How does a PIV system work?
A PIV system operates by continuously introducing filtered, tempered air into a building to create slight positive internal pressure. This pressure gently displaces stale, moisture-laden air through natural leakage points (e.g., gaps around windows, extractor fans, or trickle vents), reducing condensation and improving air quality.
Key Operational Stages
Air Intake: Draws external air (typically from a loft space or directly outdoors) through a filter that removes pollutants, pollen, and particulates.
Filtration: Filters (often F7/G4 grade) trap particles as small as 0.4 microns, improving air quality in urban UK areas with high pollution levels.
Tempering: In colder months, air is gently heated to near room temperature using low-energy elements or residual loft heat, minimising cold draughts.
Distribution: Conditioned air is dispersed via a central ceiling-mounted unit, circulating passively without complex ductwork.
Pressure Regulation: Maintains positive pressure to push stale air outward, targeting humidity from daily activities (cooking, showering, breathing).
Risk of Moisture Entrapment
If trickle vents or other natural leakage points are permanently sealed, the positive pressure created by the PIV system may force moisture-laden air into the building fabric (walls, ceilings, or floor voids) instead of expelling it. This can lead to:
- Interstitial condensation: Moisture condensing within wall cavities or under floors.
- Structural degradation: Timber rot, plaster damage, or insulation inefficiency over time.
- Mould growth: Hidden spores developing in enclosed spaces, posing health risks.
Mitigation
- Ensure trickle vents remain unobstructed to allow controlled airflow.
- Avoid over-pressurising tightly sealed modern homes; consult a ventilation specialist to balance airflow rates.
- Combine PIV with periodic manual ventilation (e.g., opening windows) in highly airtight properties.
PIV systems provide a low-energy solution for managing humidity in UK homes but require careful integration with a building’s existing airflow pathways. Their effectiveness hinges on maintaining a balance between controlled air ingress and unimpeded egress points.
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