re: new refrigerators and power outages
4 jan 2004
len budney wrote:
>>> ...dehumidification is a side-effect of lowering temperature:
>> not necessarily...
>but holding the lowered temperature constant, the moisture will (eventually)
>condense out, unless the new temperature is still higher than the dew point.
"the moisture" will condense until it reaches the dew point near the "new
temperature" of the ac coil, which has little to do with the room air temp.
some moisture remains. if an ac coil never ices, the vapor pressure will
never drop below e^(17.863-9621/(460+32)) = 0.184 "hg, approximately, ie
about 25% rh at 70 f.
>>> ...the vapor pressure of any liquid decreases with temperature,
>> simply cooling a sample of air containing water vapor does not change
>> the vapor pressure. if a pound of dry air contains w pounds of water,
>> the vapor pressure is 29.921/(1+0.62198/w) "hg, regardless of temperature.
>only if it is allowed to expand freely. pv=nrt still holds. if the air
>is contained in a draft-free room, the partial pressure due to water
>vapor increases with temperature.
your "draft-free room" is a submarine :-) typical us houses leak 1 house
volume per hour, vs 0.025 ach for a new swedish house. in both cases,
"air expands freely."
>>but that constant temperature depends on the size of the unit.
>unless it has a thermostat, which was also implicitly assumed.
it was? the ac may also be underpowered...
>assuming that the a/c unit maintains a constant temperature, and
>ignoring the fact that the exchanger is colder than the room, my
>analysis remains correct. it merely fails to describe the behavior of
>real-world a/c units. :-)
and real-world air, and real-world houses.