Static is [not] your friend - vacuuming PC?

[Robert Redelmeier]

And that *you* have little to no exposure to Arctic conditions

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 doesn't????

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

you claiming it is always high.

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'.

However, if you have *ever* experienced 6% relative humidity,
you know that static just crackles out of everything.
Yep!

You can't move without generating a charge. Everything you
touch gets zapped. You can't pet the cat, because it will
run when you so much as look at it.

And hair stands up at a distance.

Now, I'm not going to figure out what's wrong with
your calculations,

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.

I lived in Tucson AZ as a teenager. Trust me, in Phoenix
they have *lots* of static problems in the summer!

Thanks for the data.

-- Robert

 

[Floyd L. Davidson]

You only heat your house to 32F (RH=44%)? ;-)

http://web.newsguy.com/floyd_davidson/sensors/cfdataH.png

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

http://web.newsguy.com/floyd_davidson/sensors/index.html

shows several other plots.)

Seriously, your washing of circuit boards isn't as silly as people here
seem to think. The manufacturer washes flux off in what amounts to a

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...

dish-washer. I don't think I'd want to leave a soap residue though.
Analogs certainly wouldn't like that much. A DI or distilled water
rinse would seem appropriate.

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.

BTW, that's first-aid for electronics (and even cameras) after being
dropped in water. Take out the batteries immediately, then dunk in DI
or distilled water as soon as practical. ...cook on low heat until
done.

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

 

[CBFalconer]

.... snip ...

That would indeed be pretty dry. Now, your next assignment is
to figure out why the air in my house *isn't* that dry! ;-)

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.

 

[Floyd L. Davidson]

In support of that ...

Where I live (Moose Jaw, SK, Canada) isn't 1000+ miles further
south than Fairbanks, but -30'C days are common during Dec,
Jan, and Feb, and most years we get a few days of -40'C weather.
100% or near %100 relative humidity on days like that is nothing
unusual - *outdoors*.

It takes trivial amounts of moisture in the air to cause near
100% RH at low temperatures like that. When it is -30'C and
100% RH, there is so little water in the air that if you heated
a volume of that air up to room temperature the RH would fall
to near zero.

However, except when guys like me do crazy overclocking experiments
outdoors on a cold day, the outdoor relative humidity is irrelevant.
It is the RH *indoors* that matters, and the colder it gets outside,
the harder it is to maintain a sufficient RH inside. Warm air is
constantly leaking out around doors and windows, up the chimney,
etc, and carrying away lots of water with it. If the water is not
replenished, such as by a humidifier mounted on the furnace, it is
very easy to have a 20% RH indoors even when the outdoor RH is close
to 100%.

Over the three coldest months of the year the humidifier for my
tiny 800 square foot apartment goes through about 6 liters of water
per day if I want to maintain a 40% RH. And that is over and
above the humidity replenished by things like cooking, bathing,
and simply breathing.

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.

 

[Robert Redelmeier]

I thought "fixer" was sodium thiosulfate and some other stuff.
Sodium Hypochlorite is laundry bleach and pool chlorine.

Exactly right. Pretty good for a non-chemist.

-- Robert

 

[Floyd L. Davidson]

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.

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... ;-)

 

[Floyd L. Davidson]

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.

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

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'.

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.

And hair stands up at a distance.


I doubt anything is wrong with the calcs, but the assumptions
might be mistaken.

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.

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.

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.)

Thanks for the data.

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%

 

[Robert Redelmeier]

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

It's easy to overlook the common.

But think about all those moisture laden clouds swirling around

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.

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.

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.

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.)

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

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.

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?

60's most homes were cooled with evaporative cooling,

Swamp coolers.

-- Robert

 

[Floyd L. Davidson]

Yes, I'm aware of that. Rather unsettling, thunder during
winter. But lightening storms are _not_ what we're talking

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

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?

Yes. It is very dry there.

 

[keith]

Exactly right. Pretty good for a non-chemist.

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

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

 

[Gumby]

Static charge on the nozzle is not the only problem. The buildup
of static on the various components as a result of blowing dry air
on them is just as serious as the nozzle (same source of charge!).

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

 

[Gumby]

You folks should stop obsessing about the damn dust in your machine. If
you are really that concerned, take it in the bathroom, turn on the shower
and steam the place up, then dust it out.
Personally I don't think a little dust is going to hurt anything. If it
ain't broke don't fix it!

Some cpu coolers are much more liable to clog with dust than
others. I have a Alpha PAL8045, it looks sort of like the
surface of a hair brush (lots of metal pins). That's the only
component I try to clean of dust once a year or so.

 

[chrisv]

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

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.

 

[Robert Redelmeier]

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.

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

-- Robert

 

[chrisv]

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

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.

 

[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.

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

 

[Floyd L. Davidson]

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

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

 

[chrisv]

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

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

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.

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.

Why make people
uncomfortable to accomodate construction defects?

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

 

[Robert Redelmeier]

Condensation on your windows is evidence of excessive moisture.

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

 

[Floyd L. Davidson]

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.

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.)