The 55-story Washington Mutual Tower is one of downtown Seattle’s premier office buildings, with over 1 million square feet of tenant space and a six-level underground parking garage. Efficiently heating and cooling a building of this size is always a challenge for facilities managers as they supervise energy-intensive HVAC systems in an environment of skyrocketing energy costs and ongoing high maintenance requirements.
Chief Engineer Jeff Kasowski wanted to bring these costs under control but had limited options. The HVAC system centers around two large centrifugal pumps, a chilled water pump, and a condenser water pump that circulate water for 33 floors of the building. A thermostat, control valve, and heat exchanger use the chilled water to maintain a comfortable temperature on each floor, while warm water leaving the floor’s heat exchanger is circulated back down to the chiller and re-cooled.
In the Tower, water flow through the chiller was regulated by a hand valve to maintain a constant pressure. Manual throttling and fixed valve setpoints on both the chilled water and condenser pumps resulted in significant amounts of wasted electricity. Vibration and cavitation in the pumps generated high maintenance costs, and electronic “soft start” equipment was required to mitigate start-up spikes in the pump motors that caused overheating and degradation of motor insulation, as well as voltage sags that could disrupt sensitive electronic equipment in the building.
Kasowski was looking for a seemingly impossible solution – one that would save energy, improve process control, and reduce maintenance costs. He considered several different power transmission options, including variable frequency drives (VFDs), but finally settled on a new magnetic adjustable speed drive (ASD) technology that uses powerful, rare-earth magnets to transmit torque from a motor to a load.
Manufactured by Seattle-based MagnaDrive, the ASD operates on the principle of magnetic induction and consists of two independent components that have no physical contact. A precision rotor assembly containing high-energy permanent magnets is mounted on the load shaft, while a conductor assembly with copper rings is connected to the motor shaft. Relative motion between the magnets and copper rings creates a magnetic field that transmits torque through the air gap between the ASD’s components. Varying the width of the gap changes the coupling force, producing a controlled and infinitely variable output speed. Unlike VFDs, the ASD requires no external power source and transfers torque without vibration. Additionally, it requires no specially trained technicians to maintain, creates no electronic harmonics, and is designed to last at least 30 years.
Kasowski had two magnetic ASDs installed in his facility’s HVAC system – one on the 125 hp, 1,800 rpm motor running the centrifugal water pump and one on the 75 hp, 1,800 rpm motor running a centrifugal condenser pump. The results were immediate. Vibration and cavitation were eliminated, reducing maintenance costs and eliminating noise Kasowski had lived with for 10 years. And for the first time, the control system was programmed to allow precise control of flow rates, eliminating the use of control valves. Additionally, the ASDs produced an immediate 66-percent demand reduction on the condenser pump motor and a 31-percent reduction on the chilled water pump motor.Ken Black is senior applications engineer at Seattle-based MagnaDrive (www.magnadrive.com).