2.6
AUTOMATIC CONTROLS
Temperatures in the refrigerated rooms shall be regulated by room
thermostats and electric solenoid valves in the refrigerant supply piping
to the evaporators. Compressors for each system shall operate on suction
pressure switches, functioning in such a manner as to cut in and cut out
compressors as the suction pressure rises above or falls below
predetermined operating conditions. Provide a multiple step controller for
multiple compressor units in a single system.
2.6.1
Temperature Control Cabinets
Provide the necessary controllers, relays, clocks, alarms, and temperature
gages in or on the face of control cabinets for each system. Construct
cabinets of steel or aluminum with hinged door and lock. Provide
temperature gages, pressure switches and pilot lights flush on the cabinet
door. Provide controllers and relays in the interior of the cabinet on a
steel or aluminum subpanel which shall also act as the back of the cabinet.
Electrical controls shall be prewired to numbered screw type terminal
strips. Cabinets shall be [floor-mounted free-standing type] [or]
[integral with refrigeration compressor unit control panels].
2.6.2
Safety Cutout Switches
Provide automatic high pressure, low oil level, and compressor overload
safety cutout switches for each compressor. The switches shall be located
in the condensing unit control panel. The cutout switches shall
automatically stop the respective compressors and simultaneously ring an
alarm bell whenever the pressure within the condenser rises above the
predetermined safe point.
2.6.3
Thermostats
Shall be of a lock shield type suitable for operation in connection with
its respective solenoid valve. The thermostats shall maintain the
temperature of the refrigerated rooms within a maximum range of plus or
minus one degrees C 2 degrees F. The thermostats shall be of the
adjustable type, with gas filled tube. The thermostats shall have
temperature range of minus 34 degrees C to plus 10 degrees C 30 degrees F
to plus 50 degrees F. Thermostats shall be mounted adjacent to interior
door, unless otherwise indicated.
2.6.4
Controllers
2.6.4.1
Differential Pressure
Controller shall be provided with high and low pressure sensing ports and
shall be direct or reverse acting with calibrated proportional band and set
point adjustments. Controller output shall be [low voltage electric]
[pneumatic] [4-20 mA dc], proportional to the pressure differential sensed.
Local and remote set point adjustments shall be included. Range shall be
as required to meet system requirements.
2.6.4.2
Differential Temperature
Controller shall be provided with two filled, remote sensing bulbs
connected to the controller by [armored] capillary tubing. Controller
shall be direct or reverse acting with calibrated proportional band and set
point adjustments. Controller output shall be [low voltage electric]
SECTION 15602N
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