| A | B |
|---|
| Psychrometrics | The study of air and its properties. |
| Relative humidity (RH) | The ratio of the amount of moisture present in a given sample of air to the amount it can hold at saturation. Relative humidity is expressed as a percentage. |
| Revolutions per minute (rpm) | The speed at which the shaft of an air-moving device is rotating. |
| Sheet metal saddle | A sling-like device that cradles insulated duct from underneath. |
| SMACNA | Sheet Metal and Air Conditioning Contractors National Association. |
| Static pressure (s.p.) | The pressure exerted uniformly in all directions within a duct system, as measured in in. w.c. |
| Total pressure | The sum of the static pressure and the velocity pressure in an air duct. It is the pressure produced by the fan or blower. |
| Velocity | How fast air is moving. The rate of airflow usually measured in feet per minute. |
| Velocity pressure | The pressure in a duct due to the movement of the air. It is the difference between the total pressure and the static pressure in w.c. |
| Venturi | A ring or panel surrounding the blades on a propeller fan; used to improve fan performance. |
| Volume | The amount of air in cubic feet flowing past a point in one minute (cfm). |
| Wet-bulb temperature | Temperature taken with a thermometer that has a wick wrapped around its sensing bulb that is saturated with clean, distilled water before taking a reading. The reading from a wet-bulb thermometer, through evaporation of the distilled water, takes into account the moisture content of the air. It reflects the total heat content of the air. |
