Rotating parts shall be statically and dynamically balanced at the factory
to minimize vibration. Lubrication system shall be centrifugal pump type
equipped with a means for determining oil level and an oil charging valve.
Crankcase oil heater shall be provided if standard or if available as an
option. If provided, the crankcase oil heater shall be controlled as
recommended by the manufacturer.
2.6.5.3
Rotary Screw Compressor(s)
Compressors shall operate stably for indefinite time periods at any stage
of capacity reduction without hot-gas bypass. Provision shall be made to
insure proper lubrication of bearings and shaft seals on shutdown with or
without electric power supply. Rotary screw compressors shall include:
a.
An open or hermetic, positive displacement, oil-injected design
directly driven by the compressor driver. Compressor shall allow
access to internal compressor components for repairs, inspection,
and replacement of parts.
b.
Rotors which are solid steel forging with sufficient rigidity for
proper operation.
c.
A maximum rotor operating speed no greater than 3600 RPM.
d.
Casings of cast iron, precision machined for minimal clearance
about periphery of rotors.
e.
A lubrication system of the forced-feed type that provides oil at
the proper pressure to all parts requiring lubrication.
f.
Shaft main bearings of the sleeve type with heavy duty bushings or
rolling element type in accordance with ABMA 9 or ABMA 11.
Bearings shall be conservatively loaded and rated for an L(10)
life of not less than 200,000 hours.
g.
A differential oil pressure or flow cutout to allow the compressor
to operate only when the required oil pressure or flow is provided
to the bearings.
h.
A temperature- or pressure-initiated, hydraulically actuated,
single-slide-valve, capacity-control system to provide minimum
automatic capacity modulation from 100 percent to 15 percent.
i.
An oil separator and oil return system to remove oil entrained in
the refrigerant gas and automatically return the oil to the
compressor.
j.
Crankcase oil heaters controlled as recommended by the
manufacturer.
2.6.5.4
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NOTE: When centrifugal chillers are used for heat
recovery duty, the entering heat recovery condenser
water temperature is usually controlled to between
35 and 40 degrees C (95 and 105 degrees F) so that
the water temperature leaving the heat recovery
condenser is high enough to be used as a heat
SECTION 15620A
Page 28
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