MIL-PRF-23798D(SH)
3.11 Design requirements. Each assembly shall consist of a fan and motor, a cooling coil for chilled water, and
air filters mounted on and enclosed in a cabinet. The cabinet shall be equipped with thermal insulation and treated
for noise attenuation, and shall be constructed for deck mounting. The cabinet shall also incorporate a provision to
enable connection to supply and return ducts in the upper portion of the assembly and ready for installation and
connection to a power source, drainage, and chilled water supply and return.
3.11.1 Size. The size of fan-coil assemblies shall be limited to those listed in Table I.
3.11.2 Cooling coil. A chilled water coil shall be provided having nonferrous tubes, fins, and headers, due to
the exposure to salt water environment. The face area of the cooling coil for each size assembly shall be not less
than that shown on Figure 1. The cooling coil shall be at least 6 rows deep in direction of airflow. The tubes shall
have a minimum wall thickness of 0.025 inch throughout tube. The fins shall be not less than 0.010 inch thick and
shall be uniformly spaced. The number of fins per linear inch of tube shall be not less than 7 or more than 12. Coil
design shall be such as to prevent wear and breakage caused by shipboard vibration or expansion and contraction of
tubes. The chilled water supply and return connections shall be on the same end of the coil and shall be fitted with
union connections capable of test pressure of 300 lb/in2 gauge.
3.11.2.1 Cooling coil vent and drain. The cooling coil shall be provided with means for venting and draining
the coil. The vent shall be accessible and shall drain to the internal drain pan. Draining the coil shall be completed
by a means other than breaking of the chilled water union connections.
3.11.3 Air filters. Air filters shall be provided for filtering all air entering the assembly. The air filters shall be
in accordance with MIL-PRF-16552. Unless otherwise specified (see 6.2), air filters shall be removable through the
front of the cabinet. Air filters shall be removable via an access panel held in the closed position by means of quick
acting fasteners requiring no tools to operate. Air filters shall be removable without requiring power to the fan-coil
assembly to be secured. There shall be no danger to personnel of electrical energy or mechanical hazard when
removing or installing filters.
3.11.4 Thermal insulation. All internal surfaces of the cabinet or chassis that are subject to condensation shall
be provided with insulation to prevent dripping or a continuous flow of moisture under rated capacity conditions.
Insulation shall be of a non-halogenated closed cell type and shall not produce toxic smoke when exposed to a fire.
3.11.5 Acoustic insulation. Where acoustic insulation is required, it shall be such that it will satisfy both
thermal and airborne noise requirements. Acoustic insulation shall not produce toxic smoke when exposed to a fire.
3.11.6 Fan. The fan used in the assembly shall be a belt-driven centrifugal fan. Unless otherwise specified (see
6.2), the fan shall produce an available total discharge pressure of 2 inches of water at the outlet of the fan-coil
assembly at rated CFM delivery. The fan-motor horsepower for each assembly shall not exceed that specified in
Table I when total discharge pressure is 2 inches of water or less. All rotating parts of the fan shall be designed to
have a factor of safety of not less than eight based on the ultimate tensile strength of the material involved. The
bearing shall be in accordance with ANSI/ABMA standards 4, 9, 13, 15, and ANSI/ABMA/ISO 3290. Bearing shall
be capable of being locked onto the fan shaft and provided with a means for removal and/or replacement. The fan
shall be statically and dynamically balanced and tested after being installed in the assembly.
3.11.7 Fan drive. The fan drive shall be multiple V-belt drive and shall include the fan pulley, matched V-belts,
and motor pulley. V-belts, fan pulley, and motor shall be selected in accordance with ANSI/RMA Standards IP-20
and IP-25. The drive pulley shall be an adjustable positive locking pulley. Adjustment of pulley shall allow for at
least a 30-percent variation in fan speed. The pulleys shall be balanced. The V-belts shall be selected for at least
150 percent of motor horsepower at rated capacity conditions. A positive action single point belt adjustment device
shall be provided to permit adjustment of belt tension. A locking device to prevent loosening of belt tension shall be
provided.
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