I have a solar heat panel. I am sending the air from the house through the panel at 19 degrees Celsius and it comes back at 52 degrees celsius. The air speed of air moving through the 6" pipe is 400 CFM. I would like to know how much energy is produced in 1 hour in Kwh.
Responses (1)
You need to know the mass of air flowing through per second in Kg.
400 CFM /60 sec = 6.666 CFS
1 cubic ft = 0.02832 cubic meter (CM)
So 6.666 x 0.02832 = 0.1888 CM
1 CM = 1.2 Kg
So 0.1888 CM x 1.2 CM = 0.2266 kg/sec
It takes 1000 joules to heat 1 kg of air by 1 C at standard temperature pressure
Your temp change is 52-19 =33 C
So the joules/sec is 1000 j /c x 0.2266 kg/sec x 33 c = 7.476.4 Joules/sec
1 watt is a measure of power + 1 Joule/sec
So your system is running at 7476.4 w or 7.4764 Kw so if it maintains that power level over 1 hour it is 7.4764 KWH.
Hope that is ok & helps!
Thank you very much Ernest.
I think there is somethink missing here because the sun is giving approx 900 to 1000 W per m2.
My solar pannel is 3.6 m2 (4' by 10') so theoretically the pannel can produce 900W x 3.6 m2 = 3.24 kWh. I don't think that I have 100% conversion of the sun energy in heat + some loss, so I'm expecting the solar pannel to produce between 2.6kWh and 3 kWh.
Can you think of what else could be missing? and thank you again.
I have checked my values & only minor error quoting stp.
Air density is 1.29 kg/CM at 0C & 1 bar. This is not enough to account for the difference. Happy with dry air specific heat capacity of 1 kj/kg/C rise (1.006 is more accurate!)
Are you sure about 400 CF/min flow rate. Thats about 23 mph in a 6 " pipe, quite quick! Also the 33C rise (not unreasonable).
It is specified 400CFM but I am not sure that is the actual output.
I think the air flow is less that it is specified and that could be the issue.
Your most likely right as the 400 cfm measured without the systen back pressure, such as needed to push air round corners & through heat exchangers ect.
Another area of caution. Where are you measuring your temperatures? If you are taking the 52C in the outlet airstream, you could have higher readings ( a simular affect to wind chill).
I measure the temperature at the outlet but It cannot make that much difference. and after thinking even if the blower pushes only half, 200CFM, the result still looks high but I'm not sure what could be off.
1 CM = 1.2 kg at Standard Temp Pressure