Working links to all three models in Forma Data Management and your Forma Board
PDF sheet set at E1 size, 30 by 42 inches
Load summary table: floor total and by zone
Loads from Revit Systems Analysis (EnergyPlus), Berkeley weather. Peak cooling on 6/21 around 3:30 pm at 86°F, peak heating on 1/21 at 41°F. Parking garage excluded. In a typical unit about 83% of the cooling peak is internal gains and only about 6% is envelope.
Alternatives comparison: your representative unit and your alternative unit, compared by numbers, with your conclusion
For a mid unit like 502, Option B is clearly better. It drops the 20 ft flex run and keeps the ceiling at full height. It does not carry over to the corner units, though, since they still need long flex across the elevator and stair, and the extra drops make the corridor plenum tighter at the band beam. We keep Option A as the L5 baseline and would only use sidewall grilles for the mid units.
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
For this building, I decided to use a dedicated outdoor air system (DOAS). The outdoor unit is located on the roof, east of the penthouse, and supplies ventilation air through Shaft-1 using a 12-inch riser at 590 CFM. On each floor, the main ducts run along the corridor ceiling and branch into individual units. I used Level 5 as a typical floor for my model. The north system (L5-SA-NORTH) supplies 240 CFM to four units, with 60 CFM going to each. According to System Inspector, the critical path has a pressure drop of 0.39 in-wg. I chose this layout mainly because the corridor is the only continuous ceiling space available. Running the ducts there also reduces the amount of ductwork inside the units. Each unit would have its own heat pump for heating and cooling, although I did not include those in this model.
The results from Revit Systems Analysis were a little different from what I expected. The building has a peak cooling load of about 704,000 Btu/h, or 59 tons, and a heating load of about 507,000 Btu/h. The cooling peak occurs on June 21 at around 3:30 pm, when the outdoor temperature is 86°F. What surprised me was how much of the cooling load came from inside the building. For a typical unit, internal gains account for about 83% of the peak cooling load, while the envelope contributes only 6%. The north and south systems on Level 5 also have almost identical loads, at 29,700 and 30,000 Btu/h. I originally thought the orientation and window exposure would make a bigger difference, but that does not seem to be the case for this building. Based on these results, improving the glazing or insulation probably would not reduce the cooling system size very much.
I ran into two main problems when coordinating the ductwork with the structure. The first was the corridor between grids C and D, which is only 8 feet wide but needs to accommodate two parallel supply mains. The second was the PT band beams between grids 6 and 8. Since the beams cross the duct routes, both mains have to pass underneath them. This reduces the available ceiling height, especially where the ducts cross the beams, so I used that location for my plenum section. I also considered using sidewall grilles from the corridor instead of ceiling diffusers. This worked better for the two middle units because the ducts could stay in the corridor without lowering the ceilings inside the units. However, the corner units still required about 14 to 20 feet of flex duct around the elevator and stairs. The additional duct drops also made the beam crossings more difficult. For these reasons, I decided to keep the ceiling diffuser layout (Option A) as my baseline.
There are still several things I would need to fix or develop further. In Option A, some of the flex ducts are 20 to 23 feet long, which is much longer than the usual 6-foot limit. I would replace most of those runs with rigid ducts and use short flex connections near the diffusers. For Option B, the grilles serving units 501 and 504 are not yet connected to the main system. I also need to add openings in the structural penthouse walls for the door and duct penetration. Bathroom and kitchen exhaust systems, individual heat pumps, and the duct layouts for the other floors are not included yet. Another concern is the depth of the north units, which are about 42 feet from the corridor to the exterior windows. I am not sure one supply diffuser per unit would provide good air distribution throughout the space, so that is something I would want to check in the next stage.