The relative humidity line passing though this point indicates RH of 50%. įind out the values of various parameters at this point.Įxtend the vertical line (constant DB temperature line) from 78o and the diagonal line (constant WB temperature line) from 65oF and get the point of intersection of the two lines, which indicates the condition of the given air.Locate WB temperature of 65oF on the saturation curve scale. On the psychrometric chart locate value 78oF on the DB temperature scale located at the bottom of the chart. We will find out various values from these given values of DB and WB temperatures. Example Showing How to Use Psychrometric ChartĬonsider an example of air where the given values of DB and WB temperature are 78 degrees F and 65 degrees F respectively. If any of the two values from DB, WB, DP temperature and the relative humidity are known, all other values can be easily found from the psychrometric chart, without having to carry out any calculations. They indicate the value in either m3/kg or ft3/lb. The constant specific lines start from the saturation curve and drop down with the slight angle to the vertical lines. From the psychrometric chart we can find out the specific volume of the required air and find the total volume of the required air by multiplying it with the total weight of the air required. The specific volume of air is an important parameter since one has to consider the amount of air to be handled by the cooling coil, cooling fan, etc and accordingly the rating of cooling coil and fan has to be found out. The constant enthalpy line passing through the given value of the WB temperature indicates the enthalpy of the air. To find the value of the enthalpy of the any given air, one should know its WB temperature. The constant enthalpy lines extend from the enthalpy scale down toward the right side of the chart. The enthalpy scale in the psychrometric chart is located outside the main body. The total enthalpy of the air comprises of the sensible heat and the latent heat. Along the saturation curve all the three temperatures, the DB, WB and DP are same. The extreme left curve along the shoe indicates RH of 100% and is also called the saturation curve because the condition of air along this line is fully saturated no matter what the DB and WB temperatures are. The value of RH reduces from left towards right. The different curves of RH indicate different values of humidity measured in percentage.

The RH lines are the curves extending from the lower left to the upper right part of the psychrometric chart.

Lebanon ashrae psychrometric chart