HVAC GLOSSARY - W

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W: (Watt) A watt is a unit of electricity. A unit of measure of electric power at a point in time, as capacity or demand. It is the rate of energy transfer equivalent to 1 ampere flowing under a pressure of 1 volt at unity power factor. One watt of power maintained over time is equal to one joule per second. Some Christmas tree lights use one watt. The watt is named after Scottish inventor James Watt and is capitalized when shortened to w and used with other abbreviations, as in kWh.

Water vapor: Water vapor can be treated as a gas. At a particular temperature air for example can only hold so much water vapor. The higher the temperature the more water vapor it can hold. When saturated the relative humidity would be 100 % RH, so relative humidity describes how close to saturation the air is. It is important to remember that in a process with a high relative humidity a small drop in temperature will cause the humidity to rise and the environment to saturate. Rapid temperature changes in an environmental chamber for example could also cause condensation.

Watt-Hour: (W-hr) One watt of power expended for one hour. An electrical energy unit of measure equal to 1 watt of power supplied to, or taken from, an electric circuit steadily for 1 hour. One thousandth of a kilowatt-hour.

WB: Wet Bulb.

WC: (Water Column) Common measure of air pressure used in HVAC systems.

Weather Stripping: Specially designed strips, seals and gaskets installed around doors and windows to limit air leakage.

Wet Bulb Temperature: The temperature at which water, by evaporating into air, can bring the air to saturation at the same temperature. Wet-bulb temperature is measured by a wet-bulb psychrometer. Traditionally this was the temperature indicated by a thermometer whose bulb is wrapped in a wet sheath. The wet bulb temperature and the dry bulb temperature (i.e., air temperature) would then be used to calculate relative humidity or dewpoint. Alternatively charts or tables can be used.

Whole House Fan: A system capable of cooling a house by exhausting a large volume of warm air when the outside air is cool.