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PhD-BPD Dissertation Defense Presentation: Haipei Bie

Tuesday, April 28, 2026
9:00AM - 11:00AM
Intelligent Workplace (IW) Conference Room, MMCH 415 & Zoom
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Title: The Statistical Benefits of Economizer Operation for Indoor Air Quality and Energy in Commercial Buildings

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

Date: Tuesday, April 28, 2026
Time: 9:00-11:00am ET
Location: Intelligent Workplace (IW) Conference Room, MMCH 415 & Zoom

Advisory Committee:

Prof. Vivian Loftness, FAIA, LEED AP (Chair)
University Professor 
School of Architecture
Carnegie Mellon University

Yiqun Pan, Ph.D., ASHRAE Member, IBPSA Fellow, LEED AP
Special Faculty
School of Architecture
Carnegie Mellon University

Peter Freeman, Ph.D.
Associate Teaching Professor
Statistics & Data Science
Carnegie Mellon University

Abstract:
Outdoor air ventilation is essential for occupant health and performance, but often increases energy use, creating a perceived trade-off between indoor air quality (IAQ) and efficiency. This study evaluates air-side economizer performance using multi-year field data from 118 air handling units (AHUs) across 14 U.S. federal buildings, combined with calibrated simulations. Results show economizer operation is highly variable and underutilized (>50% variation within the same climate zone), yet significantly improves ventilation: Across 54 AHUs with high-quality CO₂ data in 10 federal buildings, economizer operation reduced median daily return-air CO₂ increase from 90 ppm (Off) to 52 ppm (Baseline) and 39 ppm (Expanded) (p < 0.001), with maximum daily increases decreasing from ~300 ppm to ~170 ppm and ~110 ppm, respectively. The baseline economizer represents standard operation with limited outdoor air, while the expanded economizer operates at or near 100% outdoor air, with mechanical cooling as needed to maximize ventilation. Simulations further show that optimized economizer strategies can increase operating hours to over 90%, reduce CO2 daily increase from ~180–200 ppm to 80–120 ppm, and achieve cooling energy savings of 26%–84%, depending on the climate. These findings demonstrate that the IAQ–energy trade-off is not inherent and that optimizing economizer control is a low-cost, high-impact strategy to improve ventilation while reducing energy use in commercial buildings.