ASHRAE PSYCHROMETRIC CHART NO NORMAL TEMPERATURE. BAROMETRIC PRESSURE: INCHES OF MERCURY. Copyright 0. 5. DRY BULB TEMPERATURE – °C. 5. Psychrometric Charts . .. . ASHRAE Fundamentals Handbook (SI) Mass of water added per unit mass of dry air is (W.* – W), which.

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Psychrometrics, psychrometry, and hygrometry are names for the field of engineering concerned with the physical and thermodynamic properties of gas-vapor mixtures. 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.


In human terms, our thermal comfort is psychromerric 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. Many substances are hygroscopicmeaning they psychroetric water, usually in proportion to the relative humidity or above a critical relative humidity.

Such substances include cotton, paper, cellulose, other wood products, sugar, calcium oxide burned lime and many chemicals and fertilizers. Industries that use these materials are concerned with relative humidity control in production and storage of such materials. 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.

In many industrial applications it is important to avoid condensation that would ruin product or cause corrosion. Molds and fungi can be controlled by keeping relative ashgae low.

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The dry-bulb temperature is the temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation.

The term dry-bulb is customarily added to temperature to distinguish it from wet-bulb and dewpoint temperature. In meteorology and psychrometrics the word temperature by itself without a prefix usually means dry-bulb temperature.

Technically, the temperature registered by the dry-bulb thermometer of a psychrometer. The name implies that the sensing bulb or element is in fact dry. WMO provides a page chapter on the measurement of temperature. The thermodynamic wet-bulb temperature is a thermodynamic property of a mixture of air and water vapor. The value indicated by a wet-bulb thermometer often provides an adequate approximation of the thermodynamic wet-bulb temperature.

The accuracy of a simple wet-bulb thermometer depends on how fast air passes over the bulb and how well the thermometer is ashgae from the radiant temperature of its surroundings. A psychrometer is a device that includes both a dry-bulb and a wet-bulb thermometer.

A sling psychrometer requires manual operation to create the airflow over the bulbs, but a powered psychrometer includes a fan for this function. Knowing both the dry-bulb temperature DBT and wet-bulb temperature WBTone can determine the relative humidity RH from the psychrometric chart chwrt to the air pressure.

The saturation temperature of the moisture present in the sample of air, it can also be defined as the temperature at which the vapour changes into liquid condensation.


Usually the level at which water vapor changes into liquid marks the base of the cloud in the atmosphere hence called condensation level. So asyrae temperature value that allows this process condensation to take place is called the ‘dew point temperature’. A simplified definition is the temperature at which the psychdometric vapour turns into “dew” Chamunoda Zambuko Specific humidity is defined as the proportion of the mass of water vapor and mass of the moist air sample including psychromeric dry air and the water vapor ; it is closely related to humidity ratio and always lower in value.

The mass of water vapor per unit volume of air containing the water vapor. This quantity unts also known as the water vapor density. The ratio of the vapor pressure of moisture in the sample to the saturation pressure at the dry bulb temperature of the sample. Analogous to the specific enthalpy of a pure substance. In psychrometrics, the term quantifies the total energy of both the dry air and water vapour per kilogram of dry air.

Analogous to the specific volume of a pure substance. However, in psychrometrics, the term quantifies the total volume of both the dry air and water ashtae per unit mass of dry air. The psychrometric ratio is the ratio of the heat transfer coefficient to the product of mass transfer coefficient and humid heat at a wetted surface. It may be cgart with the following equation: 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 the adiabatic saturation temperature.

Mixtures of air and water vapor are the most common systems unita in psychrometry. 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. This property of air-water vapor systems simplifies drying and cooling calculations often performed using psychrometic relationships.

Humid heat is the constant-pressure specific heat of moist air, per unit mass of the dry air.

Psychrometric Chart + Duct Calculator

Many psychrometric properties are dependent on pressure concept:. A psychrometric chart is a graph of the thermodynamic parameters of moist air at a constant pressure, often equated to an elevation relative to sea level.

The psychrometric chart allows all the parameters of some moist air to be determined from any three independent parameters, one of which must be the pressure. 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.

A chart is valid for a given air pressure or elevation above 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. These lines are drawn straight, not always parallel to each other, and slightly inclined from the vertical position.

This is the t —axis, the abscissa horizontal axis. Each line represents a constant temperature. The dew point temperature is equal to the fully saturated dry bulb or wet bulb temperatures. These lines are oblique lines that differ slightly from the enthalpy lines. They are identically straight but are not exactly parallel to each other. These intersect the saturation curve at DBT point. These are the horizontal lines on the chart.

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Humidity ratio is usually expressed as mass of moisture per mass of pwychrometric air pounds or kilograms of moisture per pound or kilogram of dry air, respectively. The range is from 0 for dry air up to 0. These are oblique lines drawn diagonally downward from left to right across the chart that are parallel to each other. These are not parallel to wet bulb temperature lines.

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. The protractor on the upper left of the chart has two scales.

The inner scale represents sensible-total heat ratio SHF. The outer scale gives the ratio of enthalpy difference to humidity difference. This is used to establish the slope of a condition line between two processes. The horizontal component of the condition line is the change in sensible heat while the vertical component is the change in latent heat. They are also available in low and high temperature ranges and for different pressures.

The “Mollier i – x ” Enthalpy – Humidity Mixing Ratio diagram, developed by Richard Mollier incharf is an alternative psychrometric chart, preferred by many users in Scandinavia, Eastern Europe, and Russia.

The underlying psychrometric parameter data for the psychrometric chart and the Mollier diagram are identical.

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

At first glance there chaart little resemblance between the charts, but if the chart is rotated by ninety degrees and looked at in a mirror the resemblance becomes apparent. The Mollier diagram coordinates are enthalpy and humidity ratio.

The enthalpy coordinate is skewed and the lines of constant enthalpy are parallel and evenly spaced. Some psychrometric charts use dry-bulb temperature and humidity ratio coordinates. From Wikipedia, the free encyclopedia. Not to be confused with Psychometricsa discipline of psychology and education.

It is not to be confused with Psychometry. Pressure Liquid water Avogadro’s law Nucleation Thermodynamic equilibrium. Chapter 2, Measurement of Temperature. Retrieved 18 September Archived from the original on Heating, ventilation and air conditioning. Architectural acoustics Architectural engineering Architectural technologist Building services engineering Building information modeling BIM Deep energy retrofit Duct leakage testing Environmental engineering Hydronic balancing Kitchen exhaust cleaning Mechanical engineering Mechanical, electrical, and plumbing Mold growth, assessment, and remediation Refrigerant reclamation Testing, adjusting, balancing.

Retrieved from ” https: Psychrometrics Humidity and hygrometry Uits, ventilating, and air conditioning. Archived copy as title Webarchive template wayback links. Views Read Edit View history.

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