Home' Army Acquisition Logistics and Technology Magazine : Army ALT April-June 2011 Contents Traditional MCC approaches involve
constant skin cooling with liquids at
low temperatures and high flow rates.
As a result, MCC power, size, and
weight requirements are large. A longer-
term solution was needed that increased
the efficiency of heat transfer from the
human body to the MCC system.
Scientists at the U.S. Army Research
Institute of Environmental Medicine,
with the help of engineers at the Natick
Soldier Research, Development, and
Engineering Center (NSRDEC),
discovered that over-cooling the skin
can actually slow heat loss, while under-
cooling the skin results in greater strain
on the heart.
Both problems were minimized by
allowing skin temperature to fluctuate
narrowly---in other words, using skin
temperature itself to automate cooling.
The idea and the system for
intermittently cooling the skin, rather
than cooling it continuously, were
conceived as a way to prevent the skin
from constricting. The body constricts
vessels in the skin to conserve heat
when cold, and dilates vessels to expel
heat when hot.
Although significant cooling can still
occur when the skin is constricted (such
as when we fall into ice water), it made
sense that the MCC garment would
become less efficient at removing body
heat if the skin were over-cooled.
Experimentation determined that the
choice of intermittent cooling paradigm
did not seem to matter so long as skin
temperature was kept within a nar-
row range (33-35 degrees centigrade).
Lower skin temperatures offered only a
small cooling advantage, while warmer
skin temperatures drastically increased
strain on the heart.
Using skin temperature feedback to
control MCC made the most sense; the
research team determined that a Skin
Temperature Feedback Cooler (STFC)
reduced MCC power requirements by
more than 40 percent.
A patent was awarded Nov. 23, 2010,
for body temperature regulation using
skin temperature feedback, as an MCC
methodology for maximizing heat
flux, minimizing physiological strain,
and conserving battery power. Sensors
within an MCC garment signal the
need to provide or withdraw cooling
based on an optimal skin temperature
range, as determined empirically from
the laboratory experiments. Studies
demonstrated that with this approach,
heat extraction is optimized (similar to
constant cooling), but power consump-
tion is reduced by 40-50 percent.
Temperature and Power
With STFC, application or withdrawal
of cooling is determined automatically
by skin temperature sensors.
Over-cooling the skin (to less than
33 degrees centigrade) results in body
heat conservation and inefficient
use of MCC power. Under-cooling
the skin, allowing it to heat to more
than 35 degrees centigrade, increases
cardiovascular strain because of
increased skin blood flow and skin
blood volume. When STFC is used,
cooling is automatically turned on
or off when these thresholds have
been reached. Compared with the
traditional constant-cooling approach,
STFC removes body heat and reduces
STFC also requires 40 percent less
power, which could reduce the size
and weight of batteries carried by dis-
mounted Soldiers. The net result is that
STFC feedback may allow for expan-
sion and integration of personal cooling
systems for dismounted or mounted
Soldiers. In addition, STFC improves
comfort when compared with tradi-
tional systems. The initial research was
funded as an Independent Laboratory
In-House Research project in 1999
and then funded by a grant from the
Defense Threat Reduction Agency. All
of these findings have been published in
peer-reviewed scientific journals.
The application and integration of this
MCC method will decrease the size
and weight of future MCC systems
and make possible effective MCC for
Soldiers mobilized on foot.
The technology is both evolutionary
The idea and the system for intermittently cooling
the skin, rather than cooling it continuously, were
conceived as a way to prevent the skin from constricting.
The technology is both evolutionary and revolutionary---
evolutionary because it applies existing biomedical knowledge
in a new way, and revolutionary because it heralds the
development of new cooling vests that can sense temperature
and deliver cooling to specific body areas.
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