Practice Exercise: HVAC Systems

Practice Exercise: HVAC Systems

Focus / Design Goal

The focus of this exercise is to explore how HVAC systems can be designed to meet their functional requirements without compromising the aesthetics and spatial feeling of a proposed building design.

Download these two Revit models as the starting point for this exercise:

This early version of the mechanical model already includes:

  • Spaces and zones
  • Mechanical room (Room 15) on Level 0w
  • a Heating and Cooling Loads Report produced using a prior workflow
Although the analysis workflow has changed in Revit 2023, you can use this provided Loads Report to place the required number of air terminals in the model spaces. For this practice exercise, you DO NOT need to recreate the Energy Analytical Model or run a new HVAC Loads report.

Your task is to model the supply air ducts for an Air Transport HVAC system to deliver heating and cooling from the mechanical room to each of the spaces.

Design Tasks

  1. Start by exploring the space available for your ducts and thinking about the layout you will use for routing the ducts from the mechanical room to the supply diffusers in the spaces. Consider:
    1. How much space is available overhead given the floor-to-floor height of the building and the structural beams that will support the floor?
    2. What routing will create the most efficient duct layout and not compromise the aesthetic goals for the project?
  2. Next, review the mechanical model for accuracy. You’d typically check:
    1. Are the Spaces defined appropriately to accurately predict the heating and cooling demand?
      1. Are they fully enclosed (have the right Upper Limit to intersect the roof or floor above that will provide a thermal boundary)?
      2. Are the Spaces set to the appropriate Space Type and Condition Type for their planned use?
    2. How many Zones are defined in model? Is the zoning appropriate for the level of thermal control that you’d like to offer the building’s users?
  3. Review the provided Loads Report (at Reports > Loads Reports > Loads Report - Previous Workflow in the Project Browser) and the provided Space Schedule.
    1. Do you notice anything unusual or unexpected? If so, you’d want to investigate the cause and update the model or energy settings as needed to produce accurate load predictions.
    2. Take note of the reported Heating and Cooling loads for each space and the Calculated Supply Airflow reported in the Space Schedule. This will guide you as you determine the number of supply diffusers will be needed to provide the air required for each space.
  4. Updated the mechanical model to add the supply diffusers required, place the supply ducts, and route them to the mechanical room (where an air handler could be located to provide the supply air).
    1. Add supply diffusers to each space based on the Calculated Supply Airflow reported in the Space Schedule. As you place the diffusers, think about:
      1. What height will you place the supply diffusers above the floor level?
      2. How many diffusers are needed in each space if a single diffuser can provide up to 500 CFM? Note that you can adjust the air flow planned for each diffuser. So, for example, you can provide 500 CFM with a single diffuser or two diffusers providing 250 CFM each.
      3. Do any spaces require less than 500 CFM? If so, you can set the flow for these spaces to a smaller number to accurately reflect that less airflow is needed.
    2. Check the Space Schedule to verify that the Actual Supply Airflow (based on the diffusers that you have placed) exceeds the Calculated Supply Airflow in each space.
      1. If the supply diffusers that you have placed are not showing up in the table, check to make sure that their elevation property is set to be within the limits of the space. For example, if the upper limit of your space is 10’, be sure that the elevation of your supply diffuser is less than 10’ to be counted as in the space.
    3. Place ducts to provide air to your supply diffusers from the mechanical room location, where an air handler (that you don’t need to model) will be located. As you place the ducts, think about:
      1. What height you will place the ducts above the floor level? You’d like them as high as possible (to minimize their visual impact), but low enough to clear the structural beams that support the floor above.
      2. What shape should the ducts be? Round? Rectangular?
      3. What size should the ducts be? The Duct Sizing tool will help compute the needed duct sizes, but you should have an initial size in mind as you place them in the model -- say 12x18 or 12x12.
      4. Your duct routing should match the zones that have been set up in the model.
        1. The model includes 4 zones — a West zone and a East zone at both of the floor levels. This zoning was selected to allow users to control the heating and cooling of the east and west sides of the building separately, because the loads on the east and west sides can vary greatly based on the time of day.
        2. You’ll probably want to provide two separate supply branches on each floor level, routing back to the mechanical room on that floor level
        3. Note: To simplify this exercise, DO NOT model the air handler unit in the mechanical room or any VAV zone controllers on the duct branches. Just route the ducts from the diffusers to the mechanical room location, where the air handler will be modeled later.

  5. Optional Duct Sizing (Not Required for Your Submission) If you’d like to explore how the Duct Sizing tool can help calculate the needed duct sizes in each branch of your supply duct system, you can:
    1. Select each branch separately, and run the Duct Sizing tool on each branch independently. This strategy of sizing the ducts on a single small branch at a time makes it much easier to isolate any problems and fix them.
    2. As you set the options for the Duct Sizing tool, think about whether you’d prefer to restrict the maximum duct heights (to preserve headroom) or allow them to resize in both height and width.
  6. Use the ACC Model Coordination tool to view your merged/integrated models:
    1. Upload your proposed HVAC model to your Autodesk Construction Cloud project folder, and then copy it to your Coordination Space folder.
    2. Then, merge it with the architectural model and your structural models (already uploaded to Model Coordination) from the practice exercise in the Structural Systems module.
    3. Capture a screenshot of an interior view showing the merged model similar to the image below.

  1. As you review the merged/integrated model view, consider:
    1. Did you accidentally cover any floor openings (elevator, stairs, atrium)?
    2. Are there any obvious conflicts between your structural system and your mechanical systems? (for example, ducts and beams that intersect)
    3. Would you place a ceiling to conceal the structural and mechanical systems or leave the systems exposed? What height would the ceiling be above the floor level? And would that height meet your aesthetic and use goals for the project?

Then, post your Practice Exercise results below.

Click the + New Button and add a card for your plumbing system design to this gallery. Tips for Editing: - If you don’t see the + New button, click the Edit button in the toolbar at the top of this page. - If you can’t edit your new page, click the “Open as page” link at the top of the page.

Be sure to include:

  • The screenshot of an interior view of your merged view from Model Coordination tool showing the HVAC elements.
  • A brief paragraph discussing:
    • any challenges that you encountered in this supply duct routing exercise
    • whether your proposed design meets the project’s spatial design goals
    • any recommendations to make the design more sustainable (and lower the heating and cooling loads)

HVAC System Recommendations | Winter 2023