With most bags it's hard to measure the exact volume so after doing the measurements a few times I ended up containing the bag inside a large cardboard box. This made it easier to measure the volume. I cut a flap in the box that would move out when bag filled up to let me know when to stop the time portion of the measurement.
The larger you make the bag and box, the more exact your measurements will be. zap
The sun came up and i did that trash bag test. I got 150 liters trashbag full in about 25 seconds. I tried to find some converter to get it in ft/min, but came up with nothing.(Should it be cubic feet?) Mainly because this very slow connection here. It's taking forever opening pages.
My test results are following: Duct is 0.084539 sqft Toutlet is 150F Tinlet is 37F Vair is 6 litres/second (a little help with this please)
I start to think that maybe I need a second pair of those blowers? I even saw 174F coming out from it. Anyway I think it will do okay and survive with or without those extra blowers. The area it should heat is about 2600 cubic feet. Best regards jaskiainen[ Parent ]
Ron Adventure is just bad planning." -- Roald Amundsen [ Parent ]
6 l/sec = 12.713 cubic foot/minute A good site for doing conversions is: http://www.onlineconversion.com
So, your heat output is: Qout = (air weight flow)(Tout - Tin) (Cair)
Qout = (12.71 ft^3/min)(0.065 lb/ft^3)(150F - 37F)(0.24 BTU/lb-F) = 22.4 BTU/hr or 1344 BTU/hour.
Don't know how large your collector is, but lets say its 20 sqft (you can adjust the calcs to the actual area of your collector).
Solar In = (300 BTU/sqft - hr)(20 sqft) = 6000 BTU/hr
Efficiency = (Heat out)(Solar in) = (1344 BTU/hr)(6000 BTU/hr) = 0.224 (22 %)
The 300 BTU/sqft -hr is for full sun, and for the collector being pointed right at the sun. Its best to do this test around solar noon, and aim the collector right at the sun.
The temperature rise of 150 - 37 = 113F is a lot -- the collector could use more airflow for better efficiency.
How large is the collector?
GaryGary gary@BuildItSolar.com www.BuildItSolar.com[ Parent ]
It hit me yesterday evening: I just put some rough made fins inside the inlet and forgot they were there. That I think cause some problems like overheating and much less airflow. Like yesterday the panel outlet temp was 79 Celsius degrees. A day before it was "only" 66 C.
So I think I need to fill my trash bag again? Maybe it will fill within 15-20 seconds. Gonna do that test next weekend.
My panel surface is 3.2 squaremeters or 34.5 squarefeets. It is solar can heater made out of 340 beercans with double glasing. Inner is 2mm thick polycarbonate sheet and outer is 3mm acrylic sheet. Two layers for better performance in winter. Best regards jaskiainen[ Parent ]
With the beer cans, you should be getting a pretty even distribution of air through the collector as long as the manifold delivers air evenly to the can rows. You can do a rough check on this by temporary taking off the glazing. Let the collector stabilize in the sun with the fan on. Measure the surface temps of the cans with one the IR gun style thermometers. If you find fairly even temps that increase some for the intake end to the exit end, then the airflow in the cans is even and removing heat all over. If you find hot spots, those are areas that are not getting enough airflow. If you don't have the IR temperature gadget, you may be able to feel any hot spots just touching the surface with a finger.
How hard was it to measure the airflow with the plastic bag? Does the bag technique seem to work pretty well?
