MIL-PRF-24775A(SH)
of the tubes. The chilled water supply and return connections shall be on the same end of the coil and supplied with
union connections conforming rated for 400 lb/in2 at 150 °F. The cooling coil shall be sized for a maximum chilled
flow rate of 3.6 gallons per minute per ton of cooling including fan motor heat and a maximum pressure drop of
12 lb/in2 across the coil (see 4.5.2.7). The cooling coil shall show no leakage. Tube sizes shall not be less than ⅝-
inch diameter. Ferrules shall be provided where tubes pass through tube sheets in order to prevent wear and
breakage because of shipboard vibration or expansion and contraction of tubes.
3.11.12.1 Right-/left-hand unit. The location of the chilled water supply and return connections of the cooling
coil shall determine the orientation of the fan-coil unit, when looking in the direction of the airflow with the unit in
its normal operating position. Unless otherwise specified in 6.2, fan-coil units shall be supplied right-handed. The
cooling coil shall be field interchangeable from right- to left-hand.
3.11.12.2 Vent and drain valves. Cooling coil shall be equipped with vent and drain valves in the coil inlet and
outlet lines to eliminate breaking the chilled water inlet and outlet union connections for venting and draining
purposes. Valves shall be accessible from outside the cabinet. The vent and drain shall terminate in the condensate
drain pan.
3.11.12.3 Drain pan. Fan-coil units shall have a condensate drain pan of sufficient depth to prevent spillover
when units are operated. All units shall meet this requirement when permanently inclined 15 degrees in any
direction from the normal position. The drain pan shall be fitted with drains, male connection on each end. The
drain pan shall be made of corrosion-resistant material.
3.11.13 Heater. Unless otherwise specified (see 6.2), electric heaters are optional and, if provided, shall be of
the finned type and located downstream of the cooling coil. The kilowatt (kW) rating of heaters shall be as specified
in Table I.
3.11.13.1 Heater protection. The heater shall be provided with a thermal protector (over-temperature switch)
with manual reset. The manual reset shall be accessible from the outside of the fan-coil unit. The switch shall be set
to limit the surface temperature of the heating elements to a maximum of 750 °F. The switch shall be suitable for
pilot duty on 115-volt alternating current.
3.12 Performance requirements. Performance shall be in accordance with Table I.
3.12.1 Control circuitry. Unless otherwise specified (see 6.2), fan-coil units shall be LVP, control circuitry
shall be designed for continuous airflow and give the following sequence of operation:
Entering air temperature (°F)
Unit operation (on rising temperature)
Below 72
Cooling and heating units - fans on high speed and heater on.
Cooling only units - fans on low speed.
72 to 76
Cooling and heating units - fans on low speed and heater off.
Cooling only units - fans remain on low speed.
77 to 81
Both units - fans on low speed and remote chilled water valve
energized providing water to cooling coil.
82 and above
Both units - fans on high speed, and remote chilled valve remains
energized providing water to cooling coil.
NOTE: If optional humidistat is provided for cooling and heating units, the remote chilled water valve is energized
anytime the relative humidity is above 55 percent (set point) regardless of temperature.
3.12.2 Fan motor contactor. Fan-coil units shall have internally-mounted, dual-speed, motor contactors or
power relays for fans. Contactors or power relays shall be of sufficient size to control the fan motor at high and low
speeds.
3.12.3 Heater contactor. Fan-coil units with heaters shall have an internally mounted contactor or power relay
for the heater. The contactor or power relay shall be of sufficient size to control the largest heater, as specified in
Table I, for a fan-coil unit size.
3.12.4 Thermostat. Fan-coil units shall have an internally mounted, three-stage thermostat capable of
controlling, in sequence, the fan motor speed, the remote chilled water solenoid valve, and the internal optional
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