In Alaska, where ice-skating is a favourite pastime, the municipality of Anchorage operates four public ice rinks. By next year all four will use a natural refrigerant (CO2) in a transcritical system to keep the ice frozen – the first in the US to do so.

John Rodda, director of the Parks and Recreation Department, said he launched a thorough assessment of the Department’s options in 2013 before opting to go with a transcritical CO2 system to replace the R22 cooling systems. The on-going phase out of R22 as a refrigerant under the Montreal Protocol — the global agreement calling for a reduction in the use of ozone-depleting chemicals— along with the ageing of the facilities, prompted Rodda to replace all of the existing R22 systems.

Rodda said Anchorage considered a variety of options, including ammonia-based cooling systems, indirect systems and industrial direct systems, before settling on the Advansor Transcritical Direct CO2 System from Hillphoenix. He said he decided against an ammonia system because there would be some additional costs involved for added safety and isolation requirements.

High efficiency

The system chosen by Anchorage will deliver high efficiency, said Tim Henderson, industrial programme manager, Hillphoenix. The ability to capture as much of the excess heat as possible generated by the cooling system factored into the decision to go with direct CO2, Rodda explained. The heat will be deployed for other purposes in the facility, thus lowering overall energy consumption.

The excess heat can be used for a variety of purposes in the facilities, Rodda explained, including for locker rooms, floor heating, and hot water. In addition, Anchorage is located in a northern climate favourable to the efficient operation of CO2 transcritical technology.

Larger charge

The CO2 system used at the Ben Boeke Arena will be similar to the ones at the other two installations, although the Ben Boeke installation will include a larger CO2 charge because the system will be used to cool two ice sheets rather than one (which will also be the case for the Dempsey-Anderson Arena next year).

The systems at the first two installations required CO2 charges of 4,500 lbs. at the McDonald Center and 5,000 lbs. at the Sullivan Arena, which
is a slightly larger facility. The new system at the Ben Boeke Arena will likely require a charge of about 9,000-10,000 lbs., Rodda estimated. Although each of the two ice sheets is slightly smaller than the individual sheets at the first two facilities, the overall surface area of the ice is larger at Ben Boeke.

The system will give the Ben Boeke arena managers the ability to set the temperatures independently for each of the two ice sheets — hockey calls for harder ice than figure skating, for example — or to shut one of the ice sheets down during the summer for other activities, such as basketball.

Another consideration in using CO2 systems is that the higher pressure can create perceived challenges for technicians more familiar with low-pressure systems, but Rodda said that this had not been an issue. He said Hillphoenix sent a team of people to train the technicians in Anchorage on how to work with the high-pressure systems, which are also much more computerised than the previous R22 systems.

The closed-loop system works by pumping liquid CO2 under the ice first to freeze it, then to remove residual heat. When the liquid CO2 along with some vapour comes back, it goes into a separator vessel, where the gas is sent to the compressor to be liquefied before being pumped back under the ice again. The vapour also goes through an oil separation system to remove any oil. Some of the heated vapour, as well as the heat removed from the ice, goes through a heat reclamation system to be used elsewhere in the arena, or rejected to the atmosphere.

Rodda said the system has been well received by customers who have skated on it at the McDonald and Sullivan facilities.

This is a shorter version of an article published in Issue 15 of Accelerate America. To read the full version, please click here.

Author r744