Infiltration and Exfiltration

In general, the air leakage rate through a building envelope is dependent 

The sizes and distribution of leakage paths The flow characteristics of the leakage paths The pressure difference across the leakage paths 

CHAPTER 7 PRINCIPLES OF AIR AND CONTAMINANT MOVEMENT INSIDE AND AROUND BUILDINGS 

A typical envelope opening has a complicated shape and is often subject to unsteady flow conditions at its inlet and outlet.- There are no simple analytical solutions for the flow through such openings. The most-used equation representing flow characteristics is the so-called power law  

Experimental evidence regarding the power law is somewhat contradictory. A constant value of 3 = 0..5 is considered to give a good fit to experimental data by many authors. According to Awbi, p depends on the flow regime and has a value of 0..5 for fully turbulent flow and 1,0 for laminar flow.- fn practice the value of P tends to be between 0.6 and 0.7. 

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Heat losses and gains with infiltration and exfiltration through cracks in the building envelope... 

Calculation is made in accordance with Section 7.8.2, Infiltration and Exfiltration. 

The airflow rate infiltrating and exfiltrating through each air leakage pass, Q , due to the combined effect of wind, stack, and mechanical ventilation system perfotmance can be calculated ftom the mass balance equation... 

The infiltrating and exfiltrating airflow rates can be calculated using the following equations ... 

At the height of the boundary between the infiltrating and exfiltrating flows, air pressure across the gate, - P, equals 0, and thus... 

It is generally preferred to carry out field experiments in long sewer lines that make it possible to measure relatively large differences in the wastewater quality compared with the level and the uncertainty for determination of the parameters in question. Furthermore, a sewer line without tributary sewers, infiltration and exfiltration must be preferred because of a less complicated sampling program with which to identify all inputs and outputs to the system. 

Supply, return, exhaust, infiltration, and exfiltration airflow from each room are shown on airflow diagrams... 

Airlock Entry - A building architectural element (vestibule) with two airtight doors that reduces the amount of air infiltration and exfiltration when the exterior most door is opened. 

Weatherization - Caulking and weatherstripping to reduce air infiltration and exfiltration into/out of a building. 

Bartlett et al. (2004) have modeled COj in naturally ventilated classrooms occupied by children. The only air exchange present in naturally ventilated classrooms is provided by infiltration and exfiltration, mostly through open doors and windows. Bartlett et al. (2004) gave the basic mass balance equation for COj as... 

Madding goes on to explain some of the other factors such as air infiltration and exfiltration, chimney effects, and thermal short circuits or bypasses which, in many cases, can be serious enough to completely negate the benefits of a retrofit insulation program. 

The hydrologic cycle, or moisture cycle — that may encompass the processes of rain infiltration in the soil, exfiltration from the soil to the air, surface runoff, evaporation, moisture behavior, groundwater recharge and capillary rise from the groundwater. All these processes are interconnected and are frequently referred to as the hydrologic cycle components. 

It should be pointed out that the amount of moisture that enters or leaves a building by diffusion is usually negligible compared to the amount that enters with infiltrating air or leaves with exfiltrating air. The primary cause of interest in the moisture diffusion is its impact on the performance and longevity of building materials. 

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