Posted by Wayne Langille on February 14, 2006, 10:48 pm
Does it make any difference what the cold air temp is going in panel to
calculate btus. Today iI was testing a panel and using outside air in at 42f
and getting 99f out at 143 cfm, or should I use room temp air to get a
more acurate reading. Wayne
Posted by Morris Dovey on February 14, 2006, 11:22 pm
Wayne Langille (in t4tIf.2512$_D5.email@example.com) said:
| Does it make any difference what the cold air temp is going in
| panel to calculate btus. Today iI was testing a panel and using
| outside air in at 42f and getting 99f out at 143 cfm, or should I
| use room temp air to get a more acurate reading. Wayne
If all you're doing is testing, then the input air temperature doesn't
really matter. On the other hand, if you conduct your test outdoors
(not installed) then the wind/breeze can screw up your measurements.
DeSoto, Iowa USA
Posted by Gary on February 15, 2006, 3:52 pm
Wayne Langille wrote:
You should use the temperature rise from the collector inlet to the collector
outlet (this could be inside or outside depending on your collector, but most
I just put up a whole section on measuring collector performance -- I'd be
interested in any comments you (or others) might have on it.
Also put up for download a really fine book by David Bainbridge on all kinds of
passive solar water heaters.
"Build It Yourself" Solar Projects
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Posted by schooner on February 15, 2006, 4:09 pm
I think the question is more in regard to the fact that you can get better
performance numbers when using cooler air than warmer inside air. Since the
collector has a max internal temp it can only raise the air so much in temp,
say 120F. So if you start with 40F air and can get it to say 110F it will
be higher performing than say 60F to 110F since you have a greater temp diff
in and out.
Perhaps this just means that more can be put through the system but I would
assume there is some point that the air is too fast to give up the heat to
the moving air.
So it would be possible to pad performance numbers if you had cooler input
air to start with. Is there any standard used for input air temp when
"official" performance reviews and test are done, say 70F or something?
Posted by SJC on February 15, 2006, 5:19 pm
I look at 40F as having better heat transfer from 120F collector surface.
So, if you want real world numbers, it might be best to use real inside air
temperatures. Let's say something like 60F in, coming out 90F at 100 CFM.