Watercooling is a great alternative to air, but it does have its drawbacks. With a standard watercooled system, temperatures will never go below ambient levels. This is where phase change cooling comes in. Phase Change cooling is still somewhat of a fringe technology, mainly because of the expense, and modifications that a user needs to make to their system before it can be used. However, it will cool a processor to below ambient temperatures, and this appeals to the zest for overclockabilty of many an enthusiast.

How does Phase Change cooling work?

Phase change cooling works on the same principle as a refrigerator. A compressor is used to change the state of a chemical refridgerant from liquid to vapour, and as this happens an endothermic reaction occurs where heat is absorbed causing the temperature to drop.

The system essentially works like this; the compressor compresses a gaseous refridgerant which causes it to rise in temperature. The refridgerant, still in gaseous form and under high pressure, is sent to the condenser (a heat exchanger) where it is cooled down and condenses into a liquid (this is the phase change that occurs). The now liquid refridgerant is forced at high pressure through copper capillary tubing into an evaporator chamber which is a low pressure area, and evaporates back into gaseous form, absorbing heat in an endothermic reaction (it gets very cold).

The evaporator chamber in a phase change cooling system just happens to be the block of copper which is attached to the CPU, so as the chamber decreases in temperature, it absorbs the heat energy from the processor below, lowering its overall temperature as well.

The refridgerant now in gaseous form once again, moves back through the compressor, and the entire cooling cycle repeats.

The first commercially available PC phase change cooler was built by Kryotech in 1996. The company never really succeeded as they only sold complete 'supercharged' AMD K6-2 systems. There was no option to just by the phase change cooler and use it on an Intel or AMD platform - which didn't present much of a draw for the emerging class of Celeron 300A overclocking enthusiasts. It would not be until Asetek released their Vapochill in 1998, that phase change started to appeal to overclockers.

The original Vapochill SE phase change cooler could handle a 100W heat load while maintaining -10 degrees Celsius temperatures. Best of all, enthusiasts were able to just by the cooler itself... this set the standard for the industry. As we fast forward to the present day, the most powerful systems available are Asetek's Vapochill LS and Nventiv's Mach II GT, both of which have many times more the cooling ability than the first Vapochill.

In the following tests to see how overclocking is affected by cooling, we'll be testing with an Nventiv Mach I phase change cooler. An old system by all accounts, this unit has had its R134a refridgerant professional removed (at a cost of about $200CDN), and replaced with R404A coolant which has a lower evaporation temperature. That translates into a -10 to -15 degree Celsius cooling advantage, or basically -45 degrees Celsius cooling. :-)

The biggest drawback to adopting a phase change cooling system such as the Nventiv Mach I is the cost... about $650 CDN ($500 US)! That's equivalent to the price of a small computer, and considering this is just the cooling system, it just doesn't make sense for most consumers. What's more, top of the line phase change coolers are even more expensive, ranging in price from $1100 CDN ($822 US) for a Vapochill LS to $1700 CDN ($1225 US) for a Nventive Mach II GT.