In our day and age, electrical appliances are an integral part of our daily lives and it's hard to imagine living without them.

Refrigerators are the most appreciated household appliances in a tie with washing machines in the ranking¹.

We all have a fridge at home. It is an appliance of fundamental importance that we often take for granted. It runs all year round keeping fresh, well-preserved food readily at hand.
Since it never switches off, it is also one of the appliances that cost us the most in utility bills.

Inverter technology to reduce energy consumption in the domestic market

"Inverter" technology was created in the 1980s to reduce energy consumption and was first applied to A/C systems. It soon began to be applied to refrigerators as well, with the first models being launched on the market in the late 1990s. The technology began to be adopted on a large scale in domestic refrigerators in the early 2000s and to this day it is considered standard when buying a new appliance.

Interestingly, an inverter refrigerator can reduce energy consumption by up to 50% compared to a fixed-speed appliance. This amounts to about 50 Euros per year on the utility bill.

Practical example:
The energy classes of a 300L capacity fridge with a freezer are shown below.

Source ENEA (Energy Efficiency Unit Department)

In other words, on average:

• An on/off refrigerator: ~350-400 kWh/year → € 98-112/year in the utility bill.
• An inverter refrigerator: ~150-200 kWh/year → € 42-56/year in the utility bill.

The estimated annual saving is therefore € 56.

And what about commercial refrigeration?

Let's turn to refrigerators outside homes. They are commonly found in many businesses and venues, including restaurants, bakeries, hotels, small shops and large stores. They are used to store food before it is bought or before it is cooked and served. Larger than domestic refrigerators and subjected to greater thermal stress from the constant opening of doors by customers and catering staff, they are much more energy-intensive than their home counterparts.

Although until a few years ago, capacity, robustness and durability were the main qualities required for a professional refrigerator, a rapid growth in the adoption of inverter technology compressors has recently been observed in this sector as well. This is also thanks to recent regulations in the energy field and concerning the use of natural refrigerants.

Chest freezers were the first to fit modulating compressors in the commercial sector over a decade ago. Being large, low-temperature cabinets, they were able to cut energy consumption costs, allowing the purchase costs for a modulating technology refrigerator to be recovered faster. More recently, other types of refrigerators, such as stainless-steel appliances for professional kitchens and bottle coolers, are also rapidly embracing this technology. 

VCC inverter technology

In refrigerators for the domestic market, the term "inverter" identifies the technology in which the compressor modulates its speed according to the need for cooling, the acronym "VCC" (Variable Capacitive Compressor) is used to identify the inverters used in the commercial sector but the concept is the same.
VCCs, in this context, are small hermetic piston compressors, equipped with their own inverter for speed control. They have a maximum size of around 16cc and are all ready to manage for use with new refrigerant gases: Propane (R-290) and Isobutane (R-600).

We have talked about energy benefits so far but it is worth considering that benefits are manifold:

• Temperature stability optimisation for better food preservation
• Noise reduction for a quieter and more comfortable environment
• Longer unit life
• Lower running and maintenance costs

VCC compressor control modes

Inverter/VCC technology achieves these benefits because the compressor can modulate its speed according to the cooling demand of the unit. Unlike fixed-speed (On/Off) compressors, this ensures that the number of times the compressor switches on and off is minimised and a much more stable temperature can be achieved.

A VCC compressor can be controlled mainly in two modes:

• Drop-In: the electronic thermostat enables the inverter to start (by closing/opening a relay) and it is then the inverter that regulates the compressor speed independently
• Frequency/Serial: the electronic thermostat communicates the speed at which the compressor must run to the inverter, based on advanced logic implemented in the thermostat algorithm, to optimise regulation based on the real cooling demand of the unit

In other words, VCC inverter technology allows energy savings but the actual results and the temperature stability that can be achieved are heavily influenced by how the compressor is controlled.

As shown in the chart, the Drop-In solution is better than the fixed-speed (On/Off) compressor arrangement both in terms of temperature stability and in reducing the number of times that the compressor switches off (which translates into energy savings). With a compressor controlled in Frequency/Serial mode, the temperature remains even more stable and compressor hardly ever switches off.

In conclusion

Certainly, refrigerators, both domestic and commercial, have undergone substantial technological growth in recent decades to reduce energy consumption and the adoption of modulating compressors can secure the best energy benefits.

It is equally important to remember that energy benefits can also vary depending on the chosen compressor control mode. As we have seen, the electronic control algorithms allow direct control of the compressor speed, allowing maximum energy efficiency from the VCC technology and optimising temperature stability for the best food preservation.

Sources:

¹. La Repubblica "How much do our indispensable appliances cost us?", quoting data from a survey conducted by Facile.it with the help of mUp Research and Norstat.