1. Filtration and Coil Fouling
Jeffrey Siegel and Michael Waring
The University of Texas at Austin

2. Motivation What is role of filters in protecting coils?
My intent – Predict fouling
Accidental results – Filter sales collateral

3. Courtesy Paul Francisco

4. Why do we care?
22 °C (71 °F)
8 °C (46 °F)
Courtesy Jim Westberg

5. Reduced Heat Transfer 27 °C (81 °F) 18 °C (64 °F)
Courtesy Jim Westberg

6. Coil Dust

7. Major Coil Fouling Effects
Negative – pressure drop increases,
fan energy increases
Negative – heat transfer decreases
system energy increases
Positive – surface area increases,
system energy decreases

8. Two Perspectives
Heat transfer reduction by insulation doesn’t matter that much
It is all about fan energy
Good thing – relatively easy to calculate
But, fan pressure drop and filter pressure drop have similar effect
Therefore, coil fouling doesn’t matter from an energy perspective.

9. Two Perspectives It is all about insulation on the coil
Fan energy is very small component
Bad thing – difficult to calculate
Highly dependent on particle composition and deposition location
Also, competition between small positive and large negative impact

10. Previous Studies On Coil Fouling
Krafthefter et al. (1986,1987)
Siegel and Nazaroff (2002, 2003)
Groll et al. (2004)
Others (Proctor, Braun, etc.)
Why don’t we know the answers yet?
Use of test dust for experiments
Very limited field data
Insufficient range of testing and simulations

11. Ongoing Research Simulate coil fouling in commercial systems
Need to consider several factors
Sources of particles
Air systems operation
Coil condition
Filtration
Losses in ducts

12. Simulation Parameters
Basic
12 FPI coil
2 m/s face velocity
10000 CFM
1 month of continuous operation
Assumptions
No indoor sources
Typical values for other parameters
Varying
Urban vs. rural location
100% outside air, 100% recirculating, split
Wet, dry coil
MERV 6 (clean and dust loaded), MERV 11, MERV 15
No bypass, 1 mm, 10 mm
Simple, typical, complex, duct system

15. What Size Particles are Responsible?

16. MERV 6
MERV 11 µm µm
1 - 5 µm µm µm µm µm
1 - 5 µm µm µm
MERV 15
MERV 6 Dust Loaded µm µm
1 - 5 µm µm µm µm µm
1 - 5 µm µm µm

17. MERV 6 µm µm
1 - 5 µm µm µm
MERV 6, with 1 cm bypass µm µm
1 - 5 µm µm µm
MERV 15 µm µm
1 - 5 µm µm µm
MERV 15, with 1 cm bypass µm µm
1 - 5 µm µm µm

18. Summary Filters work to protect coils
But, we have limited (and conflicting) information on energy and system consequences

19. Biological Fouling
Courtesy Richard Corsi

21. Strategies Protect coils with appropriate filtration
Avoid claiming energy savings
Appropriate to speculate about biological fouling
Support research in this area