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undamental Series Item :'HVAC Systems: How They Work file:///c~/windows/TEMP/0,2637,1 ~506,OO.h is Heat and Temperature Heat is energy in the form of molecules in motion. As a material becomes warmer, it motion and energy level (temperature) increases, and vice versa. Temp~:rature desc level of heat (energy) with refierence to no heat. Heat is a positive value relative to nc Therefore; warm, hat, cool and cold are comparative terms used to describe higher c temperature levels. The Fahrenheit scale is the standard system of temperature measurement used in tl States. The U.S. is one of the few countries in the world that still. uses this system. N countries use the metric temperature measurement system-the Celsius scale. Howe Fahrenheit and Celsius scales are currently used interchangeably in the U.S. to desc equipment and fundamentals in the heating, ventilating and air conditioning industry. Heat Transfer Heat naturally flows from a higher energy level to a lower energy level. In other word: travels from a warmer material to a cooler material. The unit of measurement used t~ the quantity of heat contained in a material is a British thermal unit (Btu). When there is a temperature difference between two materials, heat transfer will oce temperature difference is the driving force behind heat transfer, i. e., the greater the temperature difference, the greater the heat transfer. The rate o transfer can be described by adding the dimension of time, far example, British them hour (Btu/hr or Btuh). Types of Heat Transfer The three types of heat transfer are conduction, radiation, and convection. Yeur hang cold wall is an example of heat transfer by conduction. A portable electric heater than red-hot is an example of heat transfer by radiation. Heat transfer by convection is when some material that is readily movable such as a steam, and refrigerant moves heat from one location to another. For example, when heated, it rises; this is heat transfer by "natural" convection. "Forced" convection is ~ or pump is used to convey heat in fluids such as air and water. Compare the words " (the action of conveying) and "convey" (to take or carry from one place to another).