1. Do I Need a Big Ass Fan? Active Soil Depressurization Fan Selection
Chad Robinson – Building Performance Company
Bruce Snead – MURC-KSU

2. Now It’s Gonna’ Hit the Fan!
We know the fan industry is very competitive and our purpose in this is not to compare different manufacturers fans nor critique their fans.
We are using sample fans from the manufacturers in our demonstrations.

3. Everybody Keep Their Cool!

4. How “Big” a Fan Do I Need? Is this the right question?
We often hear of mitigators or customers who tell us about putting on a “bigger”fan to address failures to achieve radon reduction goals. What does this mean? Is this the right question?

5. What Does the Fan Have to Do?
The appropriate fan will have the capacity to:
move sufficient air . . .
to overcome the suction of the house on the soil ....and
pull air through the soil under the foundation
....and
pull and push air through the piping to the discharge point.

6. In Addition, the Appropriate Fan
Is the lowest wattage fan that will accomplish the job.  Lower wattage fans are almost always quieter and their long term energy costs can be significant.
Is Quiet – sound/noise are often justification for fans being turned off by occupants- less than 40 dB
Moves enough air to depressurize the sub-slab zone but minimizes air drawn from the house
Easily attaches to vent stack
Is Durable
Has no positive pressure leaks
Is moisture-resistant

7. Steps Needed for Suitable ASD System Design
Determine:
Required extent and strength of PFE
Suction locations and system air flow required to produce adequate PFE
Total resistance to air flow in system
Measure sub-slab resistance
Calculate pipe run resistance
Add the two to get total system resistance
Select fan which will produce required air flow
Simulate system operation to verify adequate PFE

8. We can measure the resistance in the “soil” part.
We can calculate the resistance in the “pipe run”
The sum of the two is the “Total System Resistance” which sets the conditions for fan performance.
Pipe Run Quantities
17' of outside pipe & s
1 - 90 & s
outside by fan
1 - 90 & s
as pipe exits basement
23' of inside piping
1 - 90 & s
by suction hole & open pipe at bottom

9. Which Fan Will Do This?
The fan has to overcome this pressure differential to reverse the flow of air into the house.
In addition, the fan has to work against the resistance of the soil materials under the basement slab.
It also has to work against the resistance created by the piping length and configuration.

10. Fan Performance and Capacity How is it Rated?
One of the most valuable pieces of information supplied by fan manufacturers is the fan performance curve.
These curves show the relationship between the quantity of air a fan will deliver and the pressure generated at various air quantities.

11. Common Radon Fan Curves
Note that fan curves indicate quantity of air fan will move (CFM) working against different levels of resistance or static pressure (inches of Water Column)
Curves derived by bench-testing fans connected to PVC pipe
(Get out fan curve graph. Explain log scale and reason for using it.)

12. How Fan Curves Are Developed-Bench Testing
The drawing below gives the general testing system layout for evaluating fan performance
Since most sub-slab depressurization systems require at least 10 feet of PVC piping to be able to carry the system exhaust above the roof line all fans were tested with 10 feet of piping.  In most cases 4" PVC piping was used. 

13. Four General Categories of Radon Fans
Low Wattage Fans  - good sub-slab gravel and slab sealing.
Mid Range Fans  -  less than optimal sub-slab aggregate and/or slab leakage
High Flow Fans  -  Lots of slab leaks or very porous soil or multiple foundations to treat
High Vacuum Fans  -  Packed dirt under the slab with likely low system airflow.

14. Low Wattage Fans

15. Mid-Range Fans

16. High Flow Fans

17. High Vacuum Fans

18. All Four Fan Categories

19. Measuring Air Flows How Many of You Measure Air Flows?
How Do You Measure the Flows?
Pitot Tube?
Flow Grid?
Manufacturer’s chart?
What Are the Average CFMs in the Housing Stock You Mitigate?

20. What Will It Take to Get Fan Man Up?
Vent stack mounted air flow supported fan figures to draw attention to your mitigation systems!!!
Seasonal, holiday, and special versions….
You know your fans……

21. What Airflow Will Get Fan Man Up?
10-20 CFM
20-40 CFM
40-60 CFM
CFM
Over 100 CFM
He won’t make it up…..

22. Measuring Air Flow
Pitot tube allows determination of velocity pressure exerted by air flowing in pipe
Velocity pressure can be converted to
Velocity using a graph or a formula
Velocity can be converted to flow volume:
Velocity in feet per minute (FPM) times cross-sectional area of pipe in square feet = cubic feet per minute (CFM)
Velocity (FPM) x area (square feet) = CFM
Using graphs allow converting velocity pressure to CFM in different diameter pipe
Without doing calculation
Saves time and eliminates calculation errors
Class looks at “Velocity Pressure vs. CFM” graphs in notebook

23. Pitot Tube and Micromanometer
The micromanometer shows the difference between total pressure and static pressure which is velocity pressure
Pitot
Tube
#.##
Pipe
Static Pressure
Airflow
Total Pressure
Fan
(Static & Velocity)
Static Pressure

24. Pitot Tube - How it Works
cfm
1000
800
600
400
300
200
100 80 60 50 40 30 20 10
Pitot Tube - How it Works
Find the velocity pressure from the Pitot tube on the horizontal scale (e.g., .2” WC)
Follow straight up to the diagonal line representing the diameter of the pipe the Pitot tube is mounted in (e.g., 2”)
Follow straight left or right to the CFM value on the vertical scale (55 CFM)
Velocity Pressure versus Cubic Feet per Minute (pitot tube in center of pipe)
6” pipe
4” pipe
3” pipe
2” pipe
Velocity Pressure in Inches of Water Column (WC)

25. The Hughes’ PFE Diagnostic Rig
Micromanometer
#.#
4” Cap
Gate Valve (not ball valve)
4” x 2”
Reducer
4” Tee
To Vac
or Fan
2” Custom- Made Pitot Tube
Port to Measure
Static Pressure
Total Pressure Port
Static Pressure Port
Notes:
10 pipe diameters from reducer to total pressure port
3” between total pressure port and static pressure port
4 pipe diameters between static pressure port and flow
modulation valve
Suction Pit

26. What About the Pipe Resistance?
We can estimate the resistance of any pipe configuration based on established resistance information about common pipe diameters, the length of pipe needed, and resistance created by each pipe coupling, expressed as equivalent to a number of feet of straight pipe resistance.

27. Pressure Drop per 100 Feet of Pipe

28. No Bends no fittings, 15 ft of pipe 3" 4" 6" 20 CFM 0.02 40 CFM 0.1
3"
4"
6"
20 CFM
0.02
40 CFM
0.1
80 CFM
0.3
160 CFM
1.1
0.4
320 CFM
2.9

29. Simple Outside System 4 elbows, 2-45's, 20' of pipe 3" 4" 6" 20 CFM
3"
4"
6"
20 CFM
0.1
40 CFM
0.2
80 CFM
0.5
160 CFM
1.8
0.7
320 CFM
4.8
2.1
0.8

30. More Complicated Interior System
6-EL, 4-45's, 45 ft of pipe
3"
4"
6"
20 CFM
0.1
40 CFM
0.3
80 CFM
0.9
160 CFM
2.8
1.1
0.4
320 CFM
7.9
3.4
1.2

31. Fan Selection Criteria
The appropriate fan:
Must move sufficient air . . .
. . . to create the desired pressure field extension
Steps in fan selection
Determine desired extent and strength of pressure field
Determine resistance to airflow in sub slab and pipe run
Select fan to produce desired air flow in that situation

32. In Addition, the Appropriate Fan
Is the lowest wattage fan that will accomplish the job.  Lower wattage fans are almost always quieter and their long term energy costs can be significant.
Is Quiet – sound/noise are often justification for fans being turned off by occupants
less than 40 dB
Easily attaches to vent stack
Is Durable
Has no positive pressure leaks
Is moisture-resistant

33. Fan Box Demonstration

34. Ten Year Fan Operating Costs ($0.12/KWH with 5 and 10% inflation)

35. In general, the higher the fan wattage, the higher the noise
Fan Noise
In general, the higher the fan wattage, the higher the noise
(Decibel reading with fan airflow at midpoint of static pressure)

36. Electrical Consumption Goes Down as Air Flow Decreases (1” WC = 250 Pa; 100 CFM = 47 L/s)
Wattage decreases as less air is available to system
Sealing not only increases sub-slab vacuums, it also decreases operating cost of fan and loss of conditioned indoor air
New graph
67 57 L/s
(120 CFM) 47
9.4 L/s (20 CFM)

37. Additional Advantages of These Procedures
Provides the ability to predict system mechanical performance before installation and allows simulation of system with different:
Fans
Lengths and diameters of pipe run
May also reveal the need for:
More excavation in suction pit or more suction points
Additional sealing not originally anticipated
With multiple suction points, allows determination of:
Unrestricted and required flow from each suction point
So that flow control measures can be designed
Most important:
Allows accurate prediction of PFE which actual system will produce BEFORE the system is installed!

38. Don’t Be A Poke and Hoper!
Thanks
Bruce Snead
Chad Robinson