Abstract
Commercial refrigeration systems applying R744 as the only refrigerant still have a large potential in
development regarding energy efficiency, heat recovery and cost efficiency. Special focus and emphasis has
to be given to the system architecture with respect to increase the system efficiency when these units are
operated at elevated ambient temperatures. The objective of this thorough theoretical study is to investigate
the energy required for different R744 refrigeration systems at 25-50-75-100% cooling load conditions. All
R744 system configurations are assumed to operate at high ambient temperatures (from 30 to 42 °C) which
mean only transcritical operations are considered for the following system configurations. Some alternatives
are sustainable and viable competitors to conventional HFC supermarket refrigeration systems, up to now
applied in warm climates:
• Standard booster cycle (baseline)
• Expander cycle (expander → electrical generator)
• R744 booster cycle with a mechanical subcooler (MS) unit: working fluid MS: hydrocarbon
• Economiser I cycle (with a flash tank, i.e. parallel compression)
• Economiser II cycle (without a flash tank; i.e. parallel compression)
• Ejector supported parallel compression system
These different cycles are evaluated with advanced spreadsheets assuming realistic component
performances. Copyright © 2014 IIR/IIF. All rights reserved.
development regarding energy efficiency, heat recovery and cost efficiency. Special focus and emphasis has
to be given to the system architecture with respect to increase the system efficiency when these units are
operated at elevated ambient temperatures. The objective of this thorough theoretical study is to investigate
the energy required for different R744 refrigeration systems at 25-50-75-100% cooling load conditions. All
R744 system configurations are assumed to operate at high ambient temperatures (from 30 to 42 °C) which
mean only transcritical operations are considered for the following system configurations. Some alternatives
are sustainable and viable competitors to conventional HFC supermarket refrigeration systems, up to now
applied in warm climates:
• Standard booster cycle (baseline)
• Expander cycle (expander → electrical generator)
• R744 booster cycle with a mechanical subcooler (MS) unit: working fluid MS: hydrocarbon
• Economiser I cycle (with a flash tank, i.e. parallel compression)
• Economiser II cycle (without a flash tank; i.e. parallel compression)
• Ejector supported parallel compression system
These different cycles are evaluated with advanced spreadsheets assuming realistic component
performances. Copyright © 2014 IIR/IIF. All rights reserved.
