A friend of mine put his washer and dryer in the basement
instead of in the ground-floor laundry room of the house
he moved into last winter. The laundry room was then
turned into his office.

Over the summer I used the existing dryer exhaust vent
to duct the hot exhaust air from his Opteron dualie directly
to the great outdoors. That changed the office from being
uncomfortably warm on hot days to being just another room.

We decided to try something different for the winter:
use the duct to draw cold air in from outside, cool the
computer, and then exhaust the warmed up air to the room.

That usually works great: on most days even under load
the cpu fans automatically turn themselves to their slowest
speed and the case fan and PSU fan can be manually turned
to their lowest speeds and everything run nice and cool.
The silence is deafening.

However, today it hit -33'C and now the air coming out the
back of the PSU is -5'C, which cools the room off pretty
darned fast. We tried ducting the cold exhaust air back
outside - which solved the room temperature problem nicely.

(The turning point seems to be about -18'C: cold air into
the computer, room temperature air out.)

However, when we do that a new problem crops up: frost builds
up on the outside of the case and also on things inside the
case that don't produce enough heat. We can't for the life
of us figure out why ducting the cold exhaust back outside
is causing this. When I stand on a ladder outside the house,
airflow from the exhaust duct is good and is noticably much
warmer than the ambient outside temperature.

One more datum: If we disconnect the five foot flexible
insulated exhaust duct from the hole in the wall and let
the exhaust blow through the ducting and into the room,
the frost problem goes away. Hook that duct back up to
the hole in the wall and the frost comes back.

Also: both the intake duct and the exhaust duct are about
4 feet above the floor in the room and horizontally about
2 feet apart. Outside, that places them about 10 feet above
the ground and 5 feet below the soffits. It is a breezy day,
but that side of the house is out of the wind.

"Rob Stow" <(E-Mail Removed)> wrote in message
news:XoCCd.705612$%k.370482@pd7tw2no...
>


At -33C, the outside air is very dry and when you vent it into the room you
are displacing warmer and moister air, particularly in the immediate
vicinity of the computer.

Once you vent the air from the computer outside again you are romoving this
drying effect in the vicinity of the computer. You may think this will only
affect the outside of the case, but there are lots of litle holes, exetra,
in your computer and air from the room will be drawn inside somewhere
(ventri effect).

Nice idea, but you will have to isolate the computer from the room, if you
want it to work with out frost.

OK you crazy guy, I'll bite:

Rob Stow <(E-Mail Removed)> wrote:
> However, today it hit -33'C and now the air coming out the
> back of the PSU is -5'C, which cools the room off pretty
> darned fast. We tried ducting the cold exhaust air back
> outside - which solved the room temperature problem nicely.

But you will frost the box from warm (semi-humid) house air.
When you exhaust to the room, it fills with dry outside air.

> (The turning point seems to be about -18'C: cold air into
> the computer, room temperature air out.)

OK, so put a side damper on the cold air to the PSU. Bleed some
warm room air in. Do not mix in humid air, or you could get
moisture in the PSU. This shouldn't be a problem if the case
fans are strong enough to put the room under positive pressure.
But watch out for static electricity in that bone-dry room!

-- Robert

Steve wrote:
> "Rob Stow" <(E-Mail Removed)> wrote in message
> news:XoCCd.705612$%k.370482@pd7tw2no...
>
>
>
> At -33C, the outside air is very dry and when you vent it into the room you
> are displacing warmer and moister air, particularly in the immediate
> vicinity of the computer.
>
> Once you vent the air from the computer outside again you are romoving this
> drying effect in the vicinity of the computer. You may think this will only
> affect the outside of the case, but there are lots of litle holes, exetra,
> in your computer and air from the room will be drawn inside somewhere
> (ventri effect).
>
> Nice idea, but you will have to isolate the computer from the room, if you
> want it to work with out frost.
>
>

Thanks. That makes sense at a first reading. I'll
have supper, a couple of beers, sleep on it and hopefully
it will still make sense ;-)

Sounds like it should be easy to verify this by shrouding
the computer in plastic and using tape to seal where the
ducts go into and out of the plastic. Not as a permanent
solution of course - just an experiment.

It's up to -25'C now but it is supposed to cool off again
overnight. Here's the forecast for Hell, if anyone is
interested:
http://www.theweathernetwork.com/wea...s/CASK0210.htm

On Tue, 04 Jan 2005 19:47:03 GMT, Rob Stow <(E-Mail Removed)> wrote:
[snipped]

No cures, I just want to compliment you on your subject line.

It's....perfect ;-)

would it not be a lot safer to build a simple heat exchanger then no
particles from outside and condensation can be kept away from the
electronic components

On Tue, 04 Jan 2005 22:43:54 +0000, daytripper wrote:

> On Tue, 04 Jan 2005 19:47:03 GMT, Rob Stow <(E-Mail Removed)> wrote:
> [snipped]
>
> No cures, I just want to compliment you on your subject line.
>
> It's....perfect ;-)

'tripper, you are such a silver-tounged devil!

--
Keith

ewan wrote:
> would it not be a lot safer to build a simple heat exchanger then no
> particles from outside and condensation can be kept away from the
> electronic components

Probably, but what has been done so far was accomplished
with nothing more that a little duct tape and $10 worth
of insulated 4" flexible ducting.

Somewhat along the heat exchanger idea I have been consider
getting a water cooling kit for myself and putting a fanless
radiator outside. Obviously I would have to use something
like ethylene-glycol as the coolant.

I've been trying to persuade my friend to try the water
cooling idea first. He owns a house that already has
holes in the wall, whereas I rent.

Thus spake Rob Stow:
<Snipped>
> Also: both the intake duct and the exhaust duct are about
> 4 feet above the floor in the room and horizontally about
> 2 feet apart. Outside, that places them about 10 feet above
> the ground and 5 feet below the soffits. It is a breezy day,
> but that side of the house is out of the wind.

-33C, heavens, that's cold. The temp dropped to -18C once about 20yrs ago
where I live 40m west of London! The lowest recorded temp for the UK appears
to have been -27C in Scotland & about -23C in England. Where your quoted
site says "Feels like", I presume that's wind chill.

Paul Busby wrote:
> Thus spake Rob Stow:
> <Snipped>
>
>>Also: both the intake duct and the exhaust duct are about
>>4 feet above the floor in the room and horizontally about
>>2 feet apart. Outside, that places them about 10 feet above
>>the ground and 5 feet below the soffits. It is a breezy day,
>>but that side of the house is out of the wind.
>
>
> -33C, heavens, that's cold. The temp dropped to -18C once about 20yrs ago
> where I live 40m west of London! The lowest recorded temp for the UK appears
> to have been -27C in Scotland & about -23C in England.

The average temp here for January is about -16'C, so
obviously we get a few nice days to balance out the
cold ones.


> Where your quoted site says "Feels like", I presume that's wind chill.

Yeah, its wind chill. Everyone had been using
"wind chill" for a million years and then some bright
boy decided that it was too technical a term for a
public web site. Go figure.