Control water heaters based on their states

Modifications
1

Hello everyone,
I don’t know if what I want to attempt is even possible without additional hardware. Bear with me.

I have a combined 4 water heaters. The 4 heaters have built-in thermostats. They are otherwise dumb. All the 4 are electrically joined. They are connected to AC out 2 of the Quattro. AC out 2 is controlled by assistants and Cerbo relays to power up when needed. As it is, everything works flawlessly but:

  1. As long as AC out 2 is powered, each heater comes on and goes off randomly depending on what its thermostat sees. I can’t control them
  2. I have to guess how much energy each heater is using.

Now I want to be able to control the heaters. No 2 heaters should be on at any time.

My first thought was to use 4 Shelly smart switches to make the 4 heaters smart and control them this way.

Is there a simpler or cheaper way?

Fideri

2

I use tuya variants for mine, though they are now backups as heating is now done via heatpump. They report power usage and aren’t overly expensive but give you huge control via nodered.
Writing a watchdog that checks for the element to switch off and then stops further use, or powers on another device, is pretty straight forward.

3

I use Shelly EM to control and monitor the energy usage of a water heater. The relay on the Shelly EM drives a contactor to switch the load and the CT clamp measures consumption.

I also use another Shelly with Add-on device and DS18B20 to monitor the temperature of the water cylinder (thermostat still controls the temperature).

The whole lot is controlled and monitored via Node Red.

4

Thanks for the suggestions. I have now broadened my search to Shelly, Tuya and Sonoff. It turns out that whichever brand I go with, I can get a 1-to-4 device instead of 4 individual devices.