TM 5-852-9/AFR 88-19, Vol. IX
(9) Utilidor entrances to buildings. Where high pressure steam lines enter a building through a
utilidor, a utilidor cutoff (separation) wall must be provided to assure that steam leaking from the main lines
does not enter the building. Cutoff walls are generally cast concrete, and the piping passes through calked
wall sleeves.
4-7. Refrigeration.
a. General. Refrigeration design for cold storage should be in accordance with TM 5-810-3/AFM 88-8,
chapter 2, and refrigeration design for air conditioning systems should be in accordance with TM 5-810-1,
except as modified herein.
b. Special considerations. Standard refrigeration systems can be used very effectively if a few
precautionary procedures are followed.
(1) Remote air condensers. Dissipating heat from refrigeration systems is a serious problem in arctic
environments. Water condensers normally are precluded, since water is not always available and the waste
water disposal is difficult. Air condensers are used but their operation is limited unless controls are provided
for low ambient temperatures. The head pressures on air cooled condensers must be kept from dropping so
low that the thermostatic expansion valve ceases to feed refrigerant. Crankcase heaters, pump-down control,
and liquid receivers are often required for cold weather operation. Many methods can be used to control
system head pressure. Some of these methods are discussed in the following paragraphs.
(a) Shutter control. Shutters which control air flow across the condenser coils will only control
the system down to 20EF to 30EF. Consequently, shutters are not satisfactory for most winter operations and
should not be used.
(b) Pressure type controls. Several standard methods can successfully control head pressure
in a refrigeration system. One method which controls fan operation with a pressure sensor is satisfactory
down to approximately 10EF. Another method utilizes a back pressure valve which bypasses and recirculates
hot gas into the liquid line. This method is by far the most successful and can effectively operate down to 0EF.
(c) Enclosures with recirculating dampers. For temperatures below 0EF, a condenser enclosure
must be provided so that the condenser can operate within a closed system. The temperature within the
enclosure is then controlled by operation of the bypass exhaust air and fresh air dampers. Heat must be
provided within the enclosure to control minimum temperatures during the off cycles. The combination of
enclosure and recirculating damper has proven to be the most successful head pressure control system.
(2) Outside air for air conditioning. Air conditioning is frequently required in the subarctic and
arctic regions to cool electronic equipment or provide climate control for scientific operations. Adequate
cooling and temperature control can usually be achieved by using one of the following systems.
(a) Mixing outside air and return air. Cool outside air can be mixed with return air to obtain
the desired cooling temperature or can be heated to the desired temperature with a heating coil. When
temperatures exceed approximately 55EF, the system must sometimes be supplemented with mechanical
refrigeration. An outside thermostat can be used to change over automatically from mechanical refrigeration
to outside air cooling. One of the drawbacks to using outside air for cooling computer room equipment is
that the air must be free of dust. Large air filter banks are used to filter the incoming outside air. An efficiency
of 99 percent plus with a 5 micron particle size is usually required.
(b) Package air conditioning units with glycols. A package air conditioning system consists of
an air conditioning unit with a mechanical refrigeration unit, an economy cycle glycol unit, and a glycol
drycooler. The drycooler is located outside the structure. A single sensing control element to automatically
control the temperature of both the freecooling coil and the refrigeration cycle shall be used to provide proper
operation sequence. The control system will direct cool glycol solution from the drycooler to the freecooling
coil as long as the glycol solution from the drycooler is providing adequate cooling capacity. The compressor
operation will only switch on when the freecooling coil cannot handle the total cooling requirements. This
type of system works well in arctic climates because of the cold outside temperatures. Most package systems
of this type can operate up to 10 or 11 months of the year.
(3) Cooling towers. Water from cooling towers used in arctic climates must be drained into a sump
during cold weather. The tower itself generally is not heated.
4-8. Miscellaneous. The following subtopics relate to many types of systems and are grouped here for
simplification purposes.
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