PhD-BPD Doctoral Proposal Presentation: Haipei Bie

Title: The Statistical Impact of Economizer Operation on Indoor Air Quality and Energy in Commercial Buildings

Name: Haipei Bie, Ph.D. candidate in Building Performance and Diagnostics (PhD-BPD)

Date: Wednesday, December 10, 2025
Time: 9:00-11:00am ET
Location: Intelligent Workplace (IW) Conference Room, MMCH 415 & Zoom

Abstract:
Outdoor air ventilation is essential for protecting occupant health, enhancing cognitive performance, and reducing exposure to indoor pollutants in commercial buildings. However, increasing ventilation frequently raises energy consumption, creating ongoing tension between indoor air quality (IAQ) and energy efficiency. Air-side economizers present a valuable opportunity to address this challenge by increasing filtered outdoor air during favorable outdoor conditions while simultaneously reducing mechanical cooling. Despite decades of research, economizer performance in real-world buildings remains poorly understood due to limited field data, inconsistent control strategies, sensor faults, and a focus on energy outcomes rather than IAQ. This dissertation addresses these gaps through a statistical evaluation of economizer operation, IAQ, and energy performance using multi-year BAS data from 118 AHUs across 14 U.S. federal buildings, followed by calibrated building simulations and reinforcement learning techniques to enhance energy savings, IAQ, and the balanced control of both. Results from the field analysis show that economizer operation is highly sporadic and often misaligned with ASHRAE recommendations, with activation hours varying by more than 50% within the same climate zone. Using descriptive analysis, non-parametric tests, and linear mixed-effects models, the study demonstrates that active economizer operation significantly reduces AHU return-air CO₂ levels. Across 54 AHUs with high-quality CO₂ data, economizer use decreased median daily CO₂ increases by 35–40 ppm after adjusting for season, weekday, building, and AHU-level differences, with expanded economizer operation (100% OAD) producing the largest reductions. Although control logic and damper configurations varied widely, all economizer types, fixed dry-bulb, differential dry-bulb, fixed enthalpy, and differential enthalpy, delivered IAQ benefits compared to non-economizer operation. These findings provide rare empirical evidence that economizers consistently improve indoor CO₂ levels across real commercial buildings, confirming the first dissertation hypothesis. Building on these findings, an EnergyPlus/OpenStudio calibrated simulation framework is developed to evaluate how extended economizer operation, revised control setpoints, ERV integration, supply-air temperature adjustments, and channel mixing technologies can increase free cooling hours while maintaining IAQ and comfort goals. This work provides large-scale statistical evidence of economizer IAQ benefits in real buildings and establishes a simulation and machine-learning framework for expanding economizer operation. The research guides building operators, engineers, and policymakers in finding strategies that simultaneously advance occupant health, energy efficiency, and operational resilience in commercial HVAC systems.