A psychrometric calculator is an engineering device used to calculate the properties of a gas-vapor mixture, and most often is employed to analyze water vapor in surrounding air. Humidity, or the amount of water that is suspended in air as a vapor, has a significant effect on both human comfort levels as it compares to the current temperature, and on weather systems in the field of meteorology. This makes calculations of humidity states, such as relative humidity, absolute humidity, and dew point, important output values for a psychrometric calculator.
Input values for a psychrometric calculator are usually Dry Bulb temperature, relative humidity, and altitude, which affects air pressure readings. Dry Bulb temperature is a measurement of air temperature where no exposure to moisture or radiation is allowed to affect the temperature measurement. Relative humidity is a percentage calculation of how much water vapor a certain volume of air actually holds compared to the maximum amount it could hold, known as saturation vapor pressure. Dew point is the temperature that this air must be cooled to at a predetermined pressure, in order for this saturation point to occur and dew to form out of the air onto plants and other objects in nature.
The usual output values of dew point temperature and humidity values for a psychometric calculator are often used in the design of heating, ventilation, and air conditioning (HVAC) systems in homes and businesses, as well as in meteorology, but that is not the only use for psychrometrics. The first psychrometric chart was created in 1904 by Willis H. Carrier, an American engineer credited with the invention of modern air-conditioning principles. Since then the data produced by psychrometric charts and various versions of psychrometric calculator software have been applied to fields as diverse as agriculture, aeronautics, food packaging, and the pharmaceutical industry.
Before the advent of computers, psychrometric chart calculations required slide rules and tables of logarithms to account for ideal-gas law, since the actual properties of any given volume of air vary significantly and require some level of standardization. Chart output results for these calculations seemed very complex and daunting to young engineers. By the 21st century, however, the psychrometric calculator was largely a computer program, which incorporated principles of ideal-gas algorithms to produce 99% accuracy ratings in output values.
As technology has progressed, computer-based psychrometric calculator software has now been designed in a way that it can be downloaded from various online vendors and run on laptop computers. Handheld electronic devices can now also install applications to perform these calculations. This makes humidity and dew point calculations much easier and immediate for engineers and other specialists in the field.