Estimated effort: 17 hours

Overview: What and Why

Your building has a skin and a skeleton. This week you make it habitable.

You will create a linked mechanical model, define the spaces and zones that let Revit compute heating and cooling loads, choose an HVAC strategy that suits your climate, and model enough of the system to show how it works.

The loads you compute are a direct consequence of decisions you already made: the glazing ratio from Week 3, the assembly R-values and shading from Week 4, the room layout from Week 5.

That is the real lesson. A mechanical engineer does not choose the loads. They inherit them from the architect. This week you find out what you handed them.

Focus: What You Are Adding This Week

• HVAC analysis features

◦  Spaces

◦  HVAC zones

• Air based system components

◦  Air handler

◦  Ducts

◦  Zone controllers

◦  Air terminals

• Fluid based or self contained components, if your strategy uses them

Design Program

• A separate linked mechanical model, sharing coordinates with the architectural and structural models.
• Spaces placed in every conditioned room, with internal loads specified for people, lighting and equipment.
• A space schedule with occupancy assumptions you have reviewed and adjusted rather than accepted by default.
• HVAC zones grouping spaces that share a thermal profile. Do not put a south facing top floor unit in the same zone as a north facing ground floor lobby.
• A declared heating, cooling and ventilation strategy appropriate to your Bay Area climate, written down in one paragraph before you model anything.
• Computed heating and cooling loads for the whole building and per zone.
• A modelled air transport system for one typical floor: air handler location, duct mains and branches, zone controllers, air terminals.
• One alternative studied: either two air handler locations or two air terminal layouts, compared.
• Ducts sized with the Duct Sizing tool against your computed airflow, not left at placeholder dimensions.

Getting Started

1.  Start with an overall HVAC strategy. The Bay Area climate is mild. Ask honestly whether you need mechanical cooling everywhere, or whether natural ventilation, night flush and a smaller system will do. Write the strategy down first.

2.  Run a climate analysis for your site to check that intuition against data.

3.  Create a new linked mechanical model and link the architectural and structural models into it.

4.  Place Spaces in every conditioned room and specify internal loads.

5.  Create a space schedule and fine tune the occupancy and people assumptions. The defaults are rarely right for your program.

6.  Group spaces into HVAC zones.

7.  Compute loads using Revit's Heating and Cooling Loads tool. If you want a second opinion, build the energy analytical model and run it through EnergyPlus, then compare.

8.  Model the air transport system on one typical floor. Place the air handler, run duct mains, add zone controllers, place air terminals, connect them.

9.  Model fluid or self contained components if your strategy calls for them, for example radiant floors in the lobby.

10.  Size the ducts from the computed airflow.

11.  Check your work with the System Inspector for air flows, the System Browser for connections, and space and zone schedules for coverage.

What Size Should the Equipment Be?

The same answer as the structure: we do not know yet. In practice you compute loads and then select equipment against them, but equipment selection is beyond this course. Place moderately sized mechanical equipment as placeholders, to be sized by an HVAC engineer later.

Duct sizing is different. That you can do now. Start with placeholder ducts around 12 by 12 or 12 by 16, then use the Duct Sizing tool to compute real sizes from the airflow at each terminal.

How Detailed Should This Model Be?

The goal is to understand the impact of your design decisions, not to build a perfect Revit model. Keep the system modeling high level. Get the main components in place so it is clear how they work with the other systems. Learn to let go of small details in an exploration phase.

Be warned specifically about duct connections. They are fiddly, and they get worse when ducts grow after resizing. Do not agonise over connections that refuse to connect. You will not resolve every HVAC detail in one week, and that is expected and fine.

How This System Affects the Others

• Your envelope drove your loads. Careful envelope design in Week 4 should be visibly reducing the size of your HVAC components now. If your loads are enormous, go back and look at your glazing ratio and your shading.
• Your structure constrains your ducts. Beam layout and depth dictate the paths and clearances available. Where your Week 6 spans were longest, your plenum is tightest.
• Your HVAC constrains Week 8. Air handlers and mechanical rooms need power. Where you put them now determines electrical routing later.

What's Expected

1.  A linked mechanical model with correct shared coordinates.

2.  Spaces in all conditioned rooms with reviewed internal loads.

3.  A space schedule showing your occupancy assumptions.

4.  HVAC zones with a stated rationale for the grouping.

5.  A written HVAC strategy paragraph, dated before your modeling.

6.  Computed heating and cooling loads, building total and by zone.

7.  A modelled air transport system on one typical floor.

8.  One documented alternative studied and compared.

9.  Ducts sized against computed airflow, with a System Inspector screenshot confirming flows.

10.  Mechanical sheets: one floor plan with ducts and terminals, one section showing the plenum against your structure, one 3D mechanical view.

What to Submit

1.  Working links to all three models in Forma Data Management.

2.  PDF sheet set at D size, 36 by 24 inches.

3.  Load summary table: building total and by zone.

4.  Your alternatives comparison.

5.  Design memo of 300 to 500 words: your strategy and why, what the loads told you about your envelope, where your structure got in the way, and what you left unresolved.

Sharing Your Project

Publish the architectural, structural and mechanical models to Forma Data Management, copy the latest versions into your Coordination Space, and walk a merged view looking for conflicts. Post links, sheets and load summary on the Module 7 Notion gallery page.

At Friday check in, show one section through your tightest plenum.

Points to Ponder

Please share your comments on 3 of the following 5 questions on this linked Notion page.