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A convenient, precise and customizable psychrometric chart & calculator tool for 25 26 27 28 29 30 m^3/kg(d.a) 10% 20% 30% 40% 50% 60% 70%. Psychrometrics, psychrometry, and hygrometry are names for the field of engineering . The ASHRAE-style psychrometric chart, shown here, was pioneered by. Use chart to analyze processes involving moist Psychrometric chart: Example 1 . Given: T = 25°C . m wide x m long, and the boards are separated by.

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The psychrometric ratio of air-water vapor mixtures is approximately unity, which implies that the difference between the adiabatic saturation temperature and wet bulb temperature of air-water vapor mixtures is small.

All the properties of air indicated in the psychrometric chart are calculated at the standard atmospheric pressure.

What is Psychrometric Chart? Introduction to Reading the Psychrometric Properties of Air

These are not parallel to wet bulb temperature lines. The four equations highlighted above were programmed in MATLAB and used to plot the simplified psychrometric charts shown above.

Locate the vapor pressure line to the right of the dew point line. At first appearence the psychrometric chart is quite confusing, however with some practice it becomes an extremely useful tool for rapidly evaluating air-conditioning processes. Such substances include cotton, paper, cellulose, other wood products, sugar, calcium oxide burned lime and many chemicals and fertilizers.

Around the extremes of the chart and just outside of the saturation curve, locate the diagonal scales which represent enthalpy in BTU per pound of dry air. Pick any 2 known measurements available and plot them on the chart where the lines intersect.

Notice that on the saturation curve the wet and dry bulb temperatures have the same values. Knowing both the dry-bulb temperature DBT and wet-bulb temperature WBTone can determine the relative humidity RH from the psychrometric chart appropriate to the air pressure. We shall now see how the air behaves when it is subjected to changes in temperature and humidity to suit the various applications for which the air conditioning is meant.


The name implies that the sensing bulb or element is in fact dry. The inner scale represents sensible-total heat ratio SHF. The mass of water vapor per unit volume of air containing the water vapor.

If the measurement that you are looking for is between the labeled temperatures, estimate its location. In meteorology and psychrometrics the word temperature by itself without a prefix usually means dry-bulb temperature.

The region above the saturation curve is a two-phase region that represents a mixture of saturated moist air and liquid water, in thermal equilibrium. Indicate all the values determined on the chart. This type of cooler is extremely popular in hot, dry climates, and is popularly known as a Swamp Cooler.

Pressure Liquid water Avogadro’s ihv Nucleation Thermodynamic equilibrium. So the temperature value that allows this process condensation to take place is called the ‘dew point temperature’. The protractor on the upper left of the chart has two scales.

This property of air-water vapor systems simplifies drying and cooling calculations often performed using psychrometic relationships. This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness.

WMO provides a page chapter on the measurement of temperature.

Chapter 10b: The Psychrometric Chart (Updated 7/22/)

It is not to be confused with Psychometry. The “Mollier i – x ” Enthalpy – Humidity Mixing Ratio diagram, developed by Richard Mollier in[12] is an alternative psychrometric chart, preferred by many users in Scandinavia, Eastern Europe, and Russia.

From there, compare the difference in the measurements and make note of how the change affected the air. This quantity is also known as the water vapor density. Changes in statesuch as when two air streams mix, can be modeled easily and somewhat graphically using the correct psychrometric chart for the location’s air pressure or elevation relative to sea level.

From any two independent ones of the six parameters dry bulb temperature, wet bulb temperature, relative humidity, humidity ratio, specific enthalpy, and specific volume, all the others can be determined. Just to the right of the Y-axis, find the line with the dew point measurement in degrees Fahrenheit or Celsius.


The dew point temperature is equal to the fully saturated dry bulb or wet bulb temperatures. Try to be as exact as possible when using the chart to read other measurements, and mark your answers in the proper units for that measurement.

This is the t —axis, the abscissa horizontal axis. Analogous to the specific volume of a pure substance. Follow the interior curved lines to see various levels of relative humidity. In many industrial applications it is important to avoid condensation that would ruin product or cause corrosion. By continuing to use our site, you agree to our cookie policy. The psychrometric chart looks like a shoe.

Humid heat is the constant-pressure specific heat of moist air, per unit mass of the dry air. Finally, the specific volume of the air-vapor mixture green lines is determined from the ideal gas relation as. Next to or along the same vertical line as the dew point measurements, there will be markings denoting the various vapor pressures in inches of mercury or millibars.

However, you can also use relative humidity, enthalpy, and specific volume to make estimated conclusions. Look on the right side of the chart to find the vertical dew point line.

Archived from the original on The psychrometric ratio is an important property in the area of psychrometry, as it relates the absolute humidity and saturation humidity to the difference between the dry bulb temperature and psychromettric adiabatic saturation temperature.

The moisture present within the air is indicated by the vertical scale located towards the extreme right. The range is from 0 for dry air up to 0.

Psychrometric charts are used by engineers and scientists to visualize the relationships of gases and vapors. The value indicated by a wet-bulb thermometer often provides an adequate approximation of the thermodynamic wet-bulb temperature.