2.6.2
Compressor
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NOTE: Delete this paragraph if a remote condensing
unit is specified.
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Compressor shall be direct drive, semi-hermetic or hermetic reciprocating,
or scroll type capable of operating at partial load conditions. Compressor
shall be capable of continuous operation down to the lowest step of
unloading as specified. Compressors of 35 kW 10 tons and larger shall be
provided with capacity reduction devices to produce automatic capacity
reduction of at least 50 percent. If standard with the manufacturer, two
or more compressors may be used in lieu of a single compressor with
unloading capabilities, in which case the compressors will operate in
sequence, and each compressor shall have an independent refrigeration
circuit through the condenser and evaporator. Each compressor shall start
in the unloaded position. Each compressor shall be provided with vibration
isolators, crankcase heater, thermal overloads, [lubrication pump,] [high]
[high and low] pressure safety cutoffs and protection against short cycling.
2.6.3
Refrigeration Circuit
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NOTE: Filter-driers are optional and may be deleted
on most precharged systems. Delete the last two
sentences if an integral water-cooled condenser is
not specified.
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Refrigerant-containing components shall comply with ASHRAE 15 and be
factory tested, cleaned, dehydrated, charged, and sealed. Refrigerant
charging valves and connections, and pumpdown valves shall be provided for
each circuit. Filter-drier shall be provided in each liquid line and be
reversible-flow type. Refrigerant flow control devices shall be an
adjustable superheat thermostatic expansion valve with external equalizer
matched to coil, capillary or thermostatic control, and a pilot solenoid
controlled, leak-tight, four-way refrigerant flow reversing valve. A
refrigerant suction line [thermostatic] [thermostatic and water flow
switch] control shall be provided to prevent freeze-up in event of loss of
water flow during heating cycle.
2.6.4
Unit Controls
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NOTE: In regards to head pressure control, insert
the appropriate minimum or lowest expected ambient
temperature. Delete head pressure controls if
inapplicable. Delete low cost cooling if
inapplicable. In those areas where the outdoor
seasonal climatic conditions permit, an outdoor
temperature sensing unit (dry bulb) may be used in
an external control circuit to take advantage of
outside air to satisfy the cooling load. Under such
conditions, the control circuit would lock out the
compressors and position the outdoor and return air
dampers to allow 100 percent fresh air to be
circulated. Enthalpy controls will not be used.
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SECTION 15700A
Page 23
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