Stairwell Pressurization - Open Door Studies

4.1. Adding New Flow Elements

To add the new Flow Elements to the model:

Now that we have the Flow Elements created, we need to create new Flow Paths on the event level to use them.

4.2. Create Flow Paths

Our Open Door scenario assumes that Level 12.0 m is the fire event floor. TO model the fire scenario on this floor, we will modify the existing stairwell door Flow Paths on that level using our new Door-Open Flow Element and the modeling method described in our Modeling Door States tutorial to model a door opening at 30s and closing at 300s. We will also add a Flow Path to each room that uses our new Window Flow Element.

The Door-Open Flow Paths will represent doors that are opened on the event floor for evacuations and firefighting actions, and the Window Flow Paths will represent windows that are either shattered due to heat, or opened for ventilation purposes.

First, we will add two Flow Paths to represent the windows. To do this:

Now we will use the Modeling Door States method to model our open door. The first step is to create our Door-Open Flow Path. To do this:

We now have all of our Flow Paths created. The final step of configuring our Flow Paths is to edit the Multiplier schedules so that the we can model the door being closed initially, opening at 30s, then closing again at 300s. To do this:

We have now modeled the closed state of our door. For more information on how this Multiplier Schedule models the door state, see the Modeling Door States tutorial. The final step is to model the open state of the door. To do this, repeat steps 3-6 above, modifying the D2_1_3_Open Flow Path using the information in the table below.

Our model is now configured to model our open door scenario. The last step before we can run our model is to set up our Simulation Parameters to run our simulation in Transient mode.

4.3. Editing Simulation Parameters to run in Transient mode

To configure our simulation settings to run in Transient mode:

We are now ready to run the simulation.

4.4. Running the Simulation

To run the study:

4.5. Analyzing Results

Unlike the Closed Door study, this is a Transient simulation, meaning that the differential pressures and flows of our Flow Paths change over time. To analyze the results of our simulation, we will need to use the Results Timeline. To begin our analysis:

As can be seen in Figure 6, the 3D flow vectors and the Path Data table update in real time based on the results data. Prior to 30s, all of the flow at our event door is moving through D2_1_3_Closed. After 30s, the flow switched to D2_1_3_Open. Let us now examine the results at 35s.

As can be seen in Figure 7, the differential pressures of our closed shaft doors drop well below our design criteria because we opened the doors and windows on the fire event level. However, the flow across the open door boundary, shown by the Flow0 column for the D2_1_3_Open Flow Path, increases significantly. To convert this Mass Flow value to a velocity at the boundary, we will assume the standard density of air at sea level to be \(1.225 \frac{kg}{m^3}\) and use the following equation:

\(\frac{flow \frac{kg}{s}}{1.225 \frac{kg}{m^3} * 1.85 m^2} = velocity \frac{m}{s}\)

Plugging in our flow value:

\(\frac{2.282573 \frac{kg}{s}}{1.225 \frac{kg}{m^3} * 1.85 m^2} = 1.007 \frac{m}{s}\)

As can be seen, this flow velocity meets our design criteria requirement of \(1 \frac{m}{s}\).

We can also analyze our Flow Path data using the 2D plotting utility available in Ventus. To do this:

As can be seen from Figure 9, The flow through D2_1_3_Open increases at 30s and quickly levels off, before dropping again at 300s. Inversely, the flow through D2_1_3_Closed decreases at 30s and stops completely, before increasing again at 300s.

Based on the transient results, we can see that our 4750 scfm fan design satisfies our \(1 \frac{m}{s}\) flow requirement within 5s of the door being opened.