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Scott Davis

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The Great Simply Solar Hot Air Collector Absorber Challenge!

Summary and Purpose:

This contest is presented as a framework to encourage useful solar hot air collector absorber testing, that will reveal designs that will help us all to build even better performing collectors in the future.

This is an informal "competition", there is no monetary award and it is really all about experimentation, encouraging new thoughts and ideas. We are a club, working together and encouraging each other in a fun way to learn, experiment and move the DIY hobby, art, science of solar forward. When one of us wins, we all do!

Good, accurate testing and data collection is strongly encouraged, however, everyone should understand that these are DIY experiments from folks at all skill levels, that unless duplicated, can't be verified. The submissions we see here will not necessarily be the "definitive" answer. The intent is to bring promising ideas and designs to light for further review.

Testing Concept:

The key to accurate performance comparisons of hot air collectors is side by side testing of the collector under test to a reference standard, using identical airflow. With everyone using an identically designed reference standard, we can make useful comparisons all over the world in widely varying conditions.

We want to open this contest to as many folks as possible, whether building specifically with testing in mind, or building a permanent collector with two or more bays to test alternative heat absorbers. Those builders may want to use glazings other than Suntuf.

We also want to collect the most meaningful data that we can. To do that, the reference standard we all use should be identical, including the glazing. We have decided to try to accommodate both goals by utilizing two award categories - Verified and Unverified.

Contest Objective:

To design a hot air collector absorber that will outperform the reference standard, double layer screen collector (with screens separated). Examples of the double layer screen design are here:


Please note that in the design above the screens are not separated, but Gary adds "For the collector used in the comparison testing with Scott, the screens were separated, and this seems sensible to me."

Or here:



For more background on how and why the double layer screen is used as the reference standard, please visit this URL and read the testing details, about half way down the page:


Competition Procedures:

Build two collectors of identical size (determined by total square feet or height and width dimensions as detailed in the rules below) and identical glazing area. Identically dimensioned collectors (same height and width) are encouraged as they will be most useful for heat absorber comparisons, but are not required for the unverified category, as long as the total square feet is identical.

One collector must be a double layer screen reference standard, designed like the examples in the objective section above. The challenger can be any design you like. The two collectors must be compared in actual, side by side operation with identical airflow and identical input temperature. If the challenger's output temperature is higher, it will be deemed the winner.

Future Competition:

This is an ongoing challenge. Each winner will remain the reigning champion until unseated by a new winner. There is plenty of incentive to submit your entry quickly, before future entrants raise the bar. Future winners will be determined based on their outperformace to the reference standard, which will remain the double layer screen, compared to the previous winner's outperformance percentage.


- Unverified

- Verified

Initial submissions will be placed in the unverified category. A submission will be considered verified on a case by case basis, either by the overall assessment of the quality of the submission (reference standard collector design construction conformity, confidence in air flow test measurements, etc.) or verified by an independent duplication of results by another member. Please see the rules that follow for additional details.


Requirements for Both Verified and Unverified Categories:

- The challenging collector heat absorber can be designed in any manner that you like. It can be a different screen configuration or an entirely different material. Since we have only meaningfully tested the straight double layer screen, the screen possibilities alone are wide open, not to mention the many other possible materials to try!

- The reference standard must be a double layer screen design. The screens should be separated by at least 1/2 inch and no more than 1 1/2 inches. The reference standard must have the interior sides and back (north) wall painted black.

- The reference standard and challenging collector must be insulated identically.

- The glazing area of the reference collector must be equal to the glazing area of the collector under test.

- Collectors must be a minimum of 4' X 2' or 8 square feet - small enough to encourage lots of experimentation, but large enough to yield meaningful results. In the case of a tie, the collector with the larger size will be deemed the winner. 4' x 8' collectors are encouraged, but not required.

- There should be no heating source other than through the collector's glazing.

- Temperature and airflow measurements must be taken at the collector's input and output (not inside the panel itself).

- Official measurements must be take after the collectors have been in full sun with the blower(s) or fans(s) running for at least 20 minutes.

- The airflow MUST be balanced identically through both the reference standard collector and the challenger during the actual test, while your temperature readings are recorded. Estimating cubic feet per minute, though strongly encouraged, is not a requirement for submission. Some methods for determining airflow include timing how long it takes to fill a large trash bag and mounting identical 12V, 2 wire DC computer fans in the air stream and reading their voltage. The tester should strive for as close to 3 cubic feet of air per minute per square foot of collector as possible.

- All construction materials must be readily available at big box stores or on line.

- Construction techniques must be easily repeatable by the majority of the DIY community. This is a subjective ruling, but I think you all know the spirit of what we are after here.

- Tests must either be conducted outdoors in full sun, or if a sun simulator is used, documentation must be provided ensuring that both collectors received equivalent energy.

Requirements for Unverified Category:

- The glazing material is at the builder's discretion. Please note the type of glazing used in your submittal. Suntuf or Tuftex glazing is strongly encouraged, but not required.

- The collector under test is strongly encouraged to be glazed identically to the reference standard; however, other glazings are acceptable for initial submittal. If the reference standard and collector under test are constructed with different glazings, a second test must be performed with identical glazing, either as a follow up by the submitter, or another member, to qualify for the Unverified category.

- Dimensions can be different as long as the total square feet of sun exposed areas and glazing size are identical

- The depth and dimensions of collector under test is at the builder's discretion, provided the total square feet of glazing area are equal to the reference standard.

Requirements for Verified Category:

- The reference collector must be built to the specs we've laid out and glazed with either Suntuf or Tuftex glazing (readily and inexpensively available at Lowes and Home Depot). Identical reference standards will provide the most useful comparisons, regardless of location.

- The collector under test must also be glazed identically with Suntuf or Tuftex.

- The collector under test must have identical width and height dimensions to the reference standard. Depth dimension can be different, but an explanation for the different depth should be included.

- Width and height dimensions must be at a 1 X 2 ratio (minimum 2 feet wide X 4 feet high)

- Airflow should aim for 3 CFM per cubic foot of collector.

- All submission will initially be placed in the unverified category. A submission will be considered verified on a case by case basis, either by the overall assessment of the quality of the submission (reference standard collector design construction conformity, confidence in air flow test measurements, etc.) or verified by an independent duplication of results by another member.


Submit your entry to the group via e-mail with the following information and attachments:

- The date and time of the test.

- The output temperature of both collectors.

- The input temperature of both collectors.

- Your estimated airflow in each collector at the time the measurements are taken (estimates based on timing the filling of a trash bag will be accepted).

- The ambient outdoor temperature (or environment indoors if a sun simulator is used)

Also please provide:

- A written description, picture or video demonstrating how you balanced the airflow.

- A picture or drawing that clearly shows your absorber design. Enough detail should be provided so that others can accurately duplicate your design and ultimately your results.

- A picture of your test setup.

- A picture of the sky conditions during the test.

- A picture of the fan(s) or blower(s) used.

Awards & Rewards:

- The winner will receive lots of great recognition, a certificate award, suitable for framing, our effusive thanks and of course, bragging rights.

- All participants will receive the fun, satisfaction and educational benefit this contest will bring, not to mention the warm inner glow of knowing we all are helping to move the hobby / art / science of DIY solar forward, saving money and benefiting the environment.

- Free heat!

Take care, Scott MD

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