Source: hydrocarbons21.com
Variable-speed propane (R290) compressors reduced freezer energy consumption by up to 29% and temperature variation by up to 35% compared to fixed-speed compressors, according to a test conducted by U.S.-based OEM Hussmann and Embraco, a Brazil-based manufacturer and brand of Nidec Global Appliance.
These savings are achieved by the compressor adjusting its running speed to the demand required by the refrigeration equipment, rather than operating at a single speed regardless of demand.
The findings were presented by John Prall, Application Engineering Expert at Embraco North America and Mike Schafer, Vice President of Core and Distributed Case Products at Hussmann during a session at the ATMOsphere (ATMO) America Summit 2022 on natural refrigerants. The conference, which took place June 7–8 in Alexandria, Virginia, was organized by ATMOsphere, publisher of Hydrocarbons21.com.
Next generation of sustainable applications
After seven years of working together on fixed-speed R290 applications, the two companies are now looking towards the “next evolution” of their collaboration. According to their presentation, Embraco and Hussmann want to provide “flexible and efficient solutions that meet new regulation requirements and sustainability goals.”
said Schafer.
"Our promise is to continuously provide the most customer-focused solutions in the food retailing industry, and we see a great demand for more energy efficiency for financial, environmental and regulatory reasons." Mike Schäfer, Hussmann
“That’s why we decided to develop with Embraco a whole new portfolio of variable speed applications.”
This next generation includes two vertical “grab n’ go” freezers from Hussmann’s MicroSC R290 product line, which were converted to use Embraco’s FMFT variable-speed R290 compressor, part of the company’s FMF portfolio. The units previously used Embraco’s fixed-speed NT R290 compressor.
The MicroSC line consists of self-contained, air-cooled R290 cabinets. Hussmann also offers its MicroDS line of R290 self-contained cases, for which heat of condensation is removed via a water-loop system.
In addition to upgrading the compressor, Hussmann took the opportunity to optimize the system, including reducing the R290 charge and making the application operate in 110V and 220V. Hussmann also converted the defrost from electric to gas and the condenser from steel tube to microchannel, in addition to optimizing the evaporator.
Efficiency savings
The case study looked at a three-door freezer that used two FMFT compressors and a two-door freezer that used one FMFT compressor.
Compared to fixed-speed compressors, the variable-speed units reduced energy consumption in the three-door and two-door freezers by 29% and 19%, respectively. According to Prall, these energy savings come from the variable-speed compressors’ ability to “provide the same cooling capacity of the previous fixed-speed models but running on lower speeds most of the time.”
These energy savings also mean a reduction in indirect greenhouse gas emissions. Embraco and Hussmann estimate these reductions to be 4,376kg of CO2e for the two-door freezer and 10,013kg of CO2e for the three-door freezer. As both the display unit and compressor use R290, which has a GWP close to zero, there is no reduction in direct emissions.
In addition to improved energy efficiency, the variable-speed compressors also reduced temperature variation by 13.5% in the three-door freezer and 35% in the two-door freezer, ensuring better food preservation.
“The variable speed compressor can overcome temperature variations caused by door openings much faster than the standard [fixed-speed] compressor models,” said Prall, “thus improving food preservation and attending to the best practices of food safety regulations in the United States.”
Efficiency savings also come from Embraco’s Smart Drop-In software, which helps to detect situations when the compressors need to accelerate, for example, when doors are opened or when the unit is going into or coming out of defrost.
According to Prall’s and Schafer’s presentation, the freezers’ payback period for end users is less than two years due to reductions in energy consumption.
Other benefits of the variable-speed system include less noise, less vibration and a wider volt tolerance
ENERGY STAR certified
With these results, both of the case study’s freezer cabinets meet the requirements of the U.S. Environmental Protection Agency’s (EPA) ENERGY STAR certification for commercial refrigeration equipment. This is true for both the current certification and the 5.0 version that is currently under development.
“Our results also meet probable future stricter standards from the [U.S.] Department of Energy, which the market expects to be issued within the next two years,” explained Prall. “That might be as rigid as the Energy Star 5.0.”
Moving forward, the partnership will look at converting larger charge, medium-temperature systems to variable-speed compressors. With forthcoming changes to R290 charge limits, Hussmann and Embraco also expect to see even higher efficiencies relative to variable speed.