Overall HVAC System Strategy
The overall HVAC design is a fairly standard system consisting of three vertically packaged interior air handling units (one on each floor). This strategy allows certain floors to be controlled individually based on their specific uses. Separate supply and return ducts were used, with air terminals connected though flex pipes for easy installation. The system was made to fit below the structural system and more details regarding the design process can be seen below. Ideally, a more detailed HVAC design would include more zones that use zone thermal controllers but was out of the scope of this design.
Heating and Cooling Strategy and Implementation
Based on the sample HVAC energy model that was created, it was shown that Jasper Ridge requires more cooling than heating. Nonetheless, there are both natural and artificial means to supply both heating and cooling in this building. For example, there are large windows and thermal mass in the exterior to allow heat in, but also window shades to help with cooling. On top of this, the AHU can supplement the rest of the heating and cooling.
The design process began with allocating spaces to each of the rooms in the building. From here, a condition could be set for each room to estimate the occupancy load. Ideally, an HVAC Analysis would have been completed using the Revit energy model. However, this process was not possible due to the long computation time. Rather, an estimated value for the required airflow was developed based on the number of people in each room.
From here, based on the airflow characteristics of the air terminals, both supply and return ducts and terminals could be designed.
To avoid spatial conflicts, the supply ducts were placed at a middle height of 10-’7”. This was done to minimize clashes with the structural system. With 14’ levels, a 5” floor, and 24” deep mass timber beams, the highest duct could be placed at 11-’7”. I decided to restrict the vertical height to 24” for the supply ducts. This resulted in the return ducts being placed at a middle height of 9’1” (9’-7” was the bottom of the supply ducts, meaning a 12” return duct could fit under with a bottom height of 8’-7”). Similarly, the air terminals were also placed at a height of 8-7”. In hindsight, I would have liked the finished ceiling height to be approximately 9-10 feet. However, I plan to have an open ceiling which helps give the impression that the ceilings are higher than 8’-7”.
The full HVAC design can be seen in the photos below, with more details about the design to follow.
The first floor was fully designed using the ‘autosizing’ feature in Revit. Due to the height restrictions (of 24” for supply and 12” for return), the ducts were quite wide (as seen in the layout above). The connection to the actual AHU was giving me trouble, so I would connect the each system (supply and return) one at a time, size the system, then remove the connection to the AHU. In addition, it should be noted that the system analysis tool for HVAC has also been removed, and without the energy analysis it was only possible to size the elements through the autosizing tool which can be quite troublesome. It was ensured that for each room (with the exception of the mechanical room, corridors, and stairs) had the proper airflow requirements based on the space schedule. It should also be noted that due to the 2-storey open atrium, the HVAC was placed on the second floor, so it still meets the 4008 CFM, just delivered through the second floor system.
Second and Third Floor:
The second and third floor were not sized using the ‘autosizing’ feature as it was quite difficult and time-consuming to implement and rework the connections. However, a tapered system was still estimated, using similar sized ducts to the autosized model. Once again, the air requirements for each room were met and can be seen in the space schedule.
The coordinated model (linked to the structural and architectural model) can be seen below:
Looking back at this module, it was quite challenging and time-consuming to get all the HVAC components to work, and correctly sizing them created additional challenges. Some specific challenges will be discussed below.
- Avoiding the Atrium
- This was particularly troublesome as the atrium makes up a large part of the first two floors. It created a bottleneck of ducts around the atrium, but I am happy that the open-ness of the atrium was preserved.
- Avoiding Clashes
- Avoiding clashes between the structural system and the HVAC was an additional spatial challenge.
- Connection Between Pipes
- Ensuring there were no clashes between supply and return ducts and terminals was difficult. Since the return ducts and terminals were roughly at the same height, the flex pipe connectors also required some spatial rework.
- Auto-sizing the ducts was troublesome and required a lot of alterations. For this reason only the first floor was modelled using the correctly sized ducts, the other floors used estimated sizes.
- Connection to AHU
- Due to the large size of the pipes, it was difficult to create a clean connection to the AHU. In addition, a connected needed to be established to use the auto-sizing feature which created an additional challenge.
- Connecting air terminals to ducts
- Ensuring the air terminals were properly connected and constrained using the flex pipes was a challenge. Often, the flex pipe would connect to the top or bottom of the duct rather than the desired side. This required a lot of rework with sections to ensure proper connections.