System Design Worksheet

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This section is explained in the Health Canada's Reducing Radon Levels in Existing Homes: A Canadian Guide for Professional Contractors, Section 4.2 Feasibility Test.

Reference from the National Standard of Canada: Radon Mitigation options for existing low-rise residential buildings: P29-149-012-2017-eng.pdf

5.1.1 Feasibility test prior to installation:

A “pressure field extension test” (i.e. communication test) shall be used to determine the number of suction points and the fan size needed for an effective system. A scheme of the communication testing results shall be documented and provided in the Homeowner radon mitigation system package. (see 7.2)

Step 1: Design Suction Pressure - This is where you take the natural pressure across the slab and multiply it by a temperature adjustment factor to get your target design pressure.

101 - Natural Pressure: Close all doors & windows. Test natural pressure at each test hole. Record highest reading. (Typical values between 0.2 and 3)

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Click to look up Winter heating degree days for Canada.

102 - Temp Adjustment: (look up in Table 4 above)

103 - Design Pressure: (multiply line 101 by line 102)

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Step 2: Design Airflow - This is where we determine the target airflow that would be required to achieve the design pressure from Step 1 at the furthest/weakest test hole.

Design Airflow = Vacuum flow X (Design Pressure / Observed Pressure)

200 - Measured airflow from vacuum with a suction pit pressure typically around -250Pa, but could be in the range between -50Pa to -1000Pa (airflow in CFM)

CFM

201 - Measured airflow from vacuum with a suction pit pressure typically around -250Pa but could be in the range between -50Pa to -1000 Pa (Airflow in L/S) (1 L/s = 2.12 CFM)

L/s

202 - Design Pressure: (line 103)

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203 - Observed Pressure Change: At furthest/weakest communication test hole

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204 - Difference between Design Pressure and Measured Pressure Change at furthest/weakest hole. (line 202-203, can't be a negative number)

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205 - Design Pressure / Calculated Pressure Change: (line 202 divided by line 204)

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206 - Design Airflow in litres per second: (line 201 multiplied by line 205)

Litres/second

Step 3: Target Cavity Pressure - This is where we determine what the design cavity pressure would be if you achieved your design airflow. Cavity pressure is 1 of 3 pressures that your radon fan will have to overcome.

Target Cavity Pressure = Observed Pressure Change X (Design Airflow/Observed Airflow)^2

301 - Measured suction pit pressure with vacuum OFF: In test hole 25cm from suction hole.

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302 - Measured suction pit pressure with vacuum ON: In test hole 25cm from suction hole.

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303 - Cavity Pit Pressure Change (line 301-line 302)

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304 - Design Airflow: (Line 206)

Litres/second

305 - Measured airflow from vacuum (in litres per second): (Line 201)

Litres/second

306 - Design Airflow/ Measured Airflow: (line 304/305) multiplied by itself

Litres/second

307 - Target Cavity Pit Pressure: (line 303 multiplied by line 306)

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Step 4: Piping Resistance - This is where you calculate the pressure drop for the piping components. This example is for 4” 100mm pipe.

401 - m of pipe

metres

402 - # of 90s

403 - # of 45s

404 - Tee fittings

405 - Cavity Fill*

Note: Input 1 if suction pit is backfilled with clean stone and input 0 if suction pit is empty.

406 - Varmint Guard

407 - Total piping resistance: (sum of lines 401 to 405)

Step 5: Determine Velocity Pressure (VP) – This is where you calculate the dynamic head based on your design airflow.

501 - System Pipe Size (mm)

502 - Design Airflow: (Line 206)

Litres/second

503 - Velocity of Air (V): Velocity (V) of air running through system piping @ design airflow in m/s

m/s

504 - Velocity Pressure : (Vp=0.6 x V2 (where V is velocity in m/s) or look up using line 502 in VP Look Up Table)

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Step 6: Determine Dynamic Piping Resistance - This is where you calculate the total dynamic resistance of your piping components at your target air flow.

Dynamic Resistance = Velocity Pressure X Total Piping Resistance

601 - Velocity Pressure : (line 504)

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602 - Total Piping Resistance : (line 407)

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603 - Dynamic Resistance : (multiply line 601 by line 602)

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Step 7: Total System Resistance – This is the sum of the dynamic piping resistance, the cavity pressure and the interior/exterior pressure difference that your fan will need to overcome to achieve the design airflow.

701 - Dynamic Piping Resistance: (line 603)

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702 - Cavity Pressure: (line 307)

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703 - Interior/ Exterior pressure: (look up in table 3 below)

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704 - Total System Pressure Drop: (sum of lines 701, 702 and 703)

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704b - (704 x 0.004)

"WC"

705 - Design Airflow - L/s: (line 206)

L/s

705b Design Airflow - CFM (Line 705 x 2.12)

CFM

Project/Name:

Location:

Plot the total System Pressure Drop (Line 704) and Design Airflow (Line 705)

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