Not irrelevant, but you shouldn't be throttling all radiators just to increase delta t, that achieves nothing other than to make the pump work harder than it needs to and slightly to increase the flow temperature your heat pump must deliver.  A balanced system with the valves as open as possible is what you are trying to achieve, which means that at least one valve will be fully open.

Remember also that deltat across radiators will reduce at higher OATs (=lower fts), unless your heat pump modulates the flow rate of the pump, which may or may not be the case.

It's best in many ways to think of delta t as a dependent variable, not one you adjust for directly.  Assuming your heat pump and radiators have been correctly sized and the water pump is adjusted for the correct flow rate then delta t at the design max FT will be 5C (because that's how the system was designed).  But since none of these assumptions will be exactly true,  it won't be exactly 5C and that doesn't matter.  Some, but only some, heat pumps adjust the water pump speed as a function of ft, which means that deltat will be closer to 5c over a wider range of fts.  For those that don't it will depart as ft departs from the design max ft.  This has some subtle  effects, but not necessarily bad ones

@raiph I’m not anyway; when my system was plumbed in with an LLH, my installer told me that this made the Delta figures less relevant as he thought that it was only necessary for the heat pump system to have the desired 5 degree drop - and that this was less relevant as far as the radiators are concerned. Well arguments about LLH’s etc. aside, I felt I wanted my emitters to show as close to a 5 degree drop across inlet to outlet as possible. Regards, Toodles. (But I am only an enthusiastic user, not an expert in any sense of the word, not a plumber, heating engineer or designer!)

Another little problem. Noise. It's been a bit cold the last few days - lots of defrosts. Any other 8kW Gen 7 users noticed?

HP running with a Water Outlet temperature of 36 degrees. Power 1.8kW. Noise about 50 to 52dB. As it 'frosts up' the noise starts to increase. Peak measured at 72dB. I thought that it was going to shake itself to bits. At least it then goes silent as it defrosts.

Is it a real problem, just a Samsung feature or do they all do it?

Contacted Samsung support (thanks Mike). Two problems a) noise, b) low Delta T.

a) Send us a video - same as our installer. Things however may have changed i.e. it seems quieter now.

b) Flow rate. Whist heating it's 15.1 lpm. Speaking to Samsung it should be 26 lpm for maximum heat transfer i.e. to give 8kW of heat it needs 26 lpm. By changing the 'Water Law' settings to 45/45 it forced the HP to slowly increase the WO temperature to 45 - takes about an hour. The Delta T seen by the HP increased to 5 - where it should be. I've come to the conclusion that the Kaiflex pipe is the issue - as the flow rate increase so does the pressure loss - about 3 times higher than 28mm copper. So I'm going to replace the Kaiflex pipe. Is there an alternative to 28mm copper?

I have managed to find 28mm copper 'swept bends' to reduce pressure losses - I'm just wandering if there is an alternative.

@raiph You seem to want a Delta T of 5, but your water pump has a fixed speed / flow rate which is currently 15 l/min. Your heat output is determined by your LWT so Delta T will rise as LWT (and heat output) rises. So when LWT = 45 C, Delta T = 5 C as you have discovered. When LWT = 30 Delta T will fall to say 3 C. If you replace your Kaiflex pipe with 28mm copper, your flow rate will increase into the 20s and Delta T will reduce in the same proportion as flow rate increased. 

So if you want Delta T to be close to 5, changing your piping will have the opposite effect to what you desire and cost you £££.

If you do change your piping, your water pump will not have to work so hard, but the saving in electricity may be modest. 

The water pump is not fixed speed - it's PWM controlled. The reason to increase the flow rate is so that the HP can deliver its rated output. Look at the Samsung Gen7 TDM (technical data manual).

@raiph I apologise for my incorrect assumption. A PWM pump should maintain your delta T, so I am not clear why you are experiencing problems with a low delta T. Do you need more than 45°C at your design temperature? If not maybe your flow rate is not such an issue?

I have a 12 kW Samsung with a flow rate of 16 l/min and it seems to work ok at my design temperature. 

New rabbit hole ...

Installed a Shelly EM and updated to premium (3 months free). Still can't get a decent power graph. I'm trying to look at the real time power consumption during a frost/de-frost cycle. So I've started to look at the Samsung API - just to log it's power. I think I'll give up on that one - no fan of HA and his mate JSON.

Is there a 'Samsung HP monitoring app' that uses their API to log what it's doing? Should have installed the Open Energy stuff. Came across something interesting in the Smart Things App - your installer should be able to remotely monitor the system. Any one know of an installer that does/can?

Anyway - the system is running quite well according to the MIM/Console COP data - last week a high of 5.47 and low of 4.2. That includes the HW (Weekly energy generation divided by weekly energy consumption). Not sure I trust the 'energy generation' as there is no sign of an 'energy meter' in the grey box outside. That was running with a Nest thermostat. Switched back to HavenWise. Should be able to compare the two.

There are still things in the Indoor Zone Status information and the Master indoor Zone information that I still don't understand and also the FSVs. Anyone know what 2094 is for? It's not in the book ... I'll e-mail Support in the new year.

@raiph there is some info on 2094 here. https://community.openenergymonitor.org/t/samsung-gen-6-8kw-efficiency/22132/189

@raiph You asked about a Samsung HP monitoring app. Have a look at Planet Devices and their Atmo device. Very helpful on the telephone.

Planet Devices - Cannot be used when a 'Manufacturer Cloud Gateway' is installed. I assume that's the Smart Things WiFi interface. That's the bit that HavenWise use. I'll speak to Planet Devices next week. Also looks like they offer three levels of service - how much do they charge?

@raiph I am running Planet at the moment via a B19 modbus board. I am still awaiting the DB98 wi-fi kit which should have been included with the pump, b ut Samsung are being very slow in correcting this omission.

I understand from the wi-fi kit manual that this plugs into a separate part of the main board, so I hope to be able to use Smartthings and the manufacturers cloud to connect up with Havenwise.  

 My Planet install was included with the overall pump price so I cannot comment on its price, sorry.