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Preventing future refrigerant conversions with low charge ammonia retail solutions

14 June 2012

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Powerful arguments for investing in ammonia refrigeration systems in the retail sector were presented in innovative projects that demonstrate good efficiency savings, and high levels of safety, at ATMOsphere America 2012. This unique event taking place on 12-13 June in Washington DC, is dedicated to innovations in natural refrigerant technologies specific for the North American market. 
In this first article, ammonia21.com outlines the key features of the technology case studies deploying ammonia working fluid presented by CTA Architects Engineers and retailer SUPERVALU.
 
Mr Rob Arthur, Ammonia/CO2 Cascade Refrigeration System at a Defense Commissary Agency Project
 
The aim of the project presented by Mr Arthur was to find a system that would be more energy efficient and more environmentally friendly than the standard grocery store refrigeration system, a four-rack 404A system, and to find a system that could be repeated in any location in the US. From the currently available low GWP options, an ammonia/CO2 cascade refrigeration system was selected for the following reasons:
 
  • Energy consumption: expected 8% energy savings on the project, countries with more experience claim around 25% energy savings;
  • Climate: in the Southern United States this type of system is currently more suitable than a CO2 only system;
  • Environmental concerns: on average a standard refrigeration system in a grocery store has a 25% leak rate, leaking 1000 lbs of refrigerant;
  • State and National Codes and Regulations: compliance with energy code requirements, State, National Codes, EPA rulings, and avoiding future penalties for HFC leaks, possible taxes on HFCs or HFC refrigerant charge limits;
  • Preventing the need for future refrigerant conversions.

The NH3/CO2 system consists of a low temperature direct expansion CO2 system and a medium temperature pumped CO2 secondary system, and NH3 chiller modules. The individual ammonia module systems have less than 10 lbs of ammonia and are separated from each other, to make them safe for highly populated areas. 
 
“We had to show why our project was not a safety concern… if we had a typical leak we would detect it with our leak detection system, but even in the worst possible weather conditions, which would be a foggy day, it would dissipate and there would be no health impact,” said Mr Rob Arthur
 
Over a 20-year life cycle there is an 8% premium, which equates to about $340,000, for this project, but it is projected that the system will be cheaper to maintain and run.
 
Mr Richard Heath, Mr Jim Armer, SUPERVALU’s Development of Next Generation Refrigeration Systems: Application of Ammonia, CO2, and Propane
 
SUPERVALU has developed a “Next Generation refrigeration System” in an Albertsons supermarket that will be opened in the summer of 2012 in Carpinteria, California. The store, which was open throughout the remodel, will feature several natural refrigerant systems:
 
  • Ammonia primary system with 250 lbs of ammonia located in an outdoor enclosure that will condense CO2;
  • A water cooled system that allows for a reduction in refrigerant charge;
  • “Combined” CO2 refrigeration system with one vessel that contains liquid pumped to the low and medium temperature display cases and walk-in cabinets;
  • R290 spot display case.

According to Jim Armer, P.E. CTA Architects Engineers, Refrigeration Group Manager, the natural refrigerant solution will allow SUPERVALU “to prepare for the future, for any refrigerant modifications that could be required in the US.” 
 
Both a 100% natural refrigerant option - a cascade NH3 and CO2, and a 90% natural refrigerant option – an R407A primary and cascade CO2 system, will be compared over the course of a year.  It is anticipated that there will be:
 
  • 29% TEWI reduction for the NH3/CO2 system compared to the R407A/CO2 system;
  • 15% compressor saving for the NH3/CO2 system compared to the R407A/CO2 system;
  • 18% first cost increase for the NH3/CO2 system compared to the R407A/CO2 system;
  • 35% life cycle cost increase for the NH3/CO2 system compared to the R407A/CO2 system.

Overall the TEWI reduction compared to an R407A DX will be 77% for the R407A/CO2 systems and 84% for the NH3/CO2 cascade system.



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