Quote Originally Posted by Martinm210 View Post
I think they are using flow rate and delta across the radiator to come up with the heat dissipated. Then they probably use delta from the air in sensors to the average of the two water sensors.

I still struggle with the whole Q = M X CP X dT equation myself with units but I think I got it.

To simplify it further and convert it to flow rate:

Q in watts = 263.43 x (Flow rate in GPM) x (dT in C)

So you need 263 watts to raise the delta 1 degree at 1 GPM

Or if you want to solve for dT

dT in Celcius = (Q in watts)/(263.42 x (Flow rate in GPM)

So for example, I've been testing with a 590 watt heat load at 1.5 GPM, so my dT would be 1.49 degrees across the radiator.

I think I need a beer, this stuff hurts..
Oh I understand the math and physics just fine, always have. I don't find it that complicated either. Protip: Stop using imperial measurements. The calculations are much simpler if you use liters per minute. What I don't understand is whether that is actually what they are doing. A google translation of their methodology page:

This temperature difference between water input and output is only a few degrees at most at very low speed and a big power to dissipate. It is less than 1 ° C typically (flow> 2 L / min). With this method, it requires appropriate instruments to measure just 0.01 ° C or better. Indeed, every hundredth of a degree equivalent to several watts after calculation, especially where high-speed input-output gap is reduced, which reduces the sensitivity of the measure:
English version

The advantage of this method is that we know exactly the power dissipated by each radiator. There is no loss side or powers unknown variables introduced in the measuring circuit (eg a pump.). Here, everything happens only between the entry and exit of the radiator.

The method is to measure the temperature rise of water compared to air in a single loop, where we introduce a constant heating power, is another method. It is valid if we take some precautions because it introduces factors more or less unknown, but it does not require tools for high resolution. Each method has its advantages and disadvantages vis-à-vis what is sought and what was available. Either one works at constant power deltaT to find the water-air, or are working on water-air deltaT to find the constant power.
Notice how they are pointing out the need for highly accurate sensors to measure the way you describe, and they go on to mention the other way of calculating it (which is using the known heating element). They never actually state, or at least I can't tell from the translation, which of the two methods they are actually using. If they are using the second method I can see how they might have made the same mistake you did.