b) The interior skin should be as vaportight as practicable. It
must be water-resistant so that cleaning does not readily soak the insulation.
c) All doors shall fit properly and shall be gasketed to minimize
air and heat leakage. Hardware for doors shall withstand the severe
conditions that may be encountered.
220.127.116.11 Finishes. Floor surfaces shall be of wood or metal. If floors are
wood, they shall be metal-faced plywood with the edges well sealed against
water penetration. Metal floors shall be watertight. Floors shall be covered
with vinyl tile for ease of cleaning. Metal-faced plywood, aluminum, certain
plastics, and other materials are suitable for interior wall surfaces. Unless
the exposed surface is metallic, the material shall have a flame spread
classification not greater than 22.8 or a smoke developed rating not greater
than 50, in accordance with UL Standard 723-1983, Test for Surface Burning
Characteristics of Building Materials. Glass-reinforced plastic materials
have been used for interior and exterior wall surfaces and, commercially,
several manufacturers now produce all-plastic containers. Where there is a
need for radar transparency, a thermosetting plastic exterior panel may be
used, provided it is painted to match the surrounding surfaces with special
radar-transparent paint. Where walls must be used to support equipment for
other loads, vinylized metal-clad plywood should be considered. These panels
are metal-clad on both sides but vinylized on the interior exposed side only.
Equipment Layout. Equipment layout shall be as specified in the
Mechanical. The general requirements of section 4 apply to the
design of transportables. Deviations and additional requirements are listed
18.104.22.168 Tactical Transportables. Tactical transportables impose severe
limitations on the mechanical equipment.
a) Air Conditioning. Air conditioning equipment must be small and
rugged. Generally customized, direct-expansion, air-cooled, through-wall
units using refrigerant R12 are provided, even though size and weight
limitations make them inefficient and expensive in comparison with standard
commercial units. Refrigerant R12 is preferred to R22 because of the high
internal pressure generated by R22 at storage temperatures encountered during
transportation. Also, commercial units normally are rated at 90 degrees F (32
degrees C) dry bulb and 75 degrees F (24 degrees C) wet bulb. These factors
preclude the use of most small commercial units currently available.
b) Backup Air Conditioning. Each unit shall be equipped with two
increments of cooling, each sized for half the design load; a third increment
shall be provided for the evaporator coil strictly for use as standby. This
requires a special evaporator coil circuited to achieve proper load balance
with any two increments operating.
c) Heating. Normally, electric strip heaters are provided with
the air conditioning units and mounted downstream of the evaporator coil.
Heaters may be used for dehumidification,, but should be controlled not to