Beyond F-Gases: Ammonia Combined With CO2
December 7, 2009
More and more projects are looking beyond F-gases for refrigerants. Among the options are ammonia (R-717) and CO2 (R-744).
Or - as in the case of a foodservice distribution center in Kitchener, Ontario - both.
Flanagan Foodservices Inc. completed a 65,000-square-foot expansion of the facility. Most of the expansion was a freezer that used technology new to Canada.
The expanded warehouse brought the total complex to 200,000 square feet. The expansion included 45,000 square feet of regular freezer space, 5,000 square feet of ice cream freezer space, a 10,000-square-foot cool dock and 5,000 square feet of refrigerated storage.
The pre-expansion facility relied on F-gases to provide 163 tons of refrigeration and maintain temperatures as low as 4°F in the regular freezer and –20° in the ice cream freezer.
“As we considered a system that would serve the new, larger facility, the low initial first cost of an F-gas system certainly appealed to us,” said Rick Flanagan, executive vice president at the company. But he said concern was raised about environmental issues such as ozone-depletion and global warming potential, especially should such refrigerants leak.
So the search was on for an alternative refrigeration system that could provide as much as 200 tons of refrigeration efficiently, environmental acceptability, and affordably. An ammonia-based system offered the efficiency the company sought. But Flanagan said he was concerned about the risk of a leak or an accident.
That caused the company to turn to what Flanagan said was “an exciting new technology that represents the best of both worlds.” It was a dual-temperature ammonia/CO2 brine packaged system supplied by Mycom Canada.
The system uses two large, insulated compressors that are isolated in an enclosed space. The compressors cool the CO2, which is then pumped into the areas of the building that require refrigeration, thus reducing the ammonia charge the warehouse holds.
“As a result,” said Len Puhacz, manager of green technologies for Mycom Canada, “Flanagan enjoys the cost benefit derived from the efficiency of ammonia and feels comfortable knowing they are pumping CO2 and not ammonia into the buildings.”
CODE CONSIDERATIONSBefore the Canadian B52 code was amended (even prior to the system design and commissioning), it allowed CO2 as long as the system was designed to ambient condensing pressure of 1,100 psig, which is not practical in industrial refrigeration, according to Puhacz. Engineers at Mycom’s parent company Mayekawa designed a system that could safely operate at a maximum of 600 psig that satisfied Canadian authorities.
Also critical to the success of the system was a valve station that feeds CO2 to the evaporators, flooded shell and the tube ammonia/CO2 exchangers. The project used the ICF valve station from Danfoss, which provided ports for up to six function device modules that are configured specifically for a customer’s application. The valve station also had a design working pressure of 754 psig, making it suitable for use with high-pressure refrigerants like CO2.
Danfoss also supplied variable-frequency drives and pressure transmitters to run the ammonia assembly.
Concerning the project, Flannagan said, “We are looking at a payback for this system of about 6.6 years, thanks to the energy savings it offers. And it is an environmentally friendly system that will reduce our carbon footprint and eliminate safety risk to our employees and the products we warehouse.”
For more information, visit www.danfoss.com.
Publication date: 12/07/2009