ENERGY SAVING
Variable speeds for variable loads
Variable speed compressors are the way forward for energy saving in refrigeration. Peter Buksar, R&D senior leader for technical support and Marino Bassi, key account senior advisor at Nidec Global Appliance explain.
E
nergy, its production and availability are not only fundamental for any country’s economy and for the health of any population, but are also global
environmental issues. It is the same with refrigeration. While it is vital for food preservation and economic development, as well as for medical and scientific progress, refrigeration is a major energy user – the estimate from the International Institute of Refrigeration is that the sector (including air conditioning) consumes about 17% of the overall electricity used worldwide. Refrigeration is a highly technological sector and
energy efficiency is among the top priorities in the constant quest for industry evolution and innovation. One of these technology drivers is variable speed compressors (VCC), which, after proving its advantages and becoming mainstream in air conditioning and household applications, is now gaining increased momentum in the commercial refrigeration industry worldwide, especially because of its energy efficiency. In comparison with a fixed speed compressor, a variable
speed has a different type of motor, the BLDC (brushless direct current) motor, also known as ECM (electronically commutated motor). Another difference is that this motor works connected with an electronic device called an inverter. The inverter controls the motor, making it rotate at different speeds, according to the targeted cooling load, decreasing it when the ideal temperature has been achieved and increasing it when there is need for more heat removal.
22 January 2021
Thanks to these characteristics, variable speed compressors have significant advantages over the fixed speed ones (also known as on-off), and here we list them from the perspective that matters the most – the end user’s.
Energy saving A traditional fixed speed (on-off) compressor operates at a constant speed, continuously switching on and off to meet the refrigeration equipment’s cooling demand. This operational pattern requires abrupt power loads when starting; furthermore, as the compressor maintains the maximum speed for all the running period independent from the thermal load, it leads to wasted energy. As described previously, variable speed compressors come with an embedded set of electronics that allow the compressor to control its working speed, decreasing it when reaching the target temperature and also increasing it when there is need for more heat removal, ideally without switching on and off – or with a consistent reduction of on-off cycles and with a limited starting torque power versus on-off compressors. This enables the compressor to use only the amount of energy required at each moment and nothing more. The energy savings from variable speed varies according to the application but are always very significant. We have made many case studies with Embraco compressors, where the only change made was the switch from a fixed to a variable speed compressor, and the results were energy savings of at least 15% up to around 40%. Just to give an example, in a horizontal island freezer
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