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

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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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