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 on a typical floor, 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.
• One typical floor for all the HVAC work. Use the same floor for spaces, zones, loads and the air transport system. If your furnished Week 5 unit is on a typical floor, choose that floor, so the loads of each room set the air terminals in it. If it is on the ground floor, a podium or the top floor, choose a typical floor instead, and use space separators to split one unit into its rooms.
• Spaces placed in every conditioned room on your typical floor, 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 on your typical floor, grouping spaces that share a thermal profile. Do not put a unit on your sunniest facade in the same zone as one on your shadiest, and split any unit that wraps a corner if its rooms face very different sun exposure.
• A declared heating, cooling and ventilation strategy appropriate to your site climate, written down in one paragraph before you model anything.
• Computed heating and cooling loads for your typical floor, as a floor total and per zone.
• A modeled air transport system for two representative units on your typical floor: one unit with a single zone and one with more than one zone, each with its air handler location, duct mains and branches, zone controllers and air terminals. If each zone has its own air handler, its thermostat is the zone controller; where one air handler serves more than one zone, model a damper or terminal unit for each zone.
• One alternative studied in another unit: pick a unit of the same type as one of your two representative units, and give it either a different air handler location or a different air terminal layout. Model it in the same file, then compare the two by numbers, for example duct length, duct sizes and velocities, ceiling clearance and service access, and state which you would choose and why.
• 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.  Choose your typical floor using the rule in the design program above. Place spaces in every conditioned room on your typical floor 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 on your typical floor into HVAC zones.

7.  Compute loads using Revit Systems Analysis tool. Your loads cover one floor, so read them per square foot when you compare zones.

8.  Model the air transport system for your two representative units on your typical floor, and the alternative in a third unit. 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 Browser for connections, and space and zone schedules for coverage. Check only your modeled units in the System Browser; terminals in the other units can stay unassigned.

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.

Working on one floor is part of that. Spaces, zones and loads on one typical floor are enough to show how your envelope drives your loads and how your structure constrains your ducts.

Be warned specifically about duct connections. They are fiddly, and they get worse when ducts grow after resizing. Do not agonize 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 separated mechanical model with correct shared coordinates, with linked Architectural and Structural models.
2. Spaces in all conditioned rooms on your typical floor with reviewed internal loads.
3. A space schedule showing your occupancy assumptions.
4. HVAC zones on your typical floor with a stated rationale for the grouping.
5. A written HVAC strategy paragraph, dated before your modeling.
6. Computed heating and cooling loads, floor total and by zone.
7. A modeled air transport system for two representative units on your typical floor, one single-zone and one multi-zone.
8. One alternative, modeled in a second unit of the same type, compared by numbers with a stated conclusion.
9. Ducts sized against computed airflow.
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 and your Forma Board.
2. PDF sheet set at E1 size, 30 by 42 inches.
3. Load summary table: floor total and by zone.
4. Alternatives comparison: the representative unit and the alternative unit compared by numbers, with your conclusion.
5. Design memo of 300 to 500 words: your strategy and why, which typical floor you chose 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.

Upload all files in your folder in Forma Data Management, create a project link, and post it with your sheet set on the Module 7 Notion gallery page. Test the link in a fresh browser window.

Upload all visuals into your Individual Forma Board. Load your Revit file in Board and enable it to display all the sheets with floor plans, the plenum section and the 3D mechanical view of your typical floor. Open your Board and copy the URL from your browser’s navigation bar, and be sure to test it in a fresh browser window to confirm that it is working. Post the URL on the Module 7 Notion gallery page.

Points to Ponder

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