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RE: [EnergyPlus_Support] Re: I wonder a part of AFN algorithm
Wonjun:
The equation is extracted from the source code written in Fortran. Here are
my answers to your questions:
1. I don't know what means "d0" in the equation you wrote
"d0" indicates double precision in Fortran
2. Does "tdb+KelvinConv"" means "Celsius Temp + 273.15 K"?
Yes. Your understanding is correct.
3. Where can I find that equation?
Here are references:
! Wylan & Sontag, Fundamentals of Classical Thermodynamics.
! ASHRAE handbook 1985 Fundamentals, Ch. 6, eqn. (6),(26)
Hope my answers help.
Lixing
-----Original Message-----
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Wonjun
Sent: Wednesday, August 03, 2011 12:10 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: I wonder a part of AFN algorithm
Thanks Lixing
I have some questions in the equation you wrote.
rhoair = pb/(287.d0*(tdb+KelvinConv)*(1.d0+1.6077687d0*w))
1.
I don't know what means "d0" in the equation you wrote
2.
Does "tdb+KelvinConv"" means "Celsius Temp + 273.15 K"?
3.
Where can I find that equation?
Thank you very much!
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Lixing Gu <gu@...> wrote:
>
> Wonjun:
>
> The air density is a function of pressure, temperature and humidity ratio
> and is calculated using the following equation in the AirflowNetwork model
> of EnergyPlus:
>
> rhoair = pb/(287.d0*(tdb+KelvinConv)*(1.d0+1.6077687d0*w))
>
> where
> pb = absolute outdoor pressure + indoor gauge pressure
> tdb = dry bulb temperature in C
> w = humidity ratio
>
> Hope this helps.
>
> Lixing
>
>
>
> -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Wonjun
> Sent: Tuesday, August 02, 2011 9:51 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] I wonder a part of AFN algorithm
>
> Hello fellows
> I wonder a part of AFN algorithm, especially the consideration of stack
> effect. I have read many text and E+ engineering references, but can't
find
> the answer of my question.
>
> As you know, bascially the air mass flow is based on the power law
equation
> like below
> air mass flow(M)=C*(dP)^n
>
> the pressure difference of two consecutive nodes (dP) in AFN is (Static P1
+
> Dynamic P1 + Stack P1) - (Static P2 + Dynamic P2 + Stack P2).
> But generally this kind of Bernoulli's Equation assumes density as the
> constant.
> If so, Stack P (=rho*g*h) is just the function of height.
> Because the density and gravity acceleration are constant.
>
> If so, how that equation considers pressure difference from temperature
> difference?
>
> I think AFN consider stack effect in this way but can't sure right or
not(I
> can't find the detailed assumption from Engineering reference).
> If I apply treat the air as an Ideal Gas
> Density(rho)=P/RT
> Then the density is function of Temperature like this (Because R is
constant
> and P would be 101.325kPa)
> or from the linear assumption
> rho=2.7567-0.0053T
> then the Stack pressure rho*g*h can consider the pressure difference from
> temperature diffrerence also.
>
> I look foward to get an answer of my question.
> Thanks in advance.
>
> Best regards.
>
>
>
>
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