Posted by: @andehh

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Hi all,

 

We had a gen6 12kw Samsung ASHP installed a few months ago. It's a Joules pre-packaged design.

Due to 4kw of South facing PV on the roof I adjusted a few of the settings to make best use of the surplus power we generate in the summer. It seemed daft to be dumping 2-3kw into the grid sunny afternoons, to then have the disinfect cycle & DHW coming on over night & pulling that energy back in.

I adjusted the DWH to come on every day between 1 and 4pm - this gives us a full tank of hot water for evening showers.

I set the disinfect cycle to come on at 2pm to 4pm (ie after our lunch time clear up) and run for 1 hour, maximum of 3 hours for 55 degrees.

 

The problem is, every disinfect cycle the tank hits about 53degrees, then seems to stop heating. It then 'times out' and I get an error message saying it did not heat max heat.

 

Has anyone come across similar or can offer a logic to this?

 

Thanks,

 

 

Does your immersion heater have a thermostat inside? If so, what is the setting?

Good shout that, though I just checked it and it looks to be set to the max! 🙁 Joules supplied the cylinder, ASHP & commissioned it so all set to their original defaults other then me adjusting it to make use of the PV!

@andehh

Do you have a power diverter connected to your immersion heater?

As far as I am aware, the legionella cycle would normally heat the water initially using the heat pump, then take the temperature the rest of the way up to 60C using the immersion heater. Is this how your system operates?

No power diverter to my knowledge & yes - that is how I assumed the system would work. When it does 'kick in' the immersion looks to be what drives the temp to 53.6degs ish before it just plateaus there.

@andehh

I would suggest that you go through all the controller settings to see what is switching the immersion on and off.

@andehh 53.5 is achievable by the heat pump alone. I have a samsung G6, if I run it in DHW mode, I can get the cylinder to 55 using purely the ASHP.  This suggests to me that your immersion may actually not be doing anything at all. one quick check, if you have any real-time load display capability, either smart meter or in your PV inverter,  you'll see a 3kw jump in load if/when the immersion comes on. or if you are electrically minded you will know what/how else to check.

I echo derek: Take a good look at all the settings in your controller , there are a lot related to hw control and they are pretty complicated.

I chose not to wire my immersion to the HP controller at all. Its wired purely to my PV diverter. I use timed boosts on that PV diverter for legionella, which find simpler than managing them through the HP.

I'm increasingly of the opinion that few DHW tank immersion heaters reach 60degC standing water temperature. There's several things to consider:

* Inaccuracy of immersion heater built in thermostat. They are notoriously inaccurate. They are sensing the water right by the heated element.

* Location of the immersion, it's normally between 1/4 and 1/3 the way up the side of the tank. Cold water is below it.

* Location of tank water temperature sensor. Hot water tanks have hottest content at the top, and almost cold at the bottom. They are designed that way, not all of the tank volume is heated to the hot water temperature set point. The height location of the sensor influences the reading significantly.

My ASHP will deliver water at 60degC, through the very large 'quick recovery' heating coil - which heats the water volume much more evenly and thoroughly than the immersion can. Using the ASHP alone, the hot water indicated temperature can reach 55degC quite quickly, within 1hr.

Using the immersion, the immersion starts to cycle on internal thermostat when the indicated tank temperature is only 53degC. It maxes out at 65degC, and never gets anywhere near an indicated 60degC.

I've abandoned the immersion and use the ASHP for HW, as it's more economical, quicker, and can reach a higher temperature. 55degC of water stood for several hours each day provides an adequate sterilisation against Legionella.

https://legionellacontrol.com/guidance/temperature-influences-legionella-growth/#:~:text=Thermal%20disinfection%20involves%20keeping%20the,system%20will%20be%20significantly%20reduced.

Just to update this thread, Joules came out & found that the temperature probes had not been pushed fully into the pocket within the tank.... instead they were only 10mm or so inside it, so were simply under reading the tank temperature!! They've been pushed further in & plugged with insulation behind.

Thanks for all the posts all the same! 🙂

glad it was an easy fix. sometimes the basics is all that needs checking!