Personal cooling systems become smaller

Infantry Magazine, Jan-Feb, 2004

Every Soldier will carry some high-temperature relief when a microclimate cooling system is incorporated into the upcoming Objective Force Warrior uniform.

Microclimate cooling has been researched and developed at the U.S. Army Soldier Systems Center in Natick, Massachusetts, since the 1980s, beginning with the Portable Vapor Compression System, a system shaped like a vacuum cleaner canister weighing 27 pounds, leading now to a couple of prototype compact systems weighing less than 5 pounds that resemble an oversized brick.

Engineers on the Chemical Technology Team are focused on having a system that weighs less than 4 pounds by 2008 and ultimately a system weighing less than 3 pounds by 2015 that will still provide the desired cooling to enhance Soldier safety and performance.

"Cooling is a medical and safety issue," said Brad Laprise, a mechanical engineer. "Comfort is a by-product. You'll never feel like you're in an air-conditioned room (with these systems), but the idea is to mitigate the Soldier's heat stress, allowing them to do their jobs safely and more effectively."

Cooling can also be a force multiplier because troops can work longer without taking frequent breaks necessary because of high ambient temperatures. It also can reduce the logistics load by decreasing the amount of drinking water, said Walter Teal, a chemical engineer.

The personal coolers designed by Aspen Systems, Inc. in Marlborough, Mass., and Foster-Miller in Waltham, Mass., are unique prototypes using the same technology as the Advanced Lightweight Microclimate Cooling System but in a smaller package. "These prototypes are stepping stones. The next step is to take the lessons learned from the Aspen and Foster-Miller units and go to something smaller," Teal said. "We know we are pushing the envelope of vapor compression, but we think there are things we can do to lower the weight and power use."

Vapor compression technology works the same way as a refrigerator or air conditioner. It's composed of a compressor, condenser, evaporator, thermal expansion tube, fan and pump working to move heat to the ambient environment. In the case of microclimate cooling, liquid is chilled and pumped through a vest lined with a network of tubing, removing excess body heat.

The Foster-Miller prototype provides 110 watts of cooling at 95 degrees F ambient temperature and weighs 4 pounds. The Aspen prototype weighs 4.65 pounds and provides 120 watts of cooling under the same conditions. Both require 50 watts of power, but engineers hope to achieve similar cooling capacity with only 30 watts of power in the future. Although 300 watts of cooling is ideal, at least 100 watts of cooling is needed to lower core body temperature according to studies they've seen, Teal said. Lower cooling capacity is a trade-off for reduced weight.

Shrinking size an inch or two and trimming a few ounces here and there will work for the next phase, but Teal said breakthrough technology is needed to achieve the most compact cooler for Objective Force Warrior. "Taking off those last two pounds will take more effort than the first 22 pounds," he said. For more information about the Soldier Systems Center, visit www.natick.army.mil.