Mechanical Ventilation

Mechanical Ventilation analyses simulate the air flow in spaces that are controlled with air management systems. Such systems typically include a network of diffusers, fans, and returns designed to ensure proper air flow and temperature control within the occupied area.

Application Examples

Data Center Optimization

Energy Audits of Laboratory and Campus spaces

Fire Contaminant / Smoke visibility and extraction

Thermal Comfort of occupants within a space or dwelling

HVAC System Design

Diffuser Throws and internal flow patterns

Modeling Strategy

Most mechanical ventilation applications consist of the following elements:

Primary modeling considerations for Mechanical Ventilation models include:

These items and several more are presented in detail in the AEC Geometry Modeling topic...

Materials

Assign the Air material to all air regions.

Note that in most mechanical ventilation applications, buoyancy effects are negligible, and the Environment setting should be set to Fixed. An important benefit of this is that the flow solution is independent of the temperature distribution. This means that the flow and heat transfer solutions can be run independently. The benefits include faster simulation times and the flexibility to run multiple thermal analyses using the same flow solution.

The default air properties are set for 68 °F. If the operating temperature is greater than 90 °F or less than 50 °F, modify the Scenario Environment temperature to the appropriate value. This ensures the air density is appropriate for the operating conditions.

Several other material types are commonly used in AEC applications:

Click here for more about materials in AEC applications...

Boundary Conditions

Flow Conditions

Air is mechanically moved in and out of the interior space at known conditions. Use boundary conditions to specify these conditions and their locations.

If all inlet and outlet flow rates are known, assign a volume flow rate condition to all openings, except one. Assign a Static Gage Pressure = 0 to this remaining outlet.

Some additional considerations for flow boundary conditions:

When assigning flow conditions, it is always a good idea to verify the flow direction with the arrow displayed on the surface. If the arrow indicates the flow is in the wrong direction, click the Reverse normal button on the Boundary Condition quick edit dialog.

Thermal Conditions

Heat transfer boundary conditions should always be applied if the objective is to learn the temperature distribution. (These can be omitted if the objective is to assess only the flow.)

Click here for more about thermal boundary conditions for AEC applications...

Mesh

A basic guideline for a high-quality analysis model is that the mesh distribution be sufficient to resolve the flow and temperature gradients efficiently. In regions where the flow circulates or experiences large gradients (such as in wakes, vortices, and separation regions), a finer mesh is required.

For most models, use Automatic Sizing to define the mesh distribution. It may be necessary to locally refine the mesh on geometric features that are highly detailed. For more information about Mesh Autosizing and model preparation...

In some cases, it may be necessary to adjust the Minimum Refinement Length to reduce their effect on the overall mesh count.

To locally refine the mesh in high-gradient flow regions:

Click here for more about mesh strategies for AEC applications...

Running

On the Physics tab of the Solve dialog:

On the Control tab of the Solve dialog:

The specified number of iterations, 750, is the maximum number of iterations that will run. (This has been found to be sufficient for most mechanical ventilation simulations.) Autodesk Simulation CFD stops the solution when either 750 iterations have been completed or when the solution reaches convergence, whichever comes first. If heat transfer and Automatic Forced Convection are enabled, Autodesk Simulation CFD automatically solves for the temperature distribution after the flow solution is complete.

Additional Solver Capabilities

Results Extraction

For more general information, use the extensive collection of results visualization tools to extract flow and thermal results.