Put one $80 AC in a window and one in the house. Wire the window AC to
the close-on-rise contact of Grainger's $16 2E158 SPDT thermostat and
the other to the close-on-fall contact. Run the common contact to
Grainger's $31 2E453 (Autoflo 052000) humidistat.
Warming air lowers the RH, but it doesn't remove any water vapor.
Your house needs air sealing.
Winter humidification uses about 10X more heat energy than it can save.
Hey, a new rule of thumb: "the quickest way is the most efficient" :-)
On 19 Sep 2006 06:13:05 -0400, firstname.lastname@example.org wrote:
Thanks for the off-the-shelf engineering, but this
was a one day thing.
Relative humidity is the important thing, the amount
of moisture in the air is meaningless, the amount of water
the air can hold relative to the amount of water in the air
is relative humidity.
Not really, the sensitive membranes in my nose
And that is one of the reasons I try to avoid
using the Cozy space heaters, they change the air
in the house very often, and even warn that space
for incoming air be provided.
Not a chance, the few hundred watts the humidifier
uses simply replaces the electric baseboard heat used.
I'd say always. Andersen says an average family of 4 puts about 2 gallons
per day of water (16.7 pounds) into house air. In an absolutely airtight
house, the RH would rise to 100% near windows with wintertime condensation.
ASHRAE says houses need 15 cfm of fresh air per full-time occupant, so
4 half-time occupants need 30 cfm at 0.075 lb/ft^3, ie 30x60mx24hx0.075
= 3240 lb/day of fresh air. January outdoor air in Phila has an average
humidity ratio wo = 0.0032 pounds of water per pound of dry air. If minimal
ventilation with no condensation removes 3240(wi-wo) = 16.7 lb/day of water
from the house, wi = 0.00834, and 70 F air at 100% RH has w = 0.0158, so
the house RH would be about 100wi/w = 53% with minimal ventilation, or more,
with a small efficient air-air heat exchanger with outgoing condensation.
Keeping the RH 60% (wi = 0.00948) means condensing 3240(wi-wo)-16.7 = 2.03
lb/day (2 pints) or 0.085 lb/h of water from the outgoing air, with a latent
heat of 1000x0.085 = 85 Btu/h (about 25 watts--not much), ie lowering the
outgoing humidity ratio to 0.00834 at 100% RH, ie lowering its temperature
to about 52 F. If we recover 90% of the heat, E = 0.9 = 1-e^-NTU, so the
Number of heat Transfer Units NTU = -ln(0.1) = 2.3 = AU/Cmin, where A is
the heat transfer area in ft^2, U is its film conductance in Btu/h-F-ft^2,
and Cmin is the heat capacity flow rate in Btu/h-F.
U = 2 and Cmin = 30 make A = 2.3x30/2 = 35 ft^2, so we might preheat
incoming 30 F outdoor air with a small fan pulling outgoing 70 F air
between 48 1'x1'x1/8" Coroplast sheets in a 1' cube with A = 96 ft^2
and NTU = 6.4 and E = 1-e^-6.4 = 99.8% heat recovery. The condensation
might drip onto a large green plant that re-evaporates it.
An average US house naturally leaks about 200 cfm. A 2400 ft^2 house
that meets the Canadian IDEAS (post R2000) standard would naturally
leak 2.5 cfm.
What do the numbers look like with an average outside dewpoint of 0F ??
While the daily 'highs' here can sometimes reach 30F, the overnight low and
dewpoint of outside air is usually much lower for Jan/Feb. My psychrometric
charts don't go down that far so I can't do the calc.
Seems like 'always' is a pretty risky statement considering some parts of
the country. Pellston MI is often one of the coldest places in CONUS, or
International Falls MN.
How much air exchange happens when the door is opened eight times a day
(four people leaving for work/school and returning). Just wondered if you
have some data on that?
Table 2 in the ASHRAE HOF says the humidity ratio wo = 0.0007875 at 0 F,
which would make wi = 0.00593 with a 38% RH above, or more, with some
Since many house materials (cloth, wood, paper, concrete) can store moisture,
it seems like a good idea to ventilate houses during the day in wintertime,
when outdoor temps are warmer. An exhaust fan might have a timer, as well
as a humidistat.
International Falls has wo = 0.0009 with an average 1.0 F outdoor temp in
I have no data, but if the door's open for 3 seconds each time, that's 24
seconds total, ie 0.4 minutes per day. With 16.6x16ft^2sqrt(70F-0F)4')
= 4444 cfm when the door is open, we might move 0.4x4444 = 1778 ft^3/day
of fresh air into the house, ie 1778/24/60 = 1.2 cfm, averaged over 24h.
Airlock entrances just for the purpose of saving heat energy (vs mudrooms
that keep a house cleaner, etc.), don't seem worth the cost except for
department stores or very large busy families.
On 19 Sep email@example.com wrote:
You need to study more about relative humidity,
and about the differences in people's nasal passages.
I would not be able to use the Cozy space heaters
if I sealed the house, they need to draft up the chimney.
Maybe you are too young to have seen a furnace
that uses indoor air for the flame?
Energy used is not even an issue with my nose,
and I have decades of experience with it.
Your number of 10 X is so absurd that it would be
laughable if you were not contaminating minds.
It is essential that the air in a house is changed at
least every 2 or 3 hours, and much more often with
some kinds of heating appliances.
A major factor in my decision to try to get by
with electric baseboard heat is the reduced number
of times the air in the house changes in 24 hours,
because one Cosy stove has the flue pipe removed
and the flue blocked (and nailed shut to keep the
chimney birds in the chimney).
And I won't light the pilot on the other stove
until the temperature goes below 20 degrees F.
It is 111 years old, so what else is new?
How did you do that, with BS or numbers?
I don't like the fan humidifiers, they need a
chemical added to the water and the water changed
every day. It is easier to change the water with a
steam humidifier, and as long as I am using electric
resistance heat anyway, your number does not apply,
no matter how low you revise it.
If doctors were to advise patients who get
head colds every winter to humidify when the
outdoor temperature is below 40 degrees F, the
number of head colds would be reduced by at
least half, and maybe as much as 80 percent less.
For those who may have believed your
mistaken opinion, I will explain why indoor air
relative humidity drops dramatically with lower
outdoor temperatures, and why humidifiers
make it seem warmer and why temperatures
are more stable with 50 percent relative humidity
indoors all winter.
The air in all house changes, and there is
a definite number of times it needs to change,
the type of heat determines that, but a house
should never be sealed so tight that it takes longer
than 3 hours to change completely.
(Check the furnace or heater instructions).
As the air changes, outdoor air that has
a relative humidity of 40 percent at 30 degrees F
that is warmed to 70 degrees F undergoes a
change in relativity humidity according to well
know charts showing how much water air at
those temperatures can hold.
At lower outdoor temperatures and
lower out door humidity, the indoor humidity
can become very low, as low as 10 percent or
less, even without any removal of water vapor.
Warm air __CAN__ hold more water,
and cooler air can only hold so much less, and
that is why _relativity_ changes when outdoor
air replaces indoor air in winter.
This is a health issue, for a large number
of people, while others have no problem at all
with head colds or sore throats in winter.
It is not an energy efficiency issue, not
a home repair issue (as long as health comes before
minor moisture damage), it is not a frugal living
issue if the doctor visit costs more than all other
associated costs, and it is not a homepower issue,
it is a health issue, so I don't know why even a
trouble maker like you would crosspost so many
I already posted the effects of low relativity
humidity on sensitive nasal membranes, and already
posted the explanation of how moisture in fabrics
in the house is drawn from the fabrics as air dries,
carrying germs, and is breathed, and the germs
are able to get a foothold in the nasal membranes
of people who do have that sensitivity problem.
So a shallow consideration of only energy
used and it's effect on air temperature is not pertinent.
But moist air carries more BTU per pound
than dry air, even though moist air occupies more
space per pound.
Between cycles of the furnace, moist air
resists cooling more than dry air in the same period
And warm moist air feels warmer than warm
dry air, although this is pretty much a personal
judgement issue. (Moist cool air feels colder than
dry cool air).
All this together makes your meddling in
the marketing practices of a company with decades
of experience in heating and cooling, despicable,
in my opinion.
When I had a house with central air, I
bought and installed a self filling humidifier from
Sears, and it make a big difference in comfort
at the same temperature settings.
So study about relative humidity, how
warming air changes the relativity without any
change in the amount of water it contains, and
the harmful effects that can have on the health
of certain people.
And also study how air too dry can
damage furniture, woodwork and other
materials, just as much as air too moist.
You might find it so, but the experience of a lot of us who have moved
south gives it a lot of credence. In Vermont, I used to get at least
four colds a winter. In the humid south, catching a cold is a rare
event for me.
I don't necessarily agree with the theory as to why, but I do agree
with the posit that proper humidifying can reduce the misery of moving
from one cold to another.
This would be easily explained if it was found that Vermonters have a
higher tendency to sneeze on each other, not wash hands often enough,
etc. Or maybe it's got nothing to do with Vermonters' habits or their
weather. I've lived in several climates and I've found that I'm more
likely to get sick when I've been around sick and/or contagious people.
Maybe it's them New Yawkers who come up to Vermont to ski that bring
their strange city germs.
I wonder what the rate of headcolds is among those of the "dry south"
compared to the "humid south"? This may shed light on the topic.
Nah, I didn't have nearly as many colds when I lived in NY as I do
now in VT (just getting over a cold now, in fact). The reason
people get more colds in cold weather is that they're holed up
closer to each other. When it's warm they're outside more with
The latter is a factor not to be underestimated.
I once had a schoolteacher who insisted on keeping the window next to
me partly open all winter. Even when I was fighting a cold, he refused
to allow any change in seating arrangement or to let me wear my
overcoat (claiming the latter was disrespectful). There was no debating
his infallible logic. "Since you like science so much," he'd say, "you
should already know that cold, fresh air doesn't have any germs in it
and can't make you sick." It sure as hell seemed to prolong my
Now that I think about it, since I've been out of school and drink more
beer, I haven't been sick nearly as often.
On 20 Sep 2006 11:45:08 -0700, firstname.lastname@example.org wrote:
Sure it's the beer, which seems to also make % look
like a letter character. :-)
It is pretty well known that A/C _can_ dry air
out enough to irritate throats and nasal airways, but
it is not the dry air, it is the rapid change indoors
where there is migration of irritants and germs
into the air that seems to be the problem.
The only head cold I had in two years in
Pasadena was in the pool house I rented and used
the gas wall heater.
I had to move out it was such a miserable
experience. The rest of the two years I rented
a room by the week in the small hotel on the
corner in front of the popular bar and club "Icehouse"
in 1964 and 1965.
It had steam heat, and had very constant
temperature and humidity and was very clean.
My experiences of waking up with burning
throat and sinus if I don't run the steam humidifier
on a night when it is below freezing, and some relief
if I run the hot water in the shower and breathe the
hot mist, is enough proof for me.
There is no way that doctors don't know that
the heating season causes head colds, but the things
that need repeated most, like "keep the humidity
constant" are the things not mentioned after a while,
just like the most popular selling item in a store is
Passive constant temperature homes need
lots of mass, and a heating system that controls
Furnace companies would not have designed
furnaces and stoves with water tanks and circulating
mechanisms if there was not a known benefit from
keeping humidity from the wide swings.
While protecting wood and fabrics, there is
an often repeated suggestion, "set a can of water
on the stove", which seems to suggest it is widely
known that air drying out causes irritated airways
and head colds.
Humidity needs to be kept as close to 50 percent
as possible, and that means adding a lot of water in
heating season, even if it takes 1060 BTU per pound
to vaporize it.
Preservation of wood and fabric would be enough
to make the extra energy used worth it, if the furniture
needs replaced because it dries out and cracks is not
Who named this thread with "dehumidification"?
On 20 Sep 2006 email@example.com wrote:
Oh, no, don't tell me you think that air can be warmed
up 50 or 60 degrees and still have the same relative humidity
without adding water.
You demonstrated knowledge of standards suggestions
for changing air, and your premise could only be valid if
there were no change of air at all.
Forget the water vapor and heat that people give off,
it isn't enough to make a difference unless it is dozens or
hundreds in a building.
It figures. :-)
In really thought your main premise was that it
doesn't pay to humidify if the cost of fuel for the latent
heat of vaporization is considered.
If you live in an ivy tower with thick walls, that
may reduce the temperature and humidity swings.
I lived in permanent housing at Randolph Field
(now Randolph Air Force Base) in all of 1948, and the
walls were more than 24 inches thick with poured
concrete floors, and even though the outdoor temperature
was cold enough at night to freeze rain on AT6
propellers and 80 by noon, the temperature inside
didn't change 2 degrees.
But houses are built in the worst way possible
to maintain constant temperature without considerable
heat added, and if heat is added, water must be added
to retain constant relative humidity, at least to the
extent that heat is added to raise migrating cold air
to indoor temperature.
Joe Fischer Quit adding groups!
On 20 Sep 2006 17:40:27 -0400, firstname.lastname@example.org wrote:
You have a communication problem, if you want
to specify a house that will never be built, just say so.
I really thought you were serious.
My premise is that protection of wood and fabrics
and health is part of any equation about costs.
Try your math on adding enough water to maintain
constant 50 percent relative humidity to change 10,000 cubic
feet of air every two hours (with zero people in the house).
Joe Fischer No pets or aquariums either.
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