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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