@jamespa & @johnmo

What will happen to my efficiency ?

@jamesPa "Only when close to the target temperature would I expect it to invoke cycling."

You are , james , again, perfectly correct , the Oscillations , wrongly attributed to "short cycling " , only occur when the Temperature approaches the target Temperature. Outwith the Target Temperature the Thermostat just switches ON or OFF.

Your comment that "The purpose of this is to avoid overshoot" now makes sense .

I stand corrected, raising the Temperature by a significant amount will force the Thermostat out of it's close approach algorithm forcing the Heat Pump to be always ON.

What will happen to my efficiency ?

Surely , there Must be a cheap  replacement Thermostat that does NOT cause " Cycling"?

A simple Thermostat controlled by  variable "Hysteresis" would do me just fine!

In Greek  Hysteresis translates as Madness! Time for a darkened room!

Posted by: @iantelescope

↑

I stand corrected, raising the Temperature by a significant amount will force the Thermostat out of it's close approach algorithm forcing the Heat Pump to be always ON.

What will happen to my efficiency ?

The heat pump should always be on, that's the whole point.  The weather compensation curve (water law) needs to be adjusted so that, with the heat pump always on, the house reaches the correct temperature.  This is the most efficient way to run a heat pump (or a gas boiler for that matter, but in the UK we sadly ignore this capability of most gas boilers).

The only purpose of the thermostat is to switch off if there is an unusual condition such as excess solar gain (and to satisfy building regs which for some unfathomable reason specify that one must be fitted,).  Other than in this unusual circumstance the thermostat should not be controlling the heat pump, that is what the heat pumps native controller is for!

This is a complete reversal of the way we have run heating systems in recent years in the UK, we need to get used to it!  Other countries, notably Germany, have been running their gas boilers on weather compensation for many years, which probably makes the transition easier.

Once you get it basically working, it may make sense to heat only during the daytime at either end of the season (using the timer function of the thermostat).   However you should consider this a refinement on the basic principle of 24*7 operation at the lowest possible flow temp to achieve the room temperature you want with thermostat and TRAs permanently 'on'.

Done correctly this gives better comfort for less energy!

One further thought, if you are going to replace the thermostat consider instead a homely.  This is essentially a learning intelligent thermostat/timer designed specifically for heat pumps.  It can interface with Samsung and reputedly delivers good results, essentially auto adapting your WC curve to suit your house.  TBH in your situation I would either keep the existing thermostat or replace it with a homely.  I wouldn't replace it with another thermostat unless I happened to have one kicking around.  

@jamespa 

Again , I now understand.

I should , initially, use the Samsung Water Law to allow the outdoor Temperature to control the pipe water Temperature with the Thermostat Temperature raised to such a level that it is permanently ON, and permanently out of the way.

I have extensively used the Samsung Water Law to adjust for the low winter temperatures , routinely setting the Water Law to "start" at a Water Temperature of + 45 C when the outdoor Temperature is -5 in Winter.

This Water Law -5 C  ordinate with a coordinate of +45 C  is recommended  by Samsung for  Scotland.

I still would like a Thermostat without Cycling !

Posted by: @johnmo

↑

Just add - I don't believe your cycling is anything to do your thermostat, I believe it's a red herring.

Your current flow path of water from the heat pump is 2 port valve, buffer then HEX and back to the ASHP. The issue, which I believe is going on, is the pressure drop across the HEX is higher than the buffer. So water (or most of it) just takes a short cut and bypasses through buffer straight back to the ASHP. So your return temp goes up too quickly and the heat pump just shuts down.

I think that you are wrong, the cycling still occurs with the buffer tank isolated. Ian and I went through all this months ago.

Posted by: @iantelescope

↑

@jamespa 

Again , I now understand.

I should , initially, use the Samsung Water Law to allow the outdoor Temperature to control the pipe water Temperature with the Thermostat Temperature raised to such a level that it is permanently ON, and permanently out of the way.

I have extensively used the Samsung Water Law to adjust for the low winter temperatures , routinely setting the Water Law to "start" at a Water Temperature of + 45 C when the outdoor Temperature is -5 in Winter.

This Water Law -5 C  ordinate with a coordinate of +45 C  is recommended  by Samsung for  Scotland

 

Exactly.

See also my comment above (following an edit so you may need to re-read) about replacing the thermostat with a homely.  Imho your best options are (1) keep the existing thermostat or (2) replace the existing thermostat with a homely which is specifically designed for heat pumps.

If I were you I would do (1) intiially and then (2) only if I proved the need.  

Incidentally you may be wondering how we got to a point where loads of 'controls' are available which don't actually help much and in some cases hinder.  The answer is twofold

1 Some of these work better (or less badly) with gas or oil boilers than they do with heat pumps

2 In the UK we lost our way when, unlike some other countries, we shunned weather compensation for gas boilers.  The consequence is that most of us have been paying probably 5-10% more than we need to for our heating since the 90s when condensing boilers were introduced, and 'enjoying' poorer comfort and requiring more user intervention in addition!

Of course the industry has responded with a variety of over-sold add on controls which go some way to correcting the initial error, but which are largely inappropriate to low temperature heating systems such as a properly adjusted condensing boiler or a heat pump.

It's a sad situation perhaps only clear with 20:20 hindsight, but is making the transition to heat pumps more difficult because it requires consumer re-education as well as plumbing.

@jamespa 

 No  Thermostat , Water Law Offset alone?

I have been pondering my current Heat Pump controlled by Weather Compensation and a Thermostat .

The Thermostat directly controls the Radiator , Secondary Water loop.

Currently, without a Thermostat I would be unable to get any heat!

After my upgrade could I permanently short out the Thermostat using the Water Law Offset Control alone ?

Essentially No Thermostat with the Heat Pump controlled by Weather compensation offset ?

Posted by: @iantelescope

↑

@jamespa 

 No  Thermostat , Water Law Offset alone?

 

I have been pondering my current Heat Pump controlled by Weather Compensation and a Thermostat .

The Thermostat directly controls the Radiator , Secondary Water loop.

Currently, without a Thermostat I would be unable to get any heat!

 

After my upgrade could I permanently short out the Thermostat using the Water Law Offset Control alone ?

-- Attachment is not available --

Essentially No Thermostat with the Heat Pump controlled by Weather compensation offset ?

 

 

 

 

That's a valid control strategy imho and indeed how Samsung most likely intends it's equipment to be used.  My earlier suggestion to set the thermostat to say 30C achieves exactly the same effect which is why I made it.

There are however a few reasons why you may want to retain the thermostat:

a. I think building regs require one (only god knows why)

b.  Your thermostat has a timer function which may be more convenient to use than the Samsung one.  Whilst 24*7 operation is undoubtedly the way to go initially and for the height of the heating season, I think it's a fair bet you will want to do part time heating at either of the season to minimise cycling.  You may also want to do a nighttime setback (implemented by switching off) in the shoulder season and it might be useful for this.  

c. If you remove it you have to cover yo wires and a hole,  By leaving it in place abd simply setting the temp high you avoid this.

d. It may yet prove useful as a temperature limiter

As I say above, I would personally either  retain it but set the temperature well above the desired level or swap it for a homely, but your suggestion is also valid.

@jamespa 

Rebuild:

I have arranged with my Plumber to start the strip-down on Wed next week.

It should not be quite as difficult as I first thought.

Homely:

Nobody , including amazon has a "homely" Thermostat .

Has it been discontinued ?

Many thanks ,ian

@iantelescope Homely are still very much alive, I have been corresponding with them in the last few days:

https://www.homelyenergy.com/

Will take you to their site.

Regards, Toodles.

Also, Homely supply to trained installers and one such can install a Homely system for you. No doubt they can give you details of fitters in your neck of the woods. Regards, Toodles.

@toodles 

"Trained installers" are an extinct species in Scotland.

Many thanks Toodles for the information about homely.

Do they ONLY sell to "trained installers" ?

"Trained installers" are an extinct species in Scotland.