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A psychrometric chart is a graph of the thermodynamic parameters of moist air at a constant pressure, often equated to an elevation relative to sea level. The ASHRAE-style psychrometric chart, shown here, was pioneered by Willis Carrier in 1904. [10] It depicts these parameters and is thus a graphical equation of state. The parameters are:
English: This psychrometric chart represents the acceptable combination of air temperature and humidity values, according to the PMV/PPD method in the ASHRAE 55-2010 Standard. The comfort zone in blue represents the 90% of acceptability, which means the conditions between -0.5 and +0.5 PMV, or PPD < 10%.
The psychrometric constant relates the partial pressure of water in air to the air temperature. This lets one interpolate actual vapor pressure from paired dry and wet thermometer bulb temperature readings. [1]
Operative temperature is used in heat transfer and thermal comfort analysis in transportation and buildings. [10] Most psychrometric charts used in HVAC design only show the dry bulb temperature on the x-axis(abscissa), however, it is the operative temperature which is specified on the x-axis of the psychrometric chart illustrated in ANSI/ASHRAE Standard 55 – Thermal Environmental Conditions ...
An enthalpy–entropy chart, also known as the H–S chart or Mollier diagram, plots the total heat against entropy, [1] describing the enthalpy of a thermodynamic system. [2] A typical chart covers a pressure range of 0.01–1000 bar , and temperatures up to 800 degrees Celsius . [ 3 ]
The graphic method utilizes an overlay on a psychrometric chart to indicate the operative temperatures and humidity at which thermal comfort is achieved in the winter (1.0 clo) and summer (0.5 clo). It is based on the Predicted Mean Vote (PMV) model. [ 4 ]
The results are displayed on a psychrometric or a temperature-relative humidity chart and indicate the ranges of temperature and relative humidity that will be comfortable with the given the values input for the remaining four parameters. [44] The PMV/PPD model has a low prediction accuracy. [45]
Thermodynamic diagrams usually show a net of five different lines: isobars = lines of constant pressure; isotherms = lines of constant temperature; dry adiabats = lines of constant potential temperature representing the temperature of a rising parcel of dry air