[EnergyPlus_Support] Re: I wonder a part of AFN algorithm

["Wonjun" <lesthesia@xxxxxxxxxxx>]

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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