[Jerry Stuckle]

On 6/30/2015 4:21 AM, Ian Jackson wrote:
In message , Jerry Stuckle
writes
On 6/27/2015 5:35 AM, Ian Jackson wrote:
In message , Irv Finkleman VE6BP
writes
Thanks Ian,

There were existing fans and holes in the rear panel, and I was
just curious before replacing the fans. Both had become noisy and
I removed them without checking air flow direction.

Ah....
I was thinking more of a 19" rack horizontal fan tray (holding maybe a
couple of 6" diameter fans - which can sound like a hovercraft on full
power!).



Ian, we do a couple of dozen racks a year. The best cooling (even
recommended by the rack manufacturers) is fans with filters at the
bottom, blowing air directly into the rack. If you need additional
cooling, you can put fans at the top pulling the air out.

You don't want fans just pulling air through, as you would have if the
fans were at the middle or top; you have no control of how or where the
air enters the rack; air can be pulled in through spaces between units,
or even through holes in equipment, for instance. But you can place
fans at the top if you have fans at the bottom; the bottom fans will
still supply the air and the top fans will increase airflow.

The biggest problem with cooling a cabinet is equipment placement. You
generally want the heaviest items near the bottom for stability, but
these also generally generate the most heat. Additionally, deeper items
will block more of the airflow. You don't, for instance, want a
full-depth item immediately above one that generates significant heat.
But most items that run hot generate the heat near the rear of the
chassis, so you can place a low depth item above it, if convenient. If
not, you may have to place a 2 or 3 RU blank panel above it to allow for
sufficient airflow.

You also need to consider things like too many full-depth items you have
in the cabinet. Each one of them adds air resistance, lowering air
flow. You may, for instance, want to go to a 28" deep rack, even if
everything will fit into a 23" deep one, to allow for more airflow. Or
you may go for two 28RU racks instead of one 44RU rack to split the
heat up.

There is a certain art to good rack design; you don't just slap
everything together and hope it works. When you're done, you should
power up everything in the cabinet and monitor temperature for a few
hours. And if you generate significant heat (or even moderate heat in
unconditioned space), it's a good idea to have a thermometer with remote
alert capabilities in case of a problem like a fan failure.

Your experimental experience is noted. I have to admit that I haven't
personally experimented with trying to optimise cooling in racks.


Actually, it's not experimental experience. It's recommendations from
rack manufacturers and the knowledge of the guy who designs the rack.

My suggestion of 'halfway up' is essentially a gut feeling - based on my
experiences where the equipment doesn't extend all the way to the back
to the rear door/wall of the rack - ie there is a gap, say, of least 6",
where the air can get from bottom to top without having to pass
completely through the intervening hot equipment.


Yes, that's typically the case. But we occasionally have a piece of
equipment which is 25" inches deep. That requires additional space for
airflow around it.

By the very nature of things, and with the best will in the world, racks
can rarely be made into air-tight tubes, and as a result, there is
usually quite a fair bit of leakage. If the fan tray is located at the
very top of the rack, a lot of the lower equipment doesn't really feel
their benefit. This may not matter much to the very lowest equipment, as
it probably doesn't really need the fans. It will be the equipment in
the centre of the rack that will suffer, because it will get the hot air
from the equipment beneath, but the fans won't have enough 'reach' to
extract it. That's why I feel that locating the fan tray about halfway
up might be the best compromise.

Locating 1/2 way up does not control the inflow of the air. If there
are vents at the top and bottom, air can enter and exit those and the
input vents can be filtered. But if there are no bottom vents or the
filters become clogged due to lack of cleaning, air will try to come in
through cracks in the front between pieces of equipment, around the rear
door, and potentially even through the equipment if the front panel is
not air tight (very little is). This airflow also allows all kinds of
contamination into the rack in the form of dirt, dust and similar. Fans
at the bottom of the rack can be filtered to limit contamination.

Or, worse yet, if there are no easy ingress/egress paths, these fans
will just circulate hot air in the cabinet.

Additionally, the heaviest equipment (i.e. high power audio amplifiers)
goes at or near the bottom for stability; this equipment also generally
creates the most heat. It would be much nicer if this could go at the
top of the cabinet, but unless the rack is bolted down, you have a
tipping danger.

Depending on the equipment in the rack, fans at the bottom may or may
not be enough. When they aren't, you add exhaust fans at the top to
increase airflow.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

[bilou]

"Irv Finkleman VE6BP" wrote in message
...
I have been wondering which way the fans on my TS-930 should be blowing.
Should they take the ambient air from outside and blow
it on the heatsink, or should they be evacuating the inside air
in the vicinity of the heatsink and blowing it out? I have been
restoring the unit and both fans required replacement.

I've surfed a number of sites on the subject but can never get
a definitive answer.

Thanks in advance for any assistance...

de Irv, VE6BP
Hi
My opinion is quite simple:
Pulling air out of an enclosure will ,at the limit, create a vacum inside
In such case radiators are totaly useless only ,by inertia,delaying
complete failure.
Pushing air in allows filtering it from dust and is clearly the way to go.

[Michael A. Terrell]

bilou wrote:

"Irv Finkleman VE6BP" wrote in message
...
I have been wondering which way the fans on my TS-930 should be blowing.
Should they take the ambient air from outside and blow
it on the heatsink, or should they be evacuating the inside air
in the vicinity of the heatsink and blowing it out? I have been
restoring the unit and both fans required replacement.

I've surfed a number of sites on the subject but can never get
a definitive answer.

Thanks in advance for any assistance...

de Irv, VE6BP
Hi
My opinion is quite simple:
Pulling air out of an enclosure will ,at the limit, create a vacum inside
In such case radiators are totaly useless only ,by inertia,delaying
complete failure.
Pushing air in allows filtering it from dust and is clearly the way to go.


As a retired broadcast and CATV engineer, I find all of this amusing.
The worst install that I've run into was at a TV station. Six or seven
full sized racks for the control room for the video gear, and three 1"
Sony VTRs. They were framed into a closet, with sliding doors on the
outside, in the hallway. They had a separate 15 ton A/C for that
closet, yet equipment had a high failure rate. The HVAC contractor had
installed the supply and return vents in the ceiling. They had been
screwing around for several years, and losing about $500 a month in
failed capacitors. I took one look, felt around in the racks and told
them that the supply line should come in at the floor. Since they racks
were sitting on a poured concrete floor, there was no way to feed the
air into the bottom of the racks. They called me a fool, and told me
that engineers from the equipment OEM had been to the site. I got them
mad enough to prove me wrong by removing the ceiling vents and using a
piece of flex duct on each, that dropped to the floor. In under five
minutes, there were no hot spots in any of the racks, and after a month,
the capacitor failure rate dropped to an acceptable level. BTW, one of
the racks had a 5 kW linear 5V power supply in the bottom. Even that ran
cool.

Another site used open racks for microwave equipment at a CATV
headend. They had a large A/C mounted through the wall. MOving one rack
just four inches to the side eliminated the problems. it was deflecting
the air flow away from the other equipment racks, and the return air was
being pulled behind it, back to the A/C.

You are never going to create a vacuum with the fans used to cool
relay racks, they just aren't designed to be that tight. Instead, they
are designed to run quietly, and for a long operating life. Decent
vacuum motors are two or more stages, and the individual fans are in
enclosed areas. AMETEK/Lamb made most of the vacuum cleaner motors in
the US at one time. They were reliable, and easy to repair. Their
website has some good information about blower/vacuum motors. I
repaired some of the motors for a local steel mill, where they were used
for air quality sampling. I also rebuilt a few truckloads of them for a
guy who rebuilt and sold used vacuum cleaners. He would give me a
truckload of motors that he considered scrap. I would repair them, and
sell them back to him. He always wanted to see my armature lathe. He
freaked out when I showed him how to clean and true an armature with a
variable voltage DC power supply, and a hard gray in eraser. ;-)