Q & A: wind chill and freezing rate

Q:
How long does it take for water to freeze when there is a wind chill factor? Our condo board thinks that water supply lines freeze faster on 3 buildings and not on the 5 other buildings due to the wind chill factor. The buildings are only 50ft apart. I am struggling with their logic.
- Nancy (age Old)
Saint Simons Island
A:

You're right that the temperature a pipe reaches sitting out in the cold for a long time doesn't depend on the wind. How long the pipe takes to cool down does depend on the wind.

Think of it this way. Some heat flows from the pipe top the surrounding air, cooling the pipe and warming the air.. If there's wind that air is quickly replaced with air just as cold as the original air, and the process keeps going at the full rate. If there's no wind, the warm air hangs around the pipe longer, slowing the rate of heat flow from the pipe. If some heat keeps flowing into the pipes, that difference in rate of cooling can make the difference between the pipe freezing or not freezing.

Whether that difference in heat flow rate is important in the case of your condo, I don't know. Taping some thermometers to the pipes would make it pretty easy to find out.

Mike W.

(published on 01/11/2017)