1.16 AIR CIRCULATION - CONTINUED.
1.16.3 In Nuclear/Biological/Chemical (NBC) environments, the unit can be fitted with NBC filters that are attached to a
special inside blower inlet collar and flexible ducts. This system draws contaminated outside air into the NBC filter using
integral blowers. The blowers push clean filtered air through flexible ducts to the adapter collar to overpressurize the air
circulation system to prevent the infiltration of NBC contaminants into the shelter.
1.16.4 The outside fan is automatically activated whenever outside ambient airflow is needed across the outside coil. Air
is drawn in through the outside coil by the outside fan and blown out the unit top.
Figure 1-5. Air Circulation System
1.17.1 Air is cooled and dehumidified by a reversing mechanical refrigeration system called a heat pump.
1.17.2 When in the cooling mode of operation, the compressor (1) moves the refrigerant through the refrigeration system
by raising the pressure of the incoming gas from the inside coil (evaporator) (2) and discharging it as a high pressure gas.
1.17.3 The high pressure gas passes through the reversing valve (7) that controls the refrigerant flow depending on the
operating mode. In this mode, the refrigerant is routed toward the outside coil (condenser) (3).
1.17.4 The high pressure gas enters the outside coil (3) where heat is released to the outside ambient air passing across
the coil. This will cause the high pressure gas to condense to a high pressure liquid.
1.17.5 The high pressure liquid reaches the outside expansion valve (10) outlet that will not allow flow in this direction. It
then passes through the outside check valve (13).
1.17.6 The inside check valve (13) will not allow flow in this mode of operation and the high pressure liquid is forced
through the filter drier (12) where any moisture that may be in the refrigerant is absorbed and any debris is removed.