Ask The HvacMan
Air Grilles
Air Diffusers
Air Quailty
All Air Systems
All Water Systems
Building .Managament Systems ..BMS
Cooling Towers
Cooling Load Calculation
Energy Saving
Duct ,Smacna
Dampers ,Air
Dust Collection
Fire Dampers
Glass Selection
Heat Exchangers,water
Heat Recovery
Heat Tracing Systems
Hepa Filters
Hvac Applications
Humidifiers / Dehumidifiers
Insulation , Duct
Insulation , Pipe
Insulation , Sound
Nano Tech.,In Building
Occupancy Sensors
Pneumatic Conveying
Pool Ventilation
Process Piping
Radiant Heating
Refrigerant Systems
Solar Collectors
Steam Generation
Tables & Charts Gnr.
VAV Sytems
VRV Systems
Solar Collectors
Flat Plate Collectors
Evacuated Tube Collectors
Concentrating Collectors
Transpired Collectors
Solar Control Systems
Standalone Systems
Grid Connected Systems
Hybrid Systems
Back-up Systems
Solar Cells
Solar Arrays
Change Controller
Hybrid Systems
Grid Systems
Water Pumping
Using Wind Energy
Enviromental Aspects
Buyer's Guide
Save Energy
Solar Water Heating
Solar Electric Systems
Wind Turbines
Passive Solar Heating
Passive Solar Cooling
Building Material
Water Conservation
Ground Source Heat-Pumps
Green Hotels

Glass &Windows Selection


Persons who want to control temperature and humidity of the air in the air conditioning system should have an understanding of psychrometry. They make use of psychrometric charts to determine various parameters of the air at any condition. For example, by knowing two parameters, you can look up the chart to find the other values. The values found in a typical psychrometric chart are:

Dry Bulb Temperature

The dry-bulb temperature of air is measured by a thermometer which is freely exposed to the air but is shielded from radiation and moisture
Wet Bulb Temperature
The Wet-bulb Temperature of air is measured by a thermometer whose bulb is covered by a muslin sleeve which is kept moist with distilled and clean water, freely exposed to the air and free from radiation
Dewpoint Temperature
Dew point temperature is the temperature at which moist air becomes saturated (100% relative humidity) with water vapour when cooled at constant pressure, i.e. temperature at which condensation of moisture begins when the moist air is cooled.
Relative Humidity
Humidity ratio or relative humidity is the ratio of the actual mass of water vapor in the air to the mass of water vapor that would saturate the air at the same temperature


The enthalpy of moist air is defined as the sum of its internal energy and the product of its pressure and volume. Specific enthalpy h (kJ/kg) of moist air is defined as the total enthalpy of the dry air and water vapour mixture per kg of moist air.
Moisture Content
Specific humidity or moisture content of air is the ratio of the mass of water to the mass of dry air in a given volume of moist air
Psychrometric processes, i.e. any changes in the condition of the atmosphere, can be represented by the movement of the state point on the psychrometric chart. Common processes include:

Sensible cooling / sensible heating

When an air-vapor mixture is heated or cooled, without the addition or removal of moisture, the resulting "process" may be plotted as a horizontal line on the chart:

Humidification / dehumidification
Humidification can be made by spraying water or steam to air.If humidification made by water, air will move through wetbulb temperature line and dry bulb temperature will decrease.If humidifaction made with steam air will move through drybulb temp line and there will be no significant change in drybulb temprature
Cooling and dehumidification / heating and humidification
Evaporative cooling / chemical dehydration
Sample Psyhrometric Systems



  Discuss on the Message Board
Legionnare Disease
Energy Saving
Control Software
Hotel Design Books

Hotel Design