Benefits of Scroll Compressors:
- High reliability.
- 100 % volumetric efficiency.
- Low sound levels.
- 70 % fewer moving parts.
- Better liquid and debris handling.
- Application flexibility.
- Cost effective.
- Self compensating for wear (wear in vs. wear out).
Scroll Protection Devices:
- Internal motor protector line break (temperature & current): Low voltage and phase loss.
- Floating seal: deep vacuum protection.
- Thermo disc: High scroll temperature protection.
- IPR valve: High discharge pressure protection.
Scroll Typical Application Envelope R-22:
A typical envelope is given below: Here X-axis gives the evaporating temperature and Y-axis gives the condensing temperature; in °F.
Following are the features of Copeland Spectar Compliant Scroll Hermetic Compressors:
- Power output 20 to 100 HP and above packaged rooftop and chiller markets. It is also designed for specialized applications, such as computer rooms, transportation cooling and mushroom coolers.
- Superior reliability, efficient operating characteristics.
- High efficiency performance at 11.5 ARI.
- Low sound levels.
- Available in 7.5, 9, 10, 13, and 15 horsepower models, five electrical configurations, and tandem offerings.
- A total of 25 models are available now in the Specter family, including compressors that use alternate refrigerants such as R-407c and R-134a. They combine to make up our extensive line of tandem offering.
- 17 - 22 pound / 7.7 - 10 kg refrigerant charge limit.
- Sight Glass and Oil Level Adjustment Port.
- Unique, Quick Responding Temperature Protection.
- Three Oil Filtration Devices and Rotary Dirt Trap.
- Integral Cast Iron Frame and Cast Iron Scrolls.
- DU (PTFE) Journal Bearings.
- Rotalock or Stub Tube Fittings.
- High & Low Pressure Taps (Shrader Valves) on Rotalock Version.
- Low Shutdown Noise.
- Available with POE for R-407c and R-134a.
- Heavy commercial capability with srnall size, fewer moving parts and rugged design.
- Wide Model Selection to Meet Diverse Market Needs.
- Flexible Voltage Options.
- Tandem Models Available.
Commissioning Tips for Copeland Scroll Compressors: Scroll compressors due to their high volumetric efficiency and high vapour handling capacity can pull down the suction pressure very low in a very quick time compared to a reciprocating compressor. If a new scroll compressor runs at vacuum or very low suction pressure during the first few minutes, lot of heat is generated inside which can damage the bearings and result in premature failure at the time of commissioning itself.
Though this care is needed while commissioning all models of scrolls, this is more pronounced in higger capacity models like Summit and Specter. Once the new compressor has run-in for few hours, subsequent low pressure operation due to any problem in the system like gas leak, evaporator fan not running, system choke etc. will not cause any damage to the compressor. This necessitates a little more attention to this aspect at the time of commissioning new scroll compressors at site-particularily in field charged units.
The commissioning technician after evacuating the system shall fill approximately 70 - 75 % of the total expected refrigerant charge before switching on the compressor. This will be enough to prevent deep vacuum operation of a few compressors during the first few minutes.
The initial filling should be based on the quantity of refrigerant charged by weight rather than by looking at the presure gauge looking for some particular standing pressure. Filling only a little refrigerant say half a kg or one kg; and trying to charge refrigerant vapour only through the compressor suction access valve, as is done in a reciprocating system, will overheat the compressor and result in a failure due to high current and tripping. Controlled liquid charging into the suction is probably better than vapour charging that allows vacuum operation.
To enable the technician to put in the initial charge, suitable access valve on the suction and liquid lines shall be provided in the unit.
To sum up the above points, f'ollowing care need to be taken at site while commissioning a new scroll compressor:
- Charging a new scroll compressor is different from a reciprocating compressor.
- After vacuumising the unit, fill-in approximately 70 -75 % of charge by weight- through the access valves on the liquid line and suction line of the system.
- Use a gauge manifold to keep a watch on the suction pressure; Do not allow it to fall to vacuum or very low suction pressure.
- After starting the new compressor, charge controlled liquid refrigerant into the suction and not vapour.
Scroll Suction Tube Brazing:
- The copper-coated steel suction tube on scroll compressors can be brazed in approximately in the same manner as any copper tube.
- Recommended brazing materials: Any silfos material is recommended, preferable with a minimum of 5 % silver. However, 0 % silver is acceptable.
- Be sure suction tube fitting I.D. and suction tube O.D. are clean prior to assembly. If oil film is present wipe with denatured alcohol, Dichloro-Trifluoroethane or other suitable solvent.
- Using a double-tipped torch apply heat in Area 1. As tube approaches brazing temperature, move torch flame to Area 2.
- Heat Area 2 until braze temperature is attained, moving torch up and down and rotating around tube as necessary to heat tube evenly. Add braze material to the joint while moving torch around joint to flow braze material around circumference.
- After braze material flows around joint, move torch to heat Area 3. This will draw the braze material down into the joint. The time spent heating Area 3 should be minimal.
- As with any brazed joint, overheating may be detrimental to the final result.
- To disconnect: Reclaim refrigerant from both the high and low side of the system. Cut tubing near compressor.
- Recommended brazing materials. Sifos with minimum 5 % silver or silver braze material with flux.
- Insert tubing stubs into fitting and connect to the system with tubing connection.
- Follow New Installation brazing instructions.
Cleanup Procedure for Compressor Motor Burnout:
- Throughly clean all system controls like suction/liquid line, filter drier, TXV etc.
- Install a oversize liquid line filter drier and suction line filter drier.
- Pressure and leak test the system.
- Tripple evacuate to at least 500 microns. Break the vacuum with clean, dry refrigerant at 0 psig pressure.
- Charge the system.
- Record pressure drop across the suction line filter drier. If the pressure drop is excessive, replace the filter drier.
- The system is to be observed for first four hours. Change the filter drier until no pressure drp is observed.
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