mand and is more vulnerable to damage through
the AES. Design an air-cooled system for the
generation equipment, by conventional methods.
worst-case ambient air temperature.
As indicated in chapter 2, the parasitic power de-
mand is very strongly influenced by the heat-
rejection system used.
quires about half of the air flow necessary for di-
rect air cooling. Because the air flow is smaller,
3-3. Nominally hardened facilities.
both the parasitic power demand and its resulting
waste heat are reduced. In addition, cooling water
a. The waste-heat rejection system for nominally
is provided at lower maximum temperatures (typi-
hardened facilities is an open system for both the
cally less than 85F) than are possible with direct
preattack and postattack periods. Design the sys-
air cooling, therefore increasing the percentage of
tem for waste-heat rejection to the air through one
waste heat handled with water-cooled heat ex-
of two types of subsystems located in hardened fa-
changers and decreasing the mechanical refrigera-
cility cavities: air-cooled heat exchanger, or
tion load. The major disadvantage of an evapora-
tive cooling system is the requirement for a
AES to conduct inlet and outlet air from the facili-
m a k e - u p water supply of approximately 55
ty cavities to the ground surface. Air from the at-
ft /MWh of waste heat rejected. Therefore, the
mosphere will be the transport medium. The AES
make-up water storage capacity imposes an addi-
will handle air for both the personnel and the air-
tional limitation on the facility's endurance. Also,
breathing power generation systems.
b. Air-cooled heat exchangers have the single
advantage of not requiring a consumable water
cooled systems for the worst-case air conditions.
supply. Consequently, their endurance (aside from
weapon effects) is limited only by the fuel supply of
3-4. Moderately hardened facilities.
the power system. In nearly all other aspects, the
As the hardness level
direct air-cooled system compares poorly with the
sponding burial depth increase, the open waste-
evaporation-cooled system, especially in that the
heat rejection system becomes less feasible for
air-cooled system has a higher parasitic power de-