Single-Compressor vs. Dual-Compressor Ultra-Low Freezers

Choosing the right ultra-low temperature freezer can be a tough decision. One factor you need to consider is whether to go with a single-compressor or dual-compressor system. While a dual-compressor system has advantages, there are pros and cons to both.

In this post, we will explain what makes a dual-compressor freezer different from a single-compressor system and describe the relative benefits of each.

Differences Between Single and Dual-Compressor Freezers

A single compressor ultra-low temperature freezer uses just one cooling cycle, much like most regular freezers. Below are some examples of freezers that use a single-compressor system.

An Arctiko SUF 100® Ultra Low Temperature 2.5 Cu ft Chest Freezer and an Arctiko ULUF Ultra Low Temperature Upright Freezer.

A dual-compressor system, as its name suggests, houses two compressors. The cooling process requires two vapor compression cycles that work in a cascade system. One is a low temperature cycle and the other is a higher temperature cycle.

First, heat is removed from the freezer chamber by the first cycle. The heat is then rejected into the second cycle. The temperature difference between the first cycle condenser and the second cycle evaporator helps to achieve ultra-low temperatures. Finally, the heat is returned from the second cycle into the atmosphere. The setpoint temperature is maintained by cycling the low and high temperature compressors.

Each compressor uses a different refrigerant, with R23 commonly being used in the low temperature side. R404a or other traditional refrigerants such as ammonia are commonly used for the higher temperature side.

Here are some examples of ultra-low temperature freezers that have a dual-compressor system.

An ABS Ultra Low Temperature Freezer and a So-Low Ultra-low Chest Freezer.

Note that the term “dual-compressor system” may also be used to describe a different type of unit that houses a second backup compressor. In these freezers, there is no cascade system, but rather the primary reason for the second compressor is to act as a failsafe that will keep the freezer running if the other compressor fails.

That said, even in some cascade systems, each compressor can serve as a backup to the other to some extent. If one of the compressors fails, the freezer will still be able to hold a low temperature, although not the ultra-low temperatures it usually can. 

Relative Benefits of a Dual-Compressor Ultra-Low Freezer

One of the main benefits of a dual-compressor system is improved longevity of the unit. When a single compressor is working, it can run hot, increasing wear and lowering the lifespan of the machine. Dual compressors share the workload, preventing either one from heating too much, limiting wear, and prolonging the life of the freezer.

Another advantage in some units is that the compressors can continue working independently should one fail. In a single-compressor system, a compressor failure will mean that the freezer will not be able to cool at all. In a dual-compressor system, the freezer will not be able to cool as much, but depending on the design, it may not completely fail. In such situations, it might be able to maintain a temperature of around -40°C (again, this would depend on the build of the freezer).

Energy efficiency is a debatable benefit. Manufacturers of both single and dual-compressor ultra-low temperature freezers often claim superior energy efficiency, but advances in design mean that both systems can be incorporated in energy-efficient units.

For example, the table below shows the power consumption for Arctiko and Haier ultra-low temperature chest freezers of similar sizes. The Arctiko units have a single-compressor system while the Haier models house a dual-compressor cascade system.

When it comes to the smaller units, the slightly larger Haier unit is a little more energy-efficient. But when we look at the larger models, after accounting for the size difference, the two units are fairly comparable in terms of energy efficiency.

Dual-compressor systems can come with some drawbacks too. They may have higher noise levels due to two cycles working instead of one. That said, certain design aspects can be used to minimize the noise level of both systems.

Another potential drawback is that dual-compressor systems can be priced a bit higher than their single-compressor counterparts. But when you weigh up the cost against the extension of the lifespan of the machine, this becomes less of a disadvantage.