The compressor is the ‘heart’ of any refrigerator or air conditioner and most of the research revolves around the compressor to make it more efficient to improve overall performance of these two types of products. Technology changes on a daily basis, and inverter compressors have started replacing conventional compressors in appliances like refrigerators and air conditioners.
The inefficient use of electricity to drive the compressors of refrigeration and air-conditioning systems is considered as an indirect contributor to the emission of greenhouse gases to the atmosphere. This emission can be reduced by improving the energy conversion efficiency of refrigeration systems.
One of the methods of achieving this is through capacity control, which matches the system capacity to the load. Capacity control reduces the on/off cycling losses of the equipment and improves the steady-state efficiency of an appliance due to a lower pressure differential across the compressor at part-load conditions.
This article explains the basics of conventional versus inverter compressors.
Working of conventional compressors
The conventional compressor works on a principle of ‘Single Speed’. They are either ‘ON’ or ‘OFF’ based on the loading/temperature setting of a thermostat in a refrigerator or air conditioner. Here most compressors are designed to handle the peak load condition (e.g., high temperature in summer), which indicates they will run in peak load even if the ambient temperature is less during the winters. This ultimately results in high power consumption and with the user paying a high electricity bill. Moreover, conventional compressors are designed to take care of heat ingress due to the frequent door openings and closings for refrigerator or to the outdoors for air conditioners.
Working of the inverter compressor
Unlike the conventional compressor, here the inverter compressor works on a principle of Variable Frequency Drive (VFD) to cause the speed of the compressor to vary _ as a result of varying load conditions. The change in speed of the compressor, in turn, causes the refrigerant flow to change.
The inverter technology is the latest evolution of technology concerning the compressor motor. An inverter is used to control the speed of the compressor motor, so as to continuously regulate the temperature. The inverter units have a variable-frequency drive that comprises an adjustable electrical inverter to control the speed of the compressor motor, which in turn adjusts the compressor output. The drive converts the incoming alternating power (A.C.) source to direct current power _ and then through a modulation in an electrical inverter produces current of desired frequency.
A microcontroller samples the ambient air temperature and adjusts the speed of the compressor accordingly. A compressor with inverter technology helps ensure that during summer months when cooling load is high, the compressor works at high capacity. At other times when cooling load is less, the compressor works at a lower capacity setting.
Comparative data between conventional & inverter compressor
Refrigerator
Displayed below, few of the actual tested data of four star and five star refrigerators of various gross capacity for their energy consumption:
It is clearly seen that inverter compressor is consuming less power compared to the conventional compressor in a range of 34% to 37%, which is a very high percentage.
Note: Few refrigerators were tested at UL Manesar lab and based on the result, percentage of saving has been calculated and highlighted. Refrigerant (134 a) was used in a conventional compressor while (600-a) was used in inverter compressor. The outcome compressor isn’t the only factor.
Advantages of inverter compressor
Inverter compressor technology is highly responsive, efficient, compact and allows flexibility of placement. The inverter air conditioning units have increased efficiency when compared to traditional air conditioners. Sharp fluctuations in the load are eliminated. This makes the inverter units quieter, with lower operating cost and more reliability. The inverter units are more expensive than the constant speed air conditioners, but this initial expense can be offset by lower energy bills.
Conclusions
The subject is entirely focused on the ‘consumers of India’, to spread the awareness for better energy efficient products available in the market. With greater awareness, it will help in saving energy and contribute in ‘India’s growth story.’
In recent years, compressors with variable speed drives have gained an increased market share in air conditioners and household refrigerators, due to improved efficiency and reliability brought about by advancements in material, manufacturing technology and optimised design.
Over the past few years, the price of inverters had been steadily decreasing. This trend is attributed generally to improved design, increased production and the decrease in price of electronic devices. The reliability of inverters is constantly improving, due to improved technology and availability of better components. Space is also decreasing, due to improved packaging, higher efficiency, more effective heat sinks and improved circuitry.
