Wine cellar cooling units often describe the “RH”, or Relative Humidity, that their products will maintain inside of a wine cellar. Relative Humidity is an often misunderstood concept, along its counterpart Absolute Humidity (AH).
According to Wikipedia, Absolute Humidity can be described thusly:
Absolute humidity is the quantity of water in a particular volume of air. The most common units are grams per cubic meter, although any mass unit and any volume unit could be used. Pounds per cubic foot is common in the U.S., and occasionally even other units mixing the Imperial and metric systems are used.
If all the water in one cubic meter of air were condensed into a container, the container could be weighed to determine absolute humidity. The amount of vapor in that cube of air is the absolute humidity of that cubic meter of air.
Relative humidity is defined as the ratio of the partial pressure of water vapor (in a gaseous mixture of air and water vapor) to the saturated vapor pressure of water at a given temperature. Relative humidity is expressed as a percentage.
Therefore in a wine cellar, RH is determined by measuring the content of the water vapor in the air at the specific temperature of the wine cellar (or the amount of humidity relative to the room’s temperature). Relative humidity is often mentioned in weather forecasts and reports, as it is an indicator of the likelihood of precipitation, dew, or fog. In hot summer weather, it also increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin as the relative humidity rises. For example, if it was 80 degrees, with a relative humidity of approximately 75%, it would feel about 84 degrees.
Remember that your wine cellar should remain a stable 55 degrees with RH of 60%-70%. Some cellar cooling units allow you to dial RH in manually and let the unit do the rest. Those without the newer humidity controls can put a hygrometer in the cellar to determine the RH, and then tweak the percentage up or down using the cooling unit on its own or in conjunction with an active wine cellar humidifier that introduces moisture into the air.
Questions about humidity in wine cellars? Let us know by calling 1-888-373-6057.