This article presents a review of the application of variable speed capacity control to refrigeration systems. The aim is to put together diversified information in a single source and to appraise recent advances in variable speed technology. The review reveals that variable speed drives based on inverters have been applied successfully to control the capacity of positive displacement machines such as compressors. Inverter-based variable speed compressor technology offers the potential for energy savings.

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 compressor 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.

The basics of Conventional versus Inverter Compressors will be discussed one by one in the following paragraphs.

Working of conventional compressor

The Conventional Compressor works on a principle of ‘Single Speed.’ They are either ‘ON’ or ‘OFF’ based on the loading or 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 inverter compressor

Unlike the Conventional Compressor here the Inverter Compressor works on a principle of ‘Variable Frequency Drive’ 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 (AC) 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


Have a look at the few of the actual tested data of 4 Star & 5 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 result percentage saving calculated and highlighted. Additionally for outcome compressor is not the only factor, refrigerant used too are different. Refrigerant (134 a) was used in a conventional compressor while (600-a) was used in inverter compressor.

Advantages of inverter compressors

Inverter compressor technology is highly responsive and efficient. Moreover, it is compact and quite unit that allows flexibility of placement. The inverter air conditioning units have increased efficiency when compared to traditional air conditioners. Also, sharp fluctuations in the load are eliminated. This makes the inverter units quieter, with lower operating cost and more reliable. The inverter units are more expensive than the constant speed air conditioners, but this is initial expense can be offset by lower energy bills.


The article is entirely focused on the ‘Consumers of India’ and to spread the awareness for the better energy efficient product available in market while purchasing and at the same time enabling each of us to save the 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 and manufacturing technology and optimised design.

Over the past few years, the price of inverters has been steadily decreasing. This trend is attributed generally to improved design, increased production and the decrease in the price of electronic devices.

The reliability of inverters is also constantly improving, due to improved technology and the availability of better components. Space requirements are also decreasing, due to improved packaging, higher efficiency, more effective heat sinks and improved circuitry.

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