Volume I - Section VII - Glossary of Terms 
Page VII - 1 
7. GLOSSARY OF TERMS 
7.1 Experimental Terms 
Absolute pressure: the sum of the indicated gage pressure plus the atmospheric pressure. 
ACH (air changes per hour): the complete replacement of air inside an area; an office or space 
that has its total air volume replaced in the time period of one hour experiences one air change 
per hour. 
Anemometer: an instrument used to measure air velocities. 
Atmospheric pressure: the pressure exerted upon the earth’s surface by the air because of the 
gravitational attraction of the earth, measured with a barometer. Standard atmospheric pressure at 
sea level is 14.7 pounds per square inch (psi). 
Barometer: an instrument for measuring atmospheric pressure. 
BTU (British thermal unit): the amount of heat required to raise or lower the temperature of one 
pound of water 1 °F. 1 BTU = 1,055 Joules. 
Calibration: determining or correcting the error of an existing scale. 
Calorie: the amount of heat needed to raise the temperature of 1 g of water by 1 °C, from 14.5 to 
15.5 °C. A kilocalorie (kilogram-calorie or large calorie) is 1,000 calories. 
Calorimeter: the measurement of heat. Heat is one of the most conveniently handled forms of 
energy. Calorimetry is used to estimate nutritional requirements of humans and farm livestock 
and to evaluate different foods. It is also a powerful research tool used to study fundamental 
nutritional and physiological life processes, and to evaluate stresses imposed by abnormal 
environments. It is used in clinics as a diagnostic tool for the investigation of metabolic 
disorders. 
Capture hood: an instrument that takes the air of a supply, return, or exhaust terminal and guides 
it over a flow-measuring device. It measures airflow in cubic feet per minute. 
Chromatography: a separation method that relies on differences in partitioning behavior between 
a flowing mobile phase and a stationary phase to separate the components in a mixture. 
CFM (cubic feet per minute): a unit of measurement representing the volume or rate of airflow. 
