The Eco-2-System's CO₂ gas-to-liquid heat rejection phase differs from conventional R-22 systems. With R-22, the refrigerant vapour exits the compressor at 270 psig at the highest. This high-pressure superheated vapour enters a condenser, where it is cooled into a high-pressure liquid during the condensation process. Then, the high-pressure liquid goes through an expansion valve and exits as a low-pressure mixture of liquid and vapor. This mixture circulates through a heat exchanger in a primary loop that cools glycol or brine in a secondary loop to freeze the ice. The entire cycle occurs below the critical pressure, which means the refrigerant exists in both vapour and liquid states during the heat rejection process. This is called a "subcritical" refrigeration cycle.
However with the Eco-2-System, the gas remains in a vapour state throughout the entire heat rejection process. Because the vapour remains above the critical pressure point and, therefore, cannot phase change into a liquid during the heat rejection process, it is called a "transcritical" refrigeration cycle.
Simard uses the Danfoss ICMTS valve to regulate the flow of CO₂ in the system. "This valve is absolutely essential to the process," he emphasized. "Without it, the refrigeration cycle doesn't work, and there's no ice."
The Danfoss ICMTS valve enables the transcritical cycle by regulating the phase change from vapour into liquid. After entering a liquid state, the CO₂ is pumped through a network of 1/2-inch-diameter copper tubes embedded four inches apart in the rink’s concrete slab. Two inches of concrete was poured on top of the existing slab to hold the new piping. Copper tubes were used to contain the pressurized liquid. The tubes are wrapped in a very thin polyethylene film to prevent any possible interaction with the concrete.
"The entire rink works like a huge freezer," continued Simard. "A small pump circulates the liquid CO₂ through the tubes. The slab functions like an evaporator coil in a food freezer."
The CO₂ is constantly boiling in the tubes. Because boiling always occurs at a constant specific temperature, the temperature of the concrete slab stays a constant 19°F (-7°C). Thanks to the Eco-2-System, when the Zamboni machine resurfaces the ice, the water freezes immediately making the ice drier and smoother.
"Another benefit of the transcritical CO₂ cycle is that it yields a lot of heat that can be reclaimed to make lots of hot water," added Simard. "We use a Danfoss EKC 326a gas cooler control to keep the CO₂ vapour in the transcritical range. Then the vapour is discharged from the gas cooler at 212°F (100°C) into two heat reclaim units to create hot water for showers and space heaters."
Thanks to heat reclaim, last winter the arena did not require any backup heating for hot water, which reduced energy costs. The Eco-2-System's Coefficient of Performance (COP) is 3.35 (11.43 EER equivalent) when operating in continuous heat reclaim mode and 3.56 (12.1 EER) when the outdoor ambient temperature falls below 41°F (5°C). Compared to a 3.2 COP with leading systems that use a glycol/brine loop, the Eco-2-System reduces annual refrigeration costs by nearly 5 percent.
"When you combine all the energy and environmental benefits, this system is a real winner," notes Simard. "And thanks to Danfoss valves, we can expand this solution to ice rinks beyond Canada to the rest of North America."
Overview of the installation
- Installation of the Eco-2-System which uses a "transcritical" refrigeration cycle
- Installation of the ICMTS to regulate the flow of CO₂ in the system
