MIL-HDBK-1003/13A
4.0 EXAMPLE PROBLEMS
See Section 3 for instructions on preparing Worksheets.
4.1 Discussion of example 1. Space and Water Heating System for
Family Housing (see Section 4.1.1). Preliminary job data are
entered on Worksheet A. The first step in the analysis (Worksheet B)
is to determine the y-intercept and slope of the collector efficiency
curve. A single glazed, all copper collector with selective coating
was chosen. The y-intercept and slope were taken directly from Table
2-6, Collector #91. They are 0.77 and 1.059 Btu/hr-ft2-deg. F,
respectively. Note absolute value of slope used. Next, the
. recommended figure of 10 Btu/hr-ft2- deg. F is selected for
(mCp)c/Ac, line 3, Worksheet B. Since there will be no heat
exchanger between collector and tank fluids, the next three factors equal
1.0. Line 7, Worksheet B is equal to 0.91 for a single glazed collector. The
.
.
FR([tau[alpha]) and FRUL are calculated and transferred to Worksheet
D-1.
The next step is to determine the heat load or demand. This is usually done
by conventional methods of estimating heat losses from buildings and water
usage per occupant. Table 3-1 provides estimates of building heat loss rates
and other sources for calculating this parameter are given in Section 3.3.
In example 1, Worksheet C-1, the fuel usage was calculated using the
Btu/ft2 degree-day (dd) method. First a rough estimate for the average
family house at Port Hueneme was obtained from 1 month's usage of gas for all
housing divided by the number of degree days in the month and the total
number of square feet in the housing area. This figure (QL = 29
Btu/ft2-dd) included hot water heating. The estimated hot water use for a
3-bedroom 2-bath home gave a figure for hot water use per square foot which
was then subtracted from total use for the 1,500 sq ft home. Resulting
figure gave space heating fuel use as 21.5 Btu/ft2-dd. This gross figure
was multiplied by furnace efficiency of 0.7 to get 15.0 Btu/ft2-dd net.
Net heat is that which must be supplied by solar heat. Gross heat represents
the heat value of fuel used by a conventional system. Heating degree days in
Worksheet C-1 are from Table 3-2 for Los Angeles.
Worksheet C-2 is used to calculate DHW use. Water usage is determined from
Table 2-9, Section 2.3 or other. For Example 1, water usage of 30
gal/day/person was chosen (from Section 2.3) and water main temperatures from
Table 3-3, Los Angeles, were used. Worksheets C-1 and C-2 can now be
completed. The DHW demand from Worksheet C-2 is transferred to Worksheet C-1
and the QL from Worksheet C-1 is transferred to Worksheet D-1. The DHW
demand could have been approximated as a constant at the highest use for
conservative design, but the calculations are made in Worksheet C-2 for
To complete Worksheet D-1, select from Table 1-1 the nearest or most
meteorologically similar located (same latitude and degree of cloudiness).
Enter insolation in Btu/ft2-day and slope factors from Figure 3-2 for the
appropriate latitude. Air temperature, Ta, is obtained from Table 3-4.
For this example, Los Angeles was selected as the nearest similar location
(latitude = 34 deg.) and the slope factor was based on latitude of 32 deg.
plus 15 deg. to emphasize winter heating (Section 1.3.3).
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