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.
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.
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.
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- New CO2 transcritical system in Lithuanian supermarket: energy consumption reduced by 30% (in Russian)
- Spanish supermarket Eroski: hybrid R-134a/CO2 systems save up to 65% of energy (in Russian)
- First Russian freon-free grocery using ozone-safe refrigerant CO2 (in Russian)
- User opinion: CO2 systems can be as efficient as ammonia ones (in Russian)
- Phase-out of ‘super’ greenhouse gas gives advantages to Great Britain (in Russian)
- US Department of Energy reviews energy efficiency standards (in Russian)
- Ammonia as refrigerant (in Russian)
- Conversion of commercial refrigeration equipment to ozone-safe refrigerants and foam agents (in Russian)
- Natural refrigerants for the future of Russia (in Russian)
- Design and selection of equipment to minimize climate impact (in Russian)
- Ozone-depleting substances and environmentally safe alternatives (in Russian)
- Results of UNIDO ATMOSPHERE (in Russian)
- Energy and environmental paradigms of refrigerants (in Russian)
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