Positive Pressure CoolingDust collection inside many computers is a big problem. Most modern computers have at least one set of cooling fins, usually associated with the main micro processors. Other areas of the computer also often have cooling fins as well.
collecting on or in these heat exchange areas can raise the operating
temperature of the devices they are intended to cool to catastrophic
levels. In some cases the devices in question may have internal
circuitry to shut themselves down before they destroy themselves with
their own heat. In other cases thermal runaway cannot be
prevented internally, and once a certain temperature is reached, the
device will destroy itself in the blink of an eye.
Thus it is important to be sure cooling fins are not choked with dust, and that cooling fans are operating normally.
my basement, where my computers must be, things are a bit dusty.
I need to keep an eye on dust collection inside the computer
cases. This got me to thinking about ways to filter the cooling
air brought into the case. If the air were filtered before it
entered the case, then dust collection would not be an issue.
So... how to filter the air entering my computer case?
is not a simple question. Most computer cases are not designed
for dust control. They have large gaps in various places,
sometime for good reasons, often for bad reasons. I have yet to
see a computer case where someone designed it from the outset for use
with air filters. But you can't just put air filters on the thing
and expect it to stop dust collection.
collection isn't just a matter of filtering things. It is also
air flow management. Does clean cool air get where it needs to
be, when it needs to be there? And after the clean cool air takes
away the heat, can the clean hot air get out? And finally can a
computer case, not designed with such things in mind, be made to behave
in more or less this desirable manner?
With this in mind I started to experiment.
Using Air Flow To HelpThe
first thing to consider is air flow. I once worked at a research
lab which had a clean room. A clean room is one where there are
active systems, and usage protocols, which are designed to limit the
amount of particles of material, including dust, to certain levels.
One of the front lines of defense in such efforts is positive air
flow. Positive air flow means that the clean spaces are at a
higher pressure than the surrounding spaces. Thus air always
flows from the higher pressure clean areas to the lower pressure
surrounding areas. In this way dust or other particles are less
likely to be brought in via air currents, and more to the point, the
air flow actively discourages such transfers. This works as a
strategy because the air is filtered before it is pumped into the clean
spaces. It also means that, because of the air flow, less
expensive door seals can be used. The room does not have to super
tight, just tight enough.
This model of dust control could be
used in a less than optimal but more or less standard computer case.
The question is to what effect, and how much of an impact on
cooling will there be?
Most computer cooling uses the opposite
strategy. Fans are place on the inside and pull or push air out
of the case. Computer power supply box almost all use this form
of negative pressure cooling. In this way there is usually one or
more fans moving air from inside the case to the outside. A
negative pressure zone is formed on the inside of the case, and cool
replacement air from outside the case is drawn in every other opening
in the case. Over time one can often see the dust building up
around the nooks and crannies of the case where the air is drawn in.
If the normal operation of the case is as a negative pressure zone, how do I make it positive?
Simple... reverse the directions the fans blow.
can be simple for wall mounted fans but things like power supply boxes
don't always lend themselves to monkey around with things.
Furthermore leaving the power supply fan as an exhaust fan may
not be such a bad thing. The trick will be to provide enough
airflow into the case such that the power supply fan can't move it all
out, thus creating the desired positive internal pressure.
the incoming air will be relatively simple. Firstly there are
commercial products for many fan sizes that will act as filters.
But more to the point of experimentation, a Swiffer cloth will
serve nicely as a dust filter.
However, we are still left with
the question of proper internal air flow. All this clean positive
pressure air flow will be useless if it doesn't get to where it is
needed, in a way that is useful. There is no point in providing
cool clean air if it arrives in direct opposition to the flow from a
cpu fan. If one fan acts against the flow of another fan the
results will be the same as cooling fins covered in dust. No heat
transfer, and a molten pile of silicon which once was the micro
So some experimentation will be called for.
Two things will be need to determine success.
The second item is readily available in moder computers. Almost all modern CPUs have temperature sensors. There are many apps on the web to read the CPU temperature. I use one called Core Temp.
- A means to determine internal case temperature
- A means to determine how hot the CPU is.
To measure case temperature I use a thermocouple, and a thermocouple reader made by Fluke.
For more accurate testing the temperature of the input air should
also be measured. However, I'm more interested in general trends,
and less interested in a research project, so I'm willing to claim that
the air temperature in my basement doesn't change all that much.
So if the ambient air is at more or less a stable temperature,
these two parameters should provide a reasonable measure of the impact
any changes may have in operating temperatures.
Image thanks to ARRL