Rainwater collection tank freezing

rowlettr(7)December 7, 2008

I have constructed a rainwater collection system at my mountain home in western NC. I use it to water my plants and garden while I am there and when I am away. When I am away, I worry about my 275 gallon, above ground tank, freezing and bursting if the temperature drops below the freezing point. I want to add a thermostatically controlled drain to empty the tank when the temerature drops below freezing. I can use an irrigation valve on a line that I can tie into my overflow drain line, whereby it will open at about 30 degrees and drain the tank. If the temperature increases, the valve will close and the tank will be allowed to refill when it rains again. My watering of plants is gravity fed with a timer control. My queston is:

What is the best/most economical/recommended type of thermostat control device available to operate the irrigation valve? It must sense the outside temperature and be able to operate a standard irrigation valve based on outside air temperature. The irrigation valve is closed unless a voltage is applied to a solenoid, which opens the valve.

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While I do not have a direct answer to your question, I may have an alternative. I am assuming by the question that you intend to collect rainwater throughout the winter. Disconnecting the tank from the downspout would definitely solve the problem for the winter; which I'm sure you already know.
How much room in the tank do you have above your overflow? If you have at least 6-inches of, let's call it 'relief space' above your outlet, you should be good. As long as the freezing water has space to expand into, the tank should not burst. The problem is when the water has no space to expand...then the ice will make its own space with little consideration for your tank.
For a more hands-on approach, I have two alternate ideas.
Those in the marine environment have to be careful of the pilings they tie their boats up to. If the canal/pond/lake/bay freezes, overall water level rises...ice attached to the pilings actually pulls them up, sometimes completely. One way to prevent this is to put bubblers at the base of each piling. The rising air bubbles keep the water around the piling moving, which prevents ice from freezing around the piling. You could drop a hardcore aquarium air pump into the tank to reduce the opportunity for freezing.
The other option...a water heater. People who keep their horses (and other livestock) outside in paddocks drop heaters into the water buckets/troughs outside to keep the water from freezing. I would consider checking Stable Supply companies for comparable products.

Good luck!

Here is a link that might be useful: The Rain Tank Depot

    Bookmark   December 8, 2008 at 3:21PM
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