MIL-HDBK-1003/19

where TLCs is the steady state total load coefficient. If on the other

hand, the effective aperture conductance (G), expressed in Btu/deg.F-day

ft2, is selected, then:

TLCe = NCL + G [multiplied by] Ac

(Equation 4.12)

where TLCe is the effective total load coefficient. The effective

conductance (G) is a system correlation parameter, as will be expanded on in

5.1.1, and includes the effect of solar aperture dynamics. The appropriate

choice of TLC parameters will be specified for each application in these

procedures.

4.4.1.9 Thermostat setpoint. The thermostat setpoint (Tset) is the

temperature setting of the thermostat that controls the auxiliary heating

system.

4.4.1.10 Diurnal heat capacity. The diurnal heat capacity (DHC) is the

amount of heat that can be stored in the thermal mass of a building, per

unit room air temperature swing, during the first half of a 24-hour cycle

and returned to the space during the second half of the cycle. The

performance of passive solar buildings is enhanced when the DHC is elevated.

Procedures for calculating this important parameter will be presented in

5.1. The DHC has units of Btu/deg.F.

4.4.1.11 Effective heat capacity. The effective heat capacity (EHC) is

a correlating parameter that relates the thermal performance of otherwise

identical direct gain buildings that have arbitrary thermal storage media

arranged in various geometric configurations. As such, the EHC, which has

units of Btu/deg.F of solar aperture, provides a measure of the amount of

heat that may be stored in the thermal mass of a building during one day and

returned to the room air on the same day or on succeeding days at times and

rates that lead to improvements in building performance. Improvements in

solar thermal performance occur when stored solar energy is delivered to the

room air in phase with the building thermal load, thereby reducing auxiliary

heating requirements. A nomograph for the EHC will be presented in 5.1.

4.4.1.12 Effective thermostat setpoint. The analysis methods presented

in this document require the use of a constant thermostat setpoint. Because

control strategies involving nightime setbacks are advantageous due to the

resultant reduction in auxiliary heat consumption, a procedure has been

developed for relating building and control parameters to a constant

effective thermostat setpoint (Te); this procedure is described in 5.1.

The temperature Te should be used in place of Tset for the analysis of

any building that employs a control strategy.

4.4.1.13 Base temperature. The base temperature (Tb) is the

thermostat setpoint (or the effective setpoint) adjusted in a manner that

accounts for internal-source heating by people, lights, appliances, office

equipment, or any other device not primarily intended as an auxiliary heat

source. The base temperature is given by:

Tb = Tset - Qint/TLCs,

(Equation 4.13)

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