Re: [EnergyPlus_Support] COMSI AIR FLOW:OPENING=>Discharge coefficient ?

["Joe Huang" <yjhuang@xxxxxxx>]

Ming,

The theoretical maximum Discharge Coefficient for an open door would be 1.0,
but in reality it never gets that high because the flow is contracted due to
the existence of the opening.  According to COMIS Fundam entals (LBL-28560,
May 1990), "[flow contraction] depends on the fluid and the local flow
characteristics caused by the shape of the opening. Its value goes from 0.61
for sharp-edged orifices to 0.98 for trumpet shaped nozzles. A brief review
[51-53] indicates that these values can be as low as 0.36 and higher than
0.75 for large openings (p. 45). "

Please note that COMIS will determine the Cd from the other input parameters
(from COMIS 3.0 User's Guide, p. 61-62):

 Internal doors:  Cd = f(Height of the door/Height of the room);
                          with this function Cd will be in the range from
0.05 to 0.5.
 External openings;  Cd= f(wind velocity, temp. difference, depth of the
room);
                          with this function Cd will be in the range from
0.6 to 1.5.
If Cd has to be calcujlated by the program, the following restructions apply
for the input:
 . LVO mustr be type 1
 . Cd=0; for all opening factors

Joe

----- Original Message -----
From: "waspoorboy" <mingsbox@xxxxxxxxxxxxxx>
To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Monday, December 08, 2003 12:54 PM
Subject: [EnergyPlus_Support] COMIS AIR FLOW:OPENING=>Discharge coefficient
?


> My understandings are:
> For a typical door,
> When a door is closed, Opening Factor=0.0; Discharge coeff =0.0
> When door is fully open, Opening Factor=1.0; Discharge coeff =1.0
> So why the discharge coeff are 0.5 and 0.6 in the example file ?
> I must missed something.
> Thanks for correcting my understandings.
> Ming
>
>      0.0,  !- Opening factor #1 {dimensionless}
>      0.5,  !- Discharge coefficient for opening factor #1
>      0.0,  !- Width factor for opening factor #1
>      1.0,  !- Height factor for opening factor #1
>      0.0,  !- Start height factor for opening factor #1
>
>      1.0,  !- Opening factor #2 {dimensionless}
>      0.6,  !- Discharge coefficient for Opening factor #2
>      1.0,  !- Width factor for for Opening factor #2
>      1.0,  !- Height factor for for Opening factor #2
>      0.0,  !- Start height factor for for Opening factor #2
>
>
>
>
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