Samsung Gen6 and anti-freeze pump cycling below 5C OAT

Hardware Heatpump
1

Hi everyone,

I know this is a topic that has come up before, and as it turns colder so we begin the fight again.

The problem: When OAT falls below 5C, the Samsung controller runs an anti-freeze protection cycle which runs the pumps circulating warm water for 5 mins to prevent the system from freezing when the pumps have been idle for 60mins.

Normally, for most systems, this would never happen as the system should be running constantly when OATs are below 5C (or at least cycling on/off within a 60min window), but because our ASHP is so oversized for our property, we cannot run constantly until temps drop closer to 0C. This means that overnight the pumps will cycle for 5mins every hour which in our case ‘steals’ hot water from the DHW cylinder, transferring it into the 50L volumiser and 28mm primaries, and we wake up each morning with not so hot water. Note we also have glycol in the system and full home battery backup so it’s extremely unlikely the system will freeze.

I know one other user here managed to trick the diverter valve into switching to the circuit rather than the DHW cylinder, but unfortunately that solution was not viable on our Joule pre-plumbed tank due to the way it’s wired.

So I’m back to scratching my head and thinking about solutions. Last year I resorted to going out in the night and grabbing hold of the temp sensor in my warm hand to temporarily increase the reading to above 5C once per hour, but that’s not sustainable if I want a full night’s sleep!

Today I’ve had the case off and measured the resistance of the thermistor at different temps (with a pint glass of water and ice cubes). The thermistor is reasonably accurate, so swapping it out isn’t really going to help unless I can find an inaccurate sensor. The sensor is a 10k Ohm at 25C type, and typically reads 20K at 7C and 22K at 5C. The full table of resistance/temperature values are in the attached document.

So I’m considering just replacing the sensor with a fixed 20K resistor and let the heat pump think it’s ~7C all year round, but I’m worried what other implications this may have:

  1. Weather Compensation. Obviously the WC curve is based on OAT and would be rendered unless as the ASHP would see a constant 7C. This isn’t really an issue for us as we run at a flat 32C LWT all year round (as the lowest LWT the system can achieve) and manually bump it up a couple degrees on the controller if the weather gets very cold and the house drops below 20C.
  2. Defrost cycles? I don’t know about defrost cycles? Does the controller use OAT at all in determining when to run defrost cycles, and would a constant OAT of 7C affect or prevent defrost cycles from running?
  3. Anti-freeze protection: This is what we are trying to fix - prevent from running.
  4. Anything else I’ve not considered that uses the OAT sensor value?

I’m hoping those with good technical knowledge of the Samsung unit will be able to help bounce around this idea with me to help find a solution.

Thanks

2

All good questions, @Old_Scientist.

The only pointer I can help with is the Samsung defrost strategy, as outlined in Samsung R32 ASHPs - when is a defrost not a defrost?

This suggests that OAT is definitely a factor in defrost cycle initiation.

Personally I’d be wary of doing anything that might override defrost initiation - that L2 line (the usual defrost start condition) extends up indefinitely, and you don’t know when the COND_OUT sensor is seeing -6degC or below (unless you have monitoring equipment on it). So fooling the OAT sensor may save you lots of money most of the time, but wreck your HP if you do need a defrost but somehow prevent it happening…

3

Thanks @SarahH, that was my fear so not an option if it is going to adversely affect defrost cycles.

I’ve also read back through the whole thread to remind myself of the discussions we had on this topic last year.

4

I’ve been think more about this recently. While I’m probably going to go down the same route as @Michal_S with the shelley relays, I thought about setting FSV #4013 to 7 and leaving the heat on. So that the heatpump comes on below 7 degrees, but, from the installers guide, it looks like the minimum value you can set for 4013 is 14. You can adjust FSVs with the Simple Setting menu, (in FSV). I might try and see if I can set it to 7 using this method later on.

5

@jakeymd1 I like your thinking.

Still trying to think outside the box…

Silly question, but what happens if one were to temporarily set FSV #3011 DHW Tank to Not Use?

If set to Not Use, would the controller logic then not be able to move the diverter valve to the DHW position, as presumably there’s no tank connected??

We have a spell of milder overnight temperatures, so may be a while before I can test, but next time we are due colder overnight temps, I’ll try setting DHW to Not Use (#3011) and see what effect that has.

6

It turns out I could set #4013 to 10 degrees on mine through the usual FSV menu, but I couldn’t set it any lower than this with the Simple Settings menu.

This might be something you could try.