It all began when I buyed my first house, 2011.
My brother is a kind of energy freak. Everything must be done without wasting energy.
In our family, we lauched many times about it. He is the one who has lights which consumes so little energy, we have to check with a flashlight if they're on or off :)
We can't help, he has affected us, me either.
So with my first house building, I spend a lot of money with isolating, floor heating, solar panels, rainwatertank, and so on
And... a woodstove. First a normal woodstove, but the interest to a boiler woodstove, grows and grows. So I made a few heat exchangers by myself.
But the great question is... what is the proceed of the heat exchanger?
So I build a measuring arduino, which calculates the power given to the boiler.
Read on, it's going to be more interesting!
Woodburning heat scale
Woodburning isn't always be done by the same proportionality. The more power the woodstove delivered, the better the efficiency of burning wood. But were is the heat delivered at?
Look at the picture. The optimum of woodburning in a boilerwoodstove, is somewhere around 75% of the maximum power. More power = efficiency increase but also increase the heat going out of the chimney. This graphic is a practice test of my boiler woodstove, with around 76% efficiency woodburn. But this scale is almost the same to every wraparound boiler.
It also shows, you have to burn at more power, than a normal woodstove, to be ensured that some power to the heat exchanger is given.
Measuring/Calculating the power to the boiler/heat exchanger
Calculating the power to the heat exchanger or boiler, isn't very diffecult.
You only must have 2 tempsensors, and a flowmeter.
1 litre water heated up 1 degree, has a caloric value of 4,19 kiloJoule.
4,19 kJ = 0,001164 kiloWatthour (kWh)
So 1 litre water heated up 1 degree = 0,001164 kWh
So you have your boilerwoodstove, 2 tempsensors. 1 is the cold water going into your woodstove heat exchanger (before the mixing valve). The other is the warm water out of your woodstove. (see picture attached). The watermeter (flowsensor) must be installed in the circuit of the tempsensors.
So now you're gonna check the power to the heat exchanger (boiler)
Took a stopwatch. Write down the temp in and temp out. Look how many litres passed in a minute. Write down the temp in and out again.
So for example: Start measuring temp in = 20,0 temp out = 60,0 litres passed in 1 minute = 2,2 End measuring temp in = 20,6 temp out 60,4
Average temp out (60,4 + 60,0 / 2 = 60,2) - average temp in (20,6 + 20,0 / 2 = 20,3) = 39,9
tempdifference x water passed in 1 minute x 0,001164 = 39,9 x 2,2 x 0,001164 = 0,1022 kWh
So in 1 minute, the energy given to the water is 0,1022 kWh.
But what is the power?
kW = kWh / h
So kW = kWh / (1/60), because we only measured 1 minute!
So kW = 0,1022 / (1/60) = 6,13 kW