Posted by: @mjw321

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Hi @jamespa,

I've attached the whole manual 

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and also a pic of my control unit display here

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Thanks,

Mark

 

The second panel of the controller with the 0 and a graph in it suggests it's operating according to water law (weather compensation). However depending on the parameters the on off thermostat control may dominate.

The basic principle for most efficient operation is to turn up the thermostats and any trvs to 2 C above the desired level, then adjust the water law parameters so that it just meets the desired level.  Fsv 20xx are the water law parameters, perhaps you could post them.  

An alternative mode is to set the thermostat and, adjust the WC and so it is just above the value needed.  The thermostat then dominates but only just.  If you get it right the efficiency penalty compared to the first mode of operation is about 6%.

Is there some sort of mixing valve between the ufh and radiators to give different flow temperatures?

What's your annual consumption and house construction/level of insulation?

@jamespa

The UFH mixing valves are shown in the final 2 photo's in the original post.

@derek-m 

Yes 😀 - I've always had this set to deliver max heat to the UFH system, having read on other posts here that those valves are intended for boiler-powered systems i.e. to reduce the flow temp, whereas I'm operating at lower flow temp anyway.

@mjw321 You can actually remove the mixing valve as even set to maximum it will still blend the hot water down slightly which will mean you need to run at a higher flow temp. I learnt the hard way too and removed mine after a couple of years.

Posted by: @mjw321

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@derek-m 

Yes 😀 - I've always had this set to deliver max heat to the UFH system, having read on other posts here that those valves are intended for boiler-powered systems i.e. to reduce the flow temp, whereas I'm operating at lower flow temp anyway.

The mixing valve arrangement, and the water pump above it, is as you say primarily for systems where the supplied water is above the temperature  limit permissible for the particular floor covering.

If the temperature of the water in the system is always below this limit then it should be feasible to remove the mixing valves and water pumps.

Hi @jamespa 

The second panel of the controller with the 0 and a graph in it suggests it's operating according to water law (weather compensation). However depending on the parameters the on off thermostat control may dominate.

That panel is just showing the temperature adjustment options - it happened to be on the WC temp when I took the pic:

The display panel at the top-left shows the mode of the space heating - I'm stuck on the sun icon for heating and cannot set it to the graph icon for Samsungs Water Law mode (WC).

Is there some sort of mixing valve between the ufh and radiators to give different flow temperatures?

Addressed in comments above - thanks @derek-m and @bontwoody - I had read elsewhere that these components were redundant here and should be removed.

What's your annual consumption and house construction/level of insulation?

2024 YTD consumption shown here. Power shower is a significant consumer here

Re construction & insulation:

Built 1960

I've added extra loft insulation to achieve a 300mm layer throughout

Windows are double-glazed but I doubt they are the most efficient for heat retention

I have a certificate from previous owner for retro-cavity wall insulation (2005) but cannot see any sign of injection holes on exterior brickwork

I've done my best with the window/door seals (replaced with new etc)

Thanks

Looking at consumption first your baseline is about 500kWh/month is summer which annualised is 6MWh/year.  That's double the UK average which is variously quoted as 2.7-4MWh/year.  Assuming the excess is largely your power shower (is there anything else you have that consumes lots of power?) thats 8kWh/day, enough to heat 170 litres by 40C (eg 10-50).  Is that plausible given your use?  At 25p/kWh thats £750 on showering per year.  If the shower were run from the heat pump you would halve this or better  and you could better still by fitting an aerator and reducing the flow rate through the shower.

By the looks of it you have space for a tall UVC.  You need a UVC with a 3 sq m coil minimum (often described as a 'heat pump' UVC) so you can operate at a low flow temperature.  If you want to go gangbusters you can get UVC with a 6sq m coil from Newark, designed by heat geek specifically for ultra efficient operation of a heat pump (the 'HG' series).  But they are very expensive.  Aim to heat your DHW to say 45C with a DHW flow temp of 50C.  Because you aren't diluting it much (since you are storing at a lot temperature) you will need a bigger cylinder than at present, if you can fit a 300l in I would go for that.  Its a simple plumbing job to fit but you may need to turn down the DHW flow temp from the heat pump to optimise.  Many say you should run a weekly legionella cycle where you heat the cylinder to 55 using the immersion (or the heat pump if it will do it).  Others say that this is necessary only in a domestic situation if you are especially vulnerable.  Your heat pump can probably control this or just use a separate timer.

Turning now to space heating and if we continue to assume that you excess due to showering is 3MWh/year and estimate your annual electricity consumption as 14MWh, then it looks like you are on course to use about 14-3-3 = 8MWh per year for space heating.  Assuming you are getting a SCOP of say 2.5 (which is low, but Im assuming the system is not optimally set up) that means that about 20MWh is supplied to your house by the heat pump, roughly equivalent to a loss at the design temperature of 9kW and costing you £2000 per year at 25p per kWh.  Thats quite a big loss for the floorplan you provided (but by no means impossible) so either the SCOP somewhat less for some reason or the house is more lossy than one might hope.  Is it detached, semi or terrace, and do you have an EPC?  If your weather compensation isn't working and you can get it working, you should be able to knock 10-30% off of this, depending on how it is currently but it still seems a bit high.  Is there anything you can think of which might account for a high-ish heat loss from the house.

To work out whats happening with water law/external thermostats we need the values of all of the 20xx Field setting values and the positions of the DIP switches, all referenced on pages 34 & 35 of the manual.  (I'm presuming from your description that the operation described on page 18 doesnt work)  We also need to know if the external thermostats are connected to the heat pump/heat pump controller or switch something (eg pumps) on/off without 'going through' the heat pump.

If you aren't comfortable working with this stuff you will need a Samsung engineer to check it out and adjust it.  An ordinary plumber not familiar with heat pumps wont have a scooby (and there are a fair few people who are familiar with heat pumps that wont have a scooby either it seems!).  However if you proceed methodically it isn't difficult.

Hope that gives some food for thought!

The following is from page 14 of the manual

This icon appears on the picture you posted.  I am still not convinced that some sort of water law isnt operating, but need the answer to the questions above (including the connection of the external thermostats) to be certain.

Samsung uses fairly confusing terminology for the effect of external thermostats, and later models of control panel have a few more options (in particular FSVs 2093,2094 which provide some additional combinations to 2091, 2092).  Its entirely possible that the original plumber didn't bother and just connected the thermostats so they turn the pumps on/off (as they might if it were a gas boiler) or as a 'demand for heat' signal only.  Values of FSVs 20** and the thermostat wiring will confirm.

Hi @jamespa,

Some success here! I checked the FSV's and yes - the 209x were set at 1 i.e. for an external thermostat. Once I changed to zero, I could activate the Water Law heating mode.

I now feel rather foolish for not having gotten here myself - I think a combination of the new (to me) principles, a very unhelpful manual (in my opinion) and a bad assumption or 2 on my part made me believe it was beyond me and/or unwise to fiddle with in the advanced settings. 

Thanks so much for getting me unblocked!

I'm now going to learn more about weather compensation and do some trial and error as the outside temp starts to drop.

From your observations on my shower usage - that's just shot up the priority list too. I basically knew it was costing me a lot but your figures drove home the need to get that sorted asap.

One final question before I go and try to make some independent progress and gain some knowledge - I'm sure I'll be back with more feedback and doubtless more questions before too long, as I'm loathe to carry out any adjustments to the system (removal/replacement of inefficient/redundant components etc.) without seeking out some opinions here first.

@mjw321

Just follow the cardinal rule. Before making any changes note down the relevant settings, then you can always put things back to how they were.

In my experience there is nothing wrong with using an external room stat with a heat pump as long as weather compensation is enabled, or your rads are sized for a suitably low flow temp at design conditions (Glynn Hudson designed for 35@0 for example).

I use a nest gen3 (because it has the finest user interface of any thermostat) and run with full weather comp. The weather comp is set to ‘just’ provide enough heat to exceed the heat loss so eventually it will turn off if the target room temp is low enough. If we request 24-25 indoors then the heat pump just runs 24/7.

The Samsung gen6 controller, when used as a stat, operates in an on/off fashion. It does not vary the flow temp in response to target temp approaching/overshoot.

This is the 'alternative method' I refer to in a post above. 

Care needs to be taken with the choice of room stat.  Some 'clever' ones, as they approach the target temperature, attempt to simulate proportional control of the heat source by (slowly) PWMing the demand signal.  This is not good for heat pumps (or boilers with WC, not that thats common in the UK).  A simple on/off thermostat is required  (or of course a more sophisticated one that can be dumbed down to an on/off mode).  

As an alternative to an external thermostat, heat pump controllers generally include a room temperature sensor and many (including later Samsung ones, Im not sure about OP's) will operate in this combined wc/thermostat mode natively.  More sophisticated heat pumps feature an auto adaption mode where the unit learns the right WC settings (from a basic starting point) based on its measurements of room temperature and the desired room temperature.  Homely implements this method (and some more advanced stuff) for many heat pumps, like Samsung, that dont feature auto adaption.

The method does slightly compromise efficiency.  If the WC curve is 1-2C above the 'perfect' curve the penalty is around 3-6%.  Many will think that this is a price worth paying and, from an installer perspective, its a bit of a no-brainer, to the extent that I'm surprised that it isn't the default way to install.