The industrial sector is the largest users of energy around the world. Industrial motor uses a major fraction of total industrial energy uses. This paper describes a comprehensive literature review about electric motor energy analysis. This paper compiles latest literatures in terms of thesis (MS and PhD), journal articles, conference proceedings, web materials, reports, books, handbooks on electrical motor energy use, losses, efficiency, energy savings strategies. Different types of losses that occur in a motor have been identified and ways to overcome these losses explained. An energy audit that helps to identify motor energy wastages have been discussed extensively. As motors are the major energy users, different energy savings strategies such as use of high-efficient motor, variable speed drive (VSD), and capacitor bank to improve the power factor to reduce their energy uses have reviewed. Different policy measures (i.e. regulatory, voluntary and incentives based) to save motor energy use have been reviewed and presented in this paper. In this review, computer tools that can be used to analyze electric motors energy used has been discussed. Cost parameters to carry out economic analysis have been shown as well. Moreover, payback period for different energy savings strategies have been identified.

A review on electrical motors energy use and energy savings

Most motors are designed to operate at a constant speed and provide a constant output; however, modern technology requires different speeds in many applications where electric motors are used. A variable speed drive (VSD) is a device that regulates the speed and rotational force, or output torque of mechanical equipment. Effects of applying VSDs are in both productivity improvements and energy savings in pumps, fans, compressors and other equipment. Variable speed drive technology and the importance of controlling the speed of existing motors have fascinated many attentions in the last years with the advent of new power devices and magnetic materials. This paper is a comprehensive review on applications of VSD in electrical motors energy savings. The aim is to identify energy saving opportunities and incorporated costs of applying variable speed drives to the existing applications of electrical motors. Subsequently, economic analysis, payback period and the effect of current and voltage harmonics generated by VSDs are presented. Authors are hopeful to provide useful information for future variable speed drive applications like fans, pumps, chillers, ventilators and heaters.

Applications of variable speed drive (VSD) in electrical motors energy savings

Dynamic Modeling and Advanced Control of Air Conditioning and Refrigeration Systems

This paper presents a comprehensive review of two-phase ejector as an expansion device in vapor compression refrigeration cycle over the past two decades. It also covers research opportunities that are still open in the field of two-phase ejectors as an expansion valve. The studies of the application of ejector as an expansion device are relatively scarce compared to the application of ejector as heat-driven refrigeration system. A better understanding of two-phase flow in the ejector is necessary to optimize energy saving of the system. This paper also presents effects of geometric parameters of the ejector as an expansion valve on the performance of vapor compression refrigeration cycle. In addition, the effect of working fluid on the two-phase expansion refrigeration system is covered. The authors predict that the challenge of future research on design of two-phase ejector is how to generate a pressure rise in diffuser for minimum compressor work and optimum COP improvement.

A review on two-phase ejector as an expansion device in vapor compression refrigeration cycle

Variable speed control of compressors is one of the best methods to regulate the capacity of heat pumps and air conditioners. An analysis is conducted for modeling the variable speed compressor for simulation of inverter air conditioner and heat pump. Having scattered the real operation performance of inverter compressor into infinite operation performance of constant speed compressor, the map-based method is utilized to fit the performance curves of inverter compressor. The model is built at the basic frequency and the map condition as the second-order function of condensation temperature and evaporation temperature. Then it is corrected by the compressor frequency as the second-order function of frequency and by the actual operating condition as the actual specific volume of the suction gas. This method is used to set up simulation models of three different compressors. Compared with the data provided by the compressor manufacturers, the average relative errors are less than 2, 3 and 4% for refrigerant mass flow rate, compressor power input and coefficient of performance (COP), respectively. This model of variable speed compressor is suitable for the simulation of inverter air conditioner and heat pump systems. Based on the experimental data and simulation model, the frequency at zero mass flow rate and power input at zero frequency are discussed and the relation between COP and compressor frequency is analyzed.

Performance representation of variable-speed compressor for inverter air conditioners based on experimental data

Variable-speed capacity control in refrigeration systems

This paper presents the results of investigations into the performance of positive-displacement refrigeration compressors for variable-speed capacity control applications Compressors tested include an open-type reciprocating, a semi-hermetic reciprocating and an open-type rotary vane All three compressors were tested under constant and variable head-pressure operating conditions The results indicate that all three compressors were designed for maximum efficiency at nominal speed At constant head-pressure only the open-type compressor exhibited an improvement in the COP at reduced speeds With variable head-pressure-control all three compressors showed an increase in the COP with a reduction in speed The results of an energy analysis carried out based on the experimental results and weather conditions for two locations representing temperate and warm weather conditions showed that all three compressors when operated at variable speed offer energy savings compared to their fixed-speed counterparts The analysis has shown the open-type reciprocating compressor to be the most efficient system offering 12% savings when operating in a temperate climate and 24% savings when operating in a warm climate

Comparative performance evaluation of positive displacement compressors in variable-speed refrigeration applications

Presents the results of an experimental investigation into the application of inverter-based variable-speed drives to positive displacement rotary vane refrigeration compressors. The investigation considers the effects of the inverter on a number of operating parameters such as the harmonic currents and voltages on both the supply side and motor side, power consumption and power factor, starting current and overall system efficiency. The results indicate that the use of off-the-shelf inverters for variable-speed control of refrigeration compressors can inject harmonics to the supply system which exceed the maximum limits imposed by BS5406. The inverter may also cause a reduction in the power factor and in the overall efficiency of the drive. Variable-speed operation of a rotary vane compressor may not offer efficiency advantages over fixed-speed operation but can provide other benefits such as better temperature control and faster response to sudden changes in load.

Performance of a variable-speed inverter/motor drive for refrigeration applications

In this study the dynamic mode performance of an inverter driven and direct mains driven compressor has been evaluated using a laboratory-based test facility. The aim was to investigate the influence of the inverter on the start-up performance of a refrigeration system and quantify and compare start-up losses for the two modes of operation. The results indicate that an inverter driven system incurs approximately 5 per cent higher start-up losses than a direct mains driven system. This is mainly due to the 'soft' starting capabilities of the inverter (gradual acceleration of the motor). An energy analysis of fixed speed and inverter driven refrigeration systems in air-conditioning applications has shown that despite the additional start-up transient losses of inverter driven systems they lead to higher seasonal efficiencies than fixed-speed systems. This arises from improved steady state performance during low-speed operation at loads below the design load of the system. It has been found that the level of energy savings is a function of the type of compressor employed in the variable-speed system.

T.Q. Qureshi

Papers

Variable-speed capacity control in refrigeration systems

Comparative performance evaluation of positive displacement compressors in variable-speed refrigeration applications

Performance of a variable-speed inverter/motor drive for refrigeration applications

Dynamic mode performance evaluation and energy analysis of mains and inverter driven refrigeration compressors