2.24.1.3
Cabinet Unit Heaters
Heaters shall be centrifugal fan type arranged for floor or ceiling
mounting as indicated. The heating elements and fans shall be housed in
steel cabinets with angle iron frames. The cabinets shall be of not
lighter than 0.912 mm 20 gauge steel. Each unit heater fan discharge shall
be provided with an approved adjustment for air diffusion and distribution.
The fans shall be mounted on a common shaft with one fan to each air
outlet. The fan shaft shall be equipped with self-aligning ball or roller
bearings accessible for lubrication. The fan shaft shall be either
directly connected to the driving motor or indirectly connected by
adjustable V-belt drive rated at 150 percent of motor capacity. All
exposed moving parts shall have guards. All fans in any one unit heater
shall be the same size.
2.24.1.4
Heating Elements
Heating coils shall be copper, and radiating fins may be copper, aluminum,
or suitable ferrous alloy. The heating elements shall be free to expand or
contract without developing leaks and shall be properly pitched for
drainage. The elements shall be tested under a hydrostatic pressure of 1.4
MPa 200 psi and a certified report of the test shall be submitted to the
Contracting Officer.
2.24.1.5
Manual Selection Switches
Motors shall be provided with manual selection switches for [on, off, and
automatic] [on-off] operation and shall be equipped with thermal-overload
protection.
2.24.1.6
Automatic Operation
a.
Thermostatic Control by Fan Regulation: The unit heaters shall be
controlled automatically by thermostats located where indicated.
The thermostats shall be adjustable and fitted with thermometers.
Each thermostat shall operate on not more than a 2 degree C 3
degree F differential over a temperature range of approximately 13
to 24 degrees C 55 to 75 degrees F. The thermostat shall start or
stop the respective unit heater fan motor when the room
temperature falls below or rises above the thermostat set point.
Summer-winter switches for fan operation shall be provided
adjacent to the thermostat for each unit heater.
b.
Thermostatic Control by Steam Valve Regulation: Cabinet type unit
heaters shall be controlled automatically by proportioning type
thermostats and modulating steam valves located where indicated.
On-Off switches for fan operation shall be provided adjacent to
the thermostat for each fan unit. The thermostats and valves
shall maintain the desired room temperature within 1 degree C 2
degrees F of the thermostat set point by regulating the steam
supplied to the coil.
2.24.2
Radiator and Convector
Each [radiator] [convector] unit shall be provided with a top supply
connection with a control valve and a bottom return connection with a
thermostatic trap. Each unit shall be tested hydrostatically at the
factory and proved tight at a pressure of not less than 690 kPa 100 pounds.
Extended surface tube-type radiators shall consist of suitable metal fins
SECTION 15559A
Page 71
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