Module 9 - Design Project Brief: System Design — HVAC Systems

Module 9 - Design Project Brief: System Design — HVAC Systems


The focus of this stage in your integrated design project is to explore how you can best implement the strategies that you identified for achieving your project goals as you design the features of your building’s HVAC system.  For this check-in you’ll add these features to your building model:

  • HVAC Analysis Features
    • Spaces
    • HVAC Zones
  • HVAC System Elements
    • Mechanical Equipment
      • Air Handlers
      • Zone Controllers
    • Air-Based System Components
      • Ducts
      • Air Terminals
    • Fluid-Based System Components (if used)
      • Piping
      • Radiators

Recommended Approach

At this point in our design process, we’ll continue adding the details to flesh out our initial building design ideas -- for this check-in, focusing on your overall heating, ventilating, and cooling strategy and the HVAC system elements that will illustrate your proposed systems.

Start with an Overall HVAC Strategy

Before you dive into building modeling in Revit, start by carefully considering your overall HVAC system strategy:

  • What type of heating and cooling loads will your building experience based on the space uses (internal loads) and the project climate and solar exposure (external loads)?
  • For your climate, do you have more of a heating problem (need to warm the spaces to keep them comfortable) or a cooling problem (need to cool the spaces)? Or is it evenly split?
  • Regardless of what strategy you use for heating and cooling, you’ll need to provide adequate ventilation to meet the minimum fresh air levels required. You may be able to use natural ventilation throughout much of the year (if the outside air is thermally comfortable), but there will likely be at least a few times where the ventilation will need to be supplied mechanically by your HVAC system.
  • What type of heating systems can you use?
    • Can you capture solar heat from your passive design features (glazing and shading) to meet part of your heating requirements during the warming months -- but provide shading to prevent excess unwanted heat gain during the cooling months?
    • What type of heating would you like to use to supplement the heating needs when required? Air-based ducted heating? Fluid-based radiant heating? Electric resistive heating?
  • What type of cooling systems can you use?
    • Can you shield your building from the solar heat using your passive design features (shading) to reduce the cooling load during the cooling months?
    • Can you use natural ventilation, air movement, or water features (evaporation) to provide some of the cooling naturally?
    • What type of cooling would you like to use to supplement the cooling needs when required? Air-based ducted cooling? Fluid-based radiant cooling? Individual AC units is specific spaces?

Create a Linked Mechanical Model

  • Create a new Revit model using the Systems Template.
  • Link your architectural model to this new mechanical model using origin-to-origin positioning.
    • Be sure to select the architectural model and edit its Type properties to turn on the Room Bounding property. That way, your architectural rooms can be used to define your HVAC spaces.
  • Use the Copy/Monitoring tool to copy these elements from your architectural model:
    • Levels -- to create matching levels with the same floor-to-floor heights in your mechanical model.

Calculate the Heating and Cooling Loads

  • Before you get started placing HVAC system elements, you’ll need to know:
    • How big the heating and cooling loads will be in each space
    • How much supply air will be required for:
      • Ventilation (all spaces require this)
      • Heating (if you’re using an air-based heating system)
      • Cooling (if you’re using an air-based cooling system)
  • Place spaces and HVAC Zones to model the way your building spaces will be used and thermally zoned.
  • Run the Heating and Cooling Loads report in Revit to compute the thermal loads and supply air requirements for each space.

Model the HVAC System Elements

  • Mechanical Equipment
    • Air Handlers
    • Zone Controllers
  • Air-Based System Components
    • Ducts
    • Air Terminals
  • Fluid-Based System Components (if used)
    • Piping
    • Radiators

How Detailed Should This Version of Model Be?

At this stage, you’ll want your mechanical model to accurately reflect the locations of the major elements and essential components of your HVAC strategy.

It’s very easy to get lost in all the detail of modeling the HVAC system components -- for example, getting all the ducts to connect properly can be very tricky, especially if they get very large when you resize them to match the airflow required -- so:

  • Focus on using this tool to help you explore how you can implement your design strategy. 
  • Keep your system modeling very high level.
  • Get the main components in your HVAC strategy modeled to illustrate how they’ll work together with the other building systems...
  • But DO NOT agonize over every last connection.

Our goal in modeling the HVAC system is to understand the impacts of your design decisions and find ways to improve your design -- NOT to create a perfect Revit model.

  • DO NOT…  I repeat, DO NOT…  I repeat again, DO NOT struggle over the duct connections that just don’t want to connect as desired.  
  • Learn to let go of the small details when you’re in this design exploration phase.  The details will get resolved later in the process.

For the scope of this course and design project, you won’t be able to resolve all the HVAC details -- and that’s okay!  There will be lots of unknowns and issues for future resolution -- that’s typical, expected and okay!

What Size Should the HVAC System Elements Be?

Similar to our challenge when doing the structural design, the answer is -- we don’t know yet!

In practice, we can compute the overall and cooling loads for the overall building (or for each zone in the building) and use this information to pick appropriately-sized heating and cooling equipment.   But, selecting that equipment is beyond the scope of this course -- so, you can place some moderately-sized mechanical equipment as placeholders (to be sized by an HVAC engineer later).

Duct sizing is something that we can do now based on the supply air requirements that you’ve computed for each space.  As you get started modeling, place ducts using an approximate size -- say 12x12 or 12x16 -- as placeholders.  Then, you can use the Duct Sizing tool to compute the actual sizes based on the airflow demands of the terminal that you connect to each duct.

Does the HVAC System affect Other Systems?

The design of your envelope system, your structural system, and your HVAC system all have to work together:

  • Your envelope system choices have a huge impact on the heating and cooling loads that your building will experience. So, careful envelope design can be used to greatly reduce the size of the components in your HVAC system.
  • Your structural system choices have a big impact on the space available for placing ducts as part of your air-based HVAC systems. The layout and depth of the beams and beam systems often dictate the space and paths available for routing ductwork.

Progress Check-In / Documenting Your Design Journey

About Design Journal Entries

You’ll be sharing your ongoing design process and progress with others in our class community through a posting in an online Design Journal using Notion.

Feel free to use whatever format best captures the ideas that you want to share -- text, images, sketches, photos of hand sketches, intermediate models, results of analyses, and so on.

For this class, your design process is as important as the final result.

Post a Design Journal Entry

Create a new posting sharing your Design Journal entry on this linked Notion page:

✏️Design Project Check-In: HVAC Systems

Your Design Journal entries this week should highlight your design thinking and analysis results that influenced your decisions about:

  • your overall HVAC system strategy
  • your heating strategy and how you implemented it in your design
  • your cooling strategy and how you implemented it
  • any special HVAC system challenges that you encountered

Model Coordination

Upload the latest versions of your architectural, structural, and HVAC models to Autodesk Construction Cloud, then copy these latest versions into your Model Coordination space to explore the integrated design.

  • Walk through a merged model view to experience how the architectural, structural, and HVAC designs work together.
  • Look for any potential conflicts or issues that require resolution.

Weekly Design Project Check-In

You’ll sign up for an appointment next week with a member of the teaching team to review your progress and share tips about how to proceed.