Dry bulb and wet bulb temperature are two measurements used to determine thermal comfort and humidity levels. Here are some key points about each:

Dry Bulb Temperature

• Refers to the ambient air temperature measured using a thermometer that is dry and shielded from direct radiation and moisture.
• An indicator of heat content and is shown along the bottom axis of the psychrometric chart.
• Constant dry bulb temperatures appear as vertical lines in the psychrometric chart.
• The temperature is usually given in degrees Celsius (oC) or degrees Fahrenheit (oF). The SI unit is Kelvin (K) .

Wet Bulb Temperature

• Refers to the temperature of adiabatic saturation, which is the temperature indicated by a moistened thermometer bulb exposed to the air flow.
• Measured using a thermometer with the bulb wrapped in wet muslin. The adiabatic evaporation of water from the thermometer and the cooling effect is indicated by a "wet bulb temperature" lower than the "dry bulb temperature" in the air.
• The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100% relative humidity.
• The wet bulb temperature is the temperature of an object that can be achieved through evaporative cooling.
• The wet bulb temperature is the lowest temperature that may be achieved by evaporative cooling of a water-wetted, ventilated surface.
• The difference between the dry bulb and wet bulb temperature is a measure of the humidity of the air.

In summary, the dry bulb temperature is the ambient air temperature, while the wet bulb temperature takes into consideration evaporation and is always lower than the dry bulb temperature. The difference between the two temperatures is a measure of the humidity of the air.