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Solar Water Heaters
Active Systems - Closed Loop
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Flat Plate Type Collector
Best suited for moderate climate |
Evacuated Tube Type Collector
Best suited for cold climate
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Active - Closed Loop Systems pump heat-transfer fluids (usually a glycol-water antifreeze mixture) through collectors. Heat exchangers transfer the heat from the fluid to the household water stored in the tanks.
Double-walled heat exchangers prevent contamination of household water. Some codes require double walls when the heat-transfer fluid is anything other than household water.
Closed-loop glycol systems are popular in areas subject to extended freezing temperatures because they offer good freeze protection. However, glycol antifreeze systems are a bit more expensive to buy and install, and the glycol must be checked each year and changed every 3 to 10 years, depending on glycol quality and system
temperatures.
Drainback Systems use water as the heat-transfer fluid in the collector loop. A pump circulates the water through the collectors. The water drains by gravity to the storage tank and heat exchanger; there are no valves to fail. When the pumps are off, the collectors are empty, which assures freeze protection and also allows the system to turn off if the water in the storage tank becomes too hot.
Collector Types:
Closed-Loop systems use Flat Plate Collectors or Evacuated Tube Collectors:
Flat Plate Collector Systems
Evacuated Tube Collector Systems
A solar water heater system components and layout is shown below (Evacuated Tube Collector):
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