Where is Your PSU Fan?

I recently had an interesting argument with one of my friends about Power Supplies.  Our argument was about cooling fan size and placement within the power supply.  His argument was that a larger fan is better than a smaller fan.  As enthusiast, we have seen both employed, but for some reason, no standard has been defined.  Are Power supply companies just playing into the idea that bigger fans are better for cooling? Needless to say, this sparked some interest in research.

Over the years, many of us started with chassis designs that really didn’t take airflow into consideration.  As these chassis evolved we moved from loud 80mm fans to more efficient larger 120mm fans.  With this evolution, airflow was also becoming a larger focus and thus a new generation of chassis was born.  This is all well and good, but how does this play out with power supplies? As our focus shifts to larger quieter fans in chassis, so has the shift to these types of fans in power supplies.

A point of interest though is that power supplies are limited in size based on ATX form factors whereas chassis designs have a bit more freedom.  Thus, leaving power supplies that incorporate larger 120mm fans instead of traditional 80mm fans to place them on the top or bottom of the PSU, and this is where the argument comes into play.  Does this affect airflow and cooling within the power supply and ultimately affect design?

This is a hard argument to benchmark as not all power supplies are created equal.  No manufacturer makes the same power supply with both cooling configurations, so there is no concrete way to benchmark the results.  However, if we examine some simple aerodynamics, we may be able to come to our own conclusion.  Does mother nature have the answer for us?

Let’s take into consideration simple airflow; if a fan is located at the top of the PSU it is forcing air down on the PCB of the power supply then out of the back.  This design requires that air magically makes an efficient 90 degree turn to exit the power supply.  Given that there are components within the PSU that vary in size this is like cooling New York City from the top then blowing the warmed air over New Jersey.  This design leaves stagnant air where there is a lack of ventilation in one area of the power supply and flowing air in another allowing components within to heat up.

If a power supply were to incorporate a fan at the front or back, airflow would travel over all components in the power supply promoting a more uniform cooling effect.  All the components within would benefit from this method of cooling as there would be no dead spots for airflow within.  This push or pull method of cooling is highly efficient and is the reason that even mother nature incorporates this method for cooling.  This raises the question as to why so many manufacturers still incorporate top cooling instead of push pull cooling.