It is computed by multiplying the amount of moisture in the air at a given temperature, dividing by the maxi- mum amount of moisture the air could contain at that same temperature, and then multiplying the quotient by 100. Relative humidity can be found by subtracting the temperature on the wet-bulb thermometer from the temperature on the dry-bulb thermometer and using a relative humidity chart.Ī sling psychrometer can be used to find relative humidity, which is expressed as a percentage. How do you calculate RH from dry and wet bulbs? It can be very helpful in troubleshooting and finding solutions to greenhouse or livestock building environmental problems. Knowing both the dry-bulb temperature (DBT) and wet-bulb temperature (WBT), one can determine the relative humidity (RH) from the psychrometric chart appropriate to the air pressure.Ī psychrometric chart presents physical and thermal properties of moist air in a graphical form. What is DBT and WBT in psychrometric chart? It accomplishes this by comparing the difference in temperature between a dry thermometer bulb and a wet thermometer bulb that has lost some of its moisture through evaporation. How does a psychrometer work?Ī psychrometer is a device used to measure the humidity of air.

Input parameters can be either wet bulb, dry bulb, relative humidity, humidity ratio, or enthalpy. 2 of 5 input parameters needed to calculate a total of 12 psychrometric properties. Humid air properties via the ASHRAE formulation. The uppermost curved line on the chart shows the saturation curve when the relative humidity is 100 percent. Main features: - An intuitive user interface. Although formulae to calculate the psychrometric properties of air are widely available. Check the vertical or Y axis for the humidity ratio. psychrometric chart excel - HVAC/R and Solar Energy Engineering. To read a psychometric chart, find the dry bulb temperature on the horizontal or X axis.

Calculate dry-bulb vapor pressure: e(dry) = 6.112*EXP.Convert RH% from percent to decimal value: rh = (RH%/100%).

Psychrometric chart excel