aRhoAIR is a state point psychrometric air properties calculator to find air density, specific heat capacity, vapour pressure, dew point temperature, moisture content, enthalpy, etc. It is specially developed by a professional engineer to replace the psychrometric chart. aRhoAIR will change the way you normally find air properties, air density and specific heat by using conventional psychrometric chart.

Aim: creating a mobile design environment for the practising engineers & designers in today's mobile world.

Results: Instant solutions at your fingertips.

Highlights:

• calculate Air Density, Specific Heat, DewPoint Temperature, various Pressure, Moisture Content, Specific Volume, Enthalpy, etc.

• input options - RH or Wet Bulb Temperature.

• input options - Z (altitude) or P (pressure) with units selection.

• calculation formulation based on ASHRAE guidelines.

• alternative on-the-move method to using conventional Psychrometric Chart.

• in SI & IP units.

Did you know? . . .about Enthalpy Units  

It is incorrect to directly convert Enthalpy from SI unit (kJ/kg) to IP unit (Btu/lb), and vice versa. Hard to believe! Test it yourself.

[Answer: This is because the reference temperature point of the (latent) heat of vaporization (hfg) in metric and imperial units are different.]

Did you know? . . .the definition of Standard air density = 1.204 kg/m3 ?  

The value is of course valid only for what is termed standard air conditions.

Dry air refers to air that does not contain water vapour, i.e. RH = 0%. Note that moist air is lighter than dry air.

• In the International Standard Atmosphere (ISA), standard temperature and pressure is 15 oC and 101325 Pa respectively. This gives the air density of 1.225 kg/m3 at sea level and the air does not contain water vapour, i.e. dry air.

• At 20 oC, the dry air has a density of 1.204 kg/m3. At 20 oC and 101325 Pa, it may be referred to as Normal temperature and pressure conditions.

• In AMCA 210 Standard for fan performance testing, standard air is defined as air with a density of 1.2 kg/m3 (at 20 oC, 50% RH and 101325 Pa approximately). 

• ASHRAE 37 Standard for unitary air-conditioning testing defines standard air as dry air having a mass density of 1.204 kg/m3  (at 20 oC and 101325 Pa).

• SMACNA 126 Standard for HVAC duct testing defines density of standard air equals 1.204 kg/m3.

Note that there are many definitions of standard temperature and pressure. To avoid confusion, it is  often necessary to state the standard reference conditions.

What is the DewPoint temperature when RH = 0%? . . .

At RH = 0% (completely dry air), there will be no DewPoint temperature as completely dry air will not reach a state of saturation.

Calculation Exapmle (in IP units)  

At 90 oF Dry Bulb and 70% RH, find air density, specific heat capacity, dewpoint temperature, moisture content, enthalphy, etc?

rhoAIR Calculation

Z (ft) = 0

Tdb (oF) = 90.0

Twb (oF) = 81.5

Tdp (oF) = 78.9

RH (%) = 70.0

rho (lb/ft3) =0.071

Cp (Btu/lb.F) = 0.250

W (lb/lb) = 0.0214

W (gr/lb) = 149.92

v (ft3/lb) = 14.334

h (Btu/lb) = 45.18 

p (in.Hg) = 29.9213

Pws (in.Hg) = 1.4230

Pw (in.Hg) = 0.9961

Legend

Z = altitude

Tdb = Dry bulb temperature

Twb = Wet bulb temperature     

Tdp = Dew point temperature

RH = Relative humidity

rho = Air density

Cp = Specific heat capacity

W = Humidity ratio

v = Specific volume

h = Enthalpy

p = Atmosphere pressure

Pws = Saturation vapour pressure

Pw = Partial water vapour pressure                                          

aRhoAIR free ? 

yes, it is free for all engineers and designers. Available in both SI & IP units, it is for world-wide users. If you need duct sizing, buy  aDuctulator.