MIL-HDBK-1003/19

where Qint (Btu/day) is the internal heat generation rate. Use of Tb

rather than Tset in heat loss calculations is a simple and reasonably

accurate way to include the effect of internal source heating on building

performance. Unless other information is available, Qint can be taken

equal to 20,000 Btu/day per person.

4.4.1.14 Heating degree days. The heating degree days (DD) is the

hourly summation of the difference between a specified base temperature and

the ambient temperature for a certain time interval, where only positive

terms are included in the summation, and the result is divided by 24. The

units of DD are deg.F-day and the time interval of interest is generally one

month or one year.

4.4.1.15 Effective building heat load. The effective building heat

load (QL) is given by the product of the effective total load coefficient

and the heating degree days for the time period of interest. Thus:

QL = TLCe [multiplied by] DD ,

(Equation 4.14)

where the units of QL are Btu.

4.4.1.16 Net building heat load. The net building heat load (QN) is

the product of the net load coefficient and the heating degree days for the

time period of interest. The defining equation is:

QN = NLC [multiplied by] DD ,

(Equation 4.15)

and the units are Btu.

4.4.1.17 Steady state heat load. The steady state heat load (QSL) is

the actual total heat load for a specified time period. The defining

equation is:

QSL = TLCs [multiplied by] DD

(Equation 4.16)

and the units are Btu.

4.4.1.18 Solar load ratio. The solar load ratio (SLR) is the ratio of

the amount of solar radiation absorbed by the system to the effective

building heat load. The defining equation is

SLR = S [multiplied by] Ac/QL ,

(Equation 4.17)

or

SLR = ST/QL

(Equation 4.18)

For tilted apertures in sunspaces, Ap must be substituted for Ac.

The

solar load ratio is dimensionless.

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