Last month we received an upgrade enquiry from a person who winters over in a cold climate. He revealed some interesting facts that I have abridged below.
I normally shut the system down after a week of 20 F (-7C). The pipe, coming down the mountain will start freezing from the outside making the ID smaller and smaller resulting, of course, in a steady loss of water pressure. Basically it is time to shut down when you start loosing pressure. I have often milked the system too long resulting in frozen broken pipes. Brass valves seem to freeze and burst faster than PVC valves.
Friends have a larger hydro system, 6" pipe- 300' head and generally go all winter as long as they can keep their catch box from freezing. My hydro is usually shut down from mid Nov to mid May but varies from year to year. Temperatures here rarely reach 0F (-18C). Normally it will be below freezing mid Nov; then snow/rain all winter. Weather is unpredictable here with some winters being brutally cold while some years it just rains in the winter. Kodiak doesn't get the cold as on the mainland Alaska.
So the top tips for freezing climates are:
- Keep it running, never stop the flow in the penstock, if you need to stop the turbine to clear a jet blockage, open a penstock exhaust valve first.
- Larger pipes take much longer to freeze than smaller pipes, you get plenty of warning of likely pipe freeze if you are observant of the pressure gauge and Watts once the temperate dips below -7C.
- Larger pipes may be able to run down to -15C if the cold snap is not too prolonged.
- If your pressure is falling and the temperature is at or below -7C, disconnect your intake and drain your penstock. Solar PV is not going to help you so it is time to start the gen-set or move to the winter residence.
- Low Head turbines can work in extreme conditions due to the large volume of water. Here is a quote from our gold dealer Florin regarding one of his LH installations:
It’s working very well, they had about -27 degree Celsius and no problem reported with the ice ! I was always convinced this LH turbine is the best option to be installed in the mountains compare with others. In especially if you face a rocky soil that can prevent you to bury the pipe. The big volume of water prevent the turbine to freeze in the winter time.