HP will give customers the option of using liquid cooling on two of its workstation models, the z400 and z800 to cutback, but not eliminate, the need for fans. With air cooling, each processor is cooled by a two-inch diameter fan.

Small fans run at a faster RPM, which produces a higher pitch and tone. With , the fan that is cooling a processor is replaced by cold plates that conduct the heat from the processors to the liquid.

One way to look at the stakes involved is to compare a workstation with the noise generated by the average household refrigerator. A refrigerator makes about 40 decibels (dB) of sound which is very close to the 38 dB generated by an air cooled z800 workstation running under a heavy CPU load. When idle, this workstation generates 27 decibels. And a working environment may have multiple workstations overall noisier

The liquid cooling is a closed system. A non-toxic coolant flows from one processor to the other and circulates back into a reservoir where a 3.5 inch, slower moving fan exhaust heat. "Given the high efficiency of liquid versus air we are able to turn those fans at a much lower speed, and thereby the overall acoustic and sound pressure level is lower," said Mike Diehl, HP product manager for workstations. The noise can be reduce by one half the loudness with 10 dB reduction, he said.

A dual socket z800 with liquid cooling will produce 22 dB at idle and 30 dB under a heavy load. That compares to this: 10 dB is the sound of normal breathing; 20 dB, rustling leaves; 30 dB a whisper; 40 dB a refrigerator humming; 50-65 dB is normal conversation, according to a chart by the National Institute on Deafness and Other Communication Disorders.