Smart Solutions

Pyke Mechanical Chooses High-Efficiency BITZER Screw for Compressor Retrofit

When the Miami International University of Arts and Design needed to upgrade its chiller, Pyke Mechanical was able to install a new, high-efficiency BITZER Screw compressor at only marginally higher cost than rebuilding the original compressor. The conversion went so well that Pyke plans to install BITZER screws whenever an upgrade opportunity presents itself.

BITZER’s Senior Application Engineer Dave Streby used the system conditions to determine the best BITZER model to match the desired capacity and recommended BITZER’s CSH8553-110-4PU. It operates at 45° saturated suction temperature, and 120° condensing temperature provides 109.9 tons of air conditioning capacity. The model comes standard with a 4-1/8” suction service valve and a 3-1/8” discharge service valve and has an integrated oil separator. The compressor uses 460 volts, 136 run load amps, and 895 locked rotor amps with direct-on-line starting.

Pyke Mechanical’s technicians completed the retrofit conversion as follows:

Step 1:  Removed the existing screw compressor and external oil separator, including all components and piping. Removed all piping associated with the heat exchanger on this circuit, as the BITZER CSH screw compressor provided the required capacity without the use of an economizer.

Step 2:  Installed two 7’-long U channels for mounting the BITZER CSH screw. The channel was attached to the base frame by drilling 3/4” holes. The BITZER CSH was attached to the mounted channel with 5/8” bolts after holes were drilled to match the footprint.

Step 3: Repiped the existing suction and discharge connections from each end of the existing compressor to the top of the CSH8553-110-4PU screw compressor. The existing piping was only removed to allow one 90° elbow in the suction piping and two 90° elbows in the discharge piping.

Step 4: Removed the existing economizer piping to the original screw compressor, capped it off, and left it in place.

Step 5: Reused the existing suction and discharge pressure transducers. The suction transducer was reinstalled into the BITZER service valve. The discharge transducer was installed into the upper pipe plug underneath the BITZER discharge service valve. The upper connection allows for the system pressure to be read by the controller.

Step 6: Installed liquid injection oil cooling using the existing piping from the economizer. Pyke also used the existing solenoid valve and only required two feet of 5/8” copper tubing and 4-5/8” 90° elbows to allow 8” of tubing rise from the inlet to the compressor.

Step 7: Installed the liquid injection controller inside the control cabinet and drilled a 3/8” hole through the panel to route the sensor cable to the compressor. Mounted the liquid injection sensor 6” from the discharge service valve and insulated the sensor. With the existing operating parameters, liquid injection oil cooling is not required, but Pyke decided to install liquid injection to address a “worst case scenario.”

Step 8: Because the existing compressor used only one capacity control solenoid, Pyke installed a stand-alone controller to control the BITZER capacity control solenoids. A simple dual-set-point capacity controller is suitable. Pyke installed the BITZER capacity controller into the control cabinet and then installed the temperature probe into the same location as the existing system probe on the fluid outlet piping.

Step 9: Evacuated and charged the system, checked all the electricals, and then bump-started the compressor to ensure proper rotation.

Since this initial retrofit conversion, Pyke has installed two more BITZER retrofit screws at Miami International University of Arts and Design. John Marinello, vice president of Pyke, said that he and his technicians were impressed with how quietly a BITZER Screw runs.

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