basic principles of heat cold n.
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BASIC PRINCIPLES OF HEAT & COLD. How the Body Produces Heat. All food & drinks contain Calories A Calorie is the heat value of food Calories in the body are converted to energy & stored, this conversion process produces heat, which generates our body temp.

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how the body produces heat
How the Body Produces Heat
  • All food & drinks contain Calories
  • A Calorie is the heat value of food
  • Calories in the body are converted to energy & stored, this conversion process produces heat, which generates our body temp.
  • Excess Calories are stored as fat cells
  • Average calorie intake is approx. 2000
calories british thermal units btu
Calories & British Thermal Units (BTU)
  • One calorie is amount of heat required to raise 1 kilogram of water 1 degree C
  • 252 calories equals 1 BTU
  • 1 BTU will raise the temp of 1 lb of water 1 degree F


1 lb H2O heated from 75 to 76 degrees, 1 BTU of heat energy absorbed into the H2O

three ways the body removes heat
Three Ways the Body Removes Heat
  • Convection – Heat flows from a hot surface to a surface (or air) with less heat
  • Radiation – Heat flows from a heat source to an object, does not heat the air
  • Evaporation – as moisture vaporizes, it removes heat from the surface, lowering its temp.
factors that effect body comfort
Factors That Effect Body Comfort
  • Temperature
  • Humidity
  • Air Movement
  • Cool air increases rate of convection, warm air slows it down
  • Cool air lowers temp of surrounding surfaces, increasing heat radiation
  • Warm air raises temp of surrounding surfaces, decreasing radiation
  • Cool air increases rate of evaporation, warm air slow it down
  • Evaporation rate dependant on humidity level of surrounding air & air movement
relative humidity rh
Relative Humidity (RH)
  • 50% RH – air contains half of moisture it is capable of holding
  • Low RH (dry) readily absorbs moisture
  • High RH(Moist) slow down evaporation
  • Human comfort level – 72 – 80 degrees, 35 – 55% humidity
other factors
Other Factors
  • Heat Index – Measurement of discomfort when heat & humidity combine
  • Dew Point – Is the amount of moisture in the air at a given temperature
  • Wind Chill – Measurement of discomfort when cold & wind combined
  • Condensation – Water vapor returned to its liquid state
air movement
Air Movement
  • Evaporation increases – moisture carried away faster
  • Convection increases as layer of warm air around body is moved away
  • Radiation increases as heat on body surface is removed
heat cold
Heat & Cold
  • Heat – Energy of molecules in motion, sensation of warmth or hotness
  • Cold – Feeling of no warmth, removal of an objects original heat
  • Laws of heat & Cold:

(Heat is present in all matter)

    • Sensible heat – any heat that can be felt & measured ie. Heat to cook
    • Latent heat – heat required to cause a change in state, can not be measured
        • Water boils at 212 degrees at sea level (14.7psi)
heat cold1
Heat & Cold
  • Specific Heat – Amount of heat require to raise the temperature of solids, liquids, or gases
  • Heat Flow – Movement of heat from an object of higher temp to one of lower temp