You can place the Ventilation elements on the side surfaces of walls and the lower surfaces of floor slabs.
Ventilation elements are represented in the FDS file using the VENT, SURF, and DEVC parameter groups if the “On Time” is set to a non-zero value.
&SURF ID='7' FYI='Ventilation 1_Y' VEL=0.101413673278638 VEL_T=0.252424359458118,0 RGB=102,1,1/
&DEVC ID='9' FYI='Ventilation 1 controller' QUANTITY='TIME' SETPOINT=10 XYZ=-0.313183754386492,1.44422896607399,1.5/
&VENT XB=-0.5,-0.5,1.5,2,1,2 IOR=-1 SURF_ID='7' DEVC_ID='9'/
The VEL parameter of the SURF group sets the air velocity normal to the VENT plane. A positive value corresponds to exhaust ventilation, while a negative value indicates supply ventilation. The VEL_T parameter, if used, specifies the tangential velocity component.
The SETPOINT parameter of the DEVC group sets the start time for ventilation.
The XB parameter of the VENT group sets the coordinates of the VENT element, with one pair being the same since the element has zero thickness. The IOR parameter can help FDS place the VENT on the correct side of the OBST if there are ambiguities due to approximating dimensions.
VENT elements must be placed on the surface of OBST elements with non-zero thickness. The conversion of Ventilation coordinates from Fenix+ 3 to VENT element coordinates is similar to the conversion of Wall and Floor Slab coordinates to OBST element coordinates. For the representation of Walls and Floor Slabs using OBST elements, see Elements with Material Property Section. As a result, all VENT elements are located on the surface of the OBST elements corresponding to the Wall or Floor Slab on which the Ventilation is located.
Due to the discreteness of the computational domain, the total area of the VENT elements describing a given ventilation element may differ from that specified in Fenix+ 3. However, the air flow rate and direction of the air movement vector remains the same. The correct air flow rate is achieved by adjusting the flow velocity.
Below is an example where a supply ventilation element is placed on a Wall. Its width and height are 1 m, and the capacity is set to 1000 m³/h.
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The black color in the picture shows the direction of the air flow vector perpendicular to the Ventilation plane.
The following picture shows how Wall and Ventilation are represented in the FDS file (view in Smokeview).
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In the FDS file, the specified ventilation corresponds to the following code:
&SURF ID='4' FYI='Ventilation 1_X' VEL=-0.22031617876375 VEL_T= 0.114923198028057,0 RGB=102,1,1/
&SURF ID='5' FYI='Ventilation 1_Y' VEL=-0.114923198028057 VEL_T= 0.22031617876375,0 RGB=102,1,1/
&VENT XB=0.75,0.75,2.5,3,1,2 IOR=-1 SURF_ID='4'/
&VENT XB=0.5,0.5,3,3.25,1,2 IOR=-1 SURF_ID='4'/
&VENT XB=1,1,2.25,2.5,1,2 IOR=-1 SURF_ID='4'/
&VENT XB=0.5,0.75,3,3,1,2 IOR=-2 SURF_ID='5'/
&VENT XB=0.75,1,2.5,2.5,1,2 IOR=-2 SURF_ID='5'/
Despite the fact that Ventilation is represented in FDS by VENT elements, the plane of each is different from the Ventilation plane in Fenix+ 3. The direction of the air blown out by each VENT element is the same as required. To verify this, it is enough to build a vector with VEL and VEL_T coordinates for each VENT element. (See picture below)
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The ventilation capacity can be estimated by multiplying the area of each VENT by the normal velocity component and adding the results. For example, we get:
Air flow rate = 0.5 m² * 0.22 m/s + 0.25 m² * 0.22 m/s + 0.25 m² * 0.22 m/s + 0.25 m² * 0.115 m/s + 0.25 m² * 0.115 m/s ≈ 0.2775 m³/s = 1000 m³/h.
The air flow rate corresponds to that specified in the Ventilation element parameters.
When placing Ventilation on a Floor Slab, the element is converted to an FDS file in the same way. Since the Floor Slab is always horizontal, the plane of the Ventilation element always coincides with or is parallel to the plane of the VENT element, so only one (normal) velocity component, VEL, is specified in the SURF group.