Title: Evaluation of High Rotor Pole Switched Reluctance Motors to Control Condenser Fans in a Commercial Refrigeration System

Abstract

A high rotor pole switched reluctance motor (HRSRM) designed by Software Motor Corporation was evaluated for use as a condenser fan motor due to its reported high motor efficiency over a broad range of speeds and added advanced control potential. The project was split into two phases; the first of which was to determine the direct energy savings due to the increased motor efficiency, the second was to leverage the additional benefits of the energy efficiency measure (EEM) to create additional energy savings. This report only discusses results from the first phase of the project. Nine 1.5hp HRSRMs were installed parallel to the same number of legacy induction motors of a supermarket commercial refrigeration system located in Lakeside, Colorado. At this site, the 1.5 hp legacy motors had historically adjusted condenser fan speed from 200-870 rpm based on outdoor air temperature and compressor discharge pressure. This type of control is known as variable head pressure control (VHPC). These nine new motors were given a signal from the legacy variable frequency drive (VFD) to match the motor speed of the legacy motors. Determination of the energy savings of the EEM was performed over a two-month period, at which time a correlationmore » between legacy and EEM power consumption was developed based on motor speed. Annual data that had been collected from 2016-2017 (before the two-month test period) was then leveraged to predict the annual energy savings of the EEM for a complete retrofit using both VHPC and constant fan speed control. Table 1 displays the quantitative results. The EEM saved 27% of total energy consumption of the condenser fan motors for constant fan speed control, while the energy savings increased to 32% when using VHPC. This was due to the improved motor efficiency of the HRSR motor at low speeds. While the constant speed fan control kept the motors running at 870 rpm, VHPC adjusted fan speed between 200-870rpm based on the outdoor air temperature and the compressor discharge pressure. These savings are assuming a direct replacement with no additional controls. Retrofitting a constant speed fan control system with HRSRMs and switching to VHPC would provide significant energy savings looking at the condenser alone. Additional considerations of the EEM were noted during the project as well. The HRSRM system made it possible to identify and remotely shutdown an individual motor when a piece of foam locked the fan and thereby the motor. With the traditional system, a locked rotor could have caused motor damage unless a breaker or fuse was activated. Furthermore, due to vibration complaints from the installation technicians, the ramp-up time of the HRSRM had to be increased to a minute. After implementing this change no complaints for excessive vibration were recorded.« less

Authors:

Wheeler, Grant  ^[1];

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Deru, Michael ^[1]

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+ Show Author Affiliations

1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Publication Date:

Sat Jun 01 00:00:00 EDT 2019

Research Org.:

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office

OSTI Identifier:

1525771

Report Number(s):

NREL/TP-5500-72476

DOE Contract Number:  

AC36-08GO28308

Resource Type:

Technical Report

Country of Publication:

United States

Language:

English

Subject:

15 GEOTHERMAL ENERGY; 29 ENERGY PLANNING, POLICY, AND ECONOMY; high rotor pole switched reluctance motor; HRSRM; energy efficiency measure; EEM; variable head pressure control; VHPC; variable frequency drive; VFD