Relative humidity

Relative humidity is the partial pressure of water vapor as a percentage of the saturated vapor pressure at a particular temperature. It is measured directly with a wet and dry bulb thermometer - the difference in temperature of the two bulbs (left) being converted to a percentage with tables.

Direct reading humidity gauges (right) are available but may not be as reliable as the more direct method.

Air conditioning removes water vapor from the air (air con's stream water). Comfort in the laboratory at ISB is improved as much by the removal of water vapor, as by the lowering of temperature, even thought the relative humidity may actually be higher inside.

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