Constant-temperature dehumidification

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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" :-)
Nick
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On 19 Sep 2006 06:13:05 -0400, snipped-for-privacy@ece.villanova.edu 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 need sealing.
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.

For one day only, of course.
Joe Fischer
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Any house that needs winter humidification needs air sealing.

Houses leak air. Especially your house :-) Lennox stopped advertising that winter humidification saves energy after I convinced their engineering VP that it uses 10X more than it can save.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

..
Not always. However I would agree that often that is the case or at least part of the problem.
--
Joseph Meehan

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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.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

You can say what you like, but I think you need to speed more time in the real world.
--
Joseph Meehan

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wrote:

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?
daestrom
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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 outgoing condensation.

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 January. Brrr.

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.
Nick
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On 19 Sep snipped-for-privacy@ece.villanova.edu 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 groups. :-)
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 of time. 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.
Joe Fischer
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On Tue, 19 Sep 2006 12:22:04 -0400, in misc.consumers.frugal-living Joe Fischer

I find this very hard to believe.
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snipped-for-privacy@aol.com wrote:

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.
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snipped-for-privacy@hotmail.com wrote:

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.
%MOD%
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snipped-for-privacy@worldnet.att.net says...

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 more separation.

...but it's a dry cold! ;-)
--
Keith

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snipped-for-privacy@hotmail.com wrote:

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 miserable recovery.
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.
%MOD%
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On 20 Sep 2006 11:45:08 -0700, snipped-for-privacy@worldnet.att.net 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 never reordered.
Passive constant temperature homes need lots of mass, and a heating system that controls humidity. 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 efficiency.
Who named this thread with "dehumidification"?
Joe Fischer
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Not if your house is airtight.

Me.
Nick
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On 20 Sep 2006 snipped-for-privacy@ece.villanova.edu 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!
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I never wrote that. Are you delusional again? :-)

YOUR premise that winter humidification saves energy could only be valid in that case.

Agreed, for non-airtight houses, in really thought :-)
Nick
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On 20 Sep 2006 17:40:27 -0400, snipped-for-privacy@ece.villanova.edu 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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No thanks. ASHRAE says houses need 15 cfm per occupant, so zero people need zero cfm.
Nick
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