[BLDG-SIM] Wet Bulb Temperatures

[Dan Cautley]

Wet bulb and dew point are independent parameters, and one cannot be
calculated from the other unless you know two independent psychrometric
parameters.  Knowing any two of the typical independent parameters  (e.g.
any two of dry bulb temperature, wet bulb temperature, relative humidity,
and/or absolute humidity) implies knowing the psychrometric state of the
air, and allows calculation of any of the other parameters.  ASHRAE
Fundamentals, Chaper 6 provides most of the relationships that are needed in
the form of empirical equations, as others have mentioned.



Note that dew point temperature, absolute humidity, and humidity ratio are
all representations of the absolute concentration of water vapor, and can be
converted back and forth without additional information (i.e. without
knowing the exact state), but wet bulb temperature is not equivalent.



Some of the psych. parameters are also dependent on absolute air pressure.
A caution:  If you use Equation (3) in the 2001 IP edition (the ASHRAE
formula for calculating absolute pressure as a function of altitude), the
result is in inches Hg, while most other pressures in the chapter are
presented in psia.  I've mentioned this to the editor with the suggestion
that all similar parameter within a chapter should have the same units.



Dan Cautley

Cautley Engineering

Washington, DC



----- Original Message ----- 
From: "Gerald Pde" <geraldpde at yahoo.com>
To: <BLDG-SIM at GARD.COM>
Sent: Monday, September 27, 2004 5:43 PM
Subject: [BLDG-SIM] Wet Bulb Temperatures


> Hello,
>
> Does anyone know if you could calculate  wet bulb
> temperatures from dew point temperature?
> your coperation is appreciated.
> Gerald
>
>
>
>
>
>
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