HVAC Room - Thunderhead Engineering · HVAC Room In this tutorial you will use the Heating Ventilation and Air Conditioning (HVAC) features to model a duct that heats and circulates

HVAC Room

2013

References

HVAC Room In this tutorial you will use the Heating Ventilation and Air Conditioning (HVAC) features to model a duct

that heats and circulates air in a room.

This tutorial demonstrates how to:

Create HVAC nodes and ducts.

Create an HVAC fan.

Create an HVAC heating coil.

Define an HVAC surface on a vent.

Use devices to plot HVAC parameters

Add slice planes for velocity visualization.

View 3D results using Smokeview.

An HVAC system is described as a network of duct segments and nodes, where a node is either a point

where two or more ducts connect or where a duct segment connects to the FDS computational domain.

The HVAC network consists of lines (ducts) and points (nodes). It is only necessary to draw the true

geometry at vents where the HVAC system connects to the FDS domain.

Figure 1. HVAC model showing the ducts (lines), nodes (points), and vents used to define the HVAC

system

Units In this example we will use SI units.

1. On the View menu, click Units

2. Select SI.

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Computational Mesh In this example we will use a 10 m x 10 m x 3 m mesh with 0.25 m cells.

1. On the Model menu, click Edit Meshes...

2. Click New.

3. Click OK to create the new mesh.

4. In the Min X box, type 0.0 and in the Max X box, type 10.0.

5. In the Min Y box, type 0.0 and in the Max Y box, type 10.0.

6. In the Min Z box, type 0.0 and in the Max Z box, type 3.0.

7. In the X Cells box, type 40.

8. In the Y Cells box, type 40.

9. In the Z Cells box, type 12.

10. Click OK to save changes and close the Edit Meshes dialog.

Create the Duct Obstruction Strictly speaking, we only need to define obstructions at the vent locations where the HVAC network

connects to the FDS computational domain. However, in this model, we will represent the entire duct

geometry, partly because it makes the final visualization more realistic.

1. On the Model menu, click New Obstruction...

2. In the Description box, type Duct.

3. Click the Geometry tab.




7. Click the Surfaces tab.

8. Select Single (all surfaces are the same) and ADIABATIC (insulated)

9. Click OK to create the obstruction.

Create Vents In this model, vents are used at the end of HVAC duct segments to connect to the FDS computational

domain. To create the inlet vent:

1. On the Model menu, click New Vent....

2. In the Description box, type Inlet.

3. In the Surface list, select HVAC. This specifies that the previously created surface will define the

properties of the vent.

4. Click on the Geometry tab.

5. Select the X Plane and type 1.001 in the box. Note: The small offset distance from the duct

geometry ensures no flashing in the display and, because FDS snaps to the grid, will not change

the final geometry.

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8. Click OK.

To create outlet vent:

1. In the Tree View, right-click on the Inlet vent and select Copy/Move…

2. Select the Copy Mode and in the Number of Copies box type 1.

3. In the Offset, in the Y box type 7.0.

4. Click OK.

5. In the Tree View, right-click the copied vent and rename it Outlet.

Figure 2. The duct and vents

Create HVAC Network We now create the HVAC network. We will split the duct between the inlet and outlet into two

segments. In one segment we will define a fan and in the other segment we will define a heater. Two

segments are needed because we can add only one HVAC component to a segment.

We will first create the HVAC nodes:

1. On the Model menu, click Edit HVAC...

2. Click New, select Type as Node and in the Name box type Inlet. Click OK.

3. For Node Type, select Vent Endpoint and in the pulldown options select Inlet (this is the inlet

vent we created above).

4. Click Apply.

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5. We repeat these steps for the outlet. Click New, select Type as Node and in the Name box type

Outlet. Click OK.

6. For Node Type, select Vent Endpoint and in the pulldown options select Outlet (this is the

outlet vent we created above).

7. Click Apply.

8. Now we create the nodes along the run of the duct. Click New, select Type as Node and in the

Name box type Left Node. Click OK.

9. For Node Type, select Internal and in the Location boxes, in X type 0.5, in Y type 1.5, and in Z

type 2.25.

10. Click Apply.

11. Click New, select Type as Node and in the Name box type Center Node. Click OK.


type 2.25.

13. Click Apply.

14. Click New, select Type as Node and in the Name box type Right Node. Click OK.


type 2.25.

16. Click Apply and then click OK to close the Edit HVAC dialog.

17. In the Tree View right-click the Duct obstruction and select Hide Object(s). The HVAC nodes are

shown in Figure 3.

Figure 3. The HVAC nodes

Now we create the HVAC fan and heater:


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2. Click New, select Type as FAN and in the Name box type Fan. Click OK.

3. For Fan Model, select Constant Flow and in the Volume Flow Rate box type 2.0.

4. Click Apply.

5. Click New, select Type as AIRCOIL and in the Name box type Heater. Click OK.

6. For Heat Transfer Model, select Direct and in the Heat Exchange Rate box type 5.0.


Now we add the HVAC ducts:


2. Click New, select Type as DUCT and in the Name box type Inlet Duct. Click OK.

3. On the Properties tab, for Node 1 select Inlet and for Node 2 select Left Node.

4. Click the Flow Model tab and type the Roughness as 0.001.

5. Click Apply.0.001

6. Click New, select Type as DUCT and in the Name box type Left Duct. Click OK.

7. For Node 1 select Left Node and for Node 2 select Center Node.

8. Click the Flow Model tab and type the Roughness as 0.001. Under Flow Device select Fan. The

previously created Fan will be selected in the pulldown menu.

9. Click Apply.

10. Click New, select Type as DUCT and in the Name box type Right Duct. Click OK.

11. On the Properties tab, for Node 1 select Center Node and for Node 2 select Right Node.

12. Click the Flow Model tab and type the Roughness as 0.001. Under Flow Device select Aircoil.

The previously created Heater will be selected in the pulldown menu.

13. Click Apply.

14. Click New, select Type as DUCT and in the Name box type Outlet Duct. Click OK.

15. On the Properties tab, for Node 1 select Right Node and for Node 2 select Outlet.

16. Click the Flow Model tab and type the Roughness as 0.001.


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Figure 4: The HVAC network

HVAC Devices We use devices to plot HVAC quantities. Both duct and node quantities can be plotted, we will illustrate

with one of each.

1. On the Devices menu, click New HVAC Duct Device....

2. In the Name box type HVAC Velocity and in the Quantity menu select HVAC Quantity. This

will open a Choose Quantity dialog.

3. For the Quantity select Velocity of a Duct and in the HVAC Duct select Left Duct.

4. Click OK to close the Choose Quantity dialog and then OK again to close the HVAC Device

dialog.

5. On the Devices menu, click New HVAC Node Device....

6. In the Name box type HVAC Outlet T and in the Quantity menu select HVAC Quantity. This

will open a Choose Quantity dialog.

7. For the Quantity select Temperature of the Flow through a Node and in the HVAC Node select

Outlet.

8. Click OK to close the Choose Quantity dialog and then OK again to close the HVAC Device

dialog.

Slice Planes Slice planes can be used to display 2D contours in the Smokeview display of the results. In this analysis,

we will save temperature and velocity data for future plotting. To define the slice planes:

1. On the Output menu, click Slices....

2. Fill the table by entering the values in Table 1. You can click on the row number to select entire

rows to copy and paste, speeding the entry.

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3. Click OK to close the Animated Planar Slices dialog.

Click the Show Slices tool to enable/disable display of the slices.

Table 1. Slice plane data

XYZ Plane Plane Value (m) Gas Phase Quantity Use Vector?

Z 2.25 Velocity YES

Z 2.25 Temperature YES

X 5.0 Velocity YES

X 5.0 Temperature YES

Y 1.25 Velocity YES

Y 1.25 Temperature YES

Y 8.75 Velocity YES

Y 8.75 Temperature YES

Statistical Data It is possible to record statistical data in the model to plot as a function of time. In this model, we will

plot the average temperature in the room, since this will increase due to the heater.

1. On the Output menu, click Statistics....

2. Click New, select Quantity as Temperature and in the Name box type Temperature. Click OK.

3. Under Statistics select Volume Mean.




7. Click OK.

Specify Simulation Properties 1. On the FDS menu, click Simulation Parameters....

2. In the End Time box, type 100.0.

3. Click the Misc tab, and select the Default Surface Type as Adiabatic (no heat transfer to

boundary)

4. Click OK.

Save the Model 1. On the File menu, click Save.

2. Choose a location to save the model. Because FDS simulations generate many files and a large

amount of data, it is a good idea to use a new folder for each simulation. For this example, we

will create a folder named HVAC and named the file hvac room.psm.

3. Click Save to save the model.

Run the Simulation 1. On the FDS menu, click Run FDS....

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2. The FDS Simulation dialog will appear and display the progress of the simulation. This should

take approximately 10 minutes to run, depending on computing hardware.

3. When the simulation is complete, Smokeview will launch automatically and display a 3D image

of the model.

View Slice Data 1. In the Smokeview window, right-click to activate the menu.

2. In the menu, click Load/Unload > Slice File > Velocity > Load All.

The plot of the velocity contours is shown in Figure 5.

On the toolbar, select Plot Device Results. The duct diameter is 0.3048 m, so the expected velocity of

flow in the duct for a volumetric flow rate of 2 m3/s is 27.4 m/s, Figure 6. The time history of the mean

temperature is plotted in Figure 7. This temperature rise is 1.92 °C. A calculation using properties for air

at 20 °C gives an expected value of 1.926 °C, verifying the FDS result.

Figure 5: Velocities in model

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Figure 6: Velocity of flow in duct

Figure 7: Increase in room temperature

References FDS-SMV Official Website. Fire Dynamics Simulator and Smokeview. Gaithersburg, Maryland, USA :

National Institute of Standards and Technology.

Klein, Bryan. 2007. Switchgear example problem, personal communication. Gaithersburg, Maryland,

USA : National Institute of Standards and Technology, 2007.

References

Korhonen, Time and Hostikka, Simo. 2009. Fire Dynamics Simulator with Evacuation: FDS+Evac. s.l.,

Finland : VTT Technical Research Centre of Finland, April 2009. VTT Working Papers 119.

McGrattan, Kevin and Forney, Glenn. 2005. Fire Dynamics Simulator (Version 4) User's Guide.

Washington, DC, USA : s.n., 2005. NIST Special Publication 1019.

McGrattan, Kevin. 2004. Fire Dynamics Simulator (Version 4) Technical Reference Guide. Washington,

DC, USA : s.n., 2004. NIST Special Publication 1018.

McGrattan, Kevin, et al. 2007. Fire Dynamics Simulator (Version 5) Technical Reference Guide.

Gaithersburg, Maryland, USA : s.n., October 2007. NIST Special Publication 1018-5.

McGrattan, Kevin, et al. 2007. Fire Dynamics Simulator (Version 5) User's Guide. Gaithersburg,

Maryland, USA : s.n., July 2007. NIST Special Publication 1019-5.

—. 2007. Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications. s.l.,

Washington DC, USA : U.S. Nuclear Regulatory Commission, Office of Regulatory Research, May 2007.

NUREG-1824, EPRI 1011999.

SFPE. 2003. Engineering Guide - Human Behavior in Fire. Bethesda, Maryland, USA : Society of Fire

Protection Engineers, June 2003.

McGrattan, Kevin, et al. 2013. Fire Dynamics Simulator User’s Guide. Gaithersburg, Maryland,

USA : s.n., November 2013. NIST Special Publication 1019.

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HVAC Room - Thunderhead Engineering · HVAC Room In this tutorial you will use the Heating Ventilation and Air Conditioning (HVAC) features to model a duct that heats and circulates