1. Chapter 6B: INFILTRATION CALCULATION
Agami Reddy (rev Dec 2017)
Component models for air infiltration
- residential doors and windows,
- closed swinging doors
- opening of doors
- curtain wall
2. Empirical methods
- Air change method (for residences and small commercial)
3. Basic LBNL model for one-zone buildings
Multi-zone network models
Natural ventilation due to opening and closing of windows
Natural ventilation through large openings
Measuring air infiltration
HCB-3: Chap 6B Infiltration Calculation

2. Component Models for Air Infiltration
Previous set of slides allowed pressure difference across building envelopes to be determined. Now, let us look at how infiltration can be determined.
Leakage Thru identifiable Components: Based on field tests on Actual Buildings:
Residential windows and doors
Commercial swinging doors when closed
Opening of commercial swinging doors
2) Background leakage
Curtain walls for commercial buildings
Use
Table 6.2
HCB-3: Chap 6B Infiltration Calculation

3. HCB-3: Chap 6B Infiltration Calculation
Background Leakage
6.20
HCB-3: Chap 6B Infiltration Calculation

4. Identifiable Components: Residential Windows and doors
Figure 6.15
Window and residential-type door air infiltration per perimeter length lp. The curves correspond to Equation 6.21, with n = 0.65 and coefficient k [(L/s · Pa0.5), (ft3/min ∙ inWG0.65)] according to construction type, as shown in the following table:
HCB-3: Chap 6B Infiltration Calculation

5. Infiltration for commercial-type swinging doors when CLOSED
because gaps
are larger
Figure 6.16
Infiltration through closed swinging door cracks, per perimeter length lp. The curves correspond to Equation 6.21, with n = 0.5 and coefficient k [(L/s · Pa0.5), (ft3/min ∙ inWG0.5)].
HCB-3: Chap 6B Infiltration Calculation

6. Infiltration through opening of doors due to traffic
Figure 6.17
Figure 6.17 Infiltration due to door openings as a function of traffic rate: (a) infiltration (with n = 0.5) and
(b) coefficient C [(L/s · Pa0.5), (ft3/min ∙ inWG0.5)].
Similar plots are available for revolving doors and automatic doors
HCB-3: Chap 6B Infiltration Calculation

7. HCB-3: Chap 6B Infiltration Calculation
Curtain wall
Figure 6.18 Infiltration per area of curtain wall for one room or one floor. The curves correspond to Equation 6.23, with coefficient K [(L/s · m2 · Pa0.65), (ft3/min · ft2 · inWG0.65)] according to construction type.
HCB-3: Chap 6B Infiltration Calculation

8. HCB-3: Chap 6B Infiltration Calculation

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10. HCB-3: Chap 6B Infiltration Calculation
due to windows + door perimeter + door opening + curtain wall
HCB-3: Chap 6B Infiltration Calculation

11. HCB-3: Chap 6B Infiltration Calculation
Empirical Methods
Air change method: for residences and small commercial
assumes that a portion of the air in the building is replaced with outdoor air which must be heated/cooled.
Number of air changes per hour (ACH): 1 ACH is equal to a flow rate equal to one volume of the house per hour
Range of ACH:
tight loose
Air infiltration volume = (ACH) x (room volume) / 60 min/hr
Tables in next slide allow determination of ACH for summer and winter conditions
HCB-3: Chap 6B Infiltration Calculation

12. Method used by some professionals because of its simplicity
HCB-3: Chap 6B Infiltration Calculation

13. Basic LBNL Model for Air leakage
Applicable for 1-zone small buildings WITHOUT mechanical ventilation:
6.25
Effective leakage area (ELA) is the equivalent amount of free open area of an
orifice that allows the same volume of air by infiltration as the actual building
(Eqn can be used for specific days as well as seasonal averages depending
on how the temperatures and wind velocity values are selected)
HCB-3: Chap 6B Infiltration Calculation

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15. HCB-3: Chap 6B Infiltration Calculation
Table 6.2
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16. HCB-3: Chap 6B Infiltration Calculation
Figure 6.19
Sketch of the building used for many of the examples in this chapter.
HCB-3: Chap 6B Infiltration Calculation

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18. HCB-3: Chap 6B Infiltration Calculation
6.25
HCB-3: Chap 6B Infiltration Calculation

19. HCB-3: Chap 6B Infiltration Calculation
Multizone Models
It is important to accurately predict inter-
zonal flow interactions for:
(i) larger buildings or for buildings
with multiple thermal zones
to predict envelope leakage over
specific portions of bldg
Set up and solve a set of simultaneous
non-linear equations for each flow
element (doors, windows,
assuming fully mixed compartments
Figure 6.20 Illustration of multizone flow paths
HCB-3: Chap 6B Infiltration Calculation

20. HCB-3: Chap 6B Infiltration Calculation
Multizone Models
Figure 6.21 Flow networks for a multizone building: (a) leakage paths in series and (b) leakage paths in parallel
HCB-3: Chap 6B Infiltration Calculation

21. HCB-3: Chap 6B Infiltration Calculation
Opening of Windows and Doors
Figure 6.22 Measured ventilation rates, as a function of wind speed, in a two-story house with windows open on lower floor
- Difficult to predict accurately
- Opening of windows led to large
changes in ACH ( 1 to 20 per hr)
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22. HCB-3: Chap 6B Infiltration Calculation
Natural Ventilation Air Flow through Large Openings
due to wind:
Eq. 6.28
If the openings are not of the same size,
the correction curve should be used:
Figure Increase in flow caused by excess area of one opening over the other
HCB-3: Chap 6B Infiltration Calculation

23. Lab Testing for Airtightness of a Component
Controlled tests are done in the lab without
the influence of climatic parameters.
A static pressure difference (about 200 Pa)
is created across the test specimen
from which the ELA can be deduced.
Often results are presented in terms of
- Flow per hour per area
- Flow per hour per unit crack length
Figure 6.26 Airtightness test arrangement
of a building component
HCB-3: Chap 6B Infiltration Calculation

24. HCB-3: Chap 6B Infiltration Calculation
Blower Door Tests
Blower door tests are done to estimate aggregate envelope leakage and to locate and fix leaks:
Device consists of a door-insert
with rubber edge.
Variable speed fan and measurements for flow and pressure difference
Tests conducted till fairly high pressures (about 50 Pa) in 10 Pa incremental steps
Done in smaller buildings
Tracer gas tests used for larger bldgs
Figure 6.25 Photo of a blower door test rig
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Presentation and Analysis of Test Data of Blower Door Tests
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27. HCB-3: Chap 6B Infiltration Calculation
Outcomes
Be able to apply models for estimating leakage through various types of envelope components
Understanding of the simple air change method
Be able to use the LBNL model to solve simple problems
Familiarity of the ELA concept and lookup tables
Understanding scope and analysis approach of multi-zone modeling methods
Understanding how opening windows and doors can lead to large variations in natural ventilation
Familiarity of how to deduce natural ventilation flow thru large openings
Familiarity with how components are tested in the lab
Understanding of the working principle of the blower door test and how to deduce whole house ELA
HCB-3: Chap 6B Infiltration Calculation