Open Forum → Calculate watts from CFM and deltaT?

I've tried to calculate how many watts of energy it takes to heat air moving at 280 cfm from 74F to 100F (deltaT of 26F). I found the formula CFM * 1.08 * tRise = Btu/hr. When I plug in the numbers I get 2304 watts. This can't be right because that would mean that my solar can heater is running >100% efficiency...

What I'm trying to do is calculate the efficiency of a home made solar air heater. Here are the numbers I am working with:

Current solar output= 761 watts/m2 (according to Davis Instruments solar sensor)
Solar can heater absorber surface area= 2112 in2
inlet air temperature= 74F
outlet air temperature= 100F
outlet= 4in diameter round opening (12.57 in2)
velocity of air= 800 linear feet/minute

I plugged in the numbers to calculate that my air flow is ~280CFM and my Btu/hr is 7862. If I convert Btu to watts I get 2304 watts. Something's not right... Can someone see what I'm missing?

What is the total watt output of this absorber? Based upon the current solar output of 761 watts/m2 I should be able to calculate the efficiency...

Maybe I have an error in my air velocity measurement. I measured again and got ~500ft/min. It seems a little difficult to get an accurate measurement. I held the anemometer out a little to get a more average flow and it fluctuated between 450 and 550 ft/min.

Ok, I may have calculated CFM incorrectly. I plugged the diameter into the equation instead of radius. Turns out my CFM may only be about 44 or so.

Problem solved. It looks like I may be around 50% efficient. Took some more measurements and averaged them. I had the solar can heater overheat once and it damaged the insulation. It used to operate around 85% or so...