HVAC Systems - Edward Chen

Journal Entry For
Module 9 - HVAC Systems
Created
Feb 28, 2022 4:17 AM
Last Edited
Mar 4, 2022 4:49 PM
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Edward Chen

HVAC System Strategy

The design of the building’s HVAC system aims to maximize the use of natural ventilation and passive heating/cooling strategies while making sure air supply is adequate. To achieve this, multiple HVAC strategies are used.

The system consists of 3 components.

  • Radiant floor system on 1st floor
  • A 15000 cfm air handling unit serving 1st and 2nd floors with VAV and reheat
  • A 12500 cfm air handling unit serving the 3rd floor with VAV and reheat
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Due to time limitation, a few details are missing from the current model:

  • Connection of the pipes from the radiant floor system to district heating/cooling or central source of hot and chilled water
  • Connection of the air ducts to air terminals
  • VAV boxes at the air ducts
  • Proper sizing of the ducts in accordance with airflow
  • Air grille on the 1st floor of the East Wing and outside of the mechanical room on the 2nd floor
  • Air vent beneath the skylight

These are further explained below.

Heating and Cooling Strategies

On the 1st floor, heating and cooling are mainly provided by the radiant floor system. It is coupled with the thermal mass — provided by the concrete walls and slabs — and natural ventilation via stack effect, by which air is drawn from the eastern facade, flows through the space, and rises up through the vertical shaft on the west. Air grilles will be placed on the floor underneath the curtain walls to allow outdoor air to enter. When airflow is too low, the air terminals at the center of the exhibition space will supply air.

1st Floor - Floor Plan and HVAC Systems
1st Floor - Floor Plan and HVAC Systems

The 2nd floor has air-side heating and cooling provided by the air terminals. The air handler in the mechanical room draws air through the wall opening (with air grilles and filters) and cools the air. VAV units at the branching air ducts adjust the airflow and reheat the air when necessary.

Note that on the 2nd floor, the North Wing is mostly enclosed rooms with individual air supply. The East Wing doesn’t have mechanical air supply because it mainly relies on the stack effect to draw air from windows and the east atrium. Return air terminals are also placed to facilitate airflow.

2nd Floor - Central Part of Floor Plan and HVAC Systems
2nd Floor - Central Part of Floor Plan and HVAC Systems

The 3rd floor has a similar system to the 2nd floor, but the air handler is placed at the rooftop. The air handler cools the air, and each branch air duct will have a VAV unit to provide reheat when necessary. Individual air terminals reach each semi-enclosed zones on the floor, while the return air is collected from the corridor. The return air terminals at the atrium help facilitate airflow and the stack effect.

3rd Floor - Central Part of Floor Plan and HVAC Systems
3rd Floor - Central Part of Floor Plan and HVAC Systems

HVAC System Challenges

The main challenge I encountered when designing the HVAC system is to ensure an adequate air supply while minimizing the HVAC system requirement. I wanted to incorporate as much passive heating, cooling, and ventilation strategies as possible to reduce the need for mechanical HVAC.

In a rough estimate, this is the amount of supply air for each space in the building:

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I eventually designed the mechanical HVAC system to provide slightly over 50% of the air supply. Note that the supply air requirements for enclosed spaces are all met, but those for open spaces are often not mechanically supplied and, instead, rely on natural ventilation between the spaces. The effectiveness of this strategy is to be verified.

In terms of modeling the HVAC system, the modeling of ducts is particularly challenging because of the limitation of spaces and their interaction with other building components such as the structural frame, walls, etc. The current HVAC model has a few clashes with the existing components (as seen below) but they can be addressed if time permits.

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