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Breakthrough Technology For Speed Control Washington Mutual Tower Seattle, WA Field Testing the MagnaDrive Adjustable Speed Drive on Northwest Industrial Applications Report on HVAC Field Test Site 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. The building is managed by Wright Runstad & Company, a major developer and manager of office properties in the Northwest. In cooperation with the Northwest Energy Efficiency Alliance, they installed the MagnaDrive Adjustable Speed Drive (ASD) on both chilled water and cooling tower pumps in the Washington Mutual Tower. Application Overview MagnaDrive installed two ASDs in the Washington Mutual Tower. One is a 125 HP 1800 RPM vertical solid shaft motor running a centrifugal chilled water pump. This pump circulates chilled water for 33 floors of the building. A thermostat, control valve and heat exchanger utilize the chilled water to maintain a comfortable temperature on each floor. Warm water leaving the floor’s heat exchanger is circulated back down to the chiller and re-cooled. Water flow through the chiller is regulated by a hand valve on the pump discharge to maintain a constant pressure. The motor load was 65 kW operating with the partially closed hand valve. The other installation is on a 75 HP 1800 RPM vertical solid shaft motor running a centrifugal condenser pump. This pump circulates water between the chiller and a cooling tower. The pump runs at full speed, and a hand valve on the discharge of the pump was set to provide sufficient flow for the greatest building demand. Power demand for this pump motor with the valve restricted was 38 kW. Manual throttling and fixed valve set points that were used on both chilled water and condenser pumps resulted in wasted energy. Other issues included high maintenance costs associated with vibration and cavitation in the pumps, and the need for electronic soft start equipment to mitigate start-up spikes in the pump motors that can cause overheating and degradation of motor insulation, as well as voltage sags that can disrupt sensitive electronic equipment in the building. Test Site Washington Mutual Tower Seattle, Washington Field test site for MagnaDrive ASD HVAC application. Problem Throttling of chiller and cooling tower pumps wasted energy. Vibration and cavitation resulted in high maintenance costs. Electronic soft start equipment was needed to mitigate the start-up spikes of the motors which could cause motor overheating, degradation of insulation, and voltage sags. Solution Two MagnaDrive ASDs were installed on a vertical solid shaft chilled water pump and condenser pump. The control system was programmed to allow precise control of flow rates, eliminate use of control valves, and reduce the harmful vibration and cavitation. Benefits Maximum energy demand savings of 66% on the condenser pump motor and 31% on the chilled water pump motor were achieved through system control with the MagnaDrive ASDs. Vibration and cavitation were eliminated, reducing noise and maintenance costs. Duration of locked rotor current on start-up was reduced significantly, prolonging motor life and eliminating the possibility of voltage sags that disrupt electronic equipment. Breakthrough Technology For Speed Control Impressive Results with the MagnaDrive ASDs Two MagnaDrive ASDs were installed, one on the condenser pump and one on the chilled water pump. The customer’s control system was programmed to automate ASD operation to provide precise flow or pressure control via a 4-20 mA signal. Power demand reductions follow: Condenser Pump – The 75 hp condenser water pump moves cool water through the chiller compressor removing heat from the refrigerant via a heat exchanger. The warm water is then circulated through the cooling tower heat exchanger and back to the chiller. Prior to the MagnaDrive ASD installation, the pump was always operated at full speed and a hand valve was placed in a restricted position. At this setting, the energy demand for the pump with the valve restricted was a constant 38 kW. After the MagnaDrive ASD installation, the condenser pumps approximately 2000 GPM with an energy demand of 13 kW, a reduction of 66% (see Figure 1). Chilled Water Pump - After the MagnaDrive ASD was installed on the 125 HP chilled water pump, the speed of the pump was slowed to achieve a constant chilled water pressure for optimum performance. Eliminating the hand valve on the discharge of the pump reduced power demand from 65 kW to 45 kW, representing a constant improvement of 20 kW, a reduction of 31%. Washington Mutual operates their HVAC cooling system for eight hours per day approximately one hundred days per year for a savings of 36,000 kWh per year. A continuously operating system could save up to 394,200 kWh per year. How the MagnaDrive ASD Operates The MagnaDrive ASD operates on the principle of magnetic induction. It 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. 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. “We don’t have to replace couplings annually and deal with aligning the pumps and motors. The cavitation noise we lived with for ten years disappeared as soon as we started the MagnaDrive ASD.” Jeff Kasowski, Chief Engineer Figure 1 shows demand in kW versus flow rate in gallons per minute for the condenser pump. The data was developed by measuring the actual power draw and water flow of the Washington Mutual Tower system over a wide range of potential operations. In practice, 2000 GPM is the flow used during condenser operations. The power required drops 25 kW at this flow rate, a 66% reduction in power. The MagnaDrive ASDs were programmed to start the motors uncoupled from the pumps, significantly reducing the start-up current duration and peak compared to the old electronic soft start systems. (See Figures 2 and 3). The high amperage levels occurring throughout the start-up period caused heating in the motors, potentially degrading motor insulation and shortening motor life. High amperage draw can also cause voltage sags in the building. Voltage sags can disrupt sensitive equipment such as computer systems, a serious problem in a large office tower. “MagnaDrive came at a perfect time. We were looking into a Variable Frequency Drive, but we had a problem finding room for it, we were worried about the harmonics and filtering devices we would have to add, not to mention powering up a VFD that large and the inevitable extra heat loads. Then came the MagnaDrive. The large footprint isn’t needed, harmonics aren’t an issue, no power is required, and the control is better than imagined.” Jeff Kasowski, Chief Engineer Figures 2 and 3 show across the line starting curves for the motors. The dashed blue lines depict starting the motors with the loads coupled through elastomeric couplings using an electronic soft start. The red lines represent the motors starting uncoupled through the MagnaDrive ASDs using electronic soft starts. The original purpose of the electronic soft start was to reduce the amplitude of locked rotor current when starting the motors rigidly coupled to the pumps. As shown, when the electronic soft start timed out, the customer still experienced a 280 Amp spike on the condenser pump motor, and 475 Amps on the chilled water pump motor. Use of the MagnaDrive ASD and the electronic soft start together eliminates the excessive current spikes and reduces the duration of locked rotor current by 4 seconds. [BACK] FAQ | Contact Us | Home Copyright © 2008 MagnaDrive Corporation, All Rights Reserved.