Energy efficiency

Refrigerating systems influence the environment directly when refrigerants with high global-warming potential (GWP) are emitted into the atmosphere, and indirectly when electrical energy, for example, is generated for those systems.

In Russia, during the generation of 1 kW·h approximately 0.51–0.52 kg of greenhouse gases in CO₂-equivalent are emitted, according to the Ministry of Economic Development and Trade. A refrigeration system of a small cold store consumes dozens of thousands of kW·h annually, so damage to the environment can significantly reduce when energy consumption is cut only by several percents.

To evaluate the energy efficiency of refrigerating equipment, coefficient of performance (ratio of refrigeration capacity to consumed energy) is used.

The energy efficiency of refrigerating equipment can be improved through:

• transition to natural refrigerants, such as carbon dioxide, ammonia, hydrocarbon refrigerants, others, or
• adoption of innovative technologies: inverter drives, EC motors, new heat exchangers, hot gas defrost systems, others.

Natural refrigerants

Conversion from hydrochloroflurocarbons (R-22) and hydrofluorocarbons to ammonia (NH₃, R-717), and application of heat pumps to recover heat and heat water can reduce energy consumption by 40%. Lower condensing temperature, higher evaporation temperature, variable speed compressors, and multi-stage systems add to reduction of energy consumption.

Carbon dioxide (CO₂, R-744) is efficient in low-temperature stages of cascade systems (NH₃/CO₂), and in a cold and moderate climate, CO₂ equipment can be up to 10% more efficient than HFC systems.

In low-temperature refrigeration (below -60°C), air can be an efficient refrigerant.

Technology solutions

The coefficient of performance of the high-pressure side depends on:

• difference between temperatures of the surrounding air and refrigerant condensation;
• conformity of equipment and materials with operational conditions (climate, application severity);
• parameters of fans (energy efficiency, speed regulation);
• potential for use of free cooling;
• refrigerant supercooling;
• heat recovery;
• correct installation and maintenance.

With the reduction of the difference between temperatures of the surrounding air and refrigerant condensation from 15 to 8–10°C through the use of a proper condenser, energy consumption in summer can be 15–20% lower.

Condensers with pipes of smaller diameter require less refrigerant and materials. Protection of condenser pipes and aluminum fins from aggressive media ensures corrosion-resistant stainless steel and special coating.

Spray systems, adiabatic pre-coolers, and stepless fan speed control improve the efficiency of condensers.

Fans with energy-efficient electrically commutated motors with permanent magnets and stepless speed control reduce the energy consumption of a condenser by up to 80–85%. As fan power consumption is proportional to cubed fan speed, then reduction of rotation speed by 50% reduces power consumption by 83–87%.

The efficiency of a condenser grows with the increase of a heat removal surface, for example, through microgrooves on the pipe inner surface.

The efficiency of the high-pressure side (evaporator side) depends on:

• parameters of operating mode;
• difference between temperatures of surrounding air and evaporation;
• energy efficiency of fans;
• location of an evaporator and its defrost.

Efficiency (and safety) of evaporators (air coolers) of refrigerating chambers can be increased by defrosting with hot gas, i.e. hot gaseous refrigerant.

A part of hot gaseous refrigerant from the suction line enters an air cooler instead of a condenser, and defrosts it by passing the pipes of a heat exchanger. The refrigerant liquefies and condenses in these pipes and then enters a receiver.

Hot gas defrost is especially efficient when not more than 20% of evaporators are defrosted, and others operate in a cooling mode.

Additional materials

• How to achieve decarbonization through HVAC automation
• Compressor technology offers up to 50% savings
• Unilever sees 12‒17% energy reduction with variable speed compressors in R290 cabinets
• Road to COP28: Energy efficiency, the key to sustainable cooling in Africa
• Automated cold-storage facility in Canada to employ integrated CO₂ system
• Combined cooling, heating and power systems can boost supermarket eficiency, says contractor Neelands
• China’s MEPS lead to major AC market transformation
• CO₂ defrost system cuts energy use by 20% for Japanese distributor Kyodo Suisan Ryutsu
• ATMO America: Evapco installs its first low-charge ammonia split systems in Nevada cold storage facility
• TEWI vs GWP
• German research institute looks into low-charge R290 heat pumps systems, especially Indoors, for multi-family housing
• Study finds ‘novel’ transcritical CO₂ ejector system outperforms conventional CO₂ system up to 82.5% in hot climate
• CO₂ refrigeration helps cut electricity use at finnish ice rink by 34%
• Danfoss introduces a new algorithm for enhanced control of ejectors and high-pressure valves in a CO₂ industrial system
• Freor’s ‘Continuous Cooling’ technology cuts energy use in R290 commercial cases up to 70%
• Energy Recovery’s pressure exchanger boosts Epta CO₂ refrigeration efficiency by over 30% at ambient temperatures above 40°C
• ‘Hybrid ejector’ found to boost efficiency of transcritical CO₂ refrigeration by up to 42%
• Chillers using ammonia mix save over 744 metric tons of CO₂e emissions at Slovak Tannery
• Scientists back propane in heat pumps
• Refrigeration and environmental and economic challenges
• New European Proposal Calls for No Fossil Fuels in Heating and Cooling of Buildings by 2040
• Climate change agreement sees cold storage energy efficiency improve by 19%
• Large Secop Variable-Speed R290 Compressor Saves Up to 40% in Energy Use
• ATMOsphere Europe Keynoter: NatRefs Outperform F-Gases in Efficiency
• French Seafood Processor Saves Up to 36% in Energy With CO₂ Cooling/Heating
• Energy and environmental paradigms of refrigerants (in Russian)
• Results of UNIDO ATMOSPHERE (in Russian)
• Ozone-depleting substances and environmentally safe alternatives (in Russian)
• Design and selection of equipment to minimize climate impact (in Russian)
• Natural refrigerants for the future of Russia (in Russian)
• Conversion of commercial refrigeration equipment to ozone-safe refrigerants and foam agents (in Russian)
• Ammonia as refrigerant (in Russian)
• US Department of Energy reviews energy efficiency standards (in Russian)
• Phase-out of ‘super’ greenhouse gas gives advantages to Great Britain (in Russian)
• User opinion: CO₂ systems can be as efficient as ammonia ones (in Russian)
• First Russian freon-free grocery using ozone-safe refrigerant CO₂ (in Russian)
• Spanish supermarket Eroski: hybrid R-134a/CO₂ systems save up to 65% of energy (in Russian)
• New CO₂ transcritical system in Lithuanian supermarket: energy consumption reduced by 30% (in Russian)
• What are natural refrigerants? (in Russian)
• Coca-Cola installs 1 millionth carbon dioxide refrigerator (in Russian)
• Concerns of operators of refrigeration and heating equipment (in Russian)