Water Technology, July/August 2019

xpanding population codes and regulations connectivity and monitoring are directly affecting HVAC R equipment requirements and market growth More equipment is needed for new project construction required retrofits and building expansions Just because more or new equipment is required does not always mean the total cost of ownership must increase This is where energy efficiency plays a role and it has never been more important Variable frequency drives VFDs have been a vehicle for improving a systems energy efficiency for over 40 years By incorporating VFDs into pump systems engineers are able to significantly decrease the overall cost of the system A standard VFD controls a motor based on a linear volts per hertz V Hz relationship The output voltage waveform of a standard VFD is typically based on pulse width modulation PWM The amplitude duty cycle and periodicity of the PWM waveform decide the effective voltage and frequency of the VFD output However this is not enough anymore especially for fan and pump motors in HVAC R applications or variable torque applications In these applications the speed of the motor is reacting to external sources that are a part of the overall system These external sources could be a temperature sensor in a refrigeration system a humidity sensor in a data center facility or a pressure sensor monitoring the room pressure in a clean room A VFD uses the external sources as input data to adjust the output frequency to the motor in turn adjusting the speed of the motor In these applications there are advantages to varying speed rather than running at 60 Hz full load amps at all times The following are three additional considerations to reduce energy costs and become more energy efficient Energy optimization software A standard VFD modulates the output voltage waveform to adjust the output frequency With new technologies in current VFDs more can be done to optimize the energy consumption in variable torque applications than just standard V Hz control Many VFDs have optimization parameters that can be used to tune the input power consumption while maintaining the loads torque or speed demand However some VFDs have built in algorithms that can conduct the tuning and monitoring automatically for example Eatons Active Energy Control technology This algorithm works right out of the box no tuning or adjusting of parameters is required The algorithm monitors the output power performance while reducing the input power requirement To ensure the stability of the motor the algorithm initially sets the drive output voltage at the same level MOTORS DRIVES WT E Using variable frequency drives to control HVAC R applications JULY AUGUST 2019 watertechonline com 23 By Seth OBrien Eaton VFDs installed on variable torque motors can reduce energy costs increase efficiency and improve system reliability iznashih iStock Eatons Enclosed PowerXL DG1s installed in a remote pumping application All images courtesy of Eaton