Dutch and Canadian NH3/CO2 facilities keep cool with Danfoss controls

By Sabine Lobnig, Nov 30, 2010, 10:13 3 minute reading

The use of pumped CO2 in industrial ammonia refrigeration systems instead of water based brine offers significant energy savings. Danfoss valves and controls for both ammonia and CO2 in secondary cooling and cascade applications helps to provide outstanding results in temperature control and energy efficiency in food storage and distribution facilities in the Netherlands and Canada. 

A typical low/medium temperature NH3/CO2 system consists of a standard NH3 refrigeration system with a cascade heat exchanger acting as evaporator. CO2 acts as an evaporating fluid in the evaporators. CO2 is circulated by gravity in the cascade heat exchanger, which gives good control of the CO2 temperature in the receiver. The CO2 gas flows up into the cascade heat exchanger, where it is cooled by NH3, condenses and flows back down into the CO2 receiver as liquid CO2. On the ammonia side the refrigeration cycle can be controlled using a high pressure float valve or by direct expansion into the evaporator.

NH3/CO2 fluid systems have significantly lower energy consumption compared to traditional systems with NH3 and water based brines. The Coefficient of Performance (COP) of the system is higher due to the increased evaporation temperature and PHE (plate heat exchanger) efficiency, as well as significant less pump energy needed to circulate the CO2 through the air coolers. Further reduction of energy consumption with NH3/CO2 systems is possible using smart control algorithms to reduce the pressure ratio in the NH3 compressor.

Experience with a NH3/CO2 fluid system in the Netherlands

A NH3/CO2 fluid solution was commissioned in 2007 for a sophisticated high-rise fruit distribution centre near the port of Rotterdam, in the Netherlands. The building is 20 meters high and can store 12,500 pallets, spread over 15 individually-controlled temperature compartments.

The facility makes use of fully automated cranes and conveyor systems for internal transport purposes. The main advantage of this automated storage system is that the logistics process operates more efficiently and reliably and because the refrigerated cells are always kept closed, the refrigeration of the cells is extremely efficient, enhancing the shelf life and quality of the products being stored.

The unique design for this NH3/CO2 pump system was employed by Dutch contractor Cofely. With air defrosting not being an option as the temperature of the different zones can be adjusted to below zero °C, a small CO2 compressor generating hot gas for defrosting was employed. It implied a maximum working pressure of 52 bar. Danfoss technology and support resulted in the application of ICF assemblies for all hundred evaporators, altogether providing 3,000 kW refrigeration capacity (NH3 at -13°C and CO2 at -8°C).

Experience with a NH3/CO2 fluid system in Canada

To keep up with growing demand, a new 6,000 square metres expansion was sought by Flanagan Foodservice, a leading distribution service company located in Kitchener, Ontario, Canada.

The facility was the first in Canada to implement a dual temperature ammonia/CO2 fluid refrigeration package system supplied by Mayekawa Canada and which refrigerates the 360 kW at -15°C of 4,200 m2 of freezer space and 120 kW at -28°C of 450 m2 of Ice Cream freezer.

Danfoss supplied the facility with its ICF valve station, a single product platform operating for both natural refrigerants in use at Flanagans. ICF feeds CO2 to the evaporators, flooded shell and tube NH3/CO2 exchangers. Danfoss supplied as well variable frequency drives and pressure transmitters, which run and control the NH3 screw compressors and CO2 pumps. Moreover, the use of ICM motorized valves in the ICF assembly played a key role in maintaining a stable liquid supply. 

Please visit the Danfoss website for more information and downloads at: http://www.danfoss.com/BusinessAreas/RefrigerationAndAirConditioning/Refrigerants/PumpedCO2Solution.htm


By Sabine Lobnig

Nov 30, 2010, 10:13

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