Overall HVAC System Process and Strategy
After creating the necessary spaces and zones in my building, I adjusted the area per person for certain space types to represent a more reasonable number of people in the building (as shown by all the space types in column C ending in “custom”). Then, I ran the the HVAC Loads Analysis and Annual Building Energy Simulation, and I needed to make some adjustments afterwards. First, the Annual Building Energy Simulation combined and/or omitted certain zones in its analysis. To supplement this, I calculated an approximate required supply airflow using the formula provided to us (as seen in column G). Using my own judgement, I chose the more reasonable of the two values (simulated vs. approximate) to populate column H. Notably, the atrium is directly over the lobby, so instead of combining these two zones into one, I simply made sure that the total CFM provided to these two spaces met the sum of their required CFM (as seen in column J).
Since some sort of air transportation system is likely needed for ventilation anyway, I decided to use an air transport system for my heating and cooling as well. This keeps things relatively simple, and simplicity has been a key design goal of mine through this whole process since it improves constructability. For each of the three levels, the supply and return air terminals are in the ceiling. For levels 1 and 2, the first 18 inches below the floor are dedicated to structural systems, the next 18 inches are for supply air, and the next 18 inches are for return air. The air terminals are then located 12 inches below the bottom of the return air space. For level 3, since I only need to supply air to one small stairway, the supply and return ducts are on the same height, and I allotted 12 inches for this space.
Because my three mechanical rooms are all stacked on top of each other (one per level), I decided to have an air handler on each floor. I prefer having three smaller air handlers on each floor as opposed to one large air handler on the roof because I want to maximize the usable roof space for the visitors. My mechanical rooms are also all centrally located on their respective floors, which was done to minimize the distance the ducts needed to travel to reach each necessary space.
In Revit, I modeled the supply air system on each floor, but I did not model the return air system. However, the layout would be almost identical to the supply air system, with the return air terminals slightly offset from the supply air terminals.
Additional Heating and Cooling Strategies
In addition to the air transport system described above, I implemented passive solar techniques during earlier stages of the building design to provide heating to the exhibition center. This involves a high window-to-wall ratio on the south face of the building with proper overhangs and light shelves. These overhangs will minimize solar heat gain in the hotter summer months, while maximizing solar heat gain in the colder winter months. Thermal mass will also help to regulate indoor temperature, since the exterior walls, green roof, and 8 inch concrete floor slab on level 1 have relatively high thermal mass values.
Air Transport System Design and Challenges
Levels 1 and 2 each have four ‘branches’ of ducts coming out the mechanical room (trunk of the tree). The northern branches were all relatively easy to design; however, the southern branches had some challenges. Needing to hook around the stairs and elevator shaft did not leave much room for error, and this ended up being a rather tight squeeze. Also, after sizing the duct system and having all the ducts expand significantly, certain air terminals suddenly became too close to the now wider ducts and needed to be moved. In narrow areas like hallways and stairways, some creativity was required to rearrange the air terminals and/or ducts to ensure the air terminals had enough clearance between the ducts.
