|MadSci Network: Agricultural Sciences|
These are difficult questions to answer, but I will make an attempt. 1. Is it wise? If you set the timer and it freezes hard before it comes on, then you may get some damage to your equipment. In winter, aren't you supposed to drain the lines etc. to prevent the expansion-contraction damage of freezing and thawing water? I the frozen north, one would do this (or for those of us in the Southern Hemisphere - the frozen south). I imagine you are in a fairly warm area where really hard freezes are non-existant. I will address the rest of this letter as if that was the case. Therefore - if a freeze is expected, I would recommend running the sprinkler the whole time. The warmer water running though the system will protect it. 2. Impossible to answer! No one can predict the time when freezing begins. If it is near 0 C (32F) when the sun goes down start it, especialy if there are no clouds. To go from 0 C not freezing to 0 C frozen takes a loss of 80 calories per gram of water (called the latent heat of fusion). To go from 1 C to 0 C only takes a loss of 1 calorie per gram. So one can be at 0 C for a long time and not see any ice. Watch a big thermometer put in a freezing room. It gets to 0 C fast enough, and then it takes its own sweet time getting to -1 C. Anyway its all a wild guess on the time of actual freezing, so turn it on early. 3. Keep it on till the sun is up or it warms up. I assume we are talking about protecting spray equipment and not plants. So maybe this is the time to go on and on about the earth's resources ... and the wise use of fresh water. If it's winter, drain the lines. If you only have one or two nights of frost a year turn it on low early and turn if off when it's warm. Hope the message gets to you before a frost. We are in mid-summer here in New Zealand. Cheers, Steve
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