This document discusses psychrometry, which is the study of atmospheric air and its associated water vapor. It defines key terms like dew point temperature, dry-bulb temperature, wet-bulb temperature, humidity ratio, and different types of humidity. It also explains the psychrometric chart, which graphically presents the physical and thermal properties of moist air. Key properties discussed include dew point, dry-bulb temperature, wet-bulb temperature, saturation line, and relative humidity.

1. RIMT
COLLEGE OF ARCHITECTURE
PSYCHROMETRIC

2. CONTENTS
 What is PSYCHROMETRY?
 Properties of
PSYCHROMETRY
 PSYCHROMETRIC CHART

3. • Psychrometry is the study of atmospheric air and its associated water
vapour.
• When designing an air conditioning system, the temperature and
moisture content of the air to be conditioned, and the same
properties of the air needed to produce the desired air conditioning
effect.
• In other words, we can say that Psychrometry is the study of MOIST
AIR or mixture of dry air and water vapour.
• A psychrometric chart presents physical and thermal properties of
moist air in a graphical form
Psychrometry

5. PROPERTIES OF PSYCHROMETRY
DEW POINT TEMPERATURE
DRY-BULB TEMPERATURE
WET BULB TEMPERATURE
HUMIDITY RATIO
HUMIDITY
• Specific humidity
• Absolute humidity
• Relative humidity

6. • the dew point (dew point
temperature or dewpoint ) is
the temperature at which a given concentration
of water vapor in air will form dew.
•More specifically it is a measure of
atmospheric moisture. It is the temperature to
which air must be cooled at constant pressure
and water content to reach saturation.
• A higher dew point indicates more moisture in
the air; a dew point greater than 20 °C (68 °F)
is considered uncomfortable and greater than
22 °C (72 °F) is considered to be extremely
humid.
•Frost point is the dew point when
temperatures are below freezing.
DEW POINT

8. The dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely
exposed to the air but shielded from radiation and moisture. It indicates the amount of heat in the
air and is directly proportional to the mean kinetic energy of the air molecules. Temperature is
usually measured in degrees Celsius (°C), Kelvin (K), or Fahrenheit (°F).
Unlike wet bulb temperature, dry bulb temperature does not indicate the amount of moisture in the air.
In construction, it is an important consideration when designing a building for a certain climate.
Dry-bulb temperature & wet-bulb temperature

9. Wet-bulb temperature

10. • Saturation line is a
temperature condition at which
water will begin to condense
out of moist air.
• It is also called the dew point
temperature line.
Saturation Line

13. Relative humidity (abbreviated RH) is the ratio of the partial pressure of water vapor to
the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on
temperature and the pressure of the system of interest. It requires less water vapour to attain
high relative humidity at low temperatures; more water vapour is required to attain high
relative humidity in warm or hot air.
Relative humidity
Relative
Humidity
Amount of moisture that a given
amount of air is holding
=
Amount of moisture that a given
amount of air can hold

15. 50% RH 100% RH - Saturated

16. Humidity is the amount of water vapor in the air. Water vapor is the gaseous state of water and is
invisible. Humidity indicates the likelihood of precipitation, dew, or fog. effectiveness of sweating in
This effect is calculated in a heat index table or humidex. The amount of water vapor that is needed
to achieve saturation increases as the temperature increases. As the temperature of a parcel of air
becomes lower it will eventually reach the point of saturation without adding or losing water mass.
HUMIDITY RATIO
There are three main measurements of humidity: absolute, relative and specific. Absolute
humidity is the water content of air at a given temperature expressed in gram per cubic
meter] Relative humidity, expressed as a percent, measures the current absolute humidity
relative to the maximum (highest point) for that temperature. Specific humidity is a ratio of the
water vapor content of the mixture to the total air content on a mass basis.