These are slightly sloped diagonal lines indicating the volume occupied by a unit mass of dry air (cubic feet per pound). This is critical for sizing fans and ducts.
The term comes from the Greek psukhros (cold) and metron (measure). While it measures "cold," its real power lies in measuring change. To read the chart, you must identify its seven fundamental components. Most charts are plotted with Dry Bulb Temperature (the temperature your thermometer reads) on the horizontal axis. psychrometric graph
Often described as a "graph of the physics of air," the psychrometric chart might look like a chaotic spiderweb of lines at first glance. However, once you learn its language, it becomes an indispensable map for controlling comfort, preserving food, drying paint, or even keeping a data center cool. Psychrometry is the study of the thermodynamic properties of gas-vapor mixtures—specifically, air and water vapor. The chart doesn't just plot temperature; it plots the relationship between heat, moisture, and energy. These are slightly sloped diagonal lines indicating the
These are straight horizontal lines measuring the actual mass of water vapor per mass of dry air (grains/lb or g/kg). This tells you how much moisture is in the air. While it measures "cold," its real power lies
These are straight vertical lines (or horizontal, depending on the chart's orientation). They represent the sensible heat level of the air—the heat you can feel.
Air is invisible. Yet, for heating, ventilation, and air conditioning (HVAC) engineers, it is a complex mixture of gases, water vapor, and energy. To visualize this invisible world, engineers rely on one of the most elegant and powerful tools ever developed: The Psychrometric Chart .
These are diagonal lines sloping downwards to the right. The wet bulb temperature is measured by a thermometer with a wet wick. It represents the cooling effect of evaporation. Along the saturation line, WBT = DBT.