Swimming Pool Heating Solar Panel Gas Problems

Q&A: what causes overnight collection of gas in a solar swimming pool heater?
Air accumulation in solar collector systems
Swimming pool heating solar collector corrosion concerns
How to purge air from a solar collector
Questions & Answers about solar collectors for swimming pools
References

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Solar collectors for swimming pool heating: this article discusses the question gas or air accumulation in solar collectors, and a possible solar collector corrosion problem with swimming pool heaters.

Overnight Gas (air) Accumulation vs. Corrosion in Solar Collectorsutton to return to this page

The question-and-answer article about the overnight accumulation of a gas (probably air) in a solar collector used for swimming pool heating, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

What Causes an Overnight Accumulation of Gas in my Solar Collector used as a Swimming Pool Heater? Corrosion?

Question: There is an overnight accumulation of gas in the solar panels that heat my swimming pool. When the solar heating system pump turns on in the morning, a small amount of gas (perhaps a quart) comes out of the discharge line. I suspected a leak in the solar collectors but found none when the water was pumped at about 15 psi.

I am concerned that this solar collector gas accumulation may indicate corrosion involving the copper solar collectors and the chemicals in the swimming pool water. Is it possible that this is dissolved gas released overnight, owing to reduced pressure in the solar panels caused by the weight of water trying to return to the swimming pool? - R.H., Lake Charles, LA.

Answer: As you suspect, the gas in your collector is quite probably nothing more than air that has come out of solution in the swimming pool water left in the collector overnight. Air developing in the solar collector in this installation would happen for two reasons:

The water in the solar panels will heat up slightly even after the controller has decided that there is no more useful energy to be collected and has shut off the solar collector pump. Air is less soluble in warmer water than cold water, and will form bubbles that might accumulate in the upper portion of the collector overnight.
If the solar collector is 12 feet above the level of the water in the swimming pool, the water is under a vacuum of about 5 psi less than atmospheric pressure. This vacuum will also draw dissolved gases (air) out of solution in the swimming pool water.

What About Solar Collector Corrosion Due to Chemicals in Swimming Pool Water?

According to Doug Root, of the Florida Solar Energy Center, there have been very few cases of actual corrosion of copper collectors by swimming pool water. In the few cases that have been documented, the pool chemicals dissolved in the swimming pool water have been grossly out of balance - such as an excessive level of chlorine.

Technical Tip for Removing Air From Swimming Pool Solar Collector Systems

Air scoop and air purge valve atop a heating boiler (C) Daniel Friedman

Air accumulating in water in hydronic home heating systems (hot water boilers) is a well-known problem for which at least two components are in common use that may help automatically purge unwanted air or other gases from inside the solar collector plumbing system: [Added, DJF, 10/2009]

An automatic float-operated air purge valve is mounted at a high point on the hot water piping (the cylindrical device at the center of our photo at left|) in order to automatically purge any excessive air in the system.

See Air Bleeder Valves for an article about how these automatic air purge valves work, and see Air-bound radiators, baseboards, boilers for examples of air-bound hot water systems.

If your solar heating system does not already contain an air purge valve, and if the system has trouble from becoming air-bound, adding the air purge might solve the problem at very little cost.
A small air expansion tank absorbs the initial pressure increase in the system when water is heated (and air is drive out of solution) to avoid opening and spilling a temperature/pressure relief valve when it's not appropriate. See EXPANSION TANKS for details. But watch out: this approach won't purge unwanted gases from the system.

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

Photo a rooftop mounted site-built solar collector at page top courtesy of Bob Cheney.

Also see SOLAR COLLECTOR OUTGASSING for more discussion of possible causes of outgassing from a solar collector. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Pool-Gas: Q&A on Overnight Gas Accumulation in a Solar Collector - original text. Use your browser's back button to return here

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

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."
Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
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
Thanks to professional inspector Bob Cheney for the photo of a site-built rooftop solar collector.
"Swimming Pool Heating" cost savings suggestions from the U.S. DOE includes suggestions on using a high efficiency (gas-fired swimming pool heater or heat pump swimmign pool heater) or solar swimming pool heater, using swimming pool covers, managing swimming pool water temperatures, and installing a more energy efficient swimming pool pump, or using it less.
"Conserving Energy and Heating Your Swimming Pool With Solar Energy [copy on file as /heat/USDOE_solar_pool_heater.pdf] - ", U.S. Department of Energy
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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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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