Wet Bulb Dew Point Chart

The dew point temperature of air depends upon its mositure content.

Wet bulb dew point chart.

Therefore the change on the chart is down and to the right. It includes a dry bulb thermometer a wet bulb thermometer and a psychrometric chart a graph that plots the relationships between the dry and wet bulb temperature relative humidity and dew point at constant pressure. By definition wet bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. Lines of constant wet bulb temperatures run diagonally from the upper left to the lower right in the psychrometric chart.

If the supply air leaving the system is at 55 f dry bulb and 53 f wet bulb we see from the chart that the dew point is 51 5 f. The knowledge of only two of these values is enough to determine the state of the moist air including the content of water vapor and the sensible and latent energy enthalpy in the air. Dew point temperature tdp. Combining the dry bulb and wet bulb temperature in a psychrometric diagram or mollier chart gives the state of the humid air.

Dew point is expressed as a temperature. The wet bulb temperature wbt is the temperature read by a thermometer covered in water soaked cloth wet bulb thermometer over which air is passed. Looking at the psychrometric chart we see the dew point is 55 f. The key difference between dewpoint and wet bulb temperature is that dewpoint temperature is the temperature to which we should cool the air to saturate the air with water vapor whereas wet bulb temperature is the temperature that we get from a moistened thermometer bulb that is exposed to air flow.

At lower humidity the wet bulb temperature is lower than dry bulb temperature because of evaporative cooling. The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. The following tables calculate dew point and relative humidity based on the observed wet bulb and dry bulb temperatures and the elevation at the site of the observation. Enter the two different temperatures.

This script will determine the relative humidity from the entered dry and wet bulb temperatures data. The coil of the air conditioner is at 45 f so the system will condense water from the air. On the right side of the chart locate the vertical line labeled dew point. Higher the mositure content of the air higher is the dew point temperature.

The dew point lines traverse the chart as horizontal lines. At 100 relative humidity the wet bulb temperature is equal to the air temperature dry bulb temperature. Dew point and wet bulb temperatures are very important in indicating the state of the humid air.