plus or minus 10 degrees from the site latitude. It should be noted that as the tilt angle

increases, the minimum spacing between rows due to shading increases and larger

roof area is required.

3-4.1.4

between the projection of the normal to the surface on a horizontal plane and the local

meridian (north-south line). Zero degrees is defined as due south, a due west facing

array is defined as plus 90 degrees, and a due east facing array is defined as minus 90

degrees (in the northern hemisphere). The optimal orientation requires the azimuth

angle to be 0 degrees (due south) whenever possible, although deviations of plus or

minus 20 degrees off of due south have a minimal effect on flat-plate system

performance.

3-4.1.5

banks ranging from four to seven collectors each, with each bank containing the same

number of collectors. Proper sizing of the collector banks is essential to maintaining

uniform flow throughout the collector array. The maximum number of collectors that

can be banked together is a function of the maximum flow rate allowed in the plumbing,

internal manifold and riser diameters, thermal expansion characteristics of the collector

piping and absorber plate assembly, and the recommended flow rate of the particular

collector chosen (usually given in gallons per minute (liters per second) per collector or

gallons per minute per square feet (liters per second per square meter) of collector

area). Thermal expansion problems are minimized by keeping the bank size less than

eight collectors**.**

3-4.1.6

calculated for multi-row arrays. A general routine for north-south spacing of collector

banks can be devised, based on a "no shading" criterion for a particular time of year.

The guidance presented assumes no shading of the array on the "worst" solar day of

the year (21 December, when the sun is lowest in the sky in the northern hemisphere)

for the designated time period of 10 a.m. to 2 p.m. solar time. Most large-scale military

solar systems are installed on low-slope flat roofs, and there are two possible cases to

consider. The first is for a flat roof with enough space to locate the collector array at

one elevation. The second case is for a flat roof with too little space for the collector

array. This requires the collector banks to be "stepped", that is, each succeeding row of

collectors must be elevated. This arrangement is necessary if the collector roof area

required is larger than that available or if roof area costs are more expensive than

elevated rack costs. The equations developed for minimum collector row spacing are

presented graphically in Figure 3-5.

3-7

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