microclimate cooling for military vehicle crews

© 2008 W L Gore & Associates GORE® and designs are registered trade marks of W L Gore & Associates

Microclimate Cooling for Military Vehicle Crews

SAFE Europe – March 31st 2010Stephen Hunter – Product Specialist


Established 1958Operations worldwideFamous GORE-TEX® andWINDSTOPPER® products4 divisions– Electronics– Medical– Industrial– Fabrics

Technically Oriented FabricsGore specializes in the development of highperformance protective apparel for the harshand demanding environments routinelyencountered by military forces, fire servicesand outdoor workers throughout the world.

W. L. Gore & Associates


Heat Stress – A Hot Topic

• Numerous countries havetroops operating in very hotclimates.

• Risk of disablement and evendeath due to heat stress is veryreal.

• Politically high profile.• Recognised need for an

effective personal coolingsolution for foot mounted troops.

• Vehicles represent a particularlysevere problem.


Heat Stress and Core Temperature

As exercise and exposure to heat increases, heart rate increases, blood flow toskin increases, skin temperature increases, body core temperature goes up.

Hypothermia HyperthermiaNormalHeat

Stress

34 C 36-37 C 39 C


Heat Stress Habitability and Performance

Def Std 0035


Testing to quantify the Effects of Heat Stress

• Goalunderstand the influence of thermal stress onvigilance

• Conductionauditory signal detection while walking on atreadmill in different temperature conditions

• FindingIncreasing body temperature impairs attentionand vigilance

Heat Stress Diminishes Vigilance

–Source: From et al, J. o. Occ. Med., Vol. 35, No 7, 1993, p 271 ff

0

10

20

30

40

50

37 38 39 40

Core Body Temperature [ C]

Missed signals [%]


Heat Stress Affects Performance

Study• Goal

Find out why there are many morecrashes in summer

• Investigation of temperaturedistribution of days with and withoutaccidents and near miss occurrences

• FindingHigher heat stress on hot dayssignificantly increases the chance ofsevere pilot errors.

0

1

2

3

4

5

6

7

24°Candlower

25 to29°C

30 to34°C

35°Candhigher

Source: Froom et al, J. o. Occ. Med., Vol. 35, No 7, 1993, p 271 ff

Heat stressed helicopter pilots are more likely to crash


Conditions inside an Armoured Vehicle

Crew-spaceTemperature

Outside air temperature(environmental conduction)

Vehicle Engine

SolarRadiated Heating

Vehicle ElectronicSystems

Crew


Interior Temperatures in AFVsVehicle Type Location Ambient temp ( C) Interior Temperature

Degrees above ambient(Average) (Max)

M114 ARV Driver 33 - 45 7.2 16Crew 7.8 16.7

M113 APC Crew 40 - 42 5.5 11LVTPX 12 Driver 35 - 43 3.3 7.8

Commander 5.5 11Cargo 6.6 8.3

M109 SPH Crew 37 – 44 6.1 8.9Driver 7.8 11

M60 tank Turret 32 – 45 5.0 11

Average temperature range 32 – 45.5Average temperature above ambient +7.3 +13.2

Potential temperatures in vehicle 39.3 C – 58.7 CData taken from “Medical Aspects of Harsh Environments” Vol. 1 (2001) Ralf GoldmanChapter 1 “Introduction to Heat-Related Problems in Military Operations”


The Cost of Traditional Cooling

• Goal is to avoid crew core temperature going above 37.5 C• Traditional approach is to cool the whole crew space with an

Environmental Control System.• This has a direct impact on vehicle design and performance.

Powerrequired tocool crewspace

Environmental temperature

Weight,spaceand costfor ECS

Range, speed &manoeuvrability ofvehicle.

Hatches open or closed ???


Cooling Strategy Efficiency Trade-off

Efficiency

PowerRequired

MACRO-CLIMATE MICRO-CLIMATE

Def Std 0035Ambient temp

of 21 C

(Individual Cooling Vest)Spot CoolingDirected Air

Crew Core TemperatureMaintained below 37.5C


Individual Cooling Solutions

Evaporativeor

Forced Air

LiquidCirculation

Phase ChangeICE / GELL

Wicking Materials


Depends onambience

conditions andclothing

Ideal Set point 37°C

Basicmetabolic heat

production

Dry / Conductive /Convective heat

loss

Activity increases set point

Metabolic heatproduction due toactivity

~30°C

~41°C

Core BodyTemperature

Depends onbody weight

~80W for75kg

Body Thermal Control Process

Evaporative heat loss.Sweating mechanismdrives missing heat loss


Skin Surface

Evaporating sweat

Heatloss

Heat loss through Sweating


Advantages of a forced air system

• Facilitates the Body’s natural thermal control process –Sweat evaporation

• Utilises systems already present in the vehicle – ECS• If not, the power, weight, space impact is least• Practical in tethered and untethered format• Very low logistic burden


The Gore Active Cooling Concept

EFFICIENT COMFORTABLE SAFE

• Active Cooling Vest worn under body armourclose to skin (typically over UBACS).

• The vest provides an efficient way ofintroducing air to the skin surface

• Cooling is achieved by removing saturatedair, and enhancing the rate of sweatevaporation, at skin level.


• Garment is a 2 layer construction.– Both layers have ‘Bump’ spacers to

create air paths.– Outer layer is impermeable.– Inner layer is controlled

permeability.• Air, pumped between the layers passes

through inner permeable layer towearers torso.

• Sweat evaporation facilitated byremoving saturated air.

• Blood cooled at skin level circulatesand helps regulate core temperature.

CoolSkin

Saturated Air out

Dry Air in

Structure and Operating Principle

HotSkin


Cooling Air Supply

Untethered SystemSelf contained rechargeable Blowers

Tethered System – Air from vehicle ECS


Designed for fixed crew positions.(Predominantly in vehicle).

Operates with air from vehicle ECS.

Tethered Variant


Cooling Performance – Vehicle Crew Version

This performance information was derived from independentlyconducted habitability testing for the Titan and Trojan (UKMOD armoured engineering vehicles).

The habitability requirement was considered failed in two crewpositions even without IPE.With the Gore Active Cooling Vest worn, all crew positionspassed, with full IPE being worn in both A1 and B2 conditions.A test with full IPE and no cooling vest was not conducted asthe risk to participants was deemed too high.

No cooling vest, no IPE

With cooling vest and full IPE


Untethered Variant.

For dismounted troops or non-fixed crew positions.Self contained for out of vehicle use.

Can charge in vehicle.


• Based on Def std 0035– 45 C (10% RH), UK BDU + CBA + 19kg

load, 5km/hr on treadmill• Demonstrated stabilisation of core temperature

and doubling of work-time (reduction in restperiods) @ 6hrs in conditions

• Cooling Power and distribution maintainedunder compressive loading

• Excellent distribution of cooling effect

Cooling Performance - Foot Mounted Version

Skin temperature in different body zones comparedwith non cooled


Longer Work Periods – Shorter Rest Periods

61

38.5

36.0

37.0

38.0

60 120 180 240 300

71

38.5

36.0

37.0

38.0

60 120 180 240 300

No Vest

With Vest

22

16

40

2336

14

19

30

3640

17

25

20

25

Work 120 mins

Rest 134 mins

Work 161 mins

Rest 80 mins


Main Garment Features

Integrated Dual Blowers• Convenient side location• Low profile• Dust Filtration• 6 hour duration• Very quiet in operation

Soft, Light Materials

One Size Fits All

Left Hand/ Right HandConfiguration

Easy connection to vehicle ECSSnap in and easy release hose connectors

Comfortable to wear

Non burn or meltAir transport layers


• Tethered– Habitation Trials by Qinetiq (2007)– A1 A2 A3 and B2 conditions– System met the requirements– Failure with no vest

• Untethered– Portsmouth University dept of Sports

Physiology (July 2007)– Met concept of doubling workload @ 6hrs

in conditions– Qinetiq March 2010

• Field trials conducted in Turkey,Morocco and Iraq.

• Extensive in house laboratorytesting.

Validation and Testing


Role Compatibility


The Challenges of System Evaluation

• Physiological effectiveness is proven• Several trials have now demonstrated core temperature control

under body armour using ambient air temperatures up to 46 C• User perceptions are more challenging

– It’s an extra layer– Does it add more thermal burden when off?– Cooling “sensation” can be subjective

• Body reacts to change• Normalisation is unremarkable once achieved

– Side by side comparison not easy to make• Education, expectation and briefing is key.


Cool The Man Directly – With Air !!

Vehicle Benefits• Save power• Save weight• Save space• Gain range• Gain manoeuvrability

Crew Benefits• Control core temp• Better performance

– Situational awareness– Reaction Time– Cognitive ability

• More comfortable


SAFETY

COMFORT

EFFICIENCY

System now specified as part of Titan and Trojan ECSIn trial and evaluation phase in several countries

Current Status

microclimate cooling for military vehicle crews

Documents