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Use of Wood for Solar Collector Construction InspectAPedia®  -     Q&A on the advisability of using wood to construct solar collector housings or frames How durable are wooden solar collectors? Is there a fire hazard with wooden solar collector devices? How does a wooden solar collector frame withstand heat and temperature changes? Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

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.

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Durability of Wood Housings for Solar Collectors

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

• Wood Housings for Solar Collectors - PDF form, use your browser's back button to return to this page

The question-and-answer article about the durability of wood for use in constructing the housing of solar collectors, quotes-from, updates, and comments an original article, (see links just above) 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 pyrolosis) 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 (pyrolosis) 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 - pyrolosis reduces the ignition point of the wood - see Fire Clearances, Single-Wall Metal Flues and also Wood & Coal Stove Flues 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.

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SOLAR ENERGY SYSTEMS
  PASSIVE SOLAR DESIGN METHOD
  PASSIVE SOLAR HEAT PERFORMANCE
  PHOTOVOLTAIC POWER SYSTEMS
  SLAB INSULATION, PASSIVE SOLAR
  SOLAR COLLECTOR AIR or GAS COLLECTION
  SOLAR COLLECTOR FILMS
  SOLAR COLLECTOR WOOD HOUSINGS
  SOLAR HEATING SYSTEMS
  SOLAR HOT WATER HEATERS
  SOLAR HOUSE EVALUATION

• Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
  
• 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. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
  Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in BUILDINGS, and other topics.
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
• Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
• Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
• The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the InspectAPedia Bookstore
• "Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
• "Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
• "Heat Exchangers for Solar Water Heating Systems", U.S. DOE describes the types of solar water heater heat exchange methods between the sun and the building's hot water supply
• "Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
• "Solar Water Heating System Maintenance and Repair", U.S. DOE
• "Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
• "Scaling and Corrosion in Solar Water Heating Systems", U.S. DOE
• www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 is the base U.S. DOE website for these articles
• "Active Solar Heating Systems", U.S. Department of Energy, including
• "Radiant Heating Systems" U.S. DOE
• "Absorption Heat Pumps & Coolers", U.S. DOE
• "Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
• "Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

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