Creating a computer cooling system

Choosing a power supply
The usual ATX design for personal computer tower and desktop cases treats the power supply fan as the principal means of drawing cooling air through the case. In a tower case, air is supposed to enter through a grille in the bottom corner at the front of the case and be blown out of the back corner, at the top of the case, by the power supply fan (see attached pdf PC-case).

Desktop cases usually use the same arrangement, but tipped on its side, so air enters through a grille at the front left of the case and is blown out at the rear right.

Whatever the layout, the power supply and its fan are crucial components for case cooling and are consequently a key source of fan noise. However a supply with a high power rating and a more powerful fan may allow the total fan count to be kept low, resulting in less noise.

Some of the high-end power supplies available have speed-controlled fans so they can be adjusted to minimum noise while still providing sufficient airflow. These include the Nesteq range from Quiet PC, which cost between £100 and £150; the Zalman ZM460B-APS 460W at £84.99; and the Q Technology Ultra-Quiet 460W at £70, which can also be bought from Quiet PC.

Remember that dual graphics card SLI or Crossfire setups can be a headache in terms of heat dissipated and in current draw from a single supply rail. This can be in excess of 20A, requiring a very careful choice of PSU.

Cable dressing
As you build a new PC it often looks tidy – until the power supply leads and disk cables are introduced. These cables can hinder airflow if they’re poorly placed. The trend is now to use round drive cables, rather than the earlier flat ribbon cables, which could block airflow. If you still have flat cables in your PC and think airflow might be a problem, swap them for round ones.

Simply strapping the power supply cables out of the way of the path between the CPU and the PSU fan using plastic cable ties can make a significant difference in case and CPU temperatures, particularly since general-purpose PSUs are designed to drive both Intel and AMD processors and often have a number of cables that will never be used.

Components
When you’ve put together case, motherboard and power supply, you need to choose the other components of your cooling system. We’ll refer to ‘coolers’ as the complete system used to cool a CPU and to the cooler’s components as heatsinks, fans and heat pipes.

A CPU cooler in its simplest form consists of a heatsink of extruded aluminium, a fan bolted onto the heatsink and a mounting kit. Even though CPU production is limited mostly to two companies, the variety of CPU and socket types is such that you have to be careful to choose a cooler and mounting kit that are compatible with the CPU and socket.

Performance, appearance and prices of CPU coolers vary, from £36.99 for a Zalman CNPS9500-LED Aero Flower with three heat pipes, multiple thin copper fins, blue LED illumination and fan, to less than £5 for an unbranded cooler with a simple, finned aluminium heatsink and fan.

Performance varies a lot too, with thermal resistances ranging from 0.12ºC per watt to 0.6ºC per watt. Frequently, thermal resistance figures aren’t given. Instead, it’s stated that a cooler is suitable for use with particular CPUs, leaving the customer with no idea what operating temperature can be expected.

Comparing coolers
Many CPU coolers are designed to appeal to those who build PCs for looks rather than function. While there’s nothing wrong with this approach, an expensive, flashy-looking CPU cooler will not necessarily be good at keeping a CPU cool.

The information you need to compare coolers is the thermal resistance, which is usually given in ºC per watt (smaller values are better). The best coolers are relatively complex and include heat pipes in their design. Achieving the best possible contact between the CPU case and the bottom of the heatsink is absolutely critical – ideally the heatsink base should be polished mirror-smooth.

A heatsink that doesn’t feel hot to the touch can be a bad sign because it could mean it isn’t conducting the heat away from the component it’s supposed to cool. This will probably be because it isn’t in proper contact – perhaps because of dirt between the CPU and the cooler surfaces, or because of too thick a layer of thermal compound.