Tweet 
Custom Search




MILHDBK1003/13A
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 yintercept and slope of the collector efficiency
curve. A single glazed, all copper collector with selective coating
was chosen. The yintercept and slope were taken directly from Table
26, Collector #91. They are 0.77 and 1.059 Btu/hrft2deg. F,
respectively. Note absolute value of slope used. Next, the
. recommended figure of 10 Btu/hrft2 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
D1.
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 31 provides estimates of building heat loss rates
and other sources for calculating this parameter are given in Section 3.3.
In example 1, Worksheet C1, the fuel usage was calculated using the
Btu/ft2 degreeday (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/ft2dd) included hot water heating. The estimated hot water use for a
3bedroom 2bath 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/ft2dd. This gross figure
was multiplied by furnace efficiency of 0.7 to get 15.0 Btu/ft2dd 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 C1 are from Table 32 for Los Angeles.
Worksheet C2 is used to calculate DHW use. Water usage is determined from
Table 29, 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 33, Los Angeles, were used. Worksheets C1 and C2 can now be
completed. The DHW demand from Worksheet C2 is transferred to Worksheet C1
and the QL from Worksheet C1 is transferred to Worksheet D1. The DHW
demand could have been approximated as a constant at the highest use for
conservative design, but the calculations are made in Worksheet C2 for
To complete Worksheet D1, select from Table 11 the nearest or most
meteorologically similar located (same latitude and degree of cloudiness).
Enter insolation in Btu/ft2day and slope factors from Figure 32 for the
appropriate latitude. Air temperature, Ta, is obtained from Table 34.
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).
130


Integrated Publishing, Inc. 