MIL-HDBK-l003/19

Air density ratio versus elevation.

FIGURE

24.

where Aa is the actual roof area and Rtot is the total Rvalue of the roof

element. If the roof is pitched over a horizontal ceiling with an attic, two

possibilities exist: (1) If the attic is vented RROOF is the total R-value o

the ceiling alone; (2) If the attic is not vented, RROOF is the sum of the

roof contribution, given by equation 5.1, and the ceiling contribution, plus

an allowance for the air gap between the two. If the surfaces bounding the

attic are non-reflective, use an R-value of 0.6 for the air gap and a value o

1.3 if the surfaces are highly reflective.

Worksheet 2 is designed to help the user obtain an estimate of the NLC

after completing the schematic design process outlined on Worksheet

Alternately, the second worksheet may be used as the starting point on

q

subsequent trial designs as the user iterates to improve the performance of

his building.

If the building of interest is a townhouse or other larger structure

containing more than one control zone, Worksheet 2 may still be used to

estimate the

By including the complete structure in the analysis, as

though only one thermal zone were present, one can determine the overall loss

characteristics of the building and estimate the total size of all solar

apertures required to provide a certain level of performance. However, this

overall approach does not help the user to partition the solar aperture among

the various thermal zones.

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