Zalman's HD135 HTPC case: Gasping for air

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We mentioned that the HD135 breathes very well. It has vents everywhere, and should have no difficulty letting heat out or fresh air in. What we didn't mention is that, despite all these vents, the airflow design is very unclear. There are a total of nine distinct openings for airflow, but only two of them provide mounting holes for fans — and they're not where you'd expect them to be. Counting generously, the power supply might count as a third fan, but that's a bit of a stretch because the airflow for the power supply is isolated from the rest of the case.

Two low-profile, 80mm fans are included: One intake, and one exhaust. Can you say bottleneck? With the power supply out of the equation, that translates into (roughly) neutral pressure system with a single intake, a single exhaust, and six mostly unused vents.

Most of the intake vents are fairly restricted— at least 50% in all cases — but that restriction isn't really an issue here. After all, with six vents to choose from, they can afford to be a bit restricted individually. What really matters is the restriction over the exhaust vent, which is at least 60% blocked.

Each of the four corners of the case has a roughly 120mm-sized vent on the side panel. Clockwise from the front left, these should provide fresh air for the hard drives, the video card, the power supply, and a second hard drive bay. However, with the exception of the power supply, none of these has any way of mounting a fan next to them, so they will not do much for airflow without some creative ducting and / or modding.

Note the two vents on the side. There are two matching vents on the other side as well.

The side vents look perfect for 120mm fans... but there's no way to mount them.

The main intake vent is located in the top panel, just above where the CPU is located on most motherboards. The intake fan is pre-installed in this position, with a plastic duct that is meant to extend over the top of the heatsink, ensuring that the CPU gets the freshest air possible.

From here, the exhaust air from the CPU heatsink trickles away, presumably escaping through the vent on the back panel (see below), or perhaps being sucked away by the exhaust fan, which is incongruously mounted on the bottom of the case just behind the power supply, away from any major heat-producing components. With the intake fan pumping air directly to the CPU heatsink, it will be the exhaust fan that gives the internal airflow what little direction it can get — drawing the air towards the top of the motherboard and completely ignoring the airflow needs of the lower half of the motherboard.

But what about the video cards, you might ask. Surely they need cooling as well. Our advice: Don't ask, you'll be less stressed out.

The back panel is well vented.

That accounts for seven of the nine vents. The remaining two are also located on the bottom of the case: One under each internal drive bay. That's a nice thought, since drive cooling is very important. Unfortunately, with so little to drive airflow, they probably won't do very much.

The photo below shows how restrictive the exhaust vent is. It's located on the right side, near the middle. The blades of the fan can just barely been seen through the vent. The photo reveals something else as well: The secret to the lower profile that Zalman was able to achieve. Like the HD160, the height is determined by the power supply, which is mounted sideways in the rear right corner. The difference? The power supply in the HD135 is sunk into the floor so that the bottom of the power supply is on the same level as the feet, not the bottom of the case.

It's worth mentioning that the height that Zalman specifies for the HD135 cannot be correct. A standard ATX12V power supply is 150mm wide, while Zalman quotes the height of the case as 135mm. Add in another ~5mm for the case material above and below the power supply, and the specification ends up being about 20mm shorter than the layout physically allows. Perhaps the 135mm measurement is without the feet...

That's odd... the feet aren't symmetrical. Why?
The "missing" 2.5cm in height have been added to the bottom for the power supply,
displacing the rear right foot in the process.

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