DIY or home made wood framed solar collector design:

This article discusses the durability of and advice on construction of solar collector housings made of wood, plywood, or OSB. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.

Durability of Wood Housings for Solar Collectors

The question-and-answer article below is about the durability of wood for use in constructing the housing of solar collectors, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Question about the structural integrity of wood frames or housings for solar collectors

In the near future I intend to construct flat-plate solar collectors for use in a hot air heating system. I would like to construct the collector structure out of wood, using commonly available materials such as pines, plywood, or waferboard (OSB).

Can I expect the wood solar collector frame to maintain its structural integrity under the high heat conditions? Is there any danger of fire? - L.P_.C. - Methuen MA

Answer: 

By the mid 1980's in the U.S., the use of wood in solar collector housings or frames had been questioned and investigated by a number of parties, particularly because of a high level of consumer interest in build-your-own solar collector projects following the spike in home heating oil prices.

The consensus on use of wood to build a solar collector seems to be: use caution or avoid the use of wood altogether.

The degradation of wood under long term exposure to high temperatures (for example by chemical change or pyrolysis - see PYROLYSIS EXPLAINED) has been well documented.

The degradation is a function of temperature and time and is cumulative from one high temperature exposure to the next.

Most researchers feel that degradation of wood is insignificant below 200 degF. Long term exposure of wood to temperatures from 200 degF. to 300 deg.F. will cause the wood to lose weight and strength, and under some conditions the wood will actually char.

Can a wooden solar collector catch fire? Wood charring in response to these high temperatures is caused by a slow glowing combustion process (pyrolysis) that is exothermic, or heat-producing. If this heat is trapped and temperatures sufficiently elevated, flaming combustion could occur.

This is why a heating system flue that is too close to wooden building framing becomes a fire hazard and can eventually begin to actually burn - pyrolysis reduces the ignition point of the wood

- see FIRE CLEARANCES, SINGLE-WALL METAL FLUES

and also FIRE CLEARANCES WOOD & COAL STOVES for details -- DF.

Specific design temperatures for wood-framed solar collectors are not available since many variables determine the ignition point of wood.

In tests conducted by the U.S. Department of Energy (DOE), charring of plywood solar collector backings was observed after one summer of stagnation in test collectors with peak temperatures of 290 degF. Plywood and waferboard (or OSB, oriented strand board) pose no greater problems than solid wood, since the phenolic adhesives used are unaffected at these temperatures.

The goal in constructing a wood-based solar collector structure, then, is to keep wood temperatures low by insulating the wood, keeping the wood from touching the solar absorber, and avoiding high-temperature stagnation conditions.

Low-temperature single-glazed solar collectors with summer venting would be in order. [This is not a new topic, and a full discussion of the issue of solar collector durability appeared in Solar Age Magazine, 8/81 p. 42.]

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

"Wood in [solar] collectors" - links to the original article in PDF form immediately below has been preceded by an expanded/updated online version of this article

• WOOD HOUSINGS FOR SOLAR COLLECTORS [PDF] use your browser's back button to return to this page

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SOLAR COLLECTOR WOOD HOUSINGS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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