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Pedrollo, Lavinia

Journal Entry For

Module 9 - HVAC Systems

ACC Folder Link

https://acc.autodesk.com/docs/files/projects/cbef7261-4ed5-4dad-99c1-e2a751c74519?folderUrn=urn%3Aadsk.wipprod%3Afs.folder%3Aco.whlGjA1_RgeACmoKzlZoRQ&viewModel=detail&moduleId=folders

ACC Revit File Link

https://acc.autodesk.com/docs/files/projects/cbef7261-4ed5-4dad-99c1-e2a751c74519?folderUrn=urn%3Aadsk.wipprod%3Afs.folder%3Aco.whlGjA1_RgeACmoKzlZoRQ&entityId=urn%3Aadsk.wipprod%3Adm.lineage%3AwqHPkQwgQI-2ZTequSKiTw&viewModel=detail&moduleId=folders

Created

Jan 6, 2025 12:34 AM

Last Edited

Jan 6, 2025 12:34 AM

Created by

Glenn Katz

ACC Coordination View Link

https://acc.autodesk.com/docs/files/projects/cbef7261-4ed5-4dad-99c1-e2a751c74519?folderUrn=urn%3Aadsk.wipprod%3Afs.folder%3Aco.whlGjA1_RgeACmoKzlZoRQ&entityId=urn%3Aadsk.wipprod%3Adm.lineage%3AjCWMlyvfTYuGfT6l7WXpMw&viewModel=detail&moduleId=folders

Overall HVAC System Strategy:

My HVAC system strategy revolves around seamlessly integrating passive and active design elements to ensure optimal occupant comfort, energy efficiency, and environmental sustainability. These are the main key considerations and features that I took into account while designing my HVAC system strategy.

1. Passive Design Integration:
• Prior designing the HVAC system, I have leveraged the building's orientation and site conditions, emphasizing passive measures to minimize the need for mechanical systems.
• I have carefully designed my facades to provide a comprehensive insulation, including a green roof with R-60 insulation, highly insulated concrete walls, as well as curtain system panels with vertical shading systems and triple Low-E glazing glass.
2. Zoned Approach:
• An essential aspect that I carefully considered during the design of the HVAC system is its zoning based on both solar exposure and the intended use of the building. This strategic approach enables me to customize the heating and cooling solutions for each specific area, ensuring optimal comfort and energy efficiency.
• I have divided each floor into three thermal zones (Zone 1 - WS, Zone 2 - Core, Zone 3 - NE). Each floor contains a mechanical room where I will place one or more air handlers.
3. HVAC type: Direct Expansion Air Handling Units both for cooling and heating

The selected HVAC system revolves around the utilization of Air Handling Units (AHUs) with Direct Expansion (DX) technology. The vertical packaged design not only ensures a compact footprint, ideal for overcoming space constraints, but also allows for customized airflow to meet specific demands. The DX technology enhances cooling efficiency, providing a reliable and energy-efficient solution.

Design Strategy Steps

Step 1: Defining the HVAC Zones.

For each floor, I have defined three HVAC zones based on both solar exposure and the intended use of the spaces included in that zone. Each floor contains a mechanical room where the the Air Handler Units (AHU) are placed. There will be an AHU for each zone, per floor. The zones are defined as follows:

The zones are represented in different colors for each floor:

Step 2: Defining the heating and cooling strategies.

In the context of an air-based HVAC system, I have ve devised specific heating and cooling strategies for different zones within the building. These strategies aim to strike a balance between occupant comfort, energy efficiency, and environmental conditions. For this reason, I have explicitly set in Revit th cooling air temperature, cooling setpoint, heating air temperature, and heating setpoint of each HVAC Zone.

Heating Strategy:

1. Zone 1 - WS:
• Heating Air Temperature: Set at 100°F due to high solar exposure.
• Heating Setpoint: Maintained at 68°F to ensure a comfortable environment.
• Rationale: The elevated heating air temperature compensates for solar heat gain, while the setpoint maintains comfort.
2. Zone 2 - Core:
• Heating Air Temperature: Moderately set at 95°F.
• Heating Setpoint: 70°F for a balanced comfort level.
• Rationale: The central hub accommodates diverse needs, striking a balance between warmth and energy efficiency.
3. Zone 3 - NE:
• Heating Air Temperature: Lowered to 90°F due to minimal solar exposure.
• Heating Setpoint: Set slightly higher at 72°F for comfort without excessive heating.
• Rationale: Energy conservation is prioritized while maintaining occupant well-being.

Cooling Strategy:

1. Zone 1 - WS:
• Cooling Air Temperature: Set at 55°F to counteract solar heat gain.
• Cooling Setpoint: Maintained at 72°F for a comfortable cooling environment.
• Rationale: The lower cooling air temperature helps combat increased heat while ensuring occupant comfort.
2. Zone 2 - Core:
• Cooling Air Temperature: Moderately set at 60°F.
• Cooling Setpoint: 74°F strikes a balance between zones 1 and 3.
• Rationale: Central hub occupants benefit from a harmonious cooling experience.
3. Zone 3 - NE:
• Cooling Air Temperature: Slightly higher at 58°F due to minimal solar exposure.
• Cooling Setpoint: Set at 76°F for comfort without excessive cooling energy consumption.
• Rationale: Energy efficiency is maintained while ensuring a pleasant indoor climate.

Step 3: Calculate the Heating and Cooling Loads

I have run the Heating and Cooling Loads report in Revit to compute the supply air volume required for ventilation, heating, and cooling. I have summarized the results in the tables below, focusing on the following fields: peak cooling load (Btu/h), peak cooling airflow (CFM), peak heating load (Btu/h), peak heating airflow (CFM), peak ventilation airflow (CFM).

For Zone 1 - WS:

For Zone 2 - Core:

For Zone 3 - NE:

Step 4: Model the HVAC System Elements

After calculating the heating and cooling loads at step 3, I have calculated what is the total supply airflow that is is required in each zone. Specifically, I have calculated the minimum volume of downstream air required for a specific zone by considering the maximum value between heating airflow, cooling airflow, and vantilation airflow. Then I have calculated the total volume of downstream air being supplied by rounding the previous value at 1000 CFM. This step is crucial to to select the correct air handling units. To meet the requirements, I have then identified the necessary cross-sectional area for the air distribution, and subsequently selected rectangular duct cross-sections to achieve the desired airflow in the designated zone.

In the following summary table I have highlighted with the same colour the zone that will employ the same air handling unit (in terms of CFM).

Step 5: Placing the HVAC System Elements

Two types of AHUs were employed:

• Air Handling Unit - Vertical Packaged - DX - 6-10 Tons (2400cfm, 3000cfm, 4000cfm)
• Air Handling Unit - Vertical Packaged - DX - 12.5-25 Tons (5000cfm, 6000cfm, 8000cfm)

I have placed the air handling units in the mechanical room of each floor, accordingly to the field column of the table at step 4 named “Total Volume of Downstream Air Being Supplied (Rounded at 1000 CFM) - Air Handling unit Employed”.

Subsequently I have placed the supply air ducts and diffusers (in blue), and return air ducts and diffusers (in pink). Please note that for the purpose of this assignment I have not explicitly selected the individual airflow values of the diffusers. These values are already mentioned in the generated report and can be added later if needed. I have been careful however to place the diffusers strategically so that the ducts do not intersect and that the diffusers cover each zone homogeneously. Other information:

• The air diffusers for supply and return air were set at the same height, in each floor: 8’ 5”.
• The ducts are all placed at a middle elevation of 10' 9 7/64”.

The resulting HVAC system design is illustrated in the pictures below.

HVAC system design - elevation

HVAC system design - Floor 1

HVAC system design - Floor 2

HVAC system design - Floor 3

HVAC system design - Floor 4

HVAC system design - 3D view, mechanical parts only

Step 6: Visualizing the coordinated models in ACC

Interior view - architectural + structural + mechanical coordination

3D view, elevation - structural + mechanical coordination

3D view, overview - structural + mechanical coordination

Challenges

• The available space for HVAC equipment was limited, requiring careful consideration of the system's size and placement. Specifically, when I tried to position the return ducts beneath the supply air ducts, considering the dimensions of the largest ducts (24x36 cross-section) and accounting for the beam systems, proved unfeasible. This arrangement would have led to a reduction in ceiling height to less than 8 feet. To address the spatial constraints, I strategically positioned the return ducts and supply air ducts at the same height, while also ensuring they did not intersect. This arrangement allowed for an efficient use of the limited space without compromising functionality.
• Another challenge involved ensuring that the HVAC ducts didn't intersect with columns and structural beam systems. Working with Revit, I meticulously adjusted the ducts' positions to avoid clashes with the building's structural elements. This was essential prevent any conflicts during the construction phase and was double-checked using the ACC model coordination tool.