MIL-PRF-24775A(SH)
panels and access openings, shall be gasketed and airtight. Gaskets shall be of heat and moisture-resistant silicone
rubber or neoprene. All access panel bolts and washers shall be corrosion resistant material. Access panels for filter
removal shall be hinged with quick-acting captive fasteners to secure the panel in a closed position. Quick-acting
captive fasteners shall not require a special tool to operate.
3.11.7 Air inlet and outlet. Air shall enter each fan-coil unit via the inlet end section and exit via the opposite
end outlet section. Both the inlet and outlet shall have smooth flat surfaces with predrilled and tapped bolt holes, as
shown on Figure 1 and Figure 2, for flanged duct connections. Unless otherwise specified (see 6.2), inlet and outlet
grilles shall be optional.
3.11.7.1 Inlet grille. The inlet grille, if provided, shall be a commercial, standard size, heavy duty, fixed louver
grille with gasket. Louvers shall not rattle or vibrate when airflow is applied.
3.11.7.2 Outlet grille. The outlet grille, if provided, shall be of the double deflection type and shall permit
adjustable, directional airflow in both horizontal and vertical planes. Grilles for fan-coil units H1, H2, V1, and V2
may have fixed louvers.
3.11.8 Air filters. Air filters shall be provided for filtering all air entering the unit. The air filters shall be Navy
standard, high velocity type in accordance with MIL-PRF-16552. Provisions shall be made to hold the filters in
place when the access door is opened.
3.11.9 Static air pressure tap. Fan-coil units shall be provided with a static air pressure tap on the downstream
side of the filters for permanent mounting of a differential pressure gauge or for checking static pressure with a
portable differential pressure gauge. The tap shall consist of a gasketed, brass or corrosion resistant steel, ¼-inch
tube, straight bulkhead connection with sealing cap and protective cover suitable for permanent mounting to side of
cabinet.
3.11.10 Fan motors. Fan motors shall be continuous duty, HI shock qualified, 440-volt, 3-phase, 60-Hertz (Hz)
with drip-proof enclosure, two speeds (1800 and 1200 r/min), fan cooled, designed in accordance with IEEE STD
45, NEMA MG 1, and MIL-S-901. Type X fan-coil units shall have commercial marine motors designed in
accordance with IEEE STD 45. A wiring terminal strip in the vicinity of fan motor(s) or a motor terminal housing
for electrical connection shall be provided to facilitate replacement of fan motors without disturbing other wiring.
3.11.10.1 Bearings. Motors shall be equipped with sealed grease-filled bearings. Bearings shall be in
accordance with ANSI/ABMA precision classification of ABEC-5 in accordance with ANSI/ABMA STDS 4, 9, 13,
20, and ANSI/ABMA/ISO 3290. Means shall be provided to ensure that grease is always available to the bearing
and to prevent the leakage of oil or grease along the shaft. Special bearings for quiet operations when specified (see
6.2) shall be in accordance with ANSI/ABMA 4, 9, 13, 20, ANSI/ABMA/ISO 3290, and MIL-B-17931. Bearings
shall be removable using standard available tools.
3.11.10.2 Thermal protection. Motors shall be equipped with thermal protection, which shall consist of a
minimum of 3 thermal protectors (switches) to detect over-temperature. Thermal protectors shall be the automatic
reset type with locked rotor temperature limit set for class B insulation systems.
3.11.10.3 Motor mount. A positive method shall be provided to prevent motors from rotating in a
frame/support/mount.
3.11.11 Fans. Fans shall be the centrifugal type with direct drive.
3.11.11.1 Fan construction. Fan wheel shall be designed for minimum tip speed of 3650 feet per minute
(ft/min). The fan shall be statically and dynamically balanced and tested after being installed in the fan-coil unit.
3.11.11.2 Fan shaft. Fan shall be direct driven with the fan wheel mounted on the motor shaft.
3.11.11.3 Resilient mounts. The fan and motor assembly shall be vibration-isolated.
3.11.12 Cooling coil. The chilled water-cooling coil shall be at least 4 rows deep in the direction of airflow.
The coil shall be designed with a minimum waterside fouling factor of 0.0005 and shall have a maximum allowable
working pressure rating of 200-lb/in2 gauge at 250 °F. Fin spacing shall be limited to 11 or 12 fins per linear inch.
The tubes shall be protected against wear and breakage because of shipboard vibration or expansion and contraction
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