Calculate energy for water usage

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1

Hey everyone,

I have an instantaneous gas water heater (around 15 years old) that I use for both hot water (drinking, showers, etc.) and underfloor heating. I’m currently working on creating a water dashboard to track various aspects of my water usage (well level, rainwater vs. city water usage, valve status, etc.). I’m also curious if it’s possible to estimate the energy (electricity and gas) used specifically for heating the water.

As an example, here are some screenshots showing shower usage around 5 PM and 7 PM, along with overall gas usage and electricity consumption for the heater.

Schermafdruk van 2024-09-25 20-27-47
Schermafdruk van 2024-09-25 20-27-471011×693 20.6 KB

Schermafdruk van 2024-09-25 20-29-19
Schermafdruk van 2024-09-25 20-29-191485×404 19.6 KB

Any suggestions on how to calculate this or other insights would be greatly appreciated! Thanks!

2

Do you know the efficiency of your water heater?

E = mc(Tf - Ti) / η

Where

E = energy in kWh

m = mass in kg (~ volume in litres for water)

c = 0.00116 W/g for water

Tf = final temperature in °C or K

Ti = initial temperature in °C or K

η = efficiency

3

Hmm, slik. I was originally considering A + B, but only if C is greater than X. :wink:

Regarding your formula:

  • E = Is kind of combination of electrical CT clamps and a gas pulse counter?
  • m = The value from the water pulse counter?
  • c = 0.00116 W/g for water
  • Tf = Temperature unknown (depends on the user’s desired temperature?)
  • Ti = Isn’t this the temperature set for the heater (eg by thermostat)?
  • n = And the efficiency value should be found in the heater’s manual? Of course, this is all theoretical, right? Old one, less efficiency?

Thanks already for this example! Gives me motivation to proceed with this measurement…

4

No, none of that is correct.

The equation tells you how much energy is required to heat water. Like your topic title asks for.

You get the energy, E, used to heat the water, from the volume or mass of water and the temperature rise of that volume or mass. That is all that is required. It’s high school physics.

Forget the efficiency. That was a mistake. It is not relevant here.