AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
In Situ Time- and Size-Resolved Particle Removal Efficiency of a HVAC Filter Bank in an Office Building
JINGLIN JIANG, Tianren Wu, Brandon E. Boor, Purdue University
Abstract Number: 816 Working Group: Control and Mitigation Technology
Abstract The size-resolved removal efficiency of HVAC filters is dynamic rather than static. Many factors can drive time-dependent changes in the in situ removal efficiencies of HVAC filters, including the operational characteristics of the HVAC system, relative humidity, deposited mass loading on the filter, and physiochemical properties of the particles to which the filter is exposed. The objective of this study is to evaluate the in situ time- and size-resolved particle removal efficiency of a HVAC filter bank in an office building under variable HVAC operational conditions.
A six-month measurement campaign was performed at the Herrick Living Laboratories at Purdue University, which are four open-plan offices with precisely controlled HVAC systems. The HVAC system included a filter bank (W: 36 in, H: 24 in) with a MERV 7 pre-filter (D: 2 in) with synthetic media and a MERV 14 filter (D: 12 in) with layered meltblown synthetic media. Particle size distributions from 6 to 10,000 nm were measured upstream and downstream of the HVAC filter bank with a High Resolution Electrical Low Pressure Impactor (HR-ELPI+) with sintered collection plates. An automated three-way valve sampled particles across the HVAC filter bank at four-minute intervals, switching between two-minutes upstream and two-minutes downstream. More than ten ventilation modes were implemented with variable supply volumetric airflow rates (1000 to 2000 cfm) and outdoor to recirculation air (O/R) ratios (0 to 1).
The in situ size-resolved removal efficiency of the MERV 7/14 filter bank exhibited a diel trend due to transient variations in the concentrations and size distributions of the mixed outdoor and recirculation air. The size-integrated particle number (6 to 1,000 nm) removal efficiency was typically greater from 08:00 to 17:00 compared to the evening. This is likely because the upstream particle size distributions were dominated by nucleation (< 10 nm) and Aitken (10 to 100 nm) mode particles during the day and shifted to larger particles during the evening. The median size-integrated particle number removal efficiency increased with increasing O/R ratios from 45% at a O/R of 0, to 49% at a O/R of 0.25, to 56% at a O/R of 0.45, and to 59% at a O/R of 1. Conversely, the size-integrated particle mass (6 to 1,000 nm) removal efficiency decreased from 92% to 71% as the O/R ratio increased from 0 to 1.