Wet Bulb Calculator

Welcome to the wet-bulb calculator, a tool that will let you calculate the wet-bulb temperature by inputting the air temperature and relative humidity. If you click on the advanced mode, you can calculate other parameters such as:

• The globe thermometer temperature;
• The Wet-Bulb Globe Temperature (outdoor); and
• Wet-Bulb Globe Temperature (indoor).

If you still don't know what wet-bulb temperature is, keep reading to learn what it is and how to calculate it.

The relative humidity is a quantity needed to calculate other important properties such as air density. One way of measuring relative humidity is passing air through an adiabatic saturator, a device in which the air exits at 100% relative humidity (saturated air). This device has the advantage that it only requires measuring temperature and pressure at the inlet and exit, but at the same time requires a long channel to achieve the saturation condition.

The wetbulb temperature arises as an alternative to the adiabatic saturation process for measuring relative humidity. We can define wet-bulb temperature as the lowest temperature a portion of air can reach by evaporative cooling. We measure it with a special thermometer whose bulb has a ventilated cotton wick that covers it with saturated water. The water of the wick starts to evaporate and transfer heat to that air, while at the same time, it receives heat from the air. The web-bulb temperature is the temperature measured by the thermometer when water-to-air and air-to-water heat transfers are the same (stable temperature).

The interesting part is we can use the wet-bulb temperature as a replacement for the exit temperature of the adiabatic saturator, as long as the pressure is at the atmospheric level. This way, we can simulate the adiabatic saturator behavior using a thermometer and a wet wick.

An improved version of the wet-bulb thermometer is the sling psychrometer. This device has the functionality of rotating its wick, intending to increase heat transfer and measurement speed.

Currently, thanks to advances in electronics, more sophisticated devices are available to measure temperature in a direct, fast, and reliable way.

To calculate the wet-bub temperature, our wet bulb calculator uses the following equation:

T_w = T × arctan[0.151977(RH% + 8.313659)^1/2]
+ arctan(T + RH%) - arctan(RH% - 1.676331)
+ 0.00391838(RH%)^3/2arctan(0.023101RH%) - 4.686035

where:

• T — Air temperature, in °C;
• RH% — relative humidity, expressed as a percentage; and
• T_w — Wetbulb temperature, in °C.