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©2017 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 59, no. 8, August 2017

By Jörgen Rogstam, Member ASHRAE; Simon Bolteau; Cajus Grönqvist

About the Authors
Jörgen Rogstam is managing director, Simon Bolteau is project engineer, and Cajus Grönqvist is project engineer at EKA (Energi & Kylanalys) in Stockholm, Sweden.

Ice rinks use a considerable amount of energy, and Sweden boasts more than 350 indoor rinks for ice hockey alone. An average Swedish ice rink uses about 1 million kWh of electricity and heat combined each year, about 40% of which is from the refrigeration system. To reduce energy use, one municipality replaced its ice rink’s old indirect refrigeration system with a direct 100% CO2 system that is combined with a heat pump function. This article reviews the technology and how it reduced the ice rink’s energy use by 50% to 60%.

 

Updated F-Gas Regulation Requires New Solutions

One reason to consider CO2 as a refrigerant is updates to the European Union (EU) F-gas Regulation in 2015. To further control emissions from fluorinated greenhouse gases (F-gases), the EU updated the regulation in which refrigerants with high global warming potential (GWP) are to be gradually phased out and replaced by substances that fulfill the environmental requirements. A group of refrigerants highly affected by the F-gas Regulation are synthetic hydrofluorocarbons (HFCs), which have been very popular over the last decades. These refrigerants also have been used to some extent in ice rink refrigeration systems. This means many existing facilities will be facing renovations in the near future. New ice rinks should naturally apply the most energy-efficient technology available.

 

Using CO2 Systems in Ice Rinks

Ammonia-based refrigeration systems that meet the GWP requirements are well documented. Lately, however, attention has also been directed toward the application of natural refrigerant CO2 (R-744). As discussed by Rogstam, CO2-based technology is potentially well suited for ice rinks due to the combined refrigeration and heating demands of these facilities. The greatest source for lower energy consumption lies in the use of an optimized heat recovery system. CO2 has very good properties in terms of heat recovery.

Figure 1 shows the share of used available heat on the x-axis at corresponding temperatures on the y-axis. The comparison is made at an ammonia (NH3) condensing temperature of 35°C (95°F) and a CO2 head pressure of 80 bar (1160 psi). The temperatures of each refrigerant are at the compressor discharge level when starting from the left side, while getting cooled in the condenser/gas cooler as we move to the right. For example, when the refrigerant temperature is cooled to 35°C (95°F), only 19% of the available heat has been extracted in the ammonia (NH3) case, whereas the corresponding figure for CO2 is close to 60%, which implies that more heat is available at a higher temperature with CO2. This advantage allows the CO2 heat recovery system to cover all heating demands in a “normal” ice rink, reducing the cost of operation considerably, which coupled with lower service costs will yield long-term benefits for the owner.

CO2 was previously used solely as the secondary refrigerant in ice rinks, but CO2 today is also applied as the primary refrigerant. Systems using CO2 as the primary refrigerant in this article are referred to as second-generation ice rink CO2 systems. These systems can be applied in direct or indirect system solutions. "Direct" refers to if the CO2 is used in the refrigeration loop as well as circulated in the rink floor. In "indirect" systems the refrigerant is only used in the machine room, together with a secondary refrigerant such as calcium chloride, glycol, or today (more commonly) ammonium hydroxide in Europe.

CO2 was previously used solely as the secondary refrigerant in ice rinks, but CO2 today is also applied as the primary refrigerant. Systems using CO2 as the primary refrigerant in this article are referred to as second-generation ice rink CO2 systems. These systems can be applied in direct or indirect system solutions. "Direct" refers to if the CO2 is used in the refrigeration loop as well as circulated in the rink floor. In "indirect" systems the refrigerant is only used in the machine room, together with a secondary refrigerant such as calcium chloride, glycol, or today (more commonly) ammonium hydroxide in Europe.

 

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