Psychrometrics

Psychrometrics © is a powerful yet easy–to-use app that accurately computes the complete set of psychrometric parameters over an extended range of pressure. The user selects English (IP) or international (SI) units, enters atmospheric pressure, dry bulb temperature, and relative humidity (or dew point, or wet bulb temperature). Output values:

 Dew Point
 Relative Humidity
 Wet Bulb Temperature
 Vapor Pressure
 Moisture Concentration (Humidity Ratio)
 Specific Volume of dry air
 Specific Volume of moist air
 Enthalpy dry air
 Enthalpy of water vapor
 Total Enthalpy

The amount of water vapor in air has a major affect on human comfort, corrosion and many natural and commercial products and processes. It also has a significant effect on air density and enthalpy or energy content. The relationships between vapor concentration, atmospheric pressure, temperature, dew point, air density and energy are shown on psychrometric charts, an important tool especially for meteorologists, HVAC engineers, and health care professionals. But these charts are difficult to use, are often misunderstood and cover only a very limited range dry bulb and dew point temperatures. Moreover, different charts are required for different values of atmospheric pressure. Generally the published charts are limited to pressures corresponding to sea level and an altitude of 5,000 ft.

The Psychrometrics calculator puts thousands of charts in your hand and instantly finds accurate values of dew point, relative humidity, moisture concentration and so on. And, atmospheric pressure is an input variable, with a range that corresponds to from seven atmospheres to 20,000 ft (6,100 m) altitude. This high pressure range is especially useful for analyzing compressed air systems.

This app is not a compilation of data points and does not use interpolation to estimate values. Rather, it is based on analytical methods. A version of the Hyland Wexler equation is used for the computation of saturation pressures and temperatures, and a proprietary set of equations, which model the exchange of latent and sensible heats at the wet bulb surface, are used to determine the complete set of parameters. Range of operation:

• Dry Bulb Temp -100°F (-73.3°C) to 212°F (100°C)
• Relative Humidity ~0 to 100%
• Dew Point -100°F (-73.3°C) to 150°F (65.56°C)
• Min Pressure 13.75 in hg (20,000 ft), (53.13 kPa (6,100 m)
• Max Pressure 204 in hg (787 kPa)

For conditions outside of these values please contact www.mainestaydesign.com.

MAINE STAY DESIGN offers engineering and consulting services specializing in heat transfer and fluid flow applications. Our work is focused in new product development including commercial and scientific refrigeration, test facilities, and heat reclamation. Years of practical experience grounded in a thorough understanding of first principles leads to innovative, yet practical and efficient design solutions. Maine stay also offers custom software for data retrieval and evaluation, and for analysis of atmospheric conditions including pressure, temperature, relative humidity, dew point, and enthalpy. Please visit www.mainestaydesign.com.