On Fri, 04 Jul 2014 00:17:36 -0400, rickman wrote:

On 7/3/2014 9:19 PM, Jeff Liebermann wrote:
However, if the system leaks and is therefore not adiabatic, the story
is a little different. Heat will be introduced into the room through
the ceiling and windows. The result with be a temperature gradient
where the ceiling and window air are warmer than the air near the
floor. The only temperature of importance is your head, which
radiates most of the waste heat from your body.

I would love to see a reference for this factoid. It is an often
perpetuated myth that half you heat leaves your body through your head.
Simply not supported by the facts.

As usual, it depends on the circumstances. At rest, the head radiates
about 7-10% of the body heat. When exercising, the increased surface
blood flow increases this to 50%. Presumably, the OP is not
exercising under his ceiling fan:
http://skeptics.stackexchange.com/questions/2839/do-we-lose-most-of-our-body-heat-through-our-heads
http://outdoors.stackexchange.com/questions/681/what-are-areas-of-the-body-which-lose-heat-more-quickly-and-how-can-i-reduce-th

Because it is closer
to the ceiling than the floor, a fan blowing downward will heat your
head instead of cooling it, as you observed.

This statement shows no understanding of human physiology. Even
ignoring the issue of perspiration and evaporative cooling, the human
body is nominally at 98°F and will be cooled better in an airstream of
even 90°F than in still air.

Correct, although I suspect the cooling is mostly from evaporative
cooling, not convection. The part of my rant that you trimmed
indicates that this was in reference to the relative merits of the fan
blowing air down or up. I indicated that blowing down would be more
effective for cooling because the head is closer to the air source and
therefore has a higher air flow rate. Further away would be less
effective. If the fan it going to cool the head, the optimum location
would be closest to the fan (unless the OP is into standing on his
head).

However, the OP didn't specify the temperature of the air near the
ceiling. If the ceiling air were hotter than body temperature, a
downward blowing fan will heat the cranium instead of cooling it. It
would be like trying to stay cool using a hair dryer blowing from
above. I can believe that blowing HOT air downward might result in
heating instead of cooling.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558