Emergency replacement of a compressor for a air-cooled rotary screw chiller

The National Plant Germplasm Quarantine Center (NPGQC) in Beltsville, Maryland, is a critical mission APHIS facility that operates 24/7. Two 150-ton ALS170As27 McQuay air-cooled rotary screw chillers were installed during the Phase I and II Planed Expansion construction at NPGQC in 2000. The chillers supply chilled water throughout the facility which is utilized in providing critical temperature controlled environmental conditions for the BSL-3AG High Containment Facility, growth chambers, growth rooms, and diagnostic laboratories. Continual operation of the two McQuay chillers is critical for conducting plant pathogen testing and guaranteeing containment of foreign pathogens. The two chillers are extremely unreliable and undersized. Compressor #2 (one of two per chiller) located in Chiller #2 went into alarm Monday afternoon (Memorial Day) resulting in the chiller shutting down which reduced the facility's chilled water cooling capacity by 50 percent. The Beltsville outdoor temperature was 96 degrees at the time. Facility Management was successful in restarting the first compressor but not the second on Chiller # 2. The internal refrigerant gate plate inside the compressor has disintegrated and damaged the internal rotary screw assembly beyond repair. A reconditioned rotary screw compressor will need to be procured immediately and installed so that NPGQC's production of critical 42 degree F. chilled cooling water can be brought back down to normal temperature levels. The compressor was replaced in 2006 and is past the warranty period. New compressors are no longer manufactured. McQuay Service is the only authorized parts/service company where the compressor can be purchased from. A direct McQuay replacement compressor is required (air-cooled rotary screw compressors are unique and specific for each manufacturer) compressors from other manufacturers, such as Trane, York, or Carrier, are not compatible with our chiller and attempted use would result in operational failure. Any non-McQuay mechanical contractor would have to deal with McQuay International/Services in order to purchase the required compressor. The entire refrigerant loop system will have to be evacuated and examined for debris from the disintegrated gate plate that could interfere with operation once the new compressor is installed. This work needs to be completed at the same time that the compressor is being replaced due to the refrigerant evacuation process.