Resorts define an energy strategy
MGM Resorts International has defined an energy and environmental strategy at its Las Vegas resorts.
John Leslie, manager of building automation, MGM Resorts International
While most visitors to the MGM Resorts International properties in Las Vegas only see the glitz and glamour, much of the action takes place behind the scenes. In 2006, MGM established the Energy & Environmental Services Division to ensure that the company’s impact on the environment is fully defined and that programs and processes are put into place to mitigate any negative environmental impacts. As a result, the company has implemented numerous conservation programs that substantially reduce electricity, gas, and water usage at all of its Las Vegas resorts.
With a renewed emphasis on energy efficiency and sustainability, the MGM team quickly realized the need to upgrade existing chiller plants with variable frequency drives (VFDs) and implement rigid plant operations procedures as a way to increase savings and become more environmentally responsible. The installation of VFDs allows for the regulation of speed, and thus power used, for the huge chiller motors that cool each resort, while integrated computer systems provide data about how much cooling is needed in a building at a particular moment. Rather than working at 100% capacity, the chillers can run more slowly at lower heat loads, saving a tremendous amount of energy.
The Mirage, MGM’s flagship Las Vegas hotel, was first on the team’s list for significant upgrades in 2006, so the team sought Siemens’ assistance from to cut the resort’s HVAC power consumption. Built in 1989, The Mirage has 9,600 tons of air conditioning capacity. Its central plant serves 3,044 hotel rooms, casinos, and a 40,000-sq-ft ballroom, while auxiliary plants cool its 90,000-sq-ft event center. With 20-year-old chillers, including six 1,350-ton chillers operating at 4,160 V and three 500-ton chillers operating at 480 V, an astronomical amount of electricity is required for operation.
The chillers were wasting power by running at full throttle, even when internal building temperatures did not require them to do so. When demand would drop, the veins of coolant inside the chillers would constrict to control the coolant flow, but the chiller motors would keep running at full capacity. It’s like driving a car at full speed with one foot on the accelerator and the other on the brake to control how fast you’re going.
The MGM team initially reached out to Tracy Bilyeu of NEDCO Supply, a Las Vegas-based Siemens VFD representative. In reviewing the project, Bilyeu noted three distinct challenges with the installing of VFDs on the chiller motors. “First, the chiller manufacturer recommended a proprietary OEM drive to reduce the chance of motor damage. Second, Leslie wanted a zero harmonic VFD to maximize the lifespan of the motors. And third, the retrofit required a human-machine interface (HMI) between the chillers and the VFDs,” said Bilyeu.
With a perfect opportunity to showcase the performance of its drivetrain solutions, the local Siemens representative recommended that The Mirage deploy two Siemens ROBICON Perfect Harmony 1,300 hp, 4,160 V, lowest available harmonic VFDs to two of the 1,350-ton chillers in the central plant, and connect a Siemens Sinamics G150 VFD to each of two 500-ton chillers in the auxiliary plant. “The VFD-equipped chillers become the buffers that provided the variable capacity needed to accommodate varying demands of time-of-day and season, thereby providing significant energy savings,” said Barb Sines, vice president of large drives at Siemens Industry Inc.
“Our Perfect Harmony Drives are a perfect fit for fans, pumps, HVAC, and other medium-voltage ac applications, especially for The Mirage’s 4,160 V chillers due to the drive’s small footprint, ease of installation, and ability to retrofit any existing ac motor,” said Sines.
To control the VFDs and provide systems interface, 11 sensors were installed on each chiller connecting them to the VFDs, which were managed by energy software programming that the Mirage put in place. Building personnel were instantly able to monitor, measure, and benchmark every kW of electricity and every drop of water running through each chiller. Through the software, the team can monitor the chillers anywhere. Even with 20-year-old chillers, MGM now has one of the most automated chiller plants in the world.
Due to varying usage demands throughout a typical day at MGM’s Las Vegas properties, the VFDs, thanks to their patented design using a series of low-voltage cells contained within each drive, can be scaled precisely for a wide range of voltage and output power. Able to bypass any one cell during operation, the VFDs can maintain the full output voltage necessary to run the process. This cell-based configuration also gives the team easy access to drive components for scheduled maintenance, thus reducing system repair time to minutes. The cell bypass ensures automatic bypass of a failed power cell in approximately 450 milliseconds. Instead of shutting down the entire drive, a process-tolerant protection system (ProToPS) provides a hierarchical system of warnings. This control strategy allows time to evaluate the situation and respond appropriately.
An integral transformer with phase-shifted secondaries provides 18-pulse or better input harmonic cancellation with a power factor above 0.95 under any operating conditions. This eliminates the need for input harmonic filters or power factor correction, and completely removes any common-mode voltages from being imposed on the motor. The VFDs supply an output voltage so close to perfect sine-wave shape that the older chiller motors can be operated without any additional stress, thus eliminating dV/dt, overheating, and increased torsion.
Through MGM’s monitoring capabilities, the team was able to test the chillers and drives, pushing each to the extreme without damaging or compromising the equipment. Engineers tested the chillers at reduced evaporator and condenser flow rates, extremely low load limits, and extreme basin water temperatures—all yielding excellent performance
The entire chiller solution allowed MGM to reduce costs through increasing system reliability, reducing downtime, reducing equipment setup time, lowering maintenance costs, ensuring smoother operations, increasing energy savings, and managing power control. The net result of these improvements is increased profitability for MGM.
[subhead] Winning big in Las Vegas
Soon after the chiller retrofit at The Mirage, the team was charged with undertaking similar cost-saving measures at MGM’s other leading Las Vegas properties, including the Luxor, MGM Grand, and Bellagio.
The Bellagio posed a unique challenge, as its chillers were a different brand from those used at The Mirage. The team had to review a different set of parameters, and with no useable software interface, it developed this program separately, using Siemens industrial PCs. Three Siemens 1,500 hp ROBICON Perfect Harmony Drives and two Sinamics S150, 500 hp low-voltage drives were used.
Some chillers run at 95% all of the time, while other chillers are used as backup during peak demand. Electricity usage during peak demand is expensive; therefore, one or two VFD chillers are ready to go for the afternoon periods, when outside temperatures rise. This strategy has reduced peak demand costs by hundreds of thousands of dollars.
The iconic pyramid-shaped Luxor proved to be a much easier project. The team installed two Siemens 1,000 hp ROBICON Perfect Harmony Drives. The MGM Grand, MGM Resorts International’s largest Las Vegas property, required the installation of two Siemens 2,000 hp ROBICON Perfect Harmony Drives, with interface coming from Siemens industrial PCs.
MGM is experiencing significant quantifiable savings, and the VFD-equipped chillers in the central plant at The Mirage alone save the company an estimated 200,000 kWh in electricity per month. Combined with power savings from the auxiliary plant, The Mirage saves an average of $27,000 per month in operating costs, reducing monthly chiller operating costs from approximately $181,000 to $154,000 per month. The power savings also qualified The Mirage for rebates of approximately $70,000 from Nevada Power.
In addition to cost savings, The Mirage is saving about 400,000 pounds of CO2 each month, or 4.8 million pounds annually, staying true to MGM Resorts International’s environmental and conservation efforts. Similar savings have been seen at the Bellagio, reducing per hour chiller operating costs from $104 to $66. MGM saves approximately 1,156,920 kWh per month, yielding a budget savings of $127,000 per month, or $1 million annually.
“Our Drive Technologies Division is in the business of providing our end users with products and solutions designed to increase productivity, ensure energy efficiency and reduce operational costs – contributing significantly to the bottom line,” said Sines. “Siemens motors, VFDs, gearboxes and drive train components manufactured in the U.S. save tens of millions of dollars in energy costs annually, delivering a solid return on investment as proven through our partnership with MGM Resorts International.”
According to Sines, operating savings from energy efficiency products and solutions can be further enhanced through government tax incentives and favorable financing opportunities provided by Siemens Financial Services.
Leslie is the manager of building automation for the MGM Resorts International in Las Vegas.
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