Effective leakage area

Effective leakage area

Calculation in square inches equal to the total area of all air leaks in a building envelope. Defined by the Lawrence Berkeley National Laboratory, the ELA is the area of a nozzle-shaped hole that would leak the same amount of air as the building does when pressurized to 4 pascals. Estimating leakage in this way enables one to visualize the cumulative impact many tiny holes can have on the air-tightness of a house.
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The rate of air leakage can depend on several factors including the effective leakage area, locations of the leakage paths, air pressure difference between the containment system and the data center room, rack heat load and associated server airflow rates, as well as on the length, width, and height of cold and hot aisles.
It was originated to test houses where one of the required results was "effective leakage area at 4 Pa." Since ambient pressure fluctuations on a house, due to stack and wind, can be close to 4 Pa, making measurements inaccurate, the standard states that preferred test conditions are "4 mph wind or less and a temperature range of 41[degrees]E to 95[degrees]E" Since these requirements make testing prohibitively expensive due to the meteorological restrictions, field testing evolved into testing at 50 Pa, which has the advantage of being repeatable.
Effective leakage area is calculated with Equation 2 and the constants in the equation are generally assumed as [C.sub.d] = 1.0 and [DELTA][P.sub.r] = 4 Pa (0.00058 psi) or [C.sub.d] = 0.6 and [DELTA][P.sub.r] = 10 Pa (0.00145 psi).
The effective leakage area of Equation 2 can be converted to the coefficient of discharge with Equation 3 (ASHRAE 2005):
Test results are often expressed as an effective leakage area, which is the equivalent orifice area across which the airflow rate through the building envelope would occur at a particular reference pressure.
The effective leakage area or ELA at a reference pressure of 0.016 in.
Monthly Average Air Change Rates for the Space for a TMY Year Determined from the Effective Leakage Area Month Temp.
The effective leakage area (ELA) infiltration rate will be used as a surrogate for the [CO.sub.2]-based and tracer gas infiltration measurements as well in the discussion that follows.
These suggestions also fail to include a discharge coefficient assumption, and they do not specify whether the leakage area is ELA ([DELTA][p.sub.r] = 4 Pa, [C.sub.D] = 1), where ELA is the effective leakage area, or EqLA ([DELTA][p.sub.r] = 10 Pa, [C.sub.D] = 0.611).
[A.sub.L] = equivalent or effective leakage area, in.(2)
These envelope leakage values are summarized in Table 1 together with Effective Leakage Area at 4 Pa (ELA4).
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