Rexnord^® Omega™ Couplings Cut Pump Maintenance Costs at Data Center

CASE STUDY

At a major California computer data center, Rexnord Omega couplings are controlling vibration, minimizing misalignment and reducing maintenance costs on large HVAC pump drives for heating and chilled water. The couplings are easy to install and do not require moving the hubs or realigning the pump and motor if the flex element ever needs replacement.

To maintain a consistent temperature for the 1.2 million sq. ft. data center’s many computers, the four buildings in the complex are served by a central plant that incorporates a chiller plant, boiler plant and electrical distribution center. The plant’s counter-flow design includes 4,000 tons of chiller capacity and 15 million Btu of heating capacity, as well as six 500-ton cooling towers.

Most of the plant’s Bell & Gossett vertical split case, dual-end suction pumps are either 1,500 gpm pumps with 50 hp motors or 1,800 gpm units with 75 hp motors. Operators noticed intermittent vibrations with different combinations of equipment on-line. After rechecking motor and pump alignment, base plate rigidity and other factors, they isolated its cause as the effect of varying velocity pressures resulting from varying flow in the system’s large pipes. The building management firm’s senior assistant chief engineer explains, “Each motor/pump unit is mounted on springs, and there are 10" pipes leading to the overhead piping system, also mounted on spring isolation. The more pumps we turned on, the greater the velocity pressure flowing through the pipe. As water flowed through the pipe elbows, the resulting pipe movement caused the pump to move and created operating misalignment between the pump and motor.”

Pump drive for the data center's HVAC system

“We mounted lasers to the motor end bell and the pump case, “the engineer recalls. “ At rest, they were in perfect alignment. With different combinations of pumps in operation, angular misalignment at the coupling would vary from as much as .008" to .015", then back to zero when the pumps were turned off.”

To accommodate the misalignment and reduce vibration, he installed a Rexnord Omega coupling. This split-in-half flexible polyurethane coupling consists of only two hubs and two half-elements. Installation was simple and was completed in well under an hour. “It was a direct replacement,” the engineer reports. “We just disassembled the old coupling, slid it off the shaft, and installed the new one. We didn’t even have to loosen the motor bolts, so everything was still aligned.”

With the torsionally soft Omega coupling installed, the misalignment no longer affects motor vibration levels and bearing wear. The solution worked so well that the company changed all HVAC pump drives in the facility to Omega couplings. The cooling system includes 19 pumps at the central plant. Another 12 are in outlying buildings, as well as six in the heating plant and an additional two on fire pumps.
The building engineer estimates that savings in parts and labor during the first two years of operation were over $6,000, which was more than enough to pay for all 39 couplings installed on the HVAC and fire pumps in the facility.