Standard Air

[AO1958]

HI there

I've searched in the past posts but with no specific answer.
I am dealing with some AHU and I am facing to standard air.

Please, is there anybody who knows the exact definition ?
Is it referring to a specific density value ?

Should it be the case, according to standard psychometric formulas, density is relating to atmospheric pressure and relative humidity.
Is this relationship respected in the case of standard air or does it refer to a specific pressure and relative humidity ?

Many thanks

 

[MintJulep]

http://lmgtfy.com/?q=http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

 

[AO1958]

Hello Mr MintJulep

you are right to suggest me to google it.
But if you see in the wikipedia page there are: several reference and pressure temperatures.
Indeed the question now is: which is the correct combination for ahu ?
If you see there is no reference to relative humidity, therefore it is not possible, unless it is already determined, air cp and viscosity.

Please, do you know this specific data ?

 

[MintJulep]

Standard air is "dry air". Zero absolute humidity.

If you look at your psychrometric chart you'll see "dry air properties" on there somewhere, or humidity will be expressed in units of mass of water per mass of dry air.

 

[lma1]

According to ASHRAE, the US standard atmosphere at sea level is 59 deg F (standard temperature) & 14.696 psia or 29.921” Hg (barometric pressure). The density of standard indoor air (@ 68 deg F & 14.696 psi) is 0.0753 lbm/ft3.

 

[Drazen]

In practice, such standard air mostly serves to present some standard capacities for your fan in technicals specs.

In your case, you certainly need to calculate with actual altitude you are on.

 

[lma1]

You may wish to look up the ASHRAE Handbook to find the pressure & temperature at the altitude for your location. You may alternatively calculate them using:

t = 59 - 0.00356620 * Z

Where:
t = temperature, deg F
Z = altitude, ft

p = 14.696 * [(1 – 6.8754 * 0.000001 * Z)] to the power of 5.2559]

Where:
p = pressure, psia