Using waste heat to cool a computer

Com­put­ers gen­er­ate a great deal of waste heat. Active cool­ing is the most pop­u­lar method of vent­ing heat, by using pow­ered fans that move air through the com­puter. How­ever, because a pow­ered fan gets elec­tric­ity from the sys­tem­board and the computer’s power sup­ply, the fan must spin fast enough to trans­fer any heat that the fan motor gen­er­ate, as well as the waste heat the fan is sup­posed to divert from the CPU and other com­puter parts. Pow­ered fans also increase the elec­tric­ity require­ments of a computer.

Res­i­den­tial users are more likely to be annoyed by fan noise than energy costs. Media cen­ter com­put­ers often use fast proces­sors, high-end graph­ics cards and large hard dri­ves to drive large video screens. Audio­philes do not want fan noise to ruin their expe­ri­ence, so these com­put­ers are often designed to reduce fan noise.

In a data cen­ter or a server room, the noise gen­er­ated by hun­dreds of fans can reach 85 dB (deci­bels) and louder. That’s loud enough to trig­ger OSHA reg­u­la­tions, so some data cen­ters pro­vide noise can­cel­ing head­phones or earplugs for their per­son­nel. As data cen­ters become larger, with faster com­put­ers that have louder fans, data cen­ters are now using noise insu­la­tion, liq­uid cool­ing, and other tech­nolo­gies to man­age their phys­i­cal envi­ron­ment. A few data cen­ters are using low power com­put­ers that pro­duce less heat and fan noise. See this 31 July 2007 arti­cle from Com­put­er­World for more details.

In some com­put­ers, pas­sive or con­vec­tion cool­ing is a key design ele­ment. Apple’s lap­tops and the Mac Mini have small fans that pro­vide active cool­ing. In fact, small fans are used in many lap­tops and small form fac­tor (SFF) desk­top com­put­ers. As I men­tioned in my 3 March 2008 post, lap­top design­ers have to with tightly inte­grated com­po­nents. There is much less air­space inside a lap­top case than in a desk­top com­puter case.

Pas­sive cool­ing is also used in many lap­top and SFF com­put­ers to reduce elec­tri­cal power con­sump­tion. Heat is diverted by con­nect­ing the sys­tem­board to the com­puter case, while small vents allow cool air to enter the com­puter case. The com­puter com­po­nents warm and expand the air inside the case, push­ing the heated air out of the case while draw­ing cool air inside. This arti­cle at Power­Book Cen­tral pro­vides a nice discussion.

Some lap­top own­ers have noticed that under­side of their com­put­ers becomes very warm dur­ing use. Many lap­top com­put­ers have vents on their under­side. Lay­ing the lap­top flat against a table will block the vents, and cause hat to build up inside the com­puter. Some lap­top com­put­ers can become too warm to be placed on a user’s lap. I use a plas­tic or metal stand to raise the com­puter off the table or away from my lap. I haven’t tried a USB-powered stand, which plugs into a lap­top computer’s USB port to spin small fans in the stand. The fans pro­vide active cool­ing, draw­ing heat away from the com­puter case and pulling air through the computer’s vents.

A Stir­ling idea

Tweak­Town (via Boing­Bo­ing Gad­gets) has an arti­cle about a clever cool­ing sys­tem that har­nesses waste heat to pro­vide active cool­ing with­out draw­ing elec­tric­ity. MSI has devised a fan motor that is pow­ered by a small Stir­ling engine, which uses waste heat to power the fan. The sys­tem is very quiet. How­Stuff­Works and Wikipedia each have arti­cles about Stir­ling engines. There are sev­eral com­pa­nies that design and sell Stir­ling engines. Amer­i­can Stir­ling Com­pany sells small motors that are used as demon­stra­tion mod­els. Swedish com­pany Kock­ums has designed and launched 8 sub­marines equipped with large Stir­ling engines.

Tweak­Town also pro­vided an MSI ani­ma­tion of this motor. I hope the real com­po­nent moves faster than the simulation!

Tagged as: Apple, CPU, electricity, hardware, heat, noise, power, Sweden, USA, USB