©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 3, March 2012.
By Luc Simard, Associate Member ASHRAE
About the Author
Luc Simard is a refrigeration engineer at Compressor Systems Control (CSC), Les Coteaux, Canada. He is a member of the ASHRAE Quebec chapter.
The Marcel Dutil Arena in the municipality of Saint-Gédéon-de-Beauce boasts the world’s first 100% CO2-based refrigeration system used in an ice rink. Saint-Gédéon-de-Beauce is in the Quebec province, about 20 miles north of the Maine border. The more than two-year-old ice rink was renovated in the summer of 2010. The existing R-22 chiller was removed, as well as the ice mat. The concrete slab was retrofitted to install the new system.
The 100% CO2-based refrigeration system for ice rinks that was developed in this project is a unique refrigeration system that uses the natural refrigerant R-744 (carbon dioxide) as primary and secondary working fluid (this system has Canadian patents with U.S. patents pending) (Figure 1). The R-744 is a natural, non-toxic, non-corrosive and highly efficient refrigerant. As opposed to the traditional solutions that use ammonia or Freon chillers, and glycol or brine as secondary fluids, this 100% CO2-based refrigeration system does not use any secondary fluid to cool the concrete slab.
In this case, carbon dioxide is pumped from a low pressure receiver directly into a tubing network installed in the concrete slab. In addition, since there is no secondary fluid, the evaporating temperature of CO2 can be set at 19°F (–7 °C) while keeping the ice sheet at 23°F (–5 °C). The result is an evaporating temperature higher than all other standard ice rink refrigeration systems. The tubing network is made of a specially designed plastic-coated soft copper tube.
The design recirculation ratio of liquid CO2 in the tubing network is 1.5. Since the phase change of liquid CO2 is not completed in the copper tubing network located in the concrete slab, no superheat is created. The tube network configuration (number of passes) does not affect ice quality because inlet and outlet temperatures of liquid CO2 are the same. So, the temperature of the concrete slab is the same over the entire surface.
By comparison, the nominal flow rate of a 90 ton (317 kW) ice rink chiller using 100% CO2 technology would be 30 gpm (1.9 L/s) compare to 500 to 600 gpm (32 L/s to 38 L/s) in secondary fluid applications. Pumping power is reduced up to 90% compared to traditional secondary fluid pump power.
The tube network configuration in the concrete slab is only limited by pressure drop. Fortunately, CO2 liquid viscosity is low even at a low temperature. For this reason, the increase in pressure of the circulating pump is small, and a design DP of 1 to 2 bar (100 kPa to 200 kPa) is common.
The tubing network is made with ½ in. OD plastic-coated copper tubing. The tube spacing is 4 in. (102 mm) center to center. The tubes are normally installed on the longest side (200 ft [61 m] for NHL size rinks) with a return bend installed at the end (two-pass configuration).
In this configuration, each pass has a length of approximately 400 ft. (122 m). The distribution manifolds are located on the shortest side. Insulated copper manifold are made with heavy wall 2 1/8 in. OD.
The Marcel Dutil Arena project retrofitted an existing ice mat, and the trench for the distribution manifolds was on the longest side of the rink.
For this reason, a four-pass tubing configuration with tubes installed on the shortest side was done. The distribution manifolds were installed in reversed return configuration with no balancing valves on the longest side of the rink. This is the first time this configuration has been used in a CO2 application.
Citation: ASHRAE Journal, vol. 54, no. 3, March 2012
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