The main purpose of commercial HVAC (heating, ventilating, and air conditioning) systems is to provide the people working inside buildings with “conditioned” air so that they will have a comfortable and safe work environment. “Conditioned” air means that air is clean and odor-free, and the temperature, humidity, and movement of the air are within certain comfort ranges.
Many factors affect the way people respond to their work environment. Air quality is one of these factors. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has established standards which outline air quality for indoor comfort conditions that are acceptable to 80% or more of a commercial building’s occupants. Generally, these indoor comfort conditions, sometimes called the “comfort zone,” are between 68 degrees F and 75 degrees F for winter and 73 degrees F to 79 degrees F during the summer. Both these temperature ranges are for room air at approximately 50% relative humidity and moving at velocity of 30 feet per minute or slower.
Heat and Temperature
Heat is energy in the form of molecules in motion. As a material becomes warmer, its molecular motion and energy level (temperature) increases, and vice versa. Temperature describes the level of heat (energy) with reference to no heat. Heat is a positive value relative to no heat. Therefore, warm, hot, cool and cold are comparative terms used to describe higher or lower temperature levels.
The Fahrenheit scale is the standard system of temperature measurement used in the United States. The U.S. is one of the few countries in the world that still uses this system. Most countries use the metric temperature measurement system-the Celsius scale. However, the Fahrenheit and Celsius scales are currently used interchangeably in the U.S. to describe 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 words, heat travels from a warmer material to a cooler material. The unit of measurement used to describe 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 occur. In fact, temperature difference is the driving force behind heat transfer, i. e., the greater the temperature difference, the greater the heat transfer. The rate of heat transfer can be described by adding the dimension of time, for example, British thermal units per hour (Btu/hr or Btuh).
Source: www.edcmag.com; November, 2000.
