IAQ & Mould: A Technical Appendix For Engineers

Once established, mould continuously releases spores, fragments, and microbial volatile organic compounds.

Mould Control, Humidity, and Bipolar Ionization in HVAC Systems

1. Mould as an HVAC-Related IAQ Risk

Mould growth within buildings is fundamentally an HVAC and moisture-management issue. In mechanically conditioned buildings, mould colonisation most commonly occurs at locations where temperature gradients, condensation, and organic particulates coincide, including:

• Cooling coils and fin surfaces

• Condensate drain pans and traps

• Internal duct liners

• Terminal units and fan housings

• Envelope-adjacent conditioned spaces

Once established, mould continuously releases spores, fragments, and microbial volatile organic compounds (mVOCs) into the air stream, contributing to indoor air quality degradation and occupant exposure.

2. Climatic Drivers in Coastal & Humid Regions

In GCC coastal and high-humidity climates, mould risk is elevated due to:

• High outdoor absolute humidity → increased latent loads

• Continuous HVAC operation → sustained moisture presence

• Negative pressure infiltration → humid air ingress

• Frequent door openings → transient humidity spikes

• Dust loading → nutrient availability for fungal growth

Even well-designed systems may experience intermittent surface wetting, particularly during off-design conditions, plant cycling, or partial-load operation.

3. Limitations of Conventional Mitigation Measures

3.1 Filtration

• Captures airborne particulates only

• Does not address microbial growth on surfaces

• Does not inactivate spores or fungi

3.2 UV-C (Coil Irradiation)

• Effective only in line-of-sight areas

• Limited downstream effect

• No impact on occupied-zone air or building surfaces

3.3 Chemical Cleaning

• Reactive, not preventive

• Requires downtime

• Re-growth occurs if moisture conditions persist

A comprehensive mould control strategy requires continuous, distributed treatment beyond point solutions.

4. Bipolar Ionization – Engineering Mechanism of Action

AtmosAir Direct Barrier Discharge (DBD) Bipolar Ionization introduces controlled concentrations of positive (H⁺) and negative (O₂⁻) ions into the HVAC air stream.

These ions act through multiple mechanisms:

4.1 Biological Disruption

• Ions interact with microbial cell membranes

• Protein denaturation inhibits replication

• Reduces viability of mould spores and fungi

4.2 Surface Suppression

• Ionized air contacts HVAC and interior surfaces

• Inhibits microbial adhesion and colonisation

• Reduces biofilm formation on coils and drain pans

4.3 Particulate Agglomeration

• Charged particles combine into larger clusters

• Improved downstream filtration efficiency

• Reduced airborne persistence of spores

This multi-path action differentiates bipolar ionization from purely filtration-based strategies.

5. IAQ & Mould - Integration Within HVAC Systems

AtmosAir systems are typically installed at:

• AHU supply plenums

• In-duct downstream of cooling coils

• Return air plenums (project-specific)

Key integration considerations:

• No increase in static pressure

• Negligible electrical load

• Continuous operation aligned with fan runtime

• No consumables or chemical by-products

Systems are designed to maintain ozone levels below ASHRAE, UL, and WHO limits.

6. Interaction with Humidity Control

Bipolar ionization is not a dehumidification technology and should not be used as a substitute for proper latent load control.

However, it provides critical risk reduction by:

• Suppressing microbial growth during humidity excursions

• Reducing biological amplification when condensation occurs

• Extending the safe operating envelope of HVAC systems

This is particularly valuable during:

• Seasonal shoulder periods

• Night-time setback conditions

• High occupancy or weather-driven humidity spikes

  
  

7. Performance Evidence

Independent laboratory testing demonstrates:

• Reduction of mould spores and fungi in treated air streams

• Decreased microbial growth on treated surfaces

• Improved IAQ stability under high-humidity conditions

Field installations in hospitality, healthcare, and coastal facilities show:

• Reduced mould-related odours

• Fewer remediation events

• Improved coil cleanliness and heat transfer stability

  
  

8. Application-Specific Considerations (Hotels & Hospitality)

Hotels benefit from bipolar ionization due to:

• Continuous occupancy

• High moisture generation (bathrooms, spas, kitchens)

• Sensitivity to odours and guest perception

Engineering benefits include:

• Reduced biological fouling of HVAC components

• Lower cleaning frequency

• Improved guest-room IAQ consistency

• Enhanced resilience in coastal climates

  
  

9. Standards & Compliance Context

Bipolar ionization may support compliance with:

• ASHRAE 62.1 IAQP (contaminant control)

• ASHRAE 241 (control of infectious aerosols)

• LEED, WELL, Fitwel IAQ credits

• Local green building and wellness frameworks

All applications should be documented in the Basis of Design and coordinated with IAQ performance objectives.

10. Engineering Summary

From an engineering perspective, bipolar ionization:

• Addresses biological contaminants that filtration cannot

• Operates continuously throughout HVAC systems

• Supports mould suppression in humid climates

• Reduces IAQ risk without energy or pressure penalties

When integrated alongside proper humidity control and ventilation design, AtmosAir provides a preventive, low-energy, standards-aligned solution to IAQ & mould risk in high-humidity buildings.