The first psychrometric chart appeared in the early 20th century, together with other humid air diagrams. At constant pressure, the enthalpy change equals the energy transferred between a system and its environment through heating or work other than expansion work. The dew point is the temperature to which the air has to be cooled at constant absolute humidity (i.e., without evaporation) to reach 100% relative humidity. Therefore, it can be used to calculate the relative humidity. The difference between the two values is proportional to the difference of the vapor pressures around the two thermometer bulbs.
![ashrae psychrometric chart no. 1 in color video ashrae psychrometric chart no. 1 in color video](https://i.ytimg.com/vi/wLk_HHCQOzQ/maxresdefault.jpg)
Its value is always lower or equal to the dry-bulb temperature because of the cooling effect of the evaporation. The wet-bulb temperature is measured with a moistened thermometer and it will be the lowest temperature that can occur under adiabatic saturation of the air by evaporating water only.
![ashrae psychrometric chart no. 1 in color video ashrae psychrometric chart no. 1 in color video](https://s3.amazonaws.com/greenbuildingadvisor.s3.tauntoncloud.com/app/uploads/2018/08/08044208/ASHRAE-psychrometric-chart-IP-thumb16x9.jpg)
By definition, the relative humidity is the ratio of the actual vapor pressure to the vapor pressure of saturated air at the same temperature. This pressure is called the saturation pressure, and at this point, the absolute humidity-the quantity of water in the air (the ratio of the water vapor mass to the dry air mass)-is at its maximum and the relative humidity is 100%. At the point of saturation, the vapor pressure is so high that no more water can evaporate. The mixture of the water vapor and the air can be considered as an ideal two-component gas system by the widely accepted simplification thus, the chemical potentials are directly proportional to the logarithm of the partial pressures. In other words, the propelling power will be the difference between the chemical potentials of water in the air as a whole and at the surface. The resulting water partial pressure of the air in the closest layer adjacent to the surface is equal to the vapor pressure that determines the total amount of water that can be evaporated into the air at a given temperature. Water vapor then exerts a force on that surface.
ASHRAE PSYCHROMETRIC CHART NO. 1 IN COLOR VIDEO SOFTWARE
This software is compatible with Windows98, Windows 2000, Windows NT & XP, and Windows 7, and Windows 10.Water evaporates when air touches its surface.
![ashrae psychrometric chart no. 1 in color video ashrae psychrometric chart no. 1 in color video](https://www.practicalhvac.com/wp-content/uploads/2020/08/ashrae-psychrometric-chart-95-76-state-points.jpg)
![ashrae psychrometric chart no. 1 in color video ashrae psychrometric chart no. 1 in color video](https://i.ytimg.com/vi/wLk_HHCQOzQ/hqdefault.jpg)
The program on the CD allows the user to plot typical psychrometric processes and perform the corresponding energy calculations on-screen, without having to first print out the individual charts. This CD includes all five of ASHRAE's I-P unit psychrometric charts and all seven SI psychrometric charts.