Walter had replaced the large reciprocating chillers with Bitzer screw compressors in the past, so he chose to upgrade to a single 50-hp screw that was rated at the same capacity as two 35-hp reciprocating chillers. Once the original compressors, condenser, evaporator, frame, and piping were removed, the area was cleaned up and prepped for the construction of the new chiller.

While Bitzer screw compressors typically replace other OEM brand Screws, this conversion of reciprocating compressors involved a few more changes than usual to the compressor mounts, piping and wiring layouts. Dave Streby, Bitzer’s application engineer, along with the local United Refrigeration branch in Berlin, MD, assisted Walter in his compressor, heat exchanger, and controls selection. The retrofit team also included Art Mathews, Northeast regional sales manager for Bitzer U.S.

In addition to upgrading to a single screw compressor, Walter also added a standalone heat exchanger for heating domestic hot water with compressor discharge gas, thus reducing the amount of time the boiler operated. The following items were used to construct the new chiller: Bitzer CSH6553-50Y-2PU for R407C refrigerant, Bitzer capacity  controller setup for four-step capacity control, a Standard™ condenser, a Standard™ evaporator, Alpha Laval™ heat exchanger, and electronic expansion valve and controller, and two Siemens™ contactors for part-winding start set-up, along with miscellaneous components and piping.

Once his new built-up system was installed and commissioned, Walter compared the energy performance with the measurements he had taken prior to the retrofit conversion.

“There was an overall energy reduction of 38% to 42%,” he said, (depending on capacity control) or about $2,085 per month in savings, which translates to $25,000 annually. Walter stated that the payback for this project will be less than 12 months, and this does not include the “free heat” for the domestic hot water heating.

An additional bonus to the compressor upgrade was the overall sound reduction, as customers had often complained about the noise and vibration coming from the nearby mechanical room. According to Walter, the complaints have stopped since installing the Bitzer screw compressor.

Walter has now completed 11 compressor conversions to date, and the Harrison Group is so impressed with the results, they now specify Bitzer compressors for all their service replacements. ES