I have floor heating in my house. Now I have installed temperature sensors and a flow meter to it. Through the formula Q = m . c . ΔT I can now calculate the “delivered energy”. The results I am getting do make sense (graph below). I am however now asking myself if I haven’t screwed up the unit of measurement. Shouldn’t that be kW instead of kWh?
If that’s so, then I should probably feed the sensor I have created into a Riemann sum sensor, but am currently unsure (apologies: has been ages ago since I had physics at high school).
In the end I would like to compare the delivered energy of my floor heating with my gas consumption to see if I can boost the efficiency of my boiler.
Did that and I then come to values or around 4 which sounds reasonable for a radiator (like floor heating), but then question remains: is that kW or kWh?
Heat capacity (Q) is usually measured in Joules, which is a unit of energy, like kWh. So you already have energy. Riemann Sum is not going to help (it integrates Power with respect to time to give Energy).
Your calculation is determining the energy supplied over the time range spanned by ΔT.
However this time appears to be quite small giving you “instantaneous energy” and it is not accumulating.
Counter-intuitively maybe if you calculate Q/s (where s is the ΔT time period) it will give you power, which you can then integrate with the Riemann sum helper.
The other problem is that you may not just be measuring heat energy supplied to the system. There are also conduction and radiation losses in the system from the floor coils that affect the temperature. Unless you are measuring ΔT across the inlet to outlet of the water heater?
the formula Q = m . C . ΔT will express Q as an energy in KJoule (in SI units), with:
m is a mass of water, expressed in kg
ΔT is variation of water temperature, expressed in °C
C = 4.18 for water.
Basically, it says you need 4.18 KJ to warm 1kg of water by 1 °C
To get the energy in kWh: You divide by 3600 (1kWh = 3600 KJ)
Now I assume that your flow meter is measuring a flow in kg/s which is usually noted w
So the formula is now : P = w . C . ΔT
P : Power, in kW ; w in kg/s; C = 4.18 and ΔT in °C