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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