Question:
My house is hot. I'd like to be able to cool down one or more rooms,
without having to install an ugly great window mounted air conditioner.
Don't portable units exist? If so, where's a good place to get one?
A window air conditioner sucks 400W of heat out of the room and kicks
it out the window. If you just took a window mounted air conditioner and
set it in the middle of the room and sat right in front of it, perhaps you
could cool your face a little, but you'd be heating up the room overall.
(You're cooling the air in front of the air conditioner, but just moving
the heat to the backside of the air conditioner, as well as generating more
heat just to accomplish the transfer.) This is why letting a refrigerator
door stand open will heat, not cool, your house.
Answer:
Air conditioners drive compressors. The amount of force needed to drive a
compressor is a function of the instanteous momentum of the piston in a
compressor, as well as the pressure in the compressor. This means that, if
the piston is already moving, it's a lot easier to keep it moving in a
pressurized compartment that if the piston isn't moving. It
takes a very large force to start moving the piston from a dead stop if the
cynlinder is still pressured. The electric motor on a portable air
conditioner doesn't have enough power to start moving the cylinder when the
compressor is still pressurized. There's a little tiny hole in the
compressor, though, that will leak off the pressure in it over the period
of a minute or so. Therefore, portable air conditioners force you to wait
until the compressor is not longer pressurized, so that the motor will be
able to start the whole system up again. (It the compressor were still
pressurized, and you tried to start the motor, and if it couldn't move, the
electric motor would burn out.
On the other hand, the compressor in a car's air conditioner is driven by
that by gas sucking internal combusition engine. The engine in your car is
designed primarily to get the car moving, and that takes one heck of a lot
more power than it does to drive a car's air conditioner. Therefore, if
you engage a car's air conditioner, even with the compressor still
pressurized, the car's engine has more than enough "reserve power" to start
the cynliner in the compressor moving again.
