Guide to the Basics of Solar Hot Water Heating Systems InspectAPedia® -
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This article explains the basic components of solar hot water heating systems used to heat water for washing and bathing. Sketch at page top courtesy of Lennox Industries.
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How to Hook Up & Use Solar Water Heating Systems to Provide Domestic Hot Water
Solar water heaters use renewable energy - sunlight - collected in outdoor rooftop or ground-mounted solar collectors to heat water which is circulated by a pump between a hot water storage tank and the panels.
The upper end of a simple solar water heater collector is shown in our photo at left. Look closely and behind the corrugated plastic surface, at the top you can see the horizontal black tubing that moves water through the top end of this collector.
Solar water heaters have been in use for decades, with popular use at remote cottages or off-the-grid buildings and are likely to see increasing use in much of the world as energy costs continue to climb.
What are the Components of a Solar Hot Water Heating System?
The schematic at above left (U.S. Department of Energy) explains a typical active, closed loop solar water heater hookup and shows the basic parts of a solar hot water system. The schematic at above right (U.S. DOE) explains a typical passive-batch solar water heating system, showing the batch collector containing a volume of hot water and located separately from a backup solar water storage or water heater tank.
Here are the key parts of solar hot water heating systems:
Our solar water heater photographs below show a convection-type solar water heater widely distributed in Mexico. The white water tank and the bank of solar heating tubes are initially filled with cold water. As the sun heats water in the parallel heater tubes, warmed water rises by convection in the tubes and enters the storage tank while cooler water from the tank falls into the tubes for further heating. Heated water is drawn from a fitting at tank top while incoming cool water is fed into the tank bottom. This system heats water and stores it in the reservoir tank using only natural convection with no pump required. Our second photo (below right) shows one of these systems installed.
One or more solar collectors are located where they will receive an appropriate (or maximum) amount of sunlight. In our photo below you can see a simple solar collector hanging at the Don Pedro Ferreteria hardware store in San Miguel de Allende, Mexico.
Heat exchanger: The solar hot water collectors are connected by a loop of piping to a heat exchanger unit located inside of a hot water storage tank located in the building. In other words, the building's domestic water supply to be heated is not itself circulated through the solar collector but rather it is heated inside the water tank by a heat exchanger which itself contains a liquid (containing an anti-freeze in northern climates) which circulates in the solar collectors and inside the heat exchanger.
A hot water storage tank contains domestic hot water heated by the heat exchanger; the tank is supplied with incoming cold water and provides outgoing hot water to the building's plumbing fixtures. In our photo below you can see a simple solar water heater tank at the Don Pedro Ferreteria hardware store in San Miguel de Allende, Mexico. In areas where there is plenty of sunlight and water usage is more modest, a simple collector, pump, controls, and small water tank such as the one we show below are often adequate.
Temperature sensors mounted at the water storage tank and also at the solar collectors monitor water temperatures and communicate with a solar controller module.
The solar controller module determines when it is appropriate to circulate water from the hot water tank through the solar collectors, preventing water circulation when it would cool rather than warm the hot water.
An expansion tank absorbs the pressure increase created in the (closed) system when water is heated. See Guide to Heating Boiler Expansion Tanks for details.
A pressure and temperature relief valve is provided on the hot water tank for safety
An air vent valve is provided at the solar collectors to avoid the piping becoming air bound, purging un-wanted air in the water circulation loop.
A tempering valve or mixing valve is installed to mix cold water in with the outgoing hot water from the hot water tank, permitting storage of more heat in the water tank without risking scalding building occupants. We discuss tempering valves or mixing valves in detail at Guide to Mixing Valves & Anti Scald Valves
A backup hot water heater is usually provided, using electricity, gas, oil, or other fuel to assure that there is adequate hot water when weather conditions do not provide enough solar energy.
As energy costs continue to increase the payback-time for the cost of solar panels and piping installation for solar hot water systems will continue to improve. The solar water heater system sketch is courtesy of Accu-Spect.
Especially in areas that receive adequate sunlight we should expect to see an increase in popularity of these systems.
A Comparison of Alternative Hot Water Heaters & Sources
This article describes the characteristics of these water heating methods:
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Desmex Solar, Blvd. José Ma. Morelos 3649, Col. Purísima de Jerez, León, Gto. C.P.37290
Tel. +52 (477) 788 06 00, Fax. +52 (477) 771 10 02, e-mail: leon@desmexsolar.com: website http://www.desmexsolar.com/ Additional offices in San Miguel de Allende, Guanajuato, Mexico - Carretera a Celaya Km. 1, Plaza Alhóndiga Local 14 (1M), Frente a Mega Comercial Mexicana, San Miguel de Allende, Gto. Tel: +52 (415) 150 73 12 e-mail: sanmiguel@desmexsolar.com, Guadalajara, Mexico - +52 (33) 3165-2454 e-mail: guadalajara@desmexsolar.com, Monterrey Mexico - Tel. +52 (818) 356 43 30 e-mail: monterrey@desmexsolar.com, and Mexico City - Tel. +52 (55) 2643 26 29, Fax. +52 (477) 771 10 02 e-mail: mexico@desmexsolar.com
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
"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 Heating: A Comprehensive Guide to Solar Water and Space Heating Systems (Mother Earth News Wiser Living Series), Bob Ramlow, Benjamin Nusz, ISBN13: 9780865715615 Heating water with the sun is almost as old as humankind itself, and it is done all over the world. Yet there are strangely few resources on the topic in North America.
Solar Water Heating fills this gap. It reviews the history of solar water and space heating systems from prehistory to the present, then presents the basics of solar water heating, including an introduction to modern solar energy systems, energy conservation and energy economics. Drawing on the author’s experience as an installer of these systems, the book goes on to cover:
* Types of solar collectors, solar water and space heating systems and solar pool heating systems, including their advantages and disadvantages
* System components, their installation, operation, and maintenance
* System sizing and siting
* Choosing the appropriate system.
Since people often get turned off by the up-front cost, the book focuses especially on the financial aspects of solar water or space heating systems, clearly showing that such systems can save significant costs in the long run. Well-illustrated, the book is designed for a wide readership from the curious to the student or professional.
"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-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 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.
"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.
"Side by Side Testing of Eight Solar Water Heating Systems", ETSU S/P3/00275/REP/2, DTI Pub URN 01/1292, Contractor, The Energy Monitoring Company Ltd., C Martin, M Watson, 2001
This study compared the amount of energy that eight modern solar water heating systems could produce over an average year. Document: - local copy
Document: - original is at
http://www.berr.gov.uk/files/file16826.pdf
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