Active vs Passive Air Purification Systems. How to Choose the Right IAQ Strategy

Indoor air quality (IAQ) is no longer a discretionary building feature. In high-occupancy, continuously air-conditioned buildings - such as offices, hospitals, schools, hotels, and government facilities - air quality is a core performance, health, and risk issue.

Yet not all air purification technologies work the same way.

The most important distinction decision-makers must understand is the difference between passive (reactive) and active (proactive) air purification systems.

This distinction determines where air is cleaned, how effectively contaminants are controlled, and whether IAQ becomes a cost burden or a performance advantage.

Passive vs Active Air Purification: How to choose the right IAQ strategy

Passive Air Purification (Reactive)

Passive air cleaning systems only treat air after contaminants are transported to the device by airflow. Their performance depends heavily on:

• Ventilation rates

• Air circulation patterns

• System runtime

• Pressure drop and fan energy

These systems clean air inside the HVAC system, not in the occupied space where people actually breathe.

Key limitation: contaminants must first reach the device before any action occurs.

Common passive technologies include:

• Mechanical (media) filtration

• UVGI in return air or AHUs

• Sorbent (chemical) filtration

• Electrostatic precipitators

Active Air Purification (Proactive)

Active air cleaning systems introduce a cleaning mechanism into the occupied space itself, allowing contaminants to be treated at their source - within the breathing zone and on surfaces.

Rather than waiting for pollutants to reach a filter, active systems work continuously throughout the space, regardless of airflow patterns.

Key advantage: contaminants are neutralised where they exist, not just where air passes through equipment.

Active air purification enables:

• Faster, more uniform IAQ improvement

• Reduced dependence on high ventilation rates

• Enhanced effectiveness of existing filtration

• Performance-based compliance (e.g., ASHRAE IAQP)

Why Active Air Purification Delivers Better Outcomes

Compared to passive systems, active purification:

• Treats pollutants throughout the occupied space

• Works continuously, independent of HVAC runtime

• Reduces airborne pathogens, VOCs, and fine particulates at source

• Improves IAQ in the breathing zone (4–7 ft / 1.2–2.1 m)

• Enables smarter ventilation strategies with lower energy use

For large, high-occupancy buildings - especially in hot, dusty, and humid climates - these advantages translate into better health outcomes, lower energy demand, and improved lifecycle performance. understanding Passive vs Active Air Purification involves understanding the following:

Active vs Passive Air Purification Technologies

Comparison Matrix

Technology	Active or Passive	Where Air Is Treated	Primary Strengths	Key Limitations
Mechanical Media Filters (MERV / HEPA)	Passive	Inside HVAC duct	Effective particle capture	High pressure drop, no VOC or pathogen neutralisation, energy penalty
UVGI (In-duct / Coil UV)	Passive	Inside AHU / duct	Coil cleanliness, limited pathogen control	Requires exposure time, no space treatment, ineffective for VOCs
Sorbent / Chemical Filters	Passive	Inside HVAC unit	VOC adsorption	High maintenance, airflow restriction, limited scope
Electrostatic Precipitators (EP)	Passive	Inside HVAC unit	Low pressure drop, fine particle capture	Maintenance-sensitive, ozone risk, no VOC breakdown
Needlepoint Bipolar Ionization (NBPI)	Active (Limited)	Near discharge point	Particle agglomeration	Low ion persistence, limited coverage in large spaces
Photocatalytic Oxidation (PCO / PHI)	Active (Limited)	Near device	Microbial inactivation	Very short radical life, limited spatial reach
Dry Hydrogen Peroxide (DHP)	Active (Limited)	Occupied space	Surface disinfection claims	Minimal peer-reviewed data, humidity dependent
Dielectric Barrier Discharge Bipolar Ionization (DBD-BPI)	Active (Comprehensive)	Entire occupied space	Pathogens, VOCs, PM reduction, ion persistence	Requires proper design and control

Performance Implications for Building Design

Passive systems often drive:

• Higher outside air requirements

• Larger HVAC equipment

• Increased CapEx and OpEx

• Value engineering of IAQ features

Active systems - when properly engineered—enable:

• Reduced outside air intake (safely)

• Smaller mechanical systems

• Lower cooling and fan energy

• Performance-based compliance under ASHRAE 62.1 IAQP

This shifts IAQ from a cost centre to a design optimisation strategy.

The Question Every Decision-Maker Should Ask

When selecting an indoor air purification system, ask one critical question:

Does it clean air only inside the duct - or throughout the occupied space?

• Passive systems react

• Active systems protect

The Bottom Line

For high-occupancy, continuously air-conditioned buildings—particularly in GCC and MENA environments - active air purification delivers:

• Cleaner indoor air

• Lower energy consumption

• Better health and productivity outcomes

• Stronger long-term asset performance

Indoor air quality is no longer about adding devices.It is about choosing the right strategy.