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Humidity Spreadsheet
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Relative humidity is the % of moisture vapor in the air relative to the saturation pressure or the maximum amount of vapor that can be present in the air. 100% Relative Humidity implies that the air is entirely saturated with water. Humidity is a function of temperature for as the temperature increases, the saturation pressure increases and the maximum amount of water that can be present in the air increases. For Example, there is twice as much water vapor in the air at 80% humidity, 80 degrees, than at 80% humidity, 60 degrees, while there is very little water present in the air even at 100% humidity at temperatures below 50 degrees.
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Partial Pressure due to Relative Humidity or Vapor Pressure (PSI)
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Relative Humidity
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Temp (F)Temp (C)20%30%40%50%60%70%80%90%PsatPsat(kPa)
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404.40.020.040.050.060.070.090.100.110.1220.836
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457.20.030.040.060.070.090.100.120.130.1481.016
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5010.00.040.050.070.090.110.130.140.160.1791.228
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5512.80.040.060.090.110.130.150.170.190.2151.478
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6015.60.050.080.100.130.150.180.210.230.2581.772
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6518.30.060.090.120.150.180.210.240.280.3062.103
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7021.10.070.110.150.180.220.250.290.330.3642.502
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7523.90.090.130.170.220.260.300.350.390.4322.966
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8026.70.100.150.200.250.310.360.410.460.5103.503
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8529.40.120.180.240.300.360.420.480.540.5974.099
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9032.20.140.210.280.350.420.490.560.630.7004.809
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9535.00.160.250.330.410.490.570.650.740.8185.623
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10037.80.190.290.380.480.570.670.760.860.9546.553
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10540.60.220.330.440.550.660.780.891.001.1087.615
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11043.30.260.380.510.640.770.891.021.151.2778.776
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Note:
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The fields highlighed in yellow are designed for the user to enter information. Changing other fields may corrupt the spreadsheet.
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Dry Air is 20.9% oxygen. Humidity in the air dilutes the other gases present (Mostly Nitrogen and Oxygen).
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How to use this spreadsheet:
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Note the Temperature, Relative Humidity and Ambient Pressure.
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Use the above table to determine the Partial Pressure due to Humidity, also called vapor pressure.
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Input the Partial Pressure due to Humidity and Ambient Pressure into the fields below.
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This Spreadsheet will calculate the percent of Oxygen present in the air and the value you should calibrate your Nitrox Controller/Oxygen Analyzer to.
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Alternately you can determine the vapor pressure of water below using the Clausius-Clapeyron Equation (table is more accurate).
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Clausius-Clapeyron Equation
Convert temp in Celsius to Farenheit
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Temp (F) Relative Humidity %Vapor Pressure (PSI)Temp (C) Temp (F)
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8080%0.472577
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You can use the functions below to convert pressure in kPa or mmHg into PSI
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Ambient Pressure (kPa)Ambient Pressure (PSI) Ambient Pressure (mmHg)Ambient Pressure (PSI)
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101.014.70 76014.70
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Controller Reading Configuration Settings
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Partial Pressure due to Humidity (PSI)Ambient Pressure (PSI)Actual Oxygen Concentration in Humid Air (in %)Calibration Setting (in %)Currently Displayed Oxygen %Current
IN2 (CTS)		Suggested IN2 (CTS)
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0.5414.7020.1320.7521.0060006073
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Desired Nitrox Mix (in %) % of Flow thru Stik from Oxygen TankWater Concentration Factor
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36.019.091.0306
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Your air compressor will remove the water vapor present in the Nitrox mix and therefore concentrate the remaining gasses. By callibrating your Nitrox Controller/Oxygen Analyzer to the Calibration Setting, you will account for this. You should calibrate your Nitrox Controller/Oxygen Analyzer to indicate the Calibration Setting oxygen percentage when the air compressor is running and you are not mixing Nitrox.
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for help with using this spreadsheet, contact: derek@rubberduckiedesigns.com
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for additional information:
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http://en.wikipedia.org/wiki/Humidity
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