









Air Density Calculator



Altitude, Temperature, Humidity and Barometric Pressure of
Weather Systems and their impact on local atmospheric air density.


For accurate measurement of local air conditions we recommend a
high quality logging weather station such as the ones sold on Wind101.net


AIR DENSITY CALCULATION INPUTS
(local atmospheric conditions)



Property

Value

Unit of Measure

Alternate
Units

Description / Note


Air Temperature =


C (degrees)


F (degrees)

Local air temperature


Air Humidity =


% (Rel. Humidity)


g/m3 (ABS Humidity)

Relative and corresponding Absolute Humidity value.


*Barometric Pressure =


hPa (heptoPascals)


mmHg (mm of Mercury)

*If pressure value is set to "0", Altitude value is
used to calculate local barometric pressure based on the 1976 Standard
Atmosphere Model.


Altitude / Elevation =


meters


ft

Altitude above Sea Level /elevation


AIR DENSITY CALCULATOR OUTPUT


**Air Density =


kg/m3


lb/ft3

Local air density corrected for local altitude, temperature,
humidity and barometric pressure.


**Local air density is a very important factor in
determinimg wind turbine performance and engine horse power output. Each factor like altitude above sea level,
air temperature, humidity, and even barometric pressure due to local weather
systems can have significant effect on local air density.
**Thus, if one wants to accurately predict wind turbine performance, it is
not only important to use an accurate anemometer to measure wind speed, but to also measure all the other
atmospheric factors which can have up to 10% influence on wind energy
calculations.


***Dew Point
Air Temperature =


C (degrees)


F (degrees)

Air temperature at which air humidity starts to condense into
water droplets.


***If an object at this temperature is located in
the air environment of the above given conditions, the object, like a car
window, will fog up due to air humidity condensing on its surface.









? =


kg/m3

air density
corrected for altitude, temperature and pressure


?_corrected =


kg/m3

air density
corrected for altitude, temperature, pressure and humidity.


D =

density,
kg/m3


P_{d} =

pressure of
dry air (partial pressure), Pascals


P_{v}=

pressure of
water vapor (partial pressure), Pascals


P =

Pd +
Pv = total air pressure, Pascals ( multiply mb by 100 to get Pascals)


Rd
=

287.05

gas constant
for dry air, J/(kg*degK) = 287.05 = R/Md


Rv
=

461.495

gas constant
for water vapor, J/(kg*degK) = 461.495 = R/Mv


R =

8314.32

universal gas
constant = 8314.32 (in 1976 Standard Atmosphere)


Md =

28.964

molecular
weight of dry air = 28.964 gm/mol


Mv =

18.016

molecular weight of water vapor = 18.016
gm/mol


T =

temperature,
deg K = deg C + 273.15




Standard Atmosphere



p0=

101325

Pa



T0=

288.15

K



?0=

1.225

kg/m³



To calculate the density of air as a function of altitude, one
requires additional parameters. They are listed below, along with their
values according to the International Standard
Atmosphere, using the universal gas constant instead
of the specific one:


Temperature at altitude h meters above sea level is
given by the following formula (only valid inside the troposphere):


T
standard =


K



T Nonstandard =


K





pressure at altitude


g*M/R/L
=





p =


Pa





density can then be
calculated according to this molar form formula


? =


kg/m3




?_non_std_temp
=


kg/m3







Temp =


C

ambient
temperature


h =


meters

Altitude
above sea level


p0 =

101325

Pa

sea level
standard atmospheric pressure


T0 =

288.15

K

sea level
standard temperature


g =

9.80665

m/s2

Earthsurface
gravitational acceleration


L =

0.0065

K/m

temperature
lapse rate


R =

8.31447

J/(mol·K)

universal gas
constant


M =

0.0289644

kg/mol

molar
mass of dry air




Es =


Pascals (Pa)

saturation pressure of water vapor


Tc =


temperature, deg C



c_{0} =

6.1078




c_{1} =

7.5




c_{2} =

237.3




Pv =

Rh*Es




Pv =



actual water
vapor pressure


Es =





RH % =





P @ Alt & Temp =


Pascals (Pa)

actual water
vapor pressure


P =


Pascals (Pa)

absolute
atmospheric pressure


h =


meters

altitude
above Sea Level




Density
correction for humidity multiplier =


ratio






td =

243.12*H/(17.62H)

°C


H =

(log10(RH)2.0)/0.4343+(17.62*T)/(243.12+T)


td =


°C

dew Point
Temperature


H =





RH % =





Temp =





m =

17.62




Tn =

243.12

°C



A =

6.112

hPa



dv =


g/m3

absolute Humidity




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