MIL-HDBK-1003/19
4.4.1.3 Transmitted solar radiation. The symbols VT1, VT2, and VT3
represent the amount of solar radiation that is transmitted through one
square foot of vertical, south-facing solar aperture during a specific
one-month period for single, double, and triple glazed systems,
respectively. The corresponding annual sums are indicated by the symbols
QTA1, QTA2, and QTA3. In the general case for which the aperture is either
tilted or not south-facing, QS is used for the monthly sum and QSA
represents the annual sum. The units of all transmitted radiation quantites
are (Btu/ft2) per unit time.
4.4.1.4 Solar aperture absorptance. The solar aperture absorptance
([alpha]) is the fraction of transmitted solar radiation that is absorbed by
the passive heating system. The part not absorbed is lost back through the
glazing by reflection.
4.4.1.5 Absorbed solar radiation. The amount of radiation absorbed by
a passive solar heating system per square foot of aperture (S) is given by
the product of the transmitted radiation and the absorptance. In the
general case, for a one-month period, we have:
S = [alpha] [multiplied by] QS.
(Equation 4.9)
The units of S are (Btu/ft2) per unit time. The total amount of solar
radiation absorbed by a particular system (ST) is given by the product of
S and Ac (or Ap where appropriate) and has units of Btu per unit time.
4.4.1.6 Net load coefficient. The net load coefficient (NLC) is
defined as the amount of heat that would be required to maintain the air
temperature in a building -1deg.F above the outdoor ambient temperature for
a period of one day if no heat losses or gains were allowed through the
solar aperture. Thus the NLC, which is expressed in units of Btu/deg.F-day,
provides a measure of how effectively the nonsolar elements of a building
have been sealed and weatherstripped to reduce infiltration and insulated to
reduce heat loss by conduction. A procedure for obtaining a quick estimate
of the NLC will be presented in 5.1.1.
4.4.1.7 Load collector ratio. The load collector ratio (LCR) is the
NLC divided by the solar collection area (Ac), or, in the case of
sunspaces with tilted glazings, it is the NLC divided by the projected area
(Ap). The units of LCR are Btu/deg.F-day ft2 and the defining equation
is:
LCR
NLC/Ac
(Equation 4.10)
4.4.1.8 Total load coefficient. The total load coefficient (TLC) is
the sum of the NLC and the load coefficient of the solar aperture and as
such, provides a measure of the total building heat loss with no credit
taken for solar gains.
One of two values for the solar aperture conductance may be selected
depending on the application at hand. If the steady state aperture
conductance (Uc), expressed in Btu/hr-ft2-deg.F, is selected, then:
TLCs = NLC + 24 [multiplied by] Uc [multiplied by] Ac (Equation 4.11)
46
Previous Page
