A/C COMPRESSOR BITZER RETROFIT LEADS TO SUBSTANTIAL ENERGY SAVINGS
Today, commercial property owners and facility managers are constantly looking for ways to reduce their utility bills. An often overlooked opportunity arises when it is time to replace old, inefficient compressors in HVAC systems.
The Harrison Group owns 10 hotel properties and various restaurants along the Ocean City, Maryland shore. One of their hotels, the Quality Inn Boardwalk Hotel, had an aging McQuay™ chiller with two 35 HP Copeland™ reciprocating compressors that needed replacing. Rather than invest in a new Chiller, Robert Walter, Harrison’s Maintenance Manager, decided to fabricate his own chiller on site.
His goal was to convert the system from R22 to R407C, reduce the hotel’s energy costs and get a pay-back in under a year if possible. The original equipment at the Quality Inn consisted of a McQuay-Perfex™ Inc. chiller with two Copeland™ 6RK2-3500-TSK-800 reciprocating compressors set-up for 208/230 volts with a rating of 135 FLA and 340 locked rotor amps each.
Robert had replaced large recips with BITZER Screw Compressors in the past, so he chose to upgrade to a single 50HP Screw that was rated at the same capacity as two 35HP recips. Once the original Copeland™ compressors, condenser, evaporator, frame and piping were removed, the area was cleaned up and prepped for the construction of the new chiller.
While BITZER Screws 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, Maryland, assisted Robert in his compressor, heat exchanger and controls selection.
In addition to upgrading to a single Screw Compressor, Robert also added a “stand alone” 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 set-up for 4 step capacity control.
// Standard™ Condenser
// Standard™ Evaporator
// Alpha Laval™ Heat Exchanger
// Electronic expansion valve and controller
// Siemens™ contractors (2) for part-winding start set-up
// Misc. components
// Misc. piping and angle iron
Once his new built-up system was installed and commissioned, Robert Walter compared the energy performance with the measurements he had taken prior to the retrofit conversion. “There was an overall energy reduction of 38-42%,” he said, (depending on capacity control) or about $2,085 per month in savings which translates to $25,000 annually. Robert 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 Robert, the complaints have stopped since installing the BITZER Screw.
Robert 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 replacement needs. Their next retrofit is scheduled to utilize BITZER’s newer CSW Series Screw, which is optimized for Low-Condensing temp applications (water-cooled chillers) and offers energy efficiencies at both full and part load conditions equivalent to oil-less, centrifugal compressors.
Upgrading compressors in aging HVAC systems is a very effective way to reduce overall power consumption. The investment payback period, even accounting for the additional labor and materials required for a retrofit conversion, is relatively short.