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Re: [EnergyPlus_Support] NV
Mohit, see answers below.
Fred Winkelmann
Mohit Mehta wrote:
> i have a couple of questions as i am still learning eplus:
>
> how can one check (from what eplus report) if sum of inflows is equal to the sum of outflows in a naturally ventilated building section?
Look at the report variables "Air Flow from FromZone to ToZone through COMIS Link [m3/s]" and "Air Flow from ToZone to FromZone through COMIS Link [m3/s]."
If you look at the Input/Output Reference section on EnergyPlus/COMIS Output Variables you will see that the first variable is defined as: The air flow through a COMIS link (a crack or window/door opening) from the link?s FromZone to the link?s ToZone. The following input will cause reporting of the FromZone
to ToZone air flow through heat transfer surface Window1, which is an openable exterior window in 3zvent.idf:
Report Variable,Window1,Air Flow from FromZone to ToZone through COMIS Link,timestep;
The second variable is the flow from the ToZone to the FromZone.
The definition of FromZone and ToZone is:
In COMIS, air flows through a link between two zones, one of which is the ?FromZone? and the other is the ?ToZone.? The FromZone and the ToZone may both be thermal zones or one of them may be an exterior air node and the other a thermal zone.
The FromZone and ToZone for a link can be determined by looking at the eplusout.eio file in the <COMIS Air-Flow Link Data> section.
The following shows an excerpt from the eplusout.eio file that gives the FromZone?s and ToZone?s for the links in the 3zvent.idf example input. (This input has three thermal zones, WEST_ZONE, EAST_ZONE and NORTH_ZONE.) For example, the FromZone for SURFACE_4 is EAST_ZONE and the ToZone is WEST_ZONE. Note
that a FromZoneName or ToZoneName of the form ?-EXN? means that the ?zone? is actually exterior air node number N. For example, the FromZone for WINDOW1 is exterior air node number 3 and the ToZone is WEST_ZONE.
! <COMIS Air-Flow Link Data>,Surface Name,Surface Class,Air-Flow Data Name,FromZone Name,ToZone Name
COMIS Air-Flow Link,SURFACE_1,WALL,CR_0000001,-EX3,WEST_ZONE
COMIS Air-Flow Link,WINDOW1,WINDOW,WI_0003_1,-EX3,WEST_ZONE
COMIS Air-Flow Link,SURFACE_2,WALL,CR_0000001,-EX4,WEST_ZONE
COMIS Air-Flow Link,SURFACE_3,WALL,CR_0000002,NORTH_ZONE,WEST_ZONE
COMIS Air-Flow Link,DOORINSURFACE_3,DOOR,WI_0004_1,NORTH_ZONE,WEST_ZONE
COMIS Air-Flow Link,SURFACE_4,WALL,CR_0000002,EAST_ZONE,WEST_ZONE
COMIS Air-Flow Link,SURFACE_8,WALL,CR_0000001,-EX3,EAST_ZONE
COMIS Air-Flow Link,SURFACE_9,WALL,CR_0000001,-EX2,EAST_ZONE
COMIS Air-Flow Link,SURFACE_11,WALL,CR_0000002,NORTH_ZONE,EAST_ZONE
COMIS Air-Flow Link,SURFACE_14,WALL,CR_0000001,-EX4,NORTH_ZONE
COMIS Air-Flow Link,SURFACE_15,WALL,CR_0000001,-EX1,NORTH_ZONE
COMIS Air-Flow Link,WINDOW2,WINDOW,WI_0003_2,-EX1,NORTH_ZONE
COMIS Air-Flow Link,SURFACE_16,WALL,CR_0000001,-EX2,NORTH_ZONE
If the sum of the "FromZone to ToZone" and "To Zone to FromZone" flows should be zero if you are careful to take into account the flow direction, which means you have to know what the FromZone and ToZone is for each crack or opening, as explained above.
Note that, depending on wind conditions, stack effect, etc., an opening can simultaneously can have a non-zero value for both the "FromZone to ToZone" and "ToZone to FromZone" flow. This is because openings (like open windows) can have bidirectional flows.
>
>
> also if the section has vents at different levels how does one know if these are experiencing inflow or outflow?
See answer above.
> how does eplus calculate and display the neutral pressure level for a tall stack?
The neutral pressure level is not displayed. The calculation is described on pp. 12-13 of H.E. Feustel, "COMIS -- An International Multizone Air-Flow and Contaminant Transport Model," LBNL report no. 42182, avaibable from http://epb1.lbl.gov/comis/users.html
>
>
> energyplus does "Automatic calculation of COMIS wind pressure coefficients for rectangular buildings" but the user is asked to input COMIS CP ARRAY and CP VALUES by wind direction... is this redundant or it uses the user defined values over calculated ones? is it better if i enter zero for all CP values?
If you specify automatic calculation of wind pressure coefficients, then COMIS CP ARRAY, COMIS CP VALUES and COMIS EXTERNAL NODE are not used. See description of "Wind Pressure Coefficients" in the COMIS Simulation object.
>
>
> thanks, ~m
>
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