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Swimming Pool Heating Solar Panel Gas Problems InspectAPedia®  -     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 Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

This article discusses the question gas or air accumulation in solar collectors, and a possible solar collector corrosion problem with swimming pool heaters. Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Photo a rooftop mounted site-built solar collector at page top courtesy of Bob Cheney.

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Overnight Gas (air) Accumulation vs. Corrosion in Solar Collectors

• Pool-Gas: Q&A on Overnight Gas Accumulation in a Solar Collector - original text. Use your browser's back button 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, (see links just above) 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 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: [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.

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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AIR CONDITIONING & HEAT PUMP SYSTEMS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR POLLUTANTS, COMMON INDOOR
AIR SEALING STRATEGIES
ENERGY SAVINGS in BUILDINGS
ENERGY SAVINGS PRIORITIES
ENERGY SAVINGS RETROFIT CASE STUDY
ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE
ENERGY SAVINGS RETROFIT OPTIONS
EVAPORATIVE COOLING SYSTEMS
EXTERIORS of BUILDINGS
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FREEZE-PROOF A BUILDING
HEAT LOSS CALCULATIONS
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSEWRAP - TYVEK INSTALLATION DETAILS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INSULATION & VENTILATION INSPECTION & IMPROVEMENT
FOUNDATION CRACKS & DAMAGE GUIDE
HEATING SMALL LOADS
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INSULATION & VENTILATION INSPECTION & IMPROVEMENT
INTERIORS of BUILDINGS
ACOUSTICAL SEALANTS
MOISTURE CONTROL in BUILDINGS
PLUMBING TOPICS
STRUCTURAL INSPECTIONS & DEFECTS
HEATING SYSTEMS
ROOFING
SHEATHING, FOIL FACED - VENTS
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
  SWIMMING POOL SOLAR HEAT, INDOOR
STRUCTURAL INSPECTIONS & DEFECTS
SUMP PUMPS GUIDE
THERMAL EXPANSION of MATERIALS
THERMAL MASS in BUILDINGS
THERMAL MASS in UPSTAIRS
THERMAL TRACKING Indicates Heat Loss
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WATER HEATERS
AGE of WATER HEATERS
ALTERNATIVE HOT WATER SOURCES
WATER SOFTENERS
WET BASEMENT PREVENTION
WIND TURBINES
WINDOWS & DOORS
  SKYLIGHT LEAK DIAGNOSIS & REPAIR
  SITE BUILT DOUBLE GLAZED WINDOWS
  SLOPED GLAZING DETAILS
  VERTICAL GLAZING DETAILS

• 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 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.
• 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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