Everyone had a hard time understanding what insulation does, it keeps the heat in or the cold in, depending on the time of year.
Technically incorrect, but first the groaner of a joke:
On a particularly dull day of a dull week, a roving TV reporter went out on the street looking for some comments to spice up the evening news. The question was "What do you think is the most important discovery of the 20th century?" He got all sorts of predictable, and therefore uninteresting, responses such as open heart surgery, artificial hearts, bionic limbs, space travel, atomic power, yada yada. Finally he came across an elderly wino and he decided for yuks to ask this guy. So he did. The wino's answer was, "The Thermos bottle."
Rep: The Thermos bottle? Sir, other people are talking about space travel, atomic power, bionic limbs, and
you think the Thermos bottle is more wonderful than things like that? Why?
Wino: Because it's what the Thermos bottle does. It keeps things warm in the winter, and cool in the summer.
Rep: Yes? What's so great about that?
Wino: Think about it, son. It keeps things warm in the winter, and cool in the summer. HOW DOES IT KNOW?
Okay, back to this morning's exercise in thermodynamic pedantry. You wrote, "what insulation does, it keeps the heat in or the cold in, depending on the time of year."
This is incorrect. In any situation involving heat flow or transfer, it only goes one way. The direction of transfer is always
from the warm side
to the cold side. Insulation impedes heat transfer, which simply means it slows down the rate of transfer. But it does not alter the direction. In Winter, heat tries to flow out, and insulation reduces the rate of heat loss. In Summer, heat tries to get
in, and insulation reduces the rate of heat gain. For Summer, it's incorrect to say insulation keeps cold in. Actually, it keeps heat out.
It's like light. Does the closet door keep light out of the closet, or does it keep dark in the closet?
