2.9.2
Defrosting
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NOTE: Spaces maintained at 2 degrees C (35 degrees
F) will be defrosted with ambient air. Spaces below
2 degrees C (35 degrees F) will use either a hot gas
or electric heat defrosting system. For a
defrosting system choose between a timer defrost
controller or a demand defrost controller.
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Unit shall be [defrosted with ambient space air.] [fitted with a [hot gas]
[electric heat] defrosting system.] [Defrost system shall be controlled by
timer defrost controller adjustable for up to 6 defrost cycles per 24
hours, each of 5 to 120 minutes duration. Controller shall include an
adjustable timer to control frequency of cycles; defrost initiating
thermostat; adjustable program timer to control sequence of defrost cycle;
defrost terminating thermostat; manual override switch; selector switch;
and status pilot light.] [Defrost system shall be controlled by demand
defrost controller. Controller shall include an automatic, solid-state
circuitry to initiate defrost cycle based on sensing adjustable temperature
difference of air moving across coil in direct proportion to frost
build-up; thermostat to terminate defrost; adjustable lockout to prevent
initiation of defrost during pull-down after defrost cycle; manual override
switch; and status pilot light.]
2.10
CONTROLS AND INSTRUMENTS
Refrigeration system controls, instruments and devices shall be industrial
quality, and shall conform to applicable requirements of ASHRAE 15. Fluid
containing surfaces shall be rated for the service and constructed of
materials suitable for the fluid. Component electrical rating shall be 120
volt ac, unless otherwise indicated and shall be suitable for imposed
loads. Ammonia systems shall conform to IIAR 2. Copper, copper alloy and
white metals, except aluminum, shall not be used for ammonia service.
2.10.1
Refrigeration System Alarms
2.10.1.1
Audible Alarm
Audible alarm shall be surface-mounted, 100 mm 4 inch vibrating bell type
suitable for indoor or outdoor service.
2.10.1.2
Visual Alarm
Visual alarm shall be pilot light type. Alarm shall be 100 watt,
incandescent, vapor-tight fixture with cast metal guard and [red] [green]
[amber] lens.
2.10.2
Controllers
2.10.2.1
Differential Pressure Controller
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 meet system requirements.
SECTION 15652A
Page 24
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