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Solar Solution: Frost valve for solar thermal
Australia has the highest average amount of solar radiation of any continent, making it the perfect place for generating power or heating water with energy from the sun. Not surprisingly, the combination of generous rebates and sunny weather has given rise to solar thermal installations across the continent. Generally these installations are quite straightforward, but in the southern part of the continent, temperatures can drop below zero (Celsius), causing freezing problems for some thermal systems.

Sidek Manufacturing, located in Adelaide, South Australia is a solar thermal system manufacturer. Their systems are a split system where the solar panels are mounted on the roof and the storage cylinder is located on the ground. There are areas that can have as many as 150 days when the temperature is low enough for pipes to freeze, and the company has had some trouble with water freezing in the riser tubes in the collector, which resulted in burst pipes.

Frost ValveNathan Tichy, General Manager of Sidek, said the solution they found is to insert a frost valve, which they place in the feed and return lines to the solar collector, next to the inlet and outlet of the pair of collectors. He said that when the water temperature approaches freezing, the valve opens and leaks a small amount of water out of the pressurized system. “This in turn, as the system is a closed system, is replaced by warmed water from the storage cylinder,” Nathan explained.

For about five months Sidek has used a frost valve from Therm-Omega-Tech, a US company based in Warminster, Pennsylvania. What is unique about this valve, Nathan said, is that it senses the actual water temperature inside the pipes.  Using their thermal actuators, he explained, the temperature detection is accurate. The amount of water discharge is “very minimal” as the valve re-seats with a small temperature rise.

Another approach that they have tried is to incorporate some frost protection into their electronics. “But this won’t protect the system when there is a power failure,” Nathan noted. They’re currently incorporating the Therm-Omega-Tech valve to be incorporated into their existing layout.

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The typical household uses 10,000 to 15,000 BTUs of hot water per person per day. A 20 vacuum tube solar collector can produce 30,000 BTUs on a summer day with a footprint on a roof of only 36 square feet. The system can provide 100% of summer hot water ... 
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