Static is [not] your friend - vacuuming PC?

An incorrect assumption on your part. I've lived where -40' was a normal temperature, and 0'F was a heatwave. Square tires, double plug-ins, and driving with the windows open. Ice-fog around open water. Now, I live someplace warmer.

It does, particularly on the east side of the Rockies.

Always is a strong word I avoid using. It is possible to get low RH cold air, but only by being colder first. Like

-80'F warming to -40'.

Yep!

And hair stands up at a distance.

I doubt anything is wrong with the calcs, but the assumptions might be mistaken. If you're running a humidifier (wet rug) or have a tightly sealed house, of course the humidity is going to be higher. As would [ice] fog.

Thanks for the data.

-- Robert

Reply to
Robert Redelmeier
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:-)

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(If you want to see what that is all about, though totally unrelated to this thread,

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shows several other plots.)

Pro's have beening doing that since day one. It was a little difficult back in the days of electron tubes because only the highest quality equipment used hermetically sealed coils and such, so only the high quality equipment could be put into a dish washer. We used to do it all the time with various components of troposcatter radio systems, and for years and years I had the most sensitive tropo receiver in Alaska. (This was reported year after year by the QC inspections, and I got lots of questions about how and why, but (you guessed it) they didn't believe me... :-)

Actually, you *do* want to leave a film of wetting agent on your motherboard. That will retain just enough moisture to dissipate static buildup (for example from the air blown into the case by fans) and will reduce the amount of dust that is attracted and sticking to the motherboard.

It has about the same effect as an air ionizer.

Which is to say, the motherboard will stay cleaner for longer.

Incidentally... that is true of gasoline engines too!

Reply to
Floyd L. Davidson

... snip ...

One (of many) possibilities is you don't knock the snow off your boots when you come in from the two-holer. :-) Or you keep a wet dog in front of the fire.

Reply to
CBFalconer

That is all true.

The two biggest factors controlling inside RH are the vapor barrier and the type of heating used.

I'd imagine that in northern parts of Canada, just as here in Alaska, buildings have *very* good vapor barriers. That is as opposed to what is used in the Lower-48, where they think the foil backing on fiber insulation is sufficient (and it is, there!).

Of course having baseboard heat and a boiler that has the air intake vented from the outside is also a *big* plus for maintaining a higher RH inside.

When I lived in Fairbanks we kept a large water container on the stove top all winter long. We burned coal for heat until the last couple years I was there.

Here I have forced air, but it burns natural gas, and there are only a few days of the year when the RH gets too low, so I haven't bothered to do anything special.

Reply to
Floyd L. Davidson

Exactly right. Pretty good for a non-chemist.

-- Robert

Reply to
Robert Redelmeier

How much effect do you figure the swimming pool in the basement has?

Or the hot tub with three cuties in it splashing around?

And that sauna is always attracting a crowd too...

It's difficult to slow down long enough to count the ways... ;-)

Reply to
Floyd L. Davidson

Interesting, given the mix of serious science and lack of awareness of some of the more common effects.

But think about all those moisture laden clouds swirling around south of the Alaska Range on an average day in January... and how high they have to get before they can move across the mountains (roughly 10,000 feet) and appear over Fairbanks. (And the same effect for any air from north of Fairbanks coming from up here on the North Slope.)

I'm sure the temperature change has an effect, but probably more significant in that particular case is the pressure change.

The typical winter air in Fairbanks moves from the Bering Sea inland along the north side of the Alaska Range though, and I suppose it is the temperature changes that dry it out so thoroughly by the time it gets that far inland.

The calcs are flawed. You are indeed using the mistaken assumption that what you calculated would be the RH of the air inside a house, and that isn't the case. You calculated the RH of air in a container as the temperature changed, with no other source of moisture and no exchange of air. Houses don't fit.

There are few houses (and all are old) here that are *not* tightly sealed. In fact sealing them up too tight is more often a problem these days than the other way around. (Which is something that has changed in the past 3-4 decades.)

They get something we never see here, which is lightning strikes that hit the ground. We've had three thunder storms here in the past 5 years, and it had been 20 years before that, but what little lightning we ever do get is strictly between clouds.

In Tucson there are localized lightning storms all summer long. It starts every afternoon about 1-3 PM as the air begins to cool off from the peak heat of the day. Really dramatic!

I'm not sure what is normal there now, but in the 50's and 60's most homes were cooled with evaporative cooling, so the RH inside most homes would have been fairly high. Of course the RH of the outside temperature is often less than 20%

Reply to
Floyd L. Davidson

It's easy to overlook the common.

Most of the moisture in clouds (even at warmer latitudes) is as ice crystals. Even if the ground temp is 60'F, around

8,000 ft, the temp has dropped below freezing (adiabatic lapse rate). Most (not all) clouds hang out 10-30 kft.

OK. What does? How many air changes with outside per hour (or per day) does your house do? How many lb/hr of internal water vaporisation? Assumptions are made to simplify, but may not fit. Then you need more data.

I don't doubt it. Perhaps to some mild toxicity.

Yes, I'm aware of that. Rather unsettling, thunder during winter. But lightening storms are _not_ what we're talking about here. The US Gulf Coast has plenty of those, but few problems from local static build-up that might threaten circuits. Does Phoenix in summer?

Swamp coolers.

-- Robert

Reply to
Robert Redelmeier

What has *winter* got to do with it? Hell will freeze over before there is a thunderstorm here in the winter.

Yes. It is very dry there.

Reply to
Floyd L. Davidson

I was quite the neighborhood chemist (and b00mb maker) some forty years ago. ;-)

I *hated* freshman chemistry though. No bangs, too much gunk. Boooring!

Reply to
keith

So delay doing this job until the next really humid day....

Reply to
Gumby

Not in my house. I have a mechanical ventilation system, with an air-to-air heat exchanger. Having one is starting to become code, in new builds, in my area. I had it built-into my house even though it was not required at the time.

Reply to
chrisv

Good for you. But that xchr won't exchange humidity.

-- Robert

Reply to
Robert Redelmeier

Indeed. The net effect is that the air in the house is significantly dryer than it otherwise would be. This, in fact, is the system's main purpose. People may prefer more water in the air, but the house does not, as it can lead to condensation in the walls, with subsequent mold and bacterial growth.

Reply to
chrisv

Is the house to keep people comfortable, or itself pristine?

I thought condensation in walls is primarily a result a defects in the vapor barrier and/or improper (too much/little) ventillation of the insulation spaces. Why make people uncomfortable to accomodate construction defects?

-- Robert

Reply to
Robert Redelmeier

Which is good, because that keeps the moisture *in* the house.

Reply to
Floyd L. Davidson

You may not be too comfortable breathing excessive mold spores. Ripping out rotted or moldy walls is also not fun or cheap.

Contributing factors, to be sure. In practice, it's very difficult to keep interior moisture from penetrating the walls. Areas around electrical outlets and windows, both interruptions in the vapor barrier, are largely to blame.

A tightly sealed house can get quite humid in the Winter, what with people breathing, taking showers, cooking with gas, doing laundry, etc. Condensation on your windows is evidence of excessive moisture.

I'm not uncomfortable, although some may be more sensitive...

Reply to
chrisv

That's more a function of window insulating value, outside temp and wind. I've had windows frost up even at 20% RH, but now my windows condense on the _outside_ :)

-- Robert

Reply to
Robert Redelmeier

What kind of climate conditions are you dealing with?

Most of the discussion so far as been about situations where the outside air is colder than the inside air. In that case the inside air is heated, and the relative humidity drops as the temperature rises simply because the air can hold more moisture at warmer temperatures. (The actual amount of moisture doesn't change because of temperature, as such. But...)

If, as is usually the case, more moisture is indeed added to the air inside the house via a humidifier perhaps, but also just due to normal activities such as running a washing machine, taking a shower, etc., the amount of moisture in the inside air is higher than can be maintained if the air is cooled to outside temperatures. (Assuming that outside air is indeed cooler...) The result is condensation as the air is cooled, at the location where that takes place. That, for example, can commonly be seen, when the weather is cold enough, as frost that forms in an unheated porch on the ceiling or even the walls close to the door. Everytime the door is opened a mass of moist warm air rushes out, cools off, the moisture condenses, and forms frost on the first surface it touches.

The same thing happens *any* place that inside air leaks to the outside, and if that is in your wall, that is where the frost forms. Common locations are breaks in the vapor barrier for electrical wiring, usually around lighting fixures, wall mounted switches or sockets. After a prolonged cold period, water dripping from a ceiling light fixture in a room than has cold air directly above the ceiling is a very good indication that there is a significant leak in the vapor barrier. Foam insulation is a good cure...

The vapor pressure is greater as the temperature difference increases on each side of the vapor barrier. That means a vapor barrier which would be fine for a wall that will never see more than say 70F degrees difference in temperature (75F inside and

+5F outside) might not work well at all where the outside temperature goes down to -45F, and the difference becomes 110F degrees!

Indeed, typical fiberglass insulation is sold with a foil backing that is perhaps an adaquate vapor barrier for a 70F degree difference, but leaks like a sieve when the difference is

110F degrees. Carefully applied sheets of visqueen plastic with *no* holes, and overlapping edges are used in such circumstance. Likewise sprayed on foam insulation is also a good vapor barrier.

What you've described sounds like a seriously faulty vapor barrier. The air-to-air heat exchanger should allow you to maintain a *higher* relative humidity inside the house than otherwise would be possible. (Assuming colder outside temperatures; though perhaps you have exactly the opposite??? That might require an entirely different construction technique as far as insulation and where the vapor barrier is placed.)

Reply to
Floyd L. Davidson

Actually it is fairly easy to keep interior moisture out of the walls, but it means using the right construction practices to begin with! Trying to fix it later can be, errr, interesting.

If you have the problems described, it is very likely that careful application of foam insulation sprayed behind the various electrical fixtures, can cure it. Getting that right the first time is important though, because one you block off the easy access to that area with foam, it gets harder to try a second application!

I lived near Fairbanks for a couple decades, in a house that had an unheated crawl space in the area between the ceiling and the roof. It turned out that a "hatch" going up through a closet to that area, and two of the several ceiling mounted light fixtures, were leaking massive amounts of moisture filled air up into the crawl space. By the second or third warm period we had water dripping out of the light fixtures. (I didn't even see the "hatch", until I crawled around up there to fix the lights and discovered the hatch from to top.)

I lifted the insulation up from between the joists, sprayed the entire area on top of each electrical fixture, and put the insulation back down. Never had another problem.

The hatch took a little more doing. I lifted all the insulation on both sides and directly over it, and put in a layer of plastic sheeting that extended 2 feet farther than the cracks, in every direction and then put the insulation back down. That cured that one.

Condensation on your windows merely indicates you've got single pane glass windows in a climate where double or even triple panes should be used! (Or that the window isn't shut tightly enough.)

Fix the problems though, not the symptoms.

Reply to
Floyd L. Davidson

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