The Heatsink Guide: Vapor Phase Refrigeration

THE HEATSINK GUIDE: Vapor Phase Refrigeration

Introduction

Fridges and freezers are cooled using vapor phase refrigeration. Just like a heat pipe, vapor phase refrigeration takes advantage of the effect that evaporating liquids cool down the surrounding area. However, vapor phase refrigeration involves a compressor, which moves the working fluid around in a closed circuit, and helps to condense it to liquid form again.

Compressor of a vapor-phase refrigeration system

Compressor of the KryoTech Renegade cooling system

History of vapor-phased PC cooling

The first company who had the idea to sell vapor-phase cooled PCs was KryoTech, a company specialized in advanced electronics cooling for industrial applications. At Comdex Fall 1997, they presented a PC with an AMD K6 CPU cooled down to -42°C, overclocked to 375MHz - which, at that time, was an amazing clock speed. AMD K6-based systems overclocked to 400 or even 550MHz followed soon after.

When AMD introduced the Athlon processor, KryoTech offered Athlon-based PCs running at 800 and 900MHz (read my review); later they were the first to break the 1GHz barrier with their "SuperG" Athlon PC.

Since prices for systems with CPUs cooled to -40°C were exorbitant, and the systems did not sell in high volume, KryoTech offered a stripped-down version of their cooling system, called the "Renegade" (read my review). This system cooled the CPU only down to room temperature, which avoided the expensive insulation/heating required to fight condensation problems.

The last KryoTech PC was the Athlon "Super2G"; after that, KryoTech discontinued the series due to lack of commercial success and high development/manufacturing costs.

The second company that started offering vapor-phase cooling systems for PCs was the Danish company Asetek. Unlike the KryoTech low-temperature coolers, which were only sold as complete PCs, Asetek's "VapoChill" systems are available separately: Either as a PC case with embedded cooling system, or in a smaller case for the cooling system, which can be combined with a standard PC case of the user's choice. This leaves customers more freedom as far as the choice of motherboard and CPU are concerned.

The VapoChill systems are still being made today, but not very widely available (they can only be ordered through a few online shops worldwide). ASETek is now making conventional watercooling systems, which are more popular and available from quite a few places.

Unfortunately, the ASETek VapoChill website is just a collection of error messages (unless you use Internet Explorer with relaxed security settings - bad idea!).

Others have tried to compete, and failed. Chip-Con developed the "Prometeia" cooling system, which also received positive reviews on many websites. Chip-Con first changed their name to nVENTIV, and went out of business soon after. The assets were purchased by ECT, who still offer a small range of "Prometeia" vapor phase coolers. It is interesting to note that the two remaining companies who sell vapor phase coolers are both Danish, just like Danfoss, the manufacturer of the compressors used in these systems.

Despite having been available for quite a few years, vapor phase coolers never reached the mass market, and were only sold in low volume to enthusiasts. It can be said that vapor phase refrigeration for PCs was a commercial failure. Why? Read below for problems...

Problems of vapor phase refrigeration

Why isn't vapor phase cooling of PCs a success on the mass-market? Reasons include:

High price. Even though vapor phase cooling will improve performance by allowing higher overclocking speeds, this will not result in a good price/performance of the overall system. What you pay for is having a PC that's a little faster than the computers of everybody else - apparently, some people need that for their ego.
Limited upgradability. The cooling system of a vapor phase cooler is a closed circuit, and normal users can't tamper with it. So, the "cold plate" that is in contact with the CPU can't be changed by the user. This limits upgradability, due to the frequent change of slot/socket format of CPU manufacturers. Asetek has solved this problem by offering separate "head units" (the mounting / case for the part of the cooler that is in contact with the CPU), so that you can upgrade across CPU platform by changing the head unit. However, a new head unit alone will cost more than a conventional air- or watercooling system. It remains to be seen to which extent upgradability is actually possible in the future; especially future dual-core CPUs may require more powerful cooling than the compressors in current VapoChill systems can provide.
High noise. The compressor is usually rather quiet (not louder than a regular fridge), but the cooling system - due to its high heat production - requires additional fans for cooling.
Ecological and economic issues. This is, in my opinion, the most important downside of vapor phase coolers - read below for details. There is enough energy being wasted already, and enough gases that harm our climate are being emitted, so having normal PCs add to these effects certainly isn't desirable.

Ecological problems

The refrigeration fluids used for vapor phase coolers include:

R134a: 1,1,1,2-tetrafluoroethane (controlled under Kyoto Protocol)
R402: mix of Pentafluoroethane (controlled under Kyoto Protocol), Chlorodifluoromethane (controlled under Montreal Protocol), and propane (ecofriendly when used alone)
R404a (mix of 1,1,1,2-tetrafluoroethane, 1,1,1-trifluoroethane, and Pentafluoroethane - all controlled under Kyoto Protocol)
R507 (50:50 mix of 1,1,1-trifluoroethane and Pentafluoroethane, both controlled under Kyoto Protocol).

All of these cooling fluids contain HFCs and/or PFCs, which massively contribute to the greenhouse effect. According to the U.S Environmental Protection Agency, R134a (for example) has a global warming potential that is 1300 times greater than carbon dioxide!

Car manufacturers, as well as manufacturers of fridges, are currently moving away from R134a and related products, as more ecofriendly alternatives, such as R600a (Isobutane) or R290 (propane) exist.

The worst thing is that neither the customers, nor the reviewers on most other websites even seem to care. It appears that to some people, a few additional MHz of overclocking speed are more important than our planet's climate.

Another problem is power consumption. Vapor phase coolers have a better ratio between transported power and power consumption than peltier elements - unlike peltiers, a vapor phase cooler can transport more power in the form of heat than it will actually consume. Still, power consumption of a vapor phase cooling system alone ranges from 75W to 150W, depending on the model and the load situation. If every PC in the USA was equiped with a vapor phase cooler, about five additional large nuclear power plants (1 gigawatt each) would have to be built just to provide power to the PC coolers (assuming 75W power usage of the cooling system, and 200 million PCs powered for 8 hours a day).

Typically, the use of a vapor phase cooler will about double the power consumption of a PC, and thus will also result in higher electricity bills.

Conclusion

Vapor phase refrigeration for PC cooling is certainly a fascinating technology. However, it was a commercial failure: Of the three companies that developed vapor phase coolers for PCs, one gave up production of supercooled PCs for economic reasons, and another one went bankrupt. Today, only a few die-hard overclockers use vapor phase coolers, but more for the emotional kick of reaching highest overclocking speeds than for rational reasons. Considering ecological aspects, this is definitely a positive development; we can be glad that vapor phase coolers never made it to the mass market, and we can only hope it will remain so in the future.