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Expanded Online: Passive Solar Offers High Efficiency
October 2008
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Indirect thermosiphoning — the natural process of convection — circulates the heat-transfer fluid inside passive Solaraide solar thermal systems. The process allowed Rheem to engineer the domestic hot water appliance without pumps or controllers. A home system combines a 47- or 80-gallon storage tank with one or two collector panels. The panels are made for Rheem by its Australian subsidiary, Solahart, they circulate a freeze-proof heat transfer fluid to absorb and deliver heat energy, even on cold and overcast days. The fluid circulates in a closed loop environment to further protect against freezing and allows the system to be used year-round, even in cold-weather locales.

How the System Works

The heat-transfer fluid, a propylene glycol solution, circulates through 35 multi-flow risers in the solar collector, absorbing the sun's heat. Typically installed on a rooftop, the collector is coated with a black polyester powder coat paint to maximize heat absorption.

The heated fluid moves to an attached storage tank, which is encased in highly durable jacket constructed of marine-grade aluminum. The tank sits above the collector to facilitate the thermosiphoning process that keeps fluid circulating.

Heat is transferred quickly and efficiently to potable water inside the tank. Pressure-injected polyurethane foam insulation keeps the water in the tank warm. To resist corrosion and prolong tank life, the tank is lined with vitreous enamel and equipped with a magnesium alloy anode rod.

An option on the water heater is an immersed copper sheath backup electric element, which automatically activates to meet hot-water demand 24/7. The element is designed to kick in to meet demand at night or on heavily overcast days.

The water heaters have been tested and certified for durability, performance, and efficiency by the Solar Rating and Certification Corp. (SRCC).

The 47-gallon model received a Solar Energy Factor (SEF) of 1.3. The 80-gallon model was rated at 1.5 SEF. These numbers represent the energy delivered by the system, divided by the electrical or gas energy put into the system.

"We are definitely witnessing a fast-growing and substantial interest in solar water heating," says Jeff Mahoney, Rheem alternative energy market manager. "(U.S.) Federal tax credits included in the Energy Policy Act of 2005, along with state and local utility incentives, are slowly but surely bringing the consumer back to this market, and builders and contractors are taking note as well."

Rheem Manufacturing Company



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