PV - Myenergi Eddi - New HWC - Bottom 1/3 warm, not hot.

banana5kin

I recently changed out my old (aging) 100l copper tank complete with Willis immersion heater for a nice new 140l indirect/vented insulated SS model. The immersion heater element is the maximum length the tank will support which is 27" (tank is 39"). The stat is set at 65 deg and the Eddi is cutting out (max temp reached) and the bottom 1/3 of the tank is warm, not hot (my DS180B located beside the CH tank stat is stating 35 deg). On the old tank, the Willis heater would heat the entire tank and I could pull 10kw of excess after the batteries were charged, now I'm lucky to see 2kw being used before the Eddi states max temp reached - and therefore exporting far too much.

I have occasionally power cycled the Eddi when I noticed that that max temp has been reached and it then resumes heating the water from surplus for a while longer. Anyone know, is there a pre-defined setting in the Eddi so as to not hammer the element with repeated on/offs?

I'm aware that the layers of Hot/Warm/Cold water is known as stratification, anyone else have this issue and maybe a solution?

Many thanks.

graememk

Yeah it's a thing. The immersion can't heat water thats below it.

The Willis heated the whole tank because it takes cold water from the bottom and puts it in the top due to convection.

You can put a pump in to de stratify the tank, and the eddi can control that via a relay board.

The eddi stops because the thermostat on the hw tank stops the power going to the eddi, the eddi can measure how much power is going to the immersion, and then if nothing is being drawn, assumes the tank is hot. It then waits a set period of time before trying that immersion again.

tnegun

I fitted a Willis type heater and it heats the tank much more efficiently its documented here along with the mistakes I made and corrections! I more than doubled the capacity from what the in-tank immersion could heat, it's not perfect as it does start to cycle on for 60 seconds off for 120 type when the bottom of the tank starts to get warm and there is more than 2kw of excess but by average export is gone from 25% or so to 15% or less and I've plenty of hot water.

https://www.boards.ie/discussion/2058243718/fitting-a-willis-immersion-heater

banana5kin

https://www.boards.ie/discussion/comment/119273148#Comment_119273148

Hi tnegun,

I had considered the Willis as the main heating element when fitting, but my past experience with the copper tank was that the Willis and surrounding pipework got very hot. The new tank has metric fittings v's the houses imperial plumbing and I used a combination adapting compression and JG Speedfit push fittings to install same. I decided to err on the side of caution, pex is great but it has it's limitations.

As per graememk's post, I've ordered a hot water circulating pump and can use the shower outlet to circulate to the CW inlet. Prior to getting PV, I had a WemosD1 and a relay controlling the immersion heater via Node Red, so I'll use it and the DS180B to control the pump for now.

graememk

https://www.boards.ie/discussion/comment/119275386#Comment_119275386

Ah an esp8266!, The number of them in my house is growing!

Been thinking of what way to circulate the water, if your immersion is at the top, pumping the bottom to the top is likely the best option.

You could measure the temperatures so you know when to turn off the pump too

I have these in a tank I have

https://www.amazon.co.uk/inch-thermowell-Stainless-thermopocket-Thermocouple/dp/B07DXFWV6B/

The DS sensors fit perfectly in them.

banana5kin

https://www.boards.ie/discussion/comment/119275889#Comment_119275889

My tank unfortunately has no option to install these and I wouldn't like to attempt to drill and tap the tank. I have 35mm foam insulation on the tank and have removed a small section to allow the DS to lie side on against the tank and packed the removed insulation back in to secure the sensor (topped off with aluminum tape), this will have to do. I searched youtube after you suggested a pump and came up with this - https://www.youtube.com/watch?v=TMEWH-2ltII&t=307s which is what I'm going to follow. ESP's are so underrated, I also have many dotted around the house, cabin and shed some using esphome other's sonoff or tasmota depending on the task.

graememk

https://www.boards.ie/discussion/comment/119277228#Comment_119277228

What you could do, is get a long thermopocket, and on the shower is put a T joint in at the shower and cold water in,

Use the right angle of the T for the water in/out and the straight fittings to mount a female 1/2" fitting that you can put the thermopocket into the tank, through the fittings.

Haven't tried that myself tho!

Under the insulation is fine too!

tnegun

Just on the heat of the pipework with the Willis I fit a pipe stat on the return which gives much better control of the temp. Without it the tank was dangerously hot easily 80-90c which was just too much for my liking and way hotter than the shower pump is rated for.

banana5kin

So the pump was installed last Saturday, but unfortunately I haven't had the dreaded Max Temp Reached on the Eddi, partly due to lack of solar, until today.

Glad to report that it works! I don't have any automation yet, but I manually activated the pump at around 1.15pm, stat was around 44 and after around 10 odd minutes the water had circulated and boosted the bottom of the tank to 51 and restarted the HWC element heating again. I think I'll just add a DS probe near the top of the tank and automate it when the max temp reached to get the bottom of the tank within 5 degree of the top (should do it).