A Critical Review of IAQ Advanced Control Strategies for Multizone VAV Air Handling and Terminal Units

Indoor Air Quality (IAQ) plays a crucial role in fostering healthy and productive office environments. Despite this, current Heating, Ventilation, and Air Conditioning (HVAC) control strategies primarily emphasize thermal comfort and energy efficiency, leaving IAQ inadequately addressed. This thesis presents an in-depth literature review of pertinent regulations, simulation and field studies, aiming to inform the development of innovative, advanced control strategies for multi-zone Variable Air Volume (VAV) systems, which represent the most prevalent HVAC system type in the United States. 

The review process identifies key sensors and actuators integral to IAQ improvement. At the zone level, these sensors encompass discharge airflow, zone temperature, occupancy, and CO2 measurements. At the system level, these include outdoor air temperature, supplemented in many cases by an outdoor weather station to monitor outdoor CO2 concentration, solar radiation, and wind speed. The main actuators utilized in the system comprise the VAV box damper position, the hot water valve of the reheat coil within the VAV box at the zone level, the supply fan speed, and the economizer outdoor air damper at the system level. 

In contrast to conventional rule-based or Proportional-Integral-Derivative (PID) controllers, the study foregrounds model-based control as an effective mechanism for managing the complexities and non-linearity of HVAC systems. This approach is further refined by integrating both zone-level and system-level controls, optimizing system performance and enhancing control reliability. A distributed control architecture is highlighted for its scalability, fault tolerance, swift response times, and unique ability to balance local optimization with global constraints. Alongside these sophisticated strategies, the often-overlooked control of pre-ventilation time is brought into focus as a simple yet impactful tactic for IAQ enhancement. The study also emphasizes the need for a more comprehensive IAQ evaluation method, solidifying the effectiveness of advanced control strategies in managing IAQ for healthier and more productive indoor environments.