On Friday, January 3, 2014 10:43:59 PM UTC-5, nestork wrote:
'Stormin Mormon[_10_ Wrote:

;3176501']

Tonight in NYS supposed to be 0F, and wind

chill -10 or so. Which number is the one

which concerns water pipes freezing?



I know the pipes won't get below the actual

temp, but are they more likely to freeze,

with wind?





The pipe will cool down to 0 degrees F., and no colder. The wind chill

only means it'll cool down faster than if there was no wind.



That isn't true. Take a somewhat drafty crawlspace. Put a
thermometer a various places inside it. Measure the low
temps recorded when:

A - It's 20F outside and no wind

B - It's 20F outside and there is a 35mph wind.

You think the low temps are going to be the same?

That's a real potential pipe freezing example and the lower
the wind chill, the more likely the pipes will freeze.




The correct way to think about it is that if the ambient temperature is

0 deg. F, then the pipe and the water in it will not get colder than 0

degrees F.



The greater the wind chill, however, the faster a pipe with warm water

in it will cool down to 0 deg. F.



Wind increases the RATE of heat loss, not the ultimate temperature a

body cools down to.

Yes, if the body is fully exposed. But many, probably most pipe
freezing situations are one where the pipe is not outside, but
partially protected, eg the crawlspace example. If it's fullly
exposed, then it;s likely drained, winterized, etc.





If the pipe were to get colder than 0 degrees F,

then the stronger the wind, the faster it would be warmed up by the air

to 0 degrees F.



So, if your pipe is gonna burst, it'll burst a few minutes sooner with a

wind than without, but the strength of the wind only determines how

quickly that pipe cools down, not what temperature it cools down to.

Per the crawlspace example, it can also effect what low temperature it
sees. Here;s another example. Suppose you have a cabin with water
pipes inside. The cabin is at 40F. Overnight it's going down to
20F. Do you not agree that it's more likely the pipes will freeze
with a 35mph wind blowing, hence a windchill of 3F, than it would be
with still air and a windchill of 20F?