BTU's and Calories

Heat is measured in British Thermal Units (BTUs) and calories.
- BTU - amount of heat energy required to raise one pound of water one degree Fahrenheit.
- Calorie - amount of heat energy required to raise one gram of water one degree Celsius.

HEAT TRANSFER







An air conditioning system's efficiency is based on how well it moves heat. Heat always travels from warm material to cold. The reverse is never true. For example, if a hot cup of coffee is left standing. it will cool off, while a cold soda will get warm. The heat from the warm coffee moves to the cooler surrounding air. The heat from the surrounding air moves to the cooler soda, until a balance is reached.

There are three processes of heat transfer:

- Conduction (heat travels along a material).







For example, if a spoon is left in a pot of boiling water, the spoon handle will get hot, even though the handle is outside the pot. Heat is conducted along the spoon handle.

- Convection (heat flows in a stream of air or liquid that is hotter than what it flows over, around, or through).







For example, a blow dryer generates a stream of heated air to dry hair. The hair is heated by convection.


- Radiation (heat moves from a heat source to an object by means of heat rays).







For example, you feel heat from a fireplace, even though air is traveling past you and going up the chimney. You are warmed by radiated heat.