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pines
07-24-2007, 12:44 PM
Outdoor summer "grains" of moisture.

Is this the same as "relative humidity"?

I am in Tucson Arizona. Dose 50 grains sound reasonable for a load calculation?

airscapes
07-24-2007, 01:37 PM
HVAC-calc has Tucson as 38 grains

pines
07-24-2007, 02:02 PM
Thanks,

airscapes
07-24-2007, 02:11 PM
I purchased the 2 month home owners license for HVAC-calc and it has all the major cities set up in it. For \$49 it is a very nice tool for the home owner and I learned a lot.
Temps for Tucson are 102 summer 32 winter daily range High.

Rookie2dafield
07-24-2007, 05:23 PM
Grains of moisture is the unit of measurement of the absolute amount of moisture in the air.

Relative humidity is the actual amount of moisture in the air compared to the total or maximum moisture the air can hold.

pines
08-02-2007, 07:12 PM
Ok, so I know that todays humidity is 50% and the temp is 95*.

Is there a way to convert that to grains of moisture?

HVAC Pro
08-02-2007, 08:25 PM
Check the ASHRAE handbook of fundamentals.

AcDOCnTRAINING
08-02-2007, 08:42 PM
Oh man Psychrometrics :eek: , RH is just a ratio of moisture in the air compared to dry air.

"Grains" is a standard or measurement of moisture, (EX) your vacumm pump oil can only hold or contain certain "grains" of moisture.

(EX) You may have a weight of 200 pounds. "Pounds" is the unit used to express the amount of gravity placed upon your mass. Your BMI (body mass index) is used to ratio your body fat & actual muscle tissue. kinda like RH & grains of moisture hope that helps! :D

BigJon3475
08-02-2007, 08:49 PM
oF db = Dry Bulb Temperature
oF wb = Wet Bulb Temperature
oF dp = Dew Point Temperature
%RH = Relative Humidity
Btu/lb* = Enthalpy
gr/lb* = Humidity Ratio
Alt in Ft = Altitude
in Hg = Pressure-inches of Mercury
psi = Pressure-pounds per square inch
ft3/lb* = Specific Volume
"Hg VP = Vapor Pressure
PPMw = Parts per Million by weight
PPMv = Parts per Million by volume
gr/ft3 = Absolute Humidity
*Computed on dry air basis

grains of moisture.......7000 grains equals 1 lb. of moisture.

RH is a term used to explain the percentage of moisture in the air to the amount that can be in the air at that temp.

Psychrometrics explains it all.

AcDOCnTRAINING
08-02-2007, 08:59 PM
oF db = Dry Bulb Temperature
oF wb = Wet Bulb Temperature
oF dp = Dew Point Temperature
%RH = Relative Humidity
Btu/lb* = Enthalpy
gr/lb* = Humidity Ratio
Alt in Ft = Altitude
in Hg = Pressure-inches of Mercury
psi = Pressure-pounds per square inch
ft3/lb* = Specific Volume
"Hg VP = Vapor Pressure
PPMw = Parts per Million by weight
PPMv = Parts per Million by volume
gr/ft3 = Absolute Humidity
*Computed on dry air basis

grains of moisture.......7000 grains equals 1 lb. of moisture.

RH is a term used to explain the percentage of moisture in the air to the amount that can be in the air at that temp.

Psychrometrics explains it all.

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Yes it does, in a very long migrain sort of way!:confused:

dan sw fl
08-02-2007, 11:11 PM
Ok, so I know that todays humidity is 50% and the temp is 95*.

Is there a way to convert that to grains of moisture?

or use a web based tool for conversion

http://www.rfcafe.com/references/general/psychrometric_chart.htm

pines
08-02-2007, 11:50 PM
O M G that was the most complicated chart I have ever squinted my eyes at.

Thank you I got it.

50%RH + 95* = 125 grains of moisture.

pstu
08-03-2007, 10:00 AM
Sometimes it takes an ignorant person to explain things in a simple way. I might fill that role with this online psycro calc I think is easy to use and most informative:

http://www.envirochex.com/psychro.htm

Hope this helps -- Pstu