The purpose of a shelter is to help your body maintain its normal temperature. If you understand these concepts, you can use your available supplies and resources to make effective, life saving shelters for the given circumstances.
Gaining & Losing Heat
In cold temperature situations, you usually want to retain and gain heat; whereas in warm temperatures, you want to promote heat loss or at least not increase your temperature. Remember that heat
always travels from warmer areas to colder areas.
Conduction: Heat transfer through direct contact, such as bare feet on a cold floor. Ice packs use conduction to pull heat away from burns or sore muscles. Prevent conduction from your body in cold temperatures by wearing socks or when camping by making an insulation barrier between your sleeping area and the ground.
Convection: Heat transfer through air and liquid currents. Wind chill is a good example of convection. When the wind blows, it feels colder than the ambient temperature because the moving air is pulling heat away from your body. You use convection in warmer temperatures to cool down when you use a fan. Prevent convection in colder temperatures by wearing clothing or using shelters that block wind.
Radiation: Heat transfer through emission. A car’s radiator radiates heat to keep the engine from overheating. You experience radiation from the sun every day. In the same way you feel warmth from a campfire without having to touch the flame. You can even feel your own body radiating heat if you put your hand just above an area of skin. Prevent radiation heat loss in cold temperatures by using insulated clothing and shelters, and by using shelters that reflect your heat back to you.
Metabolism: Converting food into energy and heat. Food is your body’s source of fuel. Help your body regulate your temperature in cold weather by eating high calorie foods like energy bars, trail mix & fruit snacks. Water is an important part in the metabolism process, be sure to stay properly hydrated in warm and cold situations.
Evaporation: Heat transfer through converting liquid to gas. When your body sweats, the sweat evaporates, or changes from a liquid into a gas, which requires heat energy. This helps keep you cool. When you get out of a pool, even on a hot day, you feel cold until you dry off because of evaporation. Promote evaporation in hot temperatures by staying hydrated. In extreme situations you can even wear wet clothing. Prevent heat loss in the cold by staying dry, minimizing sweating, and by wearing artificial fiber clothing, which wicks moisture away next to your skin. In humid climates, regulating temperature through evaporation is not effective.
Respiration: Heat loss through breathing. You breathe out warm, moist air. You can’t stop breathing, so in cold temperature situations, wear a mask or scarf that covers your mouth & nose. Breathe through your nose to warm & moisten the air before it gets to your lungs, and to retain as much heat and moisture when you breathe out.
You could also say friction generates heat, like when you rub your hands together, but heat generation is very small and can be damaging to skin tissues in extreme situations like frost bite.
Preventing or Promoting Heat Transfer
After learning how your body gains or losses heat, it is important to learn how to prevent or promote those heat losses and gains.
Insulation: Trapping air to stop or slow the transfer of heat. Air is not a good heat conductor, so it works well as a barrier. Multiple small layers of clothing trap air for insulation and allow you to regulate to a comfortable temperature by adding or removing layers as needed. Insulation prevents conduction and radiation.
Reflection: Bouncing heat back to or away from. Heat, also known as infrared light, can be deflected and directed just like a flashlight beam and a mirror. Reflect your radiated body heat back to you in
cold or reflect solar heat away from you in hot weather by using Mylar blankets, sleeping bags, or tents. Be sure to have an insulating layer of clothing or cloth between your skin & the Mylar, otherwise it turns from reflecting your heat back, to conducting your heat away.
Protection: Keeping out the heat transferring elements like sun, water, wind, and physical dangers. Maintain your body temperature by protecting yourself from the elements. Stay dry and warm by wearing an outer layer that sheds water. Shelters that block wind and/or provide shade from the hot sun are also vital to survival in extreme temperatures.
Moisture Wicking: Pulling water away from the body. Artificial fiber clothing or shelters like polyester, fleece, and nylon or a non-plant fiber like wool can actually wick, or pull moisture, away from your skin. This is essential in cold weather. You do not want evaporation happening or ice forming next to your skin when you are cold. DO NOT wear cotton in cold weather situations since cotton holds moisture and causes evaporation next to your skin.