Psychrometric Charts . .. . ASHRAE Fundamentals Handbook (SI) Mass of water added per unit mass of dry air is (W.* – W), which. AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR- CONDITIONING ENGINEERS, INC. T. SENSIBLE HEAT. 0. 5. DRY BULB TEMPERATURE – °C. 5.

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New in the Third Edition: 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. Humid heat is the constant-pressure specific heat of moist air, per unit mass of the dry air.


Email a list of all the points and their properties for a completed chart, along with a PDF of the psychromdtric itself. Create psychrometric processes by plotting points then connecting them ashtae process lines.

Mixtures of air and water vapor are the most common systems encountered in psychrometry. Although the principles of psychrometry apply to any physical system consisting of gas-vapor mixtures, the most common system of interest is the mixture of water vapor and air, because of its application in heating, ventilating, and air-conditioning and meteorology.

The user then enters a desired Dry Bulb temperature and one of three humiditymetrics: Technically, the temperature registered by the dry-bulb thermometer of a psychrometer. The program on the CD allows the user to plot typical psychrometric processes and perform the corresponding energy calculations on-screen, without having to first print out the individual charts.

Such substances include cotton, paper, cellulose, other wood products, sugar, calcium oxide burned lime and many chemicals and fertilizers. A psychrometer is a device that includes both a dry-bulb and a wet-bulb thermometer.

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Please send correspondence to: Retrieved from ” https: The horizontal component of the condition line is the change in sensible heat while the vertical component is the change in latent heat.

So the temperature value that allows this process condensation to take place is called the ‘dew point temperature’. Home Technical Resources Bookstore. These lines are oblique lines psychromeetric differ slightly from the enthalpy lines. The inner scale represents sensible-total heat ratio SHF.


In meteorology and psychrometrics the word temperature by itself without a prefix usually means dry-bulb temperature. Specific humidity is defined as the proportion of the mass of water vapor and mass of the moist air sample including both dry air and the water vapor ; it is closely related to humidity ratio and always lower in value.

Common atmospheric pressure values are:. In psychrometrics, the term quantifies the total energy of both the dry air and water vapour per kilogram of dry air. Display a fully customizable psychrometric chart in both landscape and portrait modes.

ASHRAE psychrometric chart SI [chart] – Catalog – UW-Madison Libraries

Archived from the original on Heating, ventilation and air conditioning. Humidity ratio is usually expressed as mass of moisture per mass of dry air pounds or kilograms of moisture per pound or kilogram of dry air, respectively. Usually the level at which water vapor changes into liquid marks the base of the cloud in the atmosphere hence called condensation level.

Retrieved 18 September Understanding Psychrometrics serves as a lifetime reference manual and basic refresher course for those who use psychrometrics on a recurring basis and provides a four- to six-hour psychrometrics learning module to students; air-conditioning designers; agricultural, food process, and industrial process engineers; meteorologists and others.

The accuracy of a simple wet-bulb thermometer depends on how fast air passes over the bulb and how well the thermometer is shielded from the radiant temperature of its surroundings.

In human terms, our thermal comfort is in large part a consequence of not just the temperature of the surrounding air, but because we cool ourselves via perspiration the extent to which that air is saturated with water vapor.

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. Create an unlimited number of psychrometric chart projects. Some psychrometric charts use dry-bulb temperature and humidity ratio coordinates. In industrial drying applications, such as drying paper, manufacturers usually try to achieve an optimum between low relative humidity, which increases the drying rate, and energy usage, which decreases as exhaust relative humidity increases.


The dry-bulb temperature is the temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation. Many substances are hygroscopicmeaning they attract water, usually in proportion to the relative humidity or above a critical relative humidity.

The outer scale gives the ratio of enthalpy difference to humidity difference. The psychrometric chart allows all the parameters of some moist air to be determined ashraee any three independent parameters, one of which must be the pressure. These intersect the saturation curve at DBT point. Cjart mass of water vapor per unit volume of air containing the water vapor. Vhart are oblique lines drawn diagonally downward from left to right across the chart that are parallel to each other.

The “Mollier i – x ” Enthalpy – Humidity Mixing Ratio diagram, developed by Richard Mollier in[12] is an alternative axhrae chart, preferred by many users in Scandinavia, Eastern Europe, and Russia. A sling psychrometer requires manual operation to create the airflow over the bulbs, but a powered psychrometer includes a fan for this function. These are the horizontal lines on the chart. The range is from 0 for dry air up to 0. This quantity is also known as the water vapor density. Also, create custom labels anywhere on the chart.

This second edition, available in both I-P and SI units, provides clear understanding of the state of the art in heating and cooling load calculation methods. WMO provides a page chapter on the measurement of temperature.

Dayton ASHRAE On-Line Psychrometrics

Molds and fungi can be controlled by keeping relative humidity low. 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 underlying psychrometric parameter data for the psychrometric chart and the Mollier diagram are identical.

The program can output a listing of points and processes in a tabular report with calculated properties and energy values for each. Many psychrometric properties are dependent on pressure concept:.