MIL-HDBK-1003/19
This number is entered on the worksheet and the time constant is calculated
next. Based on previously recorded values for DHC, NLC, Uc, and Ac, the
time constant is:
[tau] = 30.9 hr
.
Using this number in the following equation on the worksheet we obtain an
effective thermostat setpoint of:
Te = 67.5deg.F
.
Finally, the base temperature is calculated from the last equation on the
worksheet. The internal heat generation rate (Qint) is taken to be the
product of 20,000 Btu per person per day (a typical value) and 14, the
probable number of occupants of a quadruplex (assuming an average family
size of 3.5 persons). Using these assumptions, we obtain a base temperature
of:
Tb = 59.5 = 60deg.F
,
and enter it on the worksheet.
5.3.6 Weather parameters. We begin filling out Worksheet 5, as
indicated in the example, by entering the state and city in which the
building is located. Then we turn to the weather tables presented in
Appendix B and locate the column for a base temperature of 60deg.F and
record the ANNUAL DD given in that column on the worksheet.
Next, record the parameters that characterize the direct gain system.
The number of glazings is two, the azimuth is 15 degrees, and the tilt is
zero.
The value of the south/vertical transmitted radiation to degree day
ratio is obtained from the column marked TB60 (indicating a base temperature
of 60deg.F) and the row labeled VT2/DD (indicating a double glazed system ).
The value found in the weather tables is:
(VT2/DD)o = 27.60
.
The subscript o indicates a south/vertical orientation.
Similarly, from the same column and the row marked PARAMETER A, we
obtain:
ao = 0.637
,
for a south/vertical orientation.
To correct for the azimuth of 15 degrees east, one simply records the
value of A1 through A5 and B1 through B5 from the TB60 column and uses the
referenced equations to obtain:
VT2/DD = 27.51
,
and:
a = 0.616
,
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