editor But do you wear your peaked cap the right way round? 😉 Toodles.