Chapter 6: INFILTRATION Agami Reddy (July 2016) Definitions Energy implications Infiltration rates across building stock Typical air leakage locations and background leakage 5. Scientific background for estimating infiltration - Flow thru large and small orifices - Pressure difference due to wind effect and stack effect 6. Empirical methods for air leakage - Air change method (for residences and small commercial) 7. Basic LBNL model for one-zone buildings 8. Engineering model (residential-type doors and windows, closed swinging doors, open doors, curtain wall) 9. Multi-zone network models 10. Measuring air infiltration HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Definitions Three mechanisms that contribute to the total air exchange:   Infiltration is the uncontrolled air flow rate through all the unintentional openings such as little cracks and gaps between different components (such as ill-fitting windows or doors). It is balanced by an equal mass flow called exfiltration, since mass must be conserved Natural ventilation is the air flow rate induced by deliberate opening of windows or doors. It is a variable quantity depending on prevailing outdoor conditions and one cannot control it properly. Mechanical or forced ventilation is the air flow rate intentionally drawn-in by mechanical ventilation such as fans. It can be controlled and varied as necessary.   The term passive ventilation is also used, and applies to both infiltration and natural ventilation   HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

Infiltration Rates across Building Stock Number of air changes per hour (ACH): 1 ACH is equal to a flow rate equal to one volume of the house per hour Newer Older Older typical US homes: 0.5 – 2 ACH (seasonal averages) Newer homes: 0.3 – 0.7 ACH HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Moderately tight buildings Tight buildings In Swedish homes, it is standard practice to limit infiltration to about 0.2 ACH HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Mechanisms The cause for infiltration is basically a pressure difference due to wind, stack effect and mechanical HVAC system imbalances: In the U.S., residential buildings typically rely on infiltration to meet ventilation needs (though this is changing) In commercial and institutional buildings, infiltration may not be desirable from the view point of energy conservation and comfort. Hence, efforts are made to reduce it. However, it may be significant especially in tall buildings HCB-3: Chap 6 Infiltration

Air leakage locations and background leakage Three sources of air leakage: a) Component perforations – easy to identify (vents, stacks, chimneys) b) Openings – easy to identify (windows, doors,…) c) Background or fabric leakage - depends on construction impossible to identify all cracks,.. - generally assumed to be uniformly distributed over surface area of the building Represented in terms of “leakage/unit area of envelope” HCB-3: Chap 6 Infiltration

Scientific Background Given in textbook: Flow thru opening in building envelope treated as ORIFICE flow for sharp edge orifices In reality, flow thru building cracks is a combination of laminar and turbulent and corrections have been proposed based on experimental evaluations HCB-3: Chap 6 Infiltration

Scientific background- Wind Effect- Very complex HCB-3: Chap 6 Infiltration From Liddament, 1986

HCB-3: Chap 6 Infiltration For Time Averaged Wind Pressure HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration For Time Averaged Wind Pressure Plots to determine Cp are shown in next 2 slides HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Wind Pressure Coefficient a) For roofs of tall buildings for three different aspect ratios of length L and width W b) For roofs of low rise buildings inclined at less than 20o, c) For walls of tall buildings for three different aspect ratios of length L and width W HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration d) Walls of low rise buildings 6.9 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Effective Wind Speed HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

Scientific Background- Stack Effect Caused by temperature differences (and hence air densities) on the inside and outside Winter stack effect in tall buildings HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration 6.12 Or alternatively 6.14 h- height from neutral pressure line T is in absolute units HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Variation of pressure difference due to stack effect with vertical distance from neutral pressure line HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration 6.15 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Eq. 6.12 HCB-3: Chap 6 Infiltration

Combining wind, stack and mechanical ventilation effects HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Superimposition of stack and wind pressures along height of a building HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Empirical Models 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: 0.5 - 1.5 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 6 Infiltration

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

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 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Table 6.2 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration 6.25 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Engineering Models 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 6 Infiltration

HCB-3: Chap 6 Infiltration Background Leakage 6.20 HCB-3: Chap 6 Infiltration

IDENTIFIABLE Components Residential Windows and doors Figure 6.15 residential doors and windows : n=0.65 k=1 is tight gap width k=2 is average k= 6 is loose HCB-3: Chap 6 Infiltration

Infiltration for commercial-type swinging doors when CLOSED because gaps are larger Figure 6.16 HCB-3: Chap 6 Infiltration

Infiltration through opening of doors due to traffic Figure 6.17 Similar plots are available for revolving doors and automatic doors HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Curtain wall Figure 6.18 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Multizone Models Set up and solve a set of simultaneous non-linear equations HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Multizone Models HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Opening of Windows and Doors Figure 7.2 Measured ventilation rates, as a function of wind speed, in a two-story house with windows open on lower floor HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration 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 6.24 Increase in flow caused by excess area of one opening over the other HCB-3: Chap 6 Infiltration

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 or - Flow per hour per unit crack length HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration 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 HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration

HCB-3: Chap 6 Infiltration Presentation and Analysis of Test Data of Blower Door Tests HCB-3: Chap 6 Infiltration

HCB-3 Chap 4: Solar Radiation Outcomes Familiarity with the three causes of pressure difference across building envelopes resulting in infiltration Understanding the energy implications of air infiltration Familiarity with different pathways/locations and types of air leakage: component perforations, openings, and background or fabric leakage Familiarity with the scientific background for analyzing wind and stack effects and engineering methods of estimating the associated pressure difference Be able to analyze situations involving wind and stack effects on buildings Understanding of the ELA concept and be able to use it along with the LBNL model to solve simple problems Be able to apply engineering models for estimating leakage through various types of envelope components Familiarity with multi-zone modeling methods Familiarity with lab testing of components and with the blower door test HCB-3 Chap 4: Solar Radiation