MIL-HDBK-1003/19

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High values of Tmax indicate that the building is a poor design and

may overheat badly causing discomfort to the occupants. Inspection of the

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equations on Worksheet 8 indicates that Tmax may be reduced by:

a.

Reducing the solar collection area (Ac).

b.

Increasing the utilization efficiency (eu).

c.

Increasing the diurnal heat capacity (DHC).

5.2.4 Annual incremental cooling load. The annual incremental cooling

load (QI) associated with a passive solar heating system is defined here

as that part of the solar energy delivered to the living space that must be

removed from the building to avoid exceeding a specified maximum temperature

thereby maintaining a comfortable environment. This definition includes

excess heat delivered to the building during the winter months and does not

account for the beneficial potential of ventilation. Furthermore, the

calculation procedure presented in this section does not include the effect

of such defensive countermeasures as overhangs, drapes, shades, or covers.

Therefore, the incremental cooling load should be considered to be a worst

case indicator that emphasizes the need to employ ventilation and shading on

passive solar buildings. Also, QI provides a basis for comparing passive

solar designs in terms of their tendency to aggravate the cooling load.

5.2.4.1 Delivered solar energy worksheet. Worksheet 9 presents the

steps required to calculate (QD)a, the total solar heat delivered to the

living space during a one year period. This quantity is needed in

connection with the incremental cooling load calculation.

The first step is to read the total annual transmitted solar radiation,

OTAn, from the row marked DUE SOUTH AND VERTICAL. The number n in QTAn

indicates whether the system is single, double, or triple glazed. Next,

read coefficients, C1 through C5, from the following row marked AZIMUTH AND

TILT COEF. The transmitted radiation, corrected for azimuth and tilt, can

then be calculated from the following formula:

QTAn = (QTAn)o[1 + C1([theta]/100) + C2([theta]/100)2

+ C3([theta]/100)2([psi]/100) + C4([psi]/100)

+ C5([psi]/100)2]

(Equation 5.20)

This quantity should be entered in the worksheet in the blank labeled

(QTAn). Note that mixtures of two systems are allowed and that the mixing

algorithm for (QD)a is provided on the worksheet.

5.2.4.2 Incremental cooling load worksheet. The incremental cooling

load may be determined by following the procedure set forth on Worksheet 10.

The first step is to calculate the annual heat to load ratio using a

thermostat setting that is 10deg.F below the maximum temperature to be

tolerated in the living space. If this setting is the same as the one

previously employed in the heating analysis, no new calculations are

required. Otherwise, Worksheets 4, 5, and 6 must be re-done to determine

the new value of (QA/QL)a.

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