): The true air temperature measured by a standard thermometer. It forms the horizontal axis (x-axis), with temperatures increasing from left to right. Wet-Bulb Temperature ( Twbcap T sub w b end-sub
): The ratio of current water vapor pressure to saturation vapor pressure. It is represented by lines looping upward from the bottom left to the top right. The topmost curve is the 100% RHcap R cap H line (saturation curve). Humidity Ratio (
The psychometric chart simplifies the visualization of thermodynamic processes. Every standard air-conditioning cycle can be drawn as a line connecting an initial state point to a final state point. psychometric chart
Demystifying the Psychrometric Chart: A Guide for HVAC and Building Science
closely align with wet-bulb lines but utilize a distinct scale on the outer perimeter. Specific volume lines are much steeper than wet-bulb lines. 3. Standard HVAC Processes ): The true air temperature measured by a
To read the chart accurately, you must identify the orientation and behavior of each property line.
. ProcessSensing.com +5 Critical Chart Landmarks Saturation Curve: The outermost boundary curve on the left. At any point on this line, the air is at 100% relative humidity, meaning DBT, WBT, and Dew Point are all equal. Comfort Zone: A specific region on the chart (usually between 35% and 60% RH) where humans feel most comfortable. Engineers use this to design indoor climate controls. ResearchGate +3 Common Psychrometric Processes The chart is used to track changes in air properties during various HVAC operations: Sensible Heating/Cooling: A horizontal move on the chart. Temperature changes, but moisture content remains constant. Humidification/Dehumidification: A vertical move. Moisture is added or removed without changing the dry-bulb temperature. Cooling and Dehumidification: A diagonal move down and to the left, typically seen when air passes over a cold cooling coil. Scribd +3 Practical Applications HVAC System Design: Calculating the required cooling or heating capacity for a building. Passive Design: Identifying strategies like natural ventilation or evaporative cooling based on local climate data. Industrial Drying: Monitoring the moisture removal efficiency in agricultural or manufacturing processes. Diagnostics: Identifying why condensation (sweating) might be occurring on windows or ductwork. Penn State Extension +6 Would you like to see a It is represented by lines looping upward from
Example: Find properties of air at 25°C dry-bulb, 50% RH.
A psychometric chart is a graphical representation of the thermodynamic properties of air, specifically the relationships between temperature, humidity, and enthalpy. It's a useful tool for engineers, HVAC professionals, and researchers to analyze and visualize the properties of air in various conditions.
Air passes through a water spray or wet media. Water evaporates into the air, absorbing sensible heat and converting it to latent heat. The state point moves . Tdbcap T sub d b end-sub decreases. increases. RHcap R cap H increases. remains constant. 4. Engineering Equations
): The actual mass of water vapor per unit mass of dry air (expressed as ). It forms the vertical axis (y-axis) on the far right. Specific Enthalpy (