Introduction

Dynamic Filtration

Ventilation air is efficiently filtered of harmful Particulate Matter (PM) as it flows through the Energyflo™ cells in a DBB. Higher ventilation rate is, furthermore, an effective method of removing indoor pollutants. 

Experimentally measured dynamic filtration efficiency

The PM filtration performance of fibre-based DI media has also been derived theoretically and an experimentally calibrated 1-D, multi-layer PM filtration model was developed.  This model, which applies solely to fibre-based materials, has been used to address the questions of (a) what is the efficiency of filtration of a DI layer as a function of media physical properties, particle size distribution and air flow rate, and (b) what is the lifetime of the DI layer before it becomes clogged?

The single fibre model

The single-fibre model estimates the clean filter removal efficiency E, prior to particle deposition, using the following expression:

equ1

Dendrite formation and clogging model

In a loaded fibre filter the internal structure changes over time as branch-like dendrites form through the agglomeration of particles within the filter media.  Some of these dendritic fibres themselves start to act as filter fibres, increasing the packing density. Since the collection efficiency in DI media increases with dendrite formation the risk of efficiency loss is eliminated.

The predicted evolution of pressure drop over a 60 year period for a small DBB in polluted Marylebone Road, London, is shown below.

Evolution of pressure drop over time (Courtesy of EBP)

Correctly designed and implemented, the clogging rate of DI media can thus be slowed down to the point where it ceases to be of concern, even in the most heavily polluted urban and industrial environments, with no compromise in dynamic filtration efficiency or operation of the building.

This is a significant finding that rivals in its importance the role of near-zero dynamic U-value in reducing the carbon footprint of the built environment, to sustain occupant health and enable clean indoor environments to be achieved at any location anywhere in the world.

Click here for dynamic filtration references.

Dynamic filtration references

Imbabi M S, and A Peacock, "Smart breathing walls for integrated ventilation, heat exchange, energy efficiency and air filtration", ASHRAE/CIBSE conference, Edinburgh, September (2003).

Imbabi M S, and A D Peacock, Allowing buildings to breathe, Sovereign Publications, p85-95 (2004).

Taylor B J, R Webster and M S Imbabi, The building envelope as an air filter, Building & Environment, Vol. 34(3), p353-361 (1998).

Taylor B J and M S Imbabi, Dynamic insulation in multi-storey buildings, Proc. CIBSE A, Building Services Engineering Research & Technology (BSERT), 20(4), p175-180 (2000).

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