This paper investigates the integrated and state-of-the art features of CO 2 trans-critical booster systems. The main objective is to identify the most promising solutions in terms of energy efficiency impacts.First, the performance of modified features and integrated functions have been compared with the standard CO2 system and alternative heating and air conditioning solutions. Subsequently, the performance of the defined state-of-the-art CO 2 system is compared to natural refrigerant-based cascade and HFC/HFO-based DX and indirect refrigeration solutions operating in cold and warm climates.The results indicate that two-stage heat recovery, flooded evaporation, parallel compression and integration of air conditioning are the most promising features of the state-of-the-art integrated CO2 system. This compact and environmentally friendly system is the most energy efficient solution in cold climates, and is also an efficient solution in warm climates, with comparable efficiency to cascade and HFC/HFO DX systems, but with no existing or potential limitations.

PostprintThis is the accepted version of a paper published in International journal of refrigeration. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Tel: +46 (0)8 790 7889 Fax: +46 (0)8 204 161 E-mail: samer@energy.kth.se AbstractUsing computer simulation modeling this study investigates the performance of a CO2 transcritical system with heat recovery from the de-superheater. The influence of sub-cooling (or further cooling) in the condenser/gas cooler on system performance is investigated.Following the suggested control strategy in this study, the extra operating energy demand required to recover the needed heating energy from the analyzed CO2 system is smaller than what a typical heat pump would require for the same load. This is the case for almost all ambient temperatures over a full season. When taking the simultaneous heating and cooling loads into account, the CO2 trans-critical system has lower annual energy usage in an average size supermarket in Sweden when compared to a conventional R404A refrigeration system with separate heat pump for heating needs. CO2 trans-critical systems are efficient solutions for simultaneous cooling and heating needs in supermarkets in relatively cold climates. Keywords

This paper investigates energy efficiency of an integrated CO 2 trans-critical booster system installed in a supermarket in Sweden. The supermarket has applied several features to improve energy efficiency including space and tap water heating, air conditioning (AC), and parallel compression. Using field measurements data, the system performance is evaluated in a warm and a cold month. Furthermore, this integrated energy system concept is modelled and compared with stand-alone HFC-based energy systems. The results show that the system provides the entire AC demands and recovers a great share of the available heat, both with high COP values. The comparative analysis shows that integrated CO 2 system uses about 11% less electricity than stand-alone HFC solutions for refrigeration (i.e. indirect HFC), heating and AC in North of Europe. Energy efficiency analysis of the integrated CO2 system proves that this system is an environmentally friendly all-in-one energy efficient solution suitable for cold climate supermarkets.

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This paper analytically investigates and compares the performance of a proposed 'all-natural' NH 3 /CO 2 cascaded booster system to a conventional R404A direct expansion system as well as to an 'all-CO 2 ' system with multi-ejector unit and flooded evaporator. Performance comparison is made based on the annual combined COP and Life Cycle Climate Performance (LCCP) for operation in selected cities of Middle East and India. Our results show that in extreme warm climate, the energy efficiency of the proposed configuration exceeds that of all-CO 2 configuration by a maximum of about 12.23% and the total emissions are lower by up to 11.20%. However, the all-CO 2 multi ejector system performs better in cold and mild warm climate. In the NH 3 /CO 2 cascade, the high temperature NH 3 system can be designed to be isolated from the accessible locations of the supermarket. The work presented is expected to help adoption of natural refrigerants such as CO 2 and NH 3 for commercial application in extreme warm climate conditions prevailing in many cities of Middle East and India.