The Folk Laws of Case Cooling:
The diagram below was taken from Intel® Pentium® Pro Processors Thermal Management document.



In the world of micro-processors our arch-nemesis is heat; however, there exists a second villain, perhaps even more nefarious, Complacency. While heat affects hardware, complacency affects the entire industry especially the end-user. While we often see great advances in several fields such as CPU and graphic chip design, in the field of PC-chassis thermodynamics progress has been slow. As far as those advances we haven’t come much further then CIRCA 1987 Form Factor guidelines. In the PC-world the ole adage "If it ain't broke don't fix it." is about as correct as its grammar.

Manufacturers must be relentless in the pursuit of new technology if not their complacency / product designs will eventually impair other advances. Micro-processors continually evolve and to date the formula has been more transistors in less space = more heat. This may be the reason we see growth spurts in the tech-sector as necessity continues to be the mother of invention and a few complacent kids. Case in point; the trend among chassis manufacturers over the last few years to build their products around 25cm fans attempting to do too much too late. One of these cases graced the pages of Madshrimps in EasyPanic's review of the Aerocool ExtremEngine 3T. Today as we review the NZXT ZERO a case sporting no less than eight cooling fans we hope to find a designer more concerned with performance then size or number.

The initial diagram should send shivers up the spine of anyone remotely familiar with the subject of case cooling and airflow. Not only is the airflow direction antithetical to the basic tenets of thermodynamics (i.e. heat rises) the design relies on the Power Supply's cooling fan as the only source of airflow within the entire enclosure. Back when the ATX Form Factor was introduced processors didn't dissipate nearly as much heat. The diagram above pertains to the Pentium Pro series with a TPD (Typical Power Dissipation) between 23W ~ 40W which is less then 1/3 of dual core CPU's such as the infamous Cedar Mill. Insofar as the airflow model above Intel revised the design, effectively reversing the direction of airflow. Unfortunately over a decade later ATX Form Factor Guidelines, still designate the power supply cooling fan to be used in case ventilation (airflow). This is evident in the following ATX Form Factor document: ATX Form Factor Revision 2.2 (2003 - 2004):

5.1 Venting:
Adequate venting should be provided in the system to allow for unimpeded and well-directed airflow to cool key components such as the processor. One recommendation that is implicit in the ATX specification is the placement of the power supply. The power supply should be placed in close proximity to the processor if the power supply is expected to cool the processor properly (but be sure to observe the component height over the PC board). Chassis venting should be placed strategically to allow for proper cooling of other components such as peripherals and add-in cards. A system fan should be considered to allow for proper cooling of all system components.

From the diagram above to the diagram below taken from Processors System Thermal Management for Boxed Processor-Based Desktop PCsit seems the only pertinent changes made to the ATX Form Factor chassis has been reversing the airflow direction.



The topic of case aerodynamics essentially divides itself into three schools of thought: Balanced pressure which simply translates into equal intake and exhaust fans (equal CFM). Positive pressure, which translates into greater intake CFM then exhaust CFM and finally a misnomer referred to as "Negative pressure" which doesn’t actually exist in physics. More accurately the latter should be referred to as a Vacuum effect. This is based on greater exhaust CFM then intake CFM.

Of course things aren't always so simple, for example placing an intake fan in front of an obstruction such as the HDD cage minimizes that particular fan's effect on a front to back airflow model and the average PC-case is a plethora of angles and eddies where heat resides. Researching airflow alternatives led me to conclude positive pressure seems to be most popular. Unfortunately popularity is no measure for the best solution and it's my contention a vacuum effect is the best solution so long as quality filters are placed at each intake. Among all three models manufacturers seem to favor either the Positive case pressure model, or the Vacuum effect. Each of the aforementioned has valid benefits as well as detriments and a plethora of adamant supporters.

Case manufacturers have had a hard time of it since heat levels have risen and more powerful fans must be used, the end result is increased noise. They are now faced with designing a high airflow pc-case which also appeals to those in the silent computing community. That community is growing larger since no one really likes noise (that I’m aware of). The problem is these two attributes (high CFM fans and silence) are mutually exclusive based on the laws of physics:

Increased RPM = Greater CFM = Increased Noise (dBA)

Lower RPM = Less CFM = Decrease in Noise (dBA)

The solution of late has been larger fans, since larger blades move more air with fewer revolutions. Problem is these fans are costly, difficult to fit into ATX Tower ergonomics and most alarmingly, mounted on case side-panels because that is most convenient. Designers are obviously looking to ameliorate the heat generated by QUAD SLI solutions; problem is they seem to be missing the larger picture. What is most important isn't necessarily the design rather design execution. Where fans are placed, what type are placed there, the size of the case, whether it's sealed or not, case material, etc. these attributes will dictate performance.

An example of a Quad SLI case design can be found at Antec with their 900 series (tested by here.) The case utilizes twin stacked 120mm front intake fans each mounted to a proprietary HDD enclosure, a rear 120mm exhaust and a 200mm top mounted exhaust. Antec places the PSU on the bottom of the case where its proprietary cooling fans are not misused as part of the exhaust system. The motherboard is mounted above this and the CPU is now adjacent to the rear exhaust and top exhaust mounted fans. The Antec 900 seen below.



As I prepared for this review it occurred to me very few companies have tried to introduce new technologies and most disconcerting even fewer have at least eliminated the use of PSU cooling fans for additional or primary exhaust. Even with the recent introduction of fans as large as 250mm it seems implausible we haven't built a better mouse-trap. And while it's certainly true the proverbial mouse has grown to the size of a Capybara in a thermodynamic analogy, designing and building an effective case is not as difficult as it seems. Problem is how much profit can be made when the End-user fails to see the role his/her PC-case plays in PC thermodynamics. While some case manufacturers throw larger fans at the problem there's been little research on the subject. Zalman did come out with a passive design a few years back in their passive trio: TNN 300 the TNN 500AF and original TNN 500A. Problem is these cases are prohibitively expensive and while they excel in noiseless operation their cooling potential is limited, for the money it’s difficult to comprehend even for silent operation.

What gets stuck in my craw are the number of cases on the market which have actually done worse then follow Intel’s outdated ATX From Factor guidelines, this is evident in the following quote from one of many Intel Product Support papers with the subtitle Thermal Management; ...airflow in systems using the boxed processor should flow from the front of the chassis, directly across the motherboard and processor, and out of the power supply exhaust vents. At least they promote front to rear airflow and lean towards the vacuum. There are still a great deal of PC-users out there whom own Presler or Cedar Mill processors and running some very hot graphic cards in SLI or CrossFire. I wonder how many of these individuals are happy with their internal case temp? With the hodge podge of positive pressure cases on the market using all sorts of fans the best we may have are a large number of Hasbro Easy Bake Ovens convention style and this is where Complacency may damage more systems then heat.

Fortunately there are manufacturers out there attempting to remedy the situation, lets see if NZXT is one of those companies ->