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PC cooling

Alastair Grant | Tuesday 15 July 2014

I've been giving personal-computer cooling an unreasonable amount of thought recently; mostly the day-dream variety. It probably started around a year ago when I figured it was probably time to upgrade my case: an Antec SX835 II. Coming in a fetching shade of off-white it boasted five 80mm fan positions (three front, two back) plus an optional side fan fitting on the side panel. The removable drive bay and screwless door made it a pleasure to tinker with.

I spent a fair bit of time getting back up-to-speed with the latest cooling, the world had moved on from 80mm fans and everything was about 120mm fans and bottom-mounted power supplies. I figured I didn't need a lot of space and had to get with the times and accept that everything PC orientated (especially in the enthusiasts realms) came in black. I researched a bit and bought a gorgeous looking BitFenix Shinobi. With fan options including x2 120mm fronts, x1 120mm rear, it also boasts twin 140mm top-mounted and a 120mm bottom mounted. Spoilt for cooling options.

So a year later and I'm not happy with PC cooling. The issue comes from the movement of the PSU from the top of the tower, to the bottom; a craze that seems to be spear-headed by Corsair. The theory is sound, PSUs are sensitive to heat, so it was silly pumping all the heat from the CPU into the PSU, instead you mount it at the bottom where it can get its own source of fresh air from under the case (and a lot of dust). And true to this theory, the PSU does indeed stay cool. The snag is, now the CPU is directly below the top of the case - to the front you have your optical drive bays and below you still have your graphics card. The net result is there is no source of fresh air being pushed towards your CPU - instead air has to work its way between the back of your graphics card and the optical bays - hardly optimal. And a knock to the BitFenix design, whilst it looks good, having a solid front to the case is never going to be great for air-flow.

I have since been considering my options for better air-flow. There are many, many discussions on the optimal placement of fans and how to cool. A lot of "definitive" articles, with no evidence to back them up. A few experiments done by computer-magazines suggest that traditional thinking doesn't always work. My reading so far suggests that these are the key points into actively air-cooling your computer:

  • Direct air-flow on hot area works the best
  • Keep air-flow as straight as possible
  • The aim of the game is to get hot-air out and replace it with cool air
  • Extra fans are only beneficial providing they compliment the above
  • Heat only rises when there are no other forces working against it
  • Fans are only affective for a short-range

Positive and negative air-flow are a big conversation piece. Positive pressure could lead to having hot air caught up in the out-of-flow areas, whilst negative pressure lets exhausted hot air right back into the case. And the latest craze is high-static-pressure fans instead of high-air-flow. It's all very well having a lot of flow if there is not enough pressure to overcome any obstacles (stupid solid case fronts, fan filters, cable mess, etc). Is there any reason not to get the highest pressure fans possible? And then there is a complete lack of conversation on well-established science, such as Bernoulli's principle - why aren't we seeing velocity stacks on computers more?

On my old Antec case, I used to have the side fan-position filled, I eventually removed it as I discovered things were in fact warmer by a degree or two when it was in operation - I suspect this was due to the side fan pushing the front-air flow into the wall and destroying it's ability.

The main issue in computer cooling seems to be the layout of current cases are not optimal, which means a lot of fans are required to overcome the physical limitations. A more intelligent layout of components would allow cleaner airflow and less effort required to move it around. A few manufacturers have played with alternative layouts, Lian-Li have used a reverse flow (which is fine providing you can get your graphics card and CPU cooling to work backwards) and Silverstone have dabbled with rotating the motherboard 90° so that the expansion slots exit at the top - this seems the best approach but only available in the large variety. I hope to see more innovation and I also hope to see review-sites building cases and using appropriate fans optimally when reviewing instead of relying on the bundled fan(s).

Breaking from the voyeuristic norms of the Internet, any comments can be made in private by contacting me.