Instructions for the Psychrometric Calculator
This on-line program calculates typical psychrometric state point properties. It will also provide a number of other thermodynamic properties not found on a typical psychrometric chart.
To calculate properties, the user must enter either a site elevation (from which an average barometric pressure is calculated) or an actual barometric pressure. The user then enters a desired Dry Bulb temperature and one of three humiditymetrics: Relative Humidity, Wet Bulb temperature, or Dew Point temperature. At the end of the calculation, the user has the option to convert from the English to the SI (or vice versa) unit system.
Common atmospheric pressure values are:
- Sea Level Pressure - 14.7 psia / 101.3 kPa / 29.92 in Hg / 760 mm Hg (Default when 'Actual Pressure' is selected)
- Average Barometric Pressure in Dayton, OH - 14.18 psia / 97.7 kPa / 28.86 in Hg / 733 mm Hg
- Site elevation for Dayton, OH - 997 ft amsl (306 m) based on the ASHRAE HOF. (Default when Elevation is selected)
- User may override default input by selecting and entering new value.
- There appears to be error in the calculations when converting from one unit system to another. Why?
- Why does this program show two different values of specific volume?
- What is the difference between the six different humidity metrics shown?
- You show a 'Virtual' Temperature under Thermodynamic properties. What is that?
- Why is the wind chill calculation only available some of the time?
This program is provided for your use without charge. However, no warranty, either expressed or implied, is given with respect to the accuracy or the sufficiency of the information provided herein, and the user must assume all risks and responsibility in connection with the use thereof.
Copyright © 2006-2015 Russell K. Marcks, P.E. and ASHRAE Dayton Chapter. All rights reserved. No part of this web page and associated script may be produced, transmitted, transcribed, stored in a retrieval system, or translated into any language in any form without the express written consent of the author.