U.S. Army Soldier Systems Center-Natick
Public Affairs Office
Natick, MA 01760-5012
Contact: Chief, Public Affairs Office
Date: July 9, 2001
Advanced lightweight microclimate cooling equals relief from heat
Natick, Mass. --- Think of it as refrigeration for the body, with one basic difference-water is cooled instead of air. The Advanced Lightweight Microclimate Cooling System is like a mini-refrigerator that pumps chilled water through a tube-type garment worn by an individual for relief in hot operating environments.
The cooling system's technology is being adapted for use in several Army helicopters as part of the Air Warrior system and will help aircrews lower body heat generated in their multi-layered flight suits beginning in fiscal year 2003. Even when aircraft have air conditioning, it's mostly ineffective.
"It makes sense to cool you from the inside out instead of the outside in," said Brad Laprise, mechanical engineer with the Chemical Technology Team at the U.S. Army Soldier Systems Center (Natick). "The air conditioning may never reach you."
Before the lightweight system, the Natick team and Foster-Miller Inc. in Waltham, Mass., developed the Portable Vapor-Compression Cooling System in 1992, which was intended for use in the Self-Contained Toxic Environment Protective Outfit (STEPO) ensemble.
At about the same time, the Personal Ice Cooling System (PICS) was developed for users of the Improved Toxicological Agent Protective (ITAP) ensemble. The STEPO and ITAP ensembles are impermeable chemical protective clothing systems that fully encapsulate the user, similar to commercial hazmat- type suits.
PICS works by pumping ice-cold water from a two-liter bottle carried by the individual through a cooling garment. The ice-water containers need to be changed periodically as they lose their cooling, and some user groups, such as pilots, can't effectively use this system because they can't re-supply the ice water, said Laprise.
The Portable Vapor-Compression Cooling System was introduced to accomplish the same job of the PICS but without water bottles. It consists of a refrigeration unit, battery module, accessory tether lines and cooling garment.
The refrigeration unit is composed of a compressor, pump, condenser, fan and evaporator. The unit chills six ounces of water and pumps it through the external tether line and into the cooling garment. Body heat is transferred to the water coolant as it flows back through another tether line to the refrigeration unit where heat is dumped. Re-chilled water is then recirculated back into the cooling garment. Coolant temperature stays at 65-70 degrees, unlike the PICS that starts cold but slowly loses its cooling ability.
The system can operate for four hours on four non-rechargeable lithium sulfur dioxide batteries or indefinitely with a DC power supply. The refrigeration unit weighs 10 pounds, and batteries add an extra 11 pounds. In field evaluations, weight was a downfall.
"One of the things we heard from all the groups was that it was too heavy," Laprise said. "We told (the contractor) to focus on something lighter weight that requires less power."
By 1997, the lightweight system was developed. Designers created a miniature rolling piston compressor and cut battery requirements in half, building a unit about half the weight of the older system and nearly the same weight as the PICS. Although the lightweight system operates for three hours with two batteries, a third battery can be used for more performance. Along with size and weight, cooling power also decreased from 300 watts to 215 watts.
"Performance is slightly less, but we were willing to take a hit on cooling for reduced weight," he said.
About the size of a large shoebox, only one Advanced Lightweight Microclimate Cooling System exists. It's carried in a soft-plastic case, which also helped reduce the system's total weight. Laprise said the lightweight system is used to demonstrate the product and create interest in it.
The item was convincing for the people managing Air Warrior, which is an Army program to standardize and integrate aviation life support equipment, clothing and individual equipment.
A cooling system leveraging the technology will be built into Blackhawk, Chinook and Kiowa helicopters to protect aircrews from overheating. To complement the system, aircrews will receive a new vest designed at Natick where cool water is circulated.
Current commercial cooling garments sew rows of plastic tubing onto the fabric. Thread and plastic touch the skin, which sacrifices some comfort, said Stephen Szczesuil, textile technologist with the Technical Support and Services Team.
The improved vest laminates two pieces of fabric around 130 feet of small diameter tubing divided into ten parallel circuits-five in front and five in back.
Various materials can be used, but cotton will be used for aircrews because of its breathability and fire retardancy properties.
The vest has an external supply and return tube which connects the vest to the cooling system on the aircraft. The connector has a quick release and hands-free break-away capability for easy evacuation.
"If you crush one tube, you can still get cooling out of the others. It fits snug, is launderable and weighs less than two pounds," Szczesuil said.
Laprise said during a 1998 study in Fort Rucker, Ala., helicopter pilots in full chemical biological protective gear operated in a 100-degree flight simulator with and without the cooling system.
When the cooling system was not operating, the pilots were able to "fly" for only about 90 minutes because of the induced heat stress. Conversely, with the system turned on, the pilots were able to complete the six-hour test.
During a recent Air Warrior sizing evaluation at Fort Rucker in May, many pilots were pleasantly surprised by how it felt.
Cooling systems improve safety by reducing the rate that core body temperature rises, and have other benefits such as increasing stamina, reducing sweat and lowering water replacement needs. However, a refreshing feeling reigns supreme.
"Physical comfort is what these guys love," Laprise said. "Once they experience it, they don't want to go without it."
Personal coolers become smaller
Developing a "pint-sized" personal cooler is the ultimate goal for engineers involved with microclimate conditioning systems. Until then, the downsizing evolution will continue with the Enhanced Vapor Compression Cooling System.
The enhanced system will shrink some of the existing components into a package about the size of the two-quart canteen.
"We're not going to stop until we achieve a lightweight, low bulk and low power cooling device that satisfies the dismounted soldier," said Roger Masadi, system engineer with the Warrior Systems Integration Team at Natick. "The smaller we make it, the more attractive it becomes to a wider user group."
Giving dismounted troops extra gear is often met with resistance considering that they now carry as much as 100 pounds.
"Some people will argue why give them the extra weight," said Walter Teal, chemical engineer with the Chemical Technology Team. "Maybe you can provide them a lighter (chemical biological protective) suit with a cooling system that's lighter than the alternative."
Microclimate cooling systems are being designed with thought given to the entire soldier ensemble, which may consist of an undershirt, uniform, body armor, load bearing equipment, and chemical biological protective clothing.
Designers first will reduce heat stress of the clothing ensemble through integration and lighter, less bulky and more breathable materials, which in turn reduces active cooling requirements needed in extreme temperatures and chemical biological environments.
Evaporative cooling, accomplished by blowing air into the suit in a warm environment, is another approach being considered as a low-power option for dismounted soldiers. Lower power helps in designing a smaller package.
Objective Force Warrior will showcase a future generation fighting ensemble for the dismounted soldier. Passive and active cooling will contribute greatly to its success and the success of other futuristic ensembles, said Masadi.
"(Microclimate cooling) is not only about comfort," he said. "The real payoff to the soldier is increased endurance and enhanced performance. The goal is to make the soldier more lethal and survivable."
Several design iterations will need to be completed as technology develops, but perhaps in another 15 years, Masadi sees the day when active microclimate cooling can be carried on the hip, in a container the volume of about one pint.
Natick is part of the U.S. Army Soldier and Biological Chemical Command (SBCCOM). For more information about SBCCOM or the Soldier Systems Center (Natick), please visit our website at http://www.sbccom.army.mil.