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The representation is made on a temperature-relative humidity, instead of a standard psychrometric chart. The comfort zone in blue represents the 90% of acceptability, which means the conditions between -0.5 and +0.5 PMV, or PPD < 10%.
In hot summer weather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the heat index, a relative humidity of 75% at air temperature of 80.0 °F (26.7 °C) would feel like 83.6 ± 1.3 °F (28.7 ± 0.7 °C). [13] [14]
The relationship between water content and equilibrium relative humidity of a material can be displayed graphically by a curve, the so-called moisture sorption isotherm. For each humidity value, a sorption isotherm indicates the corresponding water content value at a given temperature. If the composition or quality of the material changes, then ...
A relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases, but the dew point remains constant.
A given value of relative humidity causes larger increases in the heat index at higher temperatures. For example, at approximately 27 °C (81 °F), the heat index will agree with the actual temperature if the relative humidity is 45%, but at 43 °C (109 °F), any relative-humidity reading above 18% will make the heat index higher than 43 °C. [5]
Schematic of the LCL in relation to the temperature (T) and dew point and their altitude (Z); the moist adiabatic temperature curve above the LCL is also sketched for reference The lifting condensation level or lifted condensation level ( LCL ) is the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to ...
using Plots # Saturated water vapor pressure [Pa] # See Ham, 2005. Useful Equations and Tables in Micrometeorology function water_vapor_saturated_pressure (Ta, P) Ta = Ta-273.15 es = (1.0007 + (3.46e-5 * (P / 1e3))) * 0.61121 * exp ((17.502 * Ta) / (Ta + 240.97)) * 1e3 return es end function water_vapor_density (e, Tair) Rs_v = 461.5 # J/(kg.K) specific gas constant for water vapor ρv = e ...
Relationship to relative humidity: The relative humidity (RH) of air in equilibrium with a sample is also called the Equilibrium Relative Humidity (ERH) and is usually given as a percentage. [2] It is equal to water activity according to E R H = a w × 100 % . {\displaystyle \mathrm {ERH} =a_{w}\times 100\%.}