MIL-HDBK-1003/19

Having obtained the end wall loss coefficient, the net load coefficient

for an interior zone (NLCi) is given by:

NLCi = (NLC - 2 Lw)/NZONE

,

(Equation 5.21)

where NZONE is the number of zones, four in this case, for a row type

building.

The net load coefficient of an exterior zone (NLCe) is then given by:

NLCe = NLCi + Lw .

(Equation 5.22)

Carrying out the computation yields:

NLCi = 6,825 Btu/DD

,

NLCe = 7,299 Btu/DD

.

Equating the LCRs of interior and exterior sections to the original LCR

of the complete unit yields the following simple equations for determining

Aci and Ace, the solar collection areas for the two sections:

Aci = Ac(NLCi/NLC)

,

(Equation 5.23)

Ace = Ac(NLCe/NLC)

.

(Equation 5.24)

Evaluation of these equations for the four-plex unit yields:

Aci = 191 ft2

,

Ace = 204 ft2

.

Note that the aperture sizes differ by only 7 percent and the sizing could

be performed with reasonable accuracy (for this example) by simply

distributing the total aperture area uniformly among the sections. In

that case:

Aci = Ace = 198 ft2

,

is the aperture size for interior and exterior sections.

5.3.9 System efficiencies. System efficiencies for the reference month

are evaluated using Worksheet 7 in the example. The total effective load

coefficient and the solar heating fraction are evaluated using parameters

available on other worksheets, and recorded. Then the total efficiency is

calculated from the equation provided on Worksheet 7. The result is:

et = 0.86

.

Since the delivery efficiency of all direct gain systems is unity, the

utilization efficiency has the same value as et, or:

eu = 0.86

.

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