|
|
re: furnace humidifiers; was re: not needed--pyjamas
22 dec 2001
mom wrote:
>> some people measure air leakage in cfm vs oblivia,
>> and close the house doors in wintertime.
>i don't know where you live,
near philadelphia.
>here we have to open a door to get outside!
that phenomenon also occurs in philadelphia.
>we again have to open a door to get back inside.
we sometimes leave doors open for brief trips outside, but we do not
leave them open all winter. we have found that precludes efficient
house heating. arithmetic tells us that normal door openings do not
change average house air leakage rates much, and air-locks are seldom
worth what they cost, unless we live in department stores.
>> >...our natural gas company includes a flier at the start of the heating
>> >season reminding their customers of the benefits of a humidifier...
>>
>> would they, by chance, be in the business of selling energy?
>> would they sell less, if you caulked your house?
>
>let's see. increasing the humidity also makes the house feel warmer
>at a lower temperature. therefore, one does not need to have the
>house set at as high of a temperature...
as harry points out, numbers reveal that the energy saved with a lower
room temp is more than offset by the energy wasted with humidification.
otoh, caulking can be a win-win situation: higher rh, lower room temp,
less energy needed for heating, and no need to operate a humidifier.
>checking for air leaks is part of our winter preparations, just in case
>you thought we caulked it once and forgot about it.
you might consider a blower door test. air leaks are sneaky.
>our house is not dry because of air leakage, it is dry because of
>lack of humidity due to the forced air natural gas furnace.
your mind seems boggled here.
>> >...the air simply gets too dry with the natural gas, central heating.
>> >the moist air is carried to the furnace and heated where it doe s lose
>> >some of its moisture content.
>>
>> how would that happen in a closed system in which cooler room air enters
>> one end of a sealed heat exchanger and the same air exits the other end,
>> warmer?...
>> >you know the little property of water evaporation?
>>
>> sure. start out with liquid water, and end up with water vapor.
>>
>> >it happens right in the furnace...
>>
>> really? where does the liquid water come from?
>> would you care to explain further?
>
>normal human (breathing) and household (cooking, bathing, etc)
>activity produce moisture into the air in the form of vapour.
agreed :-) we call it "vapor" here.
>the air with the moisture goes into the furnace where it is heated,
>and loses the moisture in the process through evaporation.
i see a flaw here. water vapor cannot evaporate. it has already done so.
>the problem with natural gas forced heat, is the normal human and
>household activity cannot keep up with the moisture removed by
>heating the air through the furnace.
and heating air does not remove moisture from it. if you heat a mixture
of 100 pounds of air and 1 pound of water vapor, you will end up with a
mixture of 100 pounds of air and 1 pound of water vapor. it will occupy
more volume at the same pressure, and it will be warmer, and the relative
humidity will decrease, but it will still contain exactly the same amount
of water vapor, ie exactly the same absolute humidity or humidity ratio,
in pounds of water per pound of dry air.
>here is a simple test for you to perform.
ok :-)
>do not add any moisture to the air and keep all windows and doors shut.
we often do that in wintertime here.
>test the humidity level in your house and record it. then turn on your
>furnace, and record the humidity level after one hour. you will clearly
>see a reduced humidity reading from the original reading.
let's try this in our heads: the air in the house warms up. the moisture
content does not change, but the rh goes down, n'est-ce pas? what have we
learned from this gedanking? that warm air can hold more moisture than
cold air, so warming a mixture of air and water vapor lowers its relative
humidity?
>now repeat the same experiment with the first reading after boiling a pot
>of water and again after an hour. again you will see a reduced reading.
sure, but higher than before, other things being equal...
>do you have any experience with heating with natural gas?
yes. fossil fuel. bad news.
happy holidays!
nick
|
|
