Due to late entry, I have noted another working on the same concept although our design is more for the Police Officer and probably would not meet the needs for our Military / Defence. Law Enforcement doesn't get the attention that our Military does. I am not stating that this cooling device could not be used on Military but I have not researched rules for Military PPE.
This device is an air cooling system that can be turned on or off, can be used on high or low setting for cooling only. We use rechargeable Li batteries or better than Li dependant on battery pricing. A simple recharging circuit sewn into the outside of the body of the vest can keep the officer cool for hours per one charge. The batteries can be recharged with any power source such as any 12v supply from Police Cruiser or an overnight charge with a charging USB port.
I have listed this entry as individual but I am working with a local Police Officer and another design source web address: www.1-act.com a.k.a. Advanced Cooling Technologies.
Please see pics of battery type and I think we all know what a police officer's bullet protection vest looks like.
Thank you for your time and consideration.