Calculate daily temperature difference?

1

Hi,

A couple of years ago I have made my electric water heater (boiler) smart by retrofitting it with a DS18B20 temperature sensor, Raspberry Pi and a Z-Wave smart plug. This way I can control the water heater as a thermostat, like so:

- platform: generic_thermostat
  unique_id: thermostat_boiler  
  name: Boiler
  heater: switch.boiler                      # Z-Wave plug
  target_sensor: sensor.temperature_boiler   # MQTT sensor
  min_temp: 25
  max_temp: 75
  min_cycle_duration:
    minutes: 2
  cold_tolerance: 2.5
  hot_tolerance: -0.5
  precision: 0.1
  target_temp_step: 0.5

This has proven really reliable with a MQTT broker and some automations. This has saved me quite a bit of money and normally wasted heat already. As the water heater manufacturer says this device consumes about 9 kW/h a day, while I’m doing about 1.5 kW/h a day currently.

To also monitor the course of temperature I also added a Derivative sensor to calculate the temperature differences over time:

image

This has a time window of 1 hour and unit of °C/h.

However, now I would like to calculate the daily temperature difference or consumption. So I can see if how much of a surplus of power I’m potentially losing. I was thinking of doing this with a Utility Meter, but I’m unsure of what options to use… Or if this is even the best integration to use?

Otherwise I’m still looking forward to optimize my water heater :slight_smile: if you have any more ideas. Especially with the current energy prices. Thanks :heart: .

2

Is the Statistics integration worth looking at? It has a distance_absolute value which looks promising.

3

Thanks for your reply (which I just noticed, sorry about that). That sounds about right, but it isn’t. Let’s look at this graph:

image
image1503×511 35.3 KB

You’ll notice that I lose a certain amount of temperature every day, but the warm water heater can (and will) heat up multiple times a day as well. I think that detail would be lost when I use the distance_absolute Statistics integration. Or do you disagree?

Also, I think I would like to calculate the temperature loss/gain per hour also. Because that way I could plan my warm water usage ahead.