Why specify variable-speed compression in commercial refrigeration?

Maximize energy efficiency, setpoint precision and equipment reliability with variable frequency drives and compressors

By Joe Summers April 20, 2022
Courtesy: Emerson


Learning Objectives

  • Learn how variable-speed compression technology fits in to the commercial refrigeration toolbox.
  • Know the types of variable-speed solutions available and designed to support OEMs.
  • Understand what performance and operational improvements are achieved through variable-speed compression.


The use of variable-speed compression technology has been a largely underused asset in the commercial refrigeration toolbox. Long-held perceptions of high costs and implementation complexities have deterred supermarket and restaurant retailers from exploring its many benefits. Shifting market dynamics are changing perceptions and building a growing business case for variable-speed compression technology across an expanding spectrum of applications.

Sustainability initiatives, refrigerant regulations and energy-efficiency mandates are driving food retailers toward more sustainable refrigeration equipment. Many are evaluating equipment that will help them to lower their total equivalent warming impact via:

  • Delivering high energy efficiencies and/or achieving Energy Star
  • Leveraging lower-global warming potential refrigerants.

And with the trend toward smaller-format food retail stores, many owners and operators are exploring distributed alternatives to traditional centralized refrigeration architectures. This has led to the emergence of stand-alone, self-contained, reach-in refrigerators and freezers, display cases and walk-in coolers. Because these units don’t need to be connected to a centralized rack system, they offer increased merchandizing flexibility compared to fixed refrigeration units.

At the same time, the decreasing applied costs of power electronics are making them much more accessible. Manufacturers of variable frequency drives have made tremendous strides in improving their application potential and ease of use.

Combined, these dynamic market forces have changed the cost-benefit analysis of variable-speed compression technologies, bringing them into parity with other refrigeration choices while delivering a variety of end-user benefits.

Copeland reciprocating hermetic compressor paired with a variable speed drive. Courtesy: Emerson

Filling a critical industry need for variable-speed compression

For original equipment manufacturers of these self-contained systems, variable-speed compression represents one of the few remaining options capable of helping them to improve energy efficiencies or meet market demand for environmentally friendly refrigeration equipment.

By enabling variable-capacity modulation, compressors can match their capacity to the changing demands of a refrigeration load. What’s more, variable-speed compressors deliver high performance in a small footprint, allowing OEMs to easily integrate them into their designs without cutting into valuable merchandizing space.

Variable-speed compression technology consists of a variable-speed compressor — typically a low-profile horizontal or vertical scroll — paired with a VFD. Rather than using a traditional induction motor, compressors are equipped with brushless permanent magnet motors to deliver:

Pairing these low-profile scroll compressors with a VFD allows them to modulate across a much broader capacity range. Rather than cycling compressors on and off, a VFD allows compressors to precisely match capacity in response to changing refrigeration system loads. Essentially, this delivers twice the speed and capacity in a much smaller scroll compressor (e.g., 7,000 revolutions per minute versus 3,500 rpm) while delivering:

  • Improved equipment reliability.
  • Continuous and more precise temperature and humidity control.
  • Low starting torque to eliminate startup current spikes.

Copeland scroll. Courtesy: Emerson

Solutions designed to support OEMs

Complying with refrigerant regulations and energy-efficiency mandates — or achieving the efficiencies required for Energy Star certification — can present significant design challenges for OEMs. A variety of variable-capacity compression solutions and custom condensing units can be specified in refrigeration equipment.

Variable-speed horizontal scroll compressors

Horizontal scrolls are well-suited for lower-profile, medium-temperature applications such as stand-alone display cases and self-contained packaged systems.

Variable-speed vertical scroll compressors

Traditional vertical scrolls have an expanded capacity range that can cover a wide spectrum of MT and low-temperature reach-in and walk-in equipment.

Variable-speed fractional hermetic compressors

Variable speed hermetic reciprocating compressors are ideal for smaller, MT and LT reach-in units, display cases and walk-ins. Their small profile helps to maximize available merchandizing space.

Variable capacity for constant performance improvements

Advancements in compression technology — combined with the declining costs and improved usability of power electronics — have made variable-speed compression solutions more accessible for the commercial refrigeration market.

Author Bio: Joe Summers is senior product manager for scroll and drives at Emerson, where he leads new product development activities. In his role, he and his team develop variable speed compressors, variable frequency drives and low-power electronics focused on the cold chain.