Help with HVAC and Temp mixing
Help with HVAC and Temp mixing
(OP)
Hope somebody can help with this. i'm trying to found the dew point temperature.
the parameters are as follows:
Ambient Temp: 89F
Ambient Humidity: 210 gr/lb
Pressure: 14.7 psi
Hot air into tube: 575F (@ .1 lb/min flow)
Cold air into tube:-18.9F (@ 44 lb/min flow)
I know that first the mixed temperature (T3=Tout) needs to be calculated. then the dew point temperature can be calculated.
any thoughts on this...
thanks
the parameters are as follows:
Ambient Temp: 89F
Ambient Humidity: 210 gr/lb
Pressure: 14.7 psi
Hot air into tube: 575F (@ .1 lb/min flow)
Cold air into tube:-18.9F (@ 44 lb/min flow)
I know that first the mixed temperature (T3=Tout) needs to be calculated. then the dew point temperature can be calculated.
any thoughts on this...
thanks





RE: Help with HVAC and Temp mixing
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RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
TTFN
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RE: Help with HVAC and Temp mixing
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
In any case, assuming perfect mixing, the mixture temperature is -17.6 °F.
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RE: Help with HVAC and Temp mixing
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RE: Help with HVAC and Temp mixing
my challenge has been with the units i have for ambient humidity (gr/lb). which is more of the mixing ratio units.
all the table and charts that i have found have the relative humidity in % and the mixing ratio as value less that 100.
what are your thoughts?
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing
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RE: Help with HVAC and Temp mixing
Maybe I am missing the point here, but if you are going to have air of -19°F inside "just a pipe" without any insulation in an 89°F environment then never mind the dewpoint, it is frosting that is going to happen on the outside of the pipe!
RE: Help with HVAC and Temp mixing
Looking at your numbers:
Ambient Temp: 89F
Ambient Humidity: 210 gr/lb
Does "gr" mean "grams" or "grain" ???
If it is grams then these figures can not be right...
At 89F air can only hold about 30 gr/kg.
PS: I have said it before: you guys should really switch to metric - measuring airvelocities in furlongs/fortnight is just plain annoying
RE: Help with HVAC and Temp mixing
This is an aerospace application where i'm looking to insulate a system. I typically deal with high temp. where we insulate to contain or protect from heat.
In this application i'm tasked with having to insulate a system with those conditions so that NO condensation will form on the outside of the ducts.
The parameters that i have listed is all that my customer has listed in their SCD (design reqm'ts). So i'm trying to find out what the dew point temperature is (if there is), in order to determine what insulation is needed to keep it from getting there to avoid any condensation.
As for the Grams/Grain, i will need to verify that and get back with you.
thanks
RE: Help with HVAC and Temp mixing
The Trane web site has a free download for mixed air streams. I would double check the numbers if going below 32* F.
RE: Help with HVAC and Temp mixing
So now we know what we are after here:
We need the dewpoint of the ambient air, which is stated as having the properties:
Ambient Temp: 89F
Ambient Humidity: 210 gr/lb
I am not all that familiar with Imperial units of measure but it should be pretty straightforward for others around here.
From there it is a small step to figuring out what insulation will give you a surface temperature that is higher than this dewpoint temperature given the fact that you have an inside temperature of around -19F.
RE: Help with HVAC and Temp mixing
RE: Help with HVAC and Temp mixing