This is a side by side heating performance test comparing a solar air heating collector that uses two layers of aluminum screen for the absorber to a backpass collector that uses a solid sheet absorber with all the airflow behind the absorber plate.
The screen vs backpass collector test was done using the same ducting and blower setup as for the other tests. The blowers were Elicent AXC 125Bs.
Flow rates were measured using the Big Bag technique.
Flow rates used ranged from 2.3 cfm/sf up to 3.3 cfm/sf.
The plot above shows the logged inlet and outlet temperatures for the screen collector (black) and the backpass collector (red). These can NOT be used directly to compare performance as the flow rates for the two collectors were not exactly equal for the testing. In order to get a comparison of heat output for the two collectors at a given time, the product of the flow rate times the temperature rise must be compared for each collector. The table below gives this comparison for several times during the testing. For example, in the time period around 10:30 am it looks from the termperature plot like the two collectors about tied, but in fact, while the temperature rise is about the same, the screen collector air flow is 2.7 cfm/sf vs 2.4 cfm/sf for the backpass collector -- a 13% difference in flow rate and heat output.
In general, the screen collector output is about 7 to 13% greater than the backpass collector.
|Screen Absorber vs Reference Backpass Collector Solar Air Heating Collector Test|
|Janary 11, 2011|
|Reference Collector||Screen Collector||Summary|
|Time||Sun||Tamb||Tgar||Tin||Tout||dT||Vin||Vout||Fill Time||Flow Rate||Flow/sf||Ref Heat Out||Efic||Tin||Tout||dT||Vin||Vout||Fill Time||Flow Rate||Flow/sf||Scrn Heat Out||Efic||Hscrn/Href|
Note that after this test was completed and Scott and I discovered how well this simple simple collector did compared to the reference (backpass) collector, as well as its low pressure drop, we decided to start using this screen collector for the reference collector in the rest of the tests.
Gary April 12, 2011