MIL-HDBK-1003/19

5.1.7.3 Off-south or tilted apertures. If the orientation of the solar

aperture is not due south and vertical, the weather parameters must be

corrected according to the following equations:

a = ao[1 + Al([theta]/100) + A2([theta]/100)2

+ A3([theta]/100)2([psi]/100) + A4([psi]/100)

+ A5([psi]/100)2] ,

(Equation 5.16)

VTn/DD = (VTn/DD)o[1 + B1([theta]/100) + B2([theta]/100)2

+ B3([theta]/100)2([psi]/100) + B4([psi]/100)

+ B5([psi]100)2] ,

(Equation 5.17)

where ao and (VTn/DD)o are the south-vertical values. The coefficients,

A1 through A5 and B1 through B5, are obtained from labeled rows in the

weather tables in the column having the desired base temperature.

Interpolation between two base temperatures may be necessary. The angle

[theta] is the azimuth of a normal to the aperture with due south taken as

zero and east as positive. The angle [psi] is the tilt of the aperture

relative to a vertical position, i.e., [psi] is zero for a vertical

aperture. Equations 5.11 and 5.12 are applicable to azimuths of up to +/-60

degrees and tilts of up to 60 degrees.

5.1.8 Weather parameter worksheet. Worksheet 5 is provided to guide

the user through the process of obtaining and recording weather data needed

for design analysis. The first part of the worksheet calls for data about

the building location and the annual heating degree days. The next two

parts are parallel and provided a step by step procedure for calculating the

weather parameters needed for each of two separate passive solar heating

systems that may serve the building. If only one system is present, make

only one set of entries on the worksheet. Also, if two systems that have

the same number of glazings, the same orientation, and the same tilt are

present, only one set of entries on the worksheet is required.

Finally, the last part of the worksheet provides equations for

calculating the mixed system weather parameters in the event two non-similar

systems are present. Record the results of these calculations in the

indicated blanks.

5.1.9 Auxiliary heat consumption worksheet. Determination of the

auxiliary heat requirements is outlined on Worksheet 6. First, the scaled

solar load ratio of the system is calculated on the basis of parameters

previously recorded on Worksheets 2, 3, 4, and 5. The annual heat to load

ratio is read off the nomograph in figure 23 using the calculated value of

the scaled solar load ratio and the city parameter recorded on Worksheet 5.

Finally, the auxiliary heat required annually is obtained by multiplying the

heat to load ratio by the annual building load. Worksheet 6 guides the user

through the calculation and provides a written record of performance

analysis results.

5.2 Design refinement. The discussion presented in the following

subsections advises the user on how to modify the design just analyzed on

the worksheets if the results obtained were not satisfactory.

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