Design Journal Entry - Module 9

Journal Entry For
Module 9 - HVAC Systems
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My mechanical model is here: LINK

Overall HVAC system Strategy:

Heating loads: the building will need to warm up when it’s cold outside at night and during the winter season. Cooling loads: the building will need to cool down during summer when it’s boiling outside, and the building also needs to cool down the heat generated by people and machines.

My building is in California’s Climate Zone 4. It’s within a natural comfort zone, 9.2% of the annual time. The building needs 34.1% of active cooling and heating, in which the cooling is not a big concern compared to heating. Based on this information from the psychrometric chart, when I modelled my building, I placed lots of south-facing windows to maximize sun exposure to warm up the space and hopefully reduce the heating needs caused by the external loads. However, cooling might be needed to reduce the heating caused by people and machines running in the building since this is an exhibition center.

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I put spaces into my mechanical model (made sure the top limits of spaces were at the proper levels), set the project location for this model, and ensured the energy settings reflected what I wanted the building to be. I modified the space/person for some space types (exhibition, office, education rooms, etc.) to adjust the estimated number of people so that they would be more realistic. I used the system browser to create an analytical zone for each of the spaces to estimate their cooling and heating demand.

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I set five zones: center zone, north-A, north-B, South-A, and South-B, as shown below. Two air handling units will be placed in the first floor’s mechanical rooms. One AHU will handle the cooling and heating from the north side of the building, and the other will handle the loads from the south side. The two AHUs will split the center zone’s heating and cooling loads since the center zone includes all the corridors and public spaces like the lobby. There will be four branches of HVAC ducts on each floor, and each one of them will be connected to a relatively even number of air terminals. I also placed some VAV units to control the office and exhibition room airflows better.

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North-B:

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North-A:

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South-A:

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South-B: (HVAC branch will extend into the lobby in center zone)

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Center Zone (vented):

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After running the energy analysis, I obtained each space's peak cooling and heating loads. I noticed some analytical spaces that I did not create, so I investigated those extra spaces and realized that Revit created analytical spaces for the elevator shafts, which I ignored. Revit also split the space of the second floor’s hallway into two portions. Overall, they are no big deal. I used the equation provided in the kickoff meeting to calculate the heating and cooling in CFM.

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After I obtained the cooling and heating loads in CFM, I picked the max airflow demands and input them into the space schedule under specified supply airflow, so when I clicked on each space on the plan view, I could see how much airflow was needed for that space when I needed to add air terminals in.

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My heating/cooling strategy and how I implemented it: I used the air-based duct system to handle the cooling and heating loads. I believe that the overhang and shades provided for my building can reduce the cooling loads in the summer, and sunlight exposure can reduce the heating loads in the winter. However, I put enough air terminals to provide enough and excessive airflow for all spaces to ensure people are comfortable in them. The central portion and the hallway of my building will most likely be naturally ventilated. If the windows and doors are opened near the spiral staircase, heat will rise to the top of the spiral staircase and escape from the third floor’s door or the roof opening.

Mechanical system modelling: As shown below, I modeled the air-based duct system for the whole building. There are two AHU units at level 1. I used the auto-sizing tool to size all the ducts, which are all less than or equal to 20” deep and located well under my structural framing elements. I did not connect the branches to the AHUs because it would take a long time, so I stopped there. Overall, I think the ducts’ layout and sizes look reasonable. They are not in conflict with any structural beams and columns. The ducts are not blocking any stairways or openings. There is still a 10’-5” clearance between the top of the floor and the bottom of the biggest duct.

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3D overview:

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Level 1:

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Level 2:

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Level 3:

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I merged the mechanical files with the architectural and structural files on the construction cloud. Below are the merged images.

The ducts are all under the framing elements:

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Some exhibition spaces:

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Second-floor hallway:

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One of the conference rooms:

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Special HVAC system challenges that I encountered: Overall, the HVAC system modelling went well for me. I took time to figure out the cooling and heating loads using the system browser, which was a little confusing. Then I needed to copy the loads from the analytical space schedule into the space schedule for each space. The actual duct modelling was okay, and I figured out a trick to lay out the ducts and connect the air terminals to the ducts so that the auto-sizing tool wouldn’t give me too many error messages.

Future improvements: If I have more time for this exercise, I will zone the spaces more wisely and use VAV to control the airflows for the spaces to optimize the energy efficiency and the overall HVAC performance of the building. I might also add ceilings to the floors.