On Sat, 04 Jan 2014 15:39:20 -0500, Ed Pawlowski wrote:

On 1/4/2014 9:12 AM, wrote:

That's like saying the pipes will freeze if they will freeze.
Sure, if you want to define ambient to be the temperature at the
pipes. But who measures that? The point is if one hears that
it's going to be 20F tonight, is there valid reason to be more
concerned about pipes in an outside wall, a drafty crawlspace,
etc freezing if the reported windchill is 0F versus 17F? The
answer to that is yes.

Let's change the parameters. Outside temperature is 35 degrees, but
because of the wind, the weatherman says the wind chill factor is 29
degrees. Will the pipe freeze? No.

No, but it will cool faster. Wind chill is still relevant to
inanimate objects, even above freezing.

In your example you use an example of 17 and 0. The only difference
that may have a minor effect is if the wind is actually moving the air
away from the pipes.

....or the wall (and the pipes indirectly)

Many factors come into play on how the wind moves
around the pipes inside the crawlspace. It does not determine if the
pipes will freeze, on;y how fast. Rate of heat transfer is the only
difference, the temperature never goes below ambient.

Right but that's not the issue at hand.

Here's another question. If inanimate objects are not affected
by windchill, then on a night when the outside temp is 20F,
the same house is going to use the same amount of energy to
keep it at 70F when the windchill is 0F as it does if the windchill
is 17F?


The big difference is how well sealed the house is. Radiational cooling
difference will be minimal, but convection can be considerable.

Well, wind chill has no bearing on radiation cooling.