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Psychrometric Calculator

 
       
 

 
 


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WebPsycH®
Online Calculator 
Compliments of Linric

Note:  Calculations are approximations using generally accepted algorithms.  Users shall validate the accuracy of any values for their specific purposes.  
 

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Calculator Key

oF db = Dry Bulb Temperature
oF wb = Wet Bulb Temperature
oF dp = Dew Point Temperature
%RH = Relative Humidity
Btu/lb* = Enthalpy
gr/lb* = Humidity Ratio
Alt in Ft = Altitude
in Hg = Pressure-inches of Mercury
psi = Pressure-pounds per square inch
ft3/lb* = Specific Volume
"Hg VP = Vapor Pressure
PPMw = Parts per Million by weight
PPMv = Parts per Million by volume
gr/ft3 = Absolute Humidity
*Computed on dry air basis  
 
 
Example:
Determine the moisture properties of air that has a temperature of 80oF and a relative humidity of 50% RH at 597 feet above sea level (Dallas/Fort Worth Airport).

Step 1:
Set Input Units by using drop-down menus:
Input Menu 1, select oF db (Dry Bulb Temperature)
Input Menu 2, select %RH (Relative Humidity)
Input Menu 3, select Alt in Feet (Altitude)

Set Output Units by using drop-down menus:
Output Menu 1, select oF dp (Dew Point Temperature)
Output Menu 2, select gr/lb (Humidity Ratio)
Output Menu 3, select gr/ft3 (Absolute Humidity)
Output Menu 4, select ft3/lb (Specific Volume)

Step 2:
Input Values in corresponding input boxes:
Enter 80 as the Dry Bulb Temperature (oF db)
Enter 50 as the Relative Humidity (%RH)
Enter 597 as the Altitude (Alt in Feet)

Step 3:
Click Calculate Button
 

  

Example Data

Input
80  oF db
50  %RH
597  Alt in Ft

Output
Dew Point = 59.71
Humidity Ratio = 78.45
Absolute Humidity = 5.54
Specific Volume = 14.16

 
 
What the example results mean...
Our 80oF/50%RH air has a dew point near 60oF.  In other words, if we cool this air to 60oF we will reach 100%RH and moisture will begin to condense out of the air.

Our 80oF/50%RH air contains 78.45 grains of moisture per pound of air - the Humidity Ratio.  (There are 7,000 grains of moisture per pound so we have approximately 0.011 pounds of moisture per pound of air.)

Absolute Humidity is determined on a volumetric basis; therefore, our 80oF/50%RH air contains 5.54 grains of moisture per cubic foot of air.

One pound of our 80oF/50%RH air takes up 14.16 cubic feet - the Specific Volume.

If we took all of the airborne moisture from a room measuring 10' x 10' x 10' (1,000 cubic feet), we could fill a 12 ounce glass!
 
     
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