Optimal designs help CO2 supermarkets save energy 

By Huiting Jia, Jul 06, 2012, 15:24 3 minute reading

At this year’s Gustav Lorentzen Conference on Natural Refrigerants, reducing energy consumption for CO2 supermarkets thanks to optimal plant design was a hot topic. R744.com reports on some of the updated solutions for improving the energy efficiency of R744 refrigeration systems in supermarkets presented by several leading research institutes and companies from around the world. 

A supermarket has a very high energy consumption, typically in the range of  500kWh/m2. In some countries like the United States and France, the amount of energy consumed for heating, ventilation, refrigeration and air conditioning in supermarkets represents 4% of the country’s total electricity production. With supermarkets under pressure to save energy costs, the efficiency of environmentally friendly natural refrigerant technologies has been gaining interest, as evidenced at the 10th Gustav Lorentzen Conference.
 
Heat recovery solutions for R744 booster commercial refrigeration systems
 
According to a research by Denecke, Hafner, Eikevik and Ladam from the Norwegian University of Technology and Science, heat recovery from the refrigeration plants is a very efficient way to improve total energy efficiency of supermarkets. The research presented compared three heat recovery schemes for a supermarket located in Norway equipped with CO2 booster system. The CO2 systems showed good performance for cold climates making them especially suitable for heat reclaim. 
 
Heat recovery solutions for CO2 booster systems are gaining popularity. In UK, the solutions have been investigated in depth in Ge et al. (2011) for the northern UK climate and in Northern Norway a company called Kuldeteknisk AS has been a pioneer of these solutions. 
 
Integration of refrigeration and HVAC in supermarkets
 
Researchers T. S. Nordtvedt and A. Hafner from SINTEF Energy Research also believe the integration of CO2 refrigeration systems with heating and ventilation in supermarkets can potentially reduce supermarket energy consumption. SINTEF explained that thanks to the integrated energy efficient supermarket concept, the energy numbers of a typical supermarket could be reduced from the 450kWh/m2 (2007) to below 300kWh/m2.  SINTEF said a supermarket adopting this concept would be established in 2013. 
 
Cold storage device effects on the performance and regulations of CO2 supermarket 
 
A research by Maurizio Orlandi from Epta Refrigeration showed that a cold storage device could reduce the energy consumption of a transcritical CO2 plant by providing optimisation logic for the plant controller. According to the research, cold storage can extract heat from the refrigerant leaving the gascooler/condenser during the day, and can be cooled by the refrigerant before entering the evaporator during the night. In addition, cold storage can be used to reduce the electrical energy peak consumption. With a cold storage device installed in a transcritical CO2 supermarket refrigeration plant, an average 5% daily electrical power consumption reduction and 28% of peak power reduction are possible based on a 24 hour time evaluation. 
 
Groundwater sink helps to extend R744 in hot climate  
 
A groundwater sink can be used to effectively extend the use of R744 in hot climates.  According to an analysis by Mazzola, Toffolo and Orlandi from Epta Refrigeration of a CO2 Medium Temperature (MT) plant for a supermarket application, the use of ground water as a cold sink could reduce peak energy consumption and allow sizing of the plant on a lower and quite constant energy target. What’s more, the possibility of avoiding the use of air gas coolers achieves a reduction in roof occupancy and noise levels during summer nights. 
 

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By Huiting Jia

Jul 06, 2012, 15:24




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