Crackheads need for crackpot solutions to frosty problem.

[Rob Stow]

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.

 

[Steve]

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.

 

[Robert Redelmeier]

OK you crazy guy, I'll bite:

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

 

[Rob Stow]

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/weather/cities/can/pages/CASK0210.htm

 

[daytripper]

[snipped]

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

It's....perfect ;-)

 

[ewan]

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

 

[keith]

[snipped]

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

It's....perfect ;-)

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

 

[Rob Stow]

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.

 

[Paul Busby]

Thus spake Rob Stow:

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.

 

[Rob Stow]

Thus spake Rob Stow:



-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.

 

[Paul Busby]

Thus spake Rob Stow:

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

In some respects I envy you Rob: the only reliable way to tell the seasons
in Blighty is by the amount of leaves on trees. Then again, I haven't lived
in a truly cold climate, so I may have an over-romantic view.

 

[Rob Stow]

Thus spake Rob Stow:


In some respects I envy you Rob: the only reliable way to tell the seasons
in Blighty is by the amount of leaves on trees. Then again, I haven't lived
in a truly cold climate, so I may have an over-romantic view.

We get the best of both worlds here: cold, snowy winters;
warm rainy springs; hot dry summers; pleasant autumns.

Of course that doesn't stop me from grousing when it
hits -40'C in the winter or +40'C in the summer. ;-)
Even -30'C annoying if it lasts more than a few days.

 

[GSV Three Minds in a Can]

Bitstring <RRWCd.716970$%k.38805@pd7tw2no>, from the wonderful person

We get the best of both worlds here: cold, snowy winters;
warm rainy springs; hot dry summers; pleasant autumns.

Yes, we get all that too .. sometimes in the same week. 8>.

 

[Paul Busby]

Thus spake Rob Stow:

We get the best of both worlds here: cold, snowy winters;
warm rainy springs; hot dry summers; pleasant autumns.

Of course that doesn't stop me from grousing when it
hits -40'C in the winter or +40'C in the summer. ;-)
Even -30'C annoying if it lasts more than a few days.

Damn your wonderful weather Sir! I just phoned my brother on the subject who
runs a modest weather station. He suggested the phrase "Feels like" isn't
just wind chill but also factors in humidity to more closely resemble the
subjective feeling of coldness. Seems fair enough.

I used to take daily temp & humidity readings for a test equipment cal house
which involved using a swinging wet bulb thermometer, we never used the
bench hydrometer/thermometer which used a sprung-loaded multistranded horse
hair mech attached to a pen against a cylinder of paper! One could improvise
with a violin & clock of course (should they be to hand)!

 

[George Macdonald]

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.

Hmmm, I hope he has a washer which "supports" the stand-pipe height - many
are limited to ~6 feet vertical "climb".

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.

If that's basically your case temp it's far too low for many of the
components in the system, which can have a min operating temp of ~5C - hell
some have a min specified storage temp of -5->-10C. On top of that the
extremes of temp between Summer and Winter and On/Off are going to cause
temp ramps which can cause damage, not to mention operating temp gradients
on individual components and excessive fretting of contacts. Check the HDD
first for min operating temp.

(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.

Do you have a vent hood/flap on the exhaust vent, as one has with a dryer
exhaust? I don't see how you can seal the case well enough to prevent the
leakage in of some ambient room air.

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.

I'd suggest you just disconnect the external air duct in Winter and use the
computer as a background heater... unless maybe it's an overclocking
project.

Rgds, George Macdonald

 

[Rob Stow]

Hmmm, I hope he has a washer which "supports" the stand-pipe height - many
are limited to ~6 feet vertical "climb".

The stand-pipe is only about three feet tall.

If that's basically your case temp it's far too low for many of the
components in the system, which can have a min operating temp of ~5C - hell
some have a min specified storage temp of -5->-10C. On top of that the
extremes of temp between Summer and Winter and On/Off are going to cause
temp ramps which can cause damage, not to mention operating temp gradients
on individual components and excessive fretting of contacts. Check the HDD
first for min operating temp.

The hard drives do quite well. The cold air intake is
never opened up until after the system has been powered
up, so the drives never really have a chance to cool off.

Nevertheless, I will consider doing something like setting
up a lowest-priority task to continuously copy a small file
back and forth between the drives to make sure they never
go idle.

The DVD drive, however, has been a concern.

Do you have a vent hood/flap on the exhaust vent, as one has with a dryer
exhaust? I don't see how you can seal the case well enough to prevent the
leakage in of some ambient room air.

There is a hood but no flap. Just a quarter inch
mesh to keep out birds ;-) There is a lever on
each vent close them when the computer is not in
use.

I'd suggest you just disconnect the external air duct in Winter and use the
computer as a background heater... unless maybe it's an overclocking
project.

Its a silencing project. The motherboard (Tyan S2885) doesn't
provide much in the way of overclocking capabilities ;-)

Cooling the system with cold air allows both CPU fans, the
PSU fan, and the single case fan to all run at their slowest
speeds. And - so far - the Radeon 9800 Pro has been quite
happy with passive cooling.

When cooling with air from inside the house, not only do all
of the fans need to spin faster - and much louder - but a
second case fan is also needed.

 

[Rob Stow]

We have kludged up something that so far seems to work,
but a real test will have to wait until temperatures
fall again - it is only -21'C tonight.

We have connected the case fan to a thermostat, with
the exhaust air from the PSU blowing over the thermostat.
The PSU exhaust is no longer vented back outside. The
120 mm case fan has also been replaced with an 80 mm fan
with no increase in RPMs.

As many air gaps as possible were sealed with tape on the
/inside/ of the case. Around front drive bay covers, for
example. The side panels now feature weatherstripping.
This should dramatically reduce the amount of warm, moist
indoor air that leaks into the case.

The case fan now only kicks in when the PSU exhaust
convinces the thermostat that the temperature has risen
to 15'C. In case it was not clear, the case fan is used
to draw the cold air in from outside and blow it into
the case. When the case fan is not running, the PSU fan
does all of the work.

At -21'C outdoor temp, the case fan spins about 80% of
the time.

 

[Ed]

We have kludged up something that so far seems to work,
but a real test will have to wait until temperatures
fall again - it is only -21'C tonight.

We have connected the case fan to a thermostat, with
the exhaust air from the PSU blowing over the thermostat.
The PSU exhaust is no longer vented back outside. The
120 mm case fan has also been replaced with an 80 mm fan
with no increase in RPMs.

As many air gaps as possible were sealed with tape on the
/inside/ of the case. Around front drive bay covers, for
example. The side panels now feature weatherstripping.
This should dramatically reduce the amount of warm, moist
indoor air that leaks into the case.

The case fan now only kicks in when the PSU exhaust
convinces the thermostat that the temperature has risen
to 15'C. In case it was not clear, the case fan is used
to draw the cold air in from outside and blow it into
the case. When the case fan is not running, the PSU fan
does all of the work.

At -21'C outdoor temp, the case fan spins about 80% of
the time.

I like the idea, which I had a hole in my PC room wall! ;p

I'd probably add some desiccant packs (big ones) to the bottom and top
of the inside of the case to help keep moisture at a minimum, not sure
how much they'd really last or help though with constant moving air.

What sort of system do you have, you doing some massive over clocking or
just going for max cool and quite?

Cheers,
Ed

 

[Robert Redelmeier]

The PSU exhaust is no longer vented back outside.
The 120 mm case fan has also been replaced with an
80 mm fan with no increase in RPMs.

This is a _huge_ change. That case fan capacity has been
reduced by ~56%. From always positive, the case pressure
may now go negative so you'll need ...

As many air gaps as possible were sealed with tape on
the /inside/ of the case. Around front drive bay covers,

It's still very hard to seal tight.

The case fan now only kicks in when the PSU exhaust convinces
the thermostat that the temperature has risen to 15'C.
In case it was not clear, the case fan is used to draw the
cold air in from outside and blow it into the case. When the
case fan is not running, the PSU fan does all of the work.

And at these times, the case is at minimum pressure.

At -21'C outdoor temp, the case fan spins about 80% of
the time.

Interesting. That's one hot box, or airflow is somehow
restricted. IIRC, an 80 mm fan moves about 7cfm (depending
on speed & restrictions). 7cfm @ 15'C is about 4.3 g/s.
Warming air 36C' requires 36 J/g. So that box was putting
out 155W. That's quite a bit for a machine at idle.

-- Robert

 

[Rob Stow]

This is a _huge_ change. That case fan capacity has been
reduced by ~56%. From always positive, the case pressure
may now go negative so you'll need ...

The 120 mm fan went back in.

It got all the way up to -12'C and when the air is that warm
the 80 mm fan just can't push enough air into the case unless
we run it at its medium speed. At that speed it is noticeably
noisier than the slower 120 mm fan while still moving less air
We figure it is about 7 cfm for 80 mm at medium speed vs
10 cfm for 120 mm at slow speed. And the whole point of this
scheme is noise reduction.

It's still very hard to seal tight.

Even so, we got it tight enough that even with the 80 mm
fan we had positive pressure in the case. But, of course,
negative pressure when the fan wasn't spinning.

And at these times, the case is at minimum pressure.

Yup.

Tonight we are going to try something different.
Two stacked 80 mm fans case fans with one going all
the time at its lowest speed and one hooked up to the
thermostat. Hopefully that will allow us to maintain
positive pressure all the time with a fan in reserve for
when higher air flow is needed. Similarly doubling up
the PSU exhaust fan is also an option.

I have read about a cpu cooler that uses two stacked
fans spinning in opposite directions for higher airflow
and reduced noise, so we are reasonably confident that
the stacked fan idea will work.

Interesting. That's one hot box, or airflow is somehow
restricted. IIRC, an 80 mm fan moves about 7cfm (depending
on speed & restrictions). 7cfm @ 15'C is about 4.3 g/s.
Warming air 36C' requires 36 J/g. So that box was putting
out 155W. That's quite a bit for a machine at idle.

Its got a pair of Opty 248's, six 200 GB SATA drives,
a Radeon 9800 Pro, eight 1 GB PC3200 DIMMs, and sundry
others, plus heat wasted by PSU inefficiency. Not hard
to hit 155 W even when idle.

Measuring at the wall outlet shows a quick climb to 390 W
when the system boots up, then it settles down to about
360 W under normal usage (it is primarily used for semi-pro
video editting). When idle the draw is about 210 W.