# Infiltration

Infiltration is from combined effect of buoyancy and wind. Infiltration rate: O

Where Q = infiltration rate (L/s)

L = effective leakage area (cm2)

Cs = stack coefficient (L2 s’2 cm’4 K’1)

AT = average indoor-outdoor temperature difference (K)

Cw = wind coefficient (L2 s’4 cm’4 K’1 m’2)

V = average wind speed measured at local weather station (m/s)

 Table 7 Local Shielding Classes Description
 Table 5 Example of Calculation of Building Effective Air Leakage Area Based on Component Leakage Areas
 Class
 Size or x Al Description Number per unit
 1 No obstructions or local shielding 2 Light local shielding; few obstructions, few trees, or small shed 3 Moderate local shielding; some obstructions within two house heights, thick hedge, solid fence, or one neighboring house 4 Heavy shielding; obstructions around most of perimeter, buildings or trees within 10 m in most directions; typical suburban shielding 5 Very heavy shielding; large obstructions surrounding perimeter within two house heights; typical downtown shielding
 2 Cm
 Component
 4.0 cm2/m 0.5 cm2 ea 4.0 cm2/m2 1.7 crrr/m2 7.7 cm2/m2 1.7 cm2/m2 350 cm2 ea 6.0 cm2 ea 144 cm2 ea
 173 10 75 54 350 42 144
 Uncaulked Sliding Single Without damper Pipes Ducts untaped.
 43.2 m 20 13.1m2 13.1m2 5.7 m2 5.7 m2 1 7 1
 Sills Electrical outlets Windows Framing Exterior doors Framing Fireplace Penetrations Heating ducts
 Calculated total building air leakage area Ac = 848 cm2 Class One Two Three 1 0.000 319 0.000 420 0.000494 Table 6 Stack Coefficient Cs 2 0.000 246 0.000 325 0.000 382 House Height (Stories) 3 0.000 174 0.000 231 0.000 271 One Two Three 4 0.000 104 0.000 137 0.000 161 Stack coefficient 0.000 145 0.000 290 0.000 435 5 0.000 032 0.000 042 0.000049
 Table 8 Wind Coefficient C*,
 ,. … House Height (Stories)
 Example 6.2 Estimate the infiltration at design conditions for a two-story house in State College. The house has an effective leakage area of 500 cm2, a volume of 340 m3, and is surrounded by a thick hedge (shielding class 3). Solution: Under winter design conditions: TD = -13 °C, V = 8 m/s, T; = 22 °C. From A Tables 25.6 and 25.8 of the handouts, Cs = 0.000290, Cw = 0.000231

O

Air change rate = 284 / 340 = 0.84 ACH.

 0.1 ACH (air change rate per hour) 0.5 ACH 1 ACH 2 ACH 3 ACH

Extremely low low normal high

Extremely high Crack method:

Q = A C Apn

Where A = effective leakage area of cracks (m2)

C = flow coefficient

Ap = pressure difference between outdoor and indoor (Pa)