Oskarström is a small town with a big ice rink – not only for families and would-be figure skating champions. The gigantic ice surface is used for playing bandy, a form of hockey and an ever-popular sport in Sweden.
Based on the total number of active players, bandy is one of the world's most popular winter sports – second only to ice hockey. Its appeal can be compared to the love of soccer in Germany. Bandy is played with passion everywhere in Sweden. The tiny municipality of Oskarström (pop. 4071) is no exception. Eleven bandy teams, each with eleven members, plus numerous families and other private skaters account for a major part of the town's population. Skates and helmets can be borrowed free of charge – which makes the ice rink even more attractive for school groups and other organizations. So when the time came to replace the ice rink's old refrigeration system with a new one, the decision-makers at Strömvallen – the ice rink operator – needed to think about a number of things.
Twice the size
System capacity was one of the main reasons the operators wanted to update the refrigeration system. The ice surface in Oskarström measures 60×115 meters – more than twice the size of a standard hockey rink. That's a lot of ice! The old system installed more than 15 years ago was no longer capable of handling the refrigeration required for such a large ice surface. Reliability of the vertical screw compressors had become a problem. Efficiency was another important aspect. In view of increasing energy costs, the new system would have to be more economical and easier to maintain.
With an average 300 skaters per day, the operators wanted to make sure the ice rink was available as often as possible – in all weather conditions. Open from November to February, the ice surface must be maintained at a steady -5 to -1 °C for months at a time.
Time-saving, convenient installation was another part of the project matrix. GEA uses the phrase "Plug & Play" to characterize the ease of implementing the package into the refrigeration plant. What it boils down to is an ingeniously engineered screw compressor unit, individually designed for specific project requirements by people with extensive industry expertise.
Redefining the total cost of ownership
Last, but certainly not least, was the question of cost – not just the price tag on the installation itself. The ice rink owners needed to think about the long-term expenditures of operating the system over, let's say, the next 20 or 30 years. GEA Grasso M packages redefine the total cost of ownership by lowering total expenses up to 20%. This made it much easier for the ice rink operators to arrive at a viable solution.
In cooperation with Strömvallen, Swedish contractor Francks Kylindustri configured a new system using two GEA Grasso M compressor packages to replace the old four-compressor units. Some 40,000 meters of new 25 mm diameter pipelines were placed at a distance of 80 mm from each other on a bed of gravel over an insulating layer. After the surface is gradually flooded with water, it takes about a week to completely freeze over. A white dye is used in the ice to reflect sunlight and reduce melting.
The bright blue GEA Grasso M screw compressor packages installed at the Strömvallen ice rink generate a total cooling capacity of 1490 kW – 20% more than the old system. The machinery footprint is significantly smaller with two instead of four units in place. High-speed motors with frequency inverters operating from 1000 rpm up to 4500 rpm improve part load efficiency.
How it works
The system is made up of two circuits. One is filled with ammonia, the other with calcium chloride. In the ammonia cycle, the GEA Grasso M system compresses the evaporated cold gas to a high temperature and pressure level. It is then condensed in the new cooling tower installed outside the machine room and turns into a liquid state at 30.0 °C. Through an expansion device, the liquefied ammonia is released to the lower pressure level of the evaporator. Here the ammonia evaporates and takes the necessary heat energy from the secondary refrigerant (calcium chloride) before it is once more sucked into the M compressors. In the second circuit, the calcium chloride brine streaming through the evaporator is cooled down to a supply temperature of -12 °C. Distributed by four pumps through 40 km of pipelines, this low temperature brine is used to freeze the water and maintain the ice surface. The brine returns to the evaporator in the machine room at a temperature of -9 °C.
Eco-friendly and efficient
The use of ammonia (R717) as a natural refrigerant is highly efficient. Thanks to its physical properties, this colorless gas is very energy-efficient. Used in the refrigeration processes, ammonia does not contribute to global warming (GWP = 0) or harm the ozone layer (ODP = 0).
Daily operation of the Strömvallen ice rink is easy-as-pie with the GEA Omni™ control panel and 15.6" HD display. Remote access via GEA OmniLink™ makes maintenance and servicing a snap and GEA OmniHistorian™ captures a complete data history.
Innovative technology is the key to mastering modern refrigeration challenges. This is impressively demonstrated by the GEA Grasso M screw compressor packages. By modernizing their refrigeration system, the ice rink operators were able to increase cooling capacity, maximize efficiency with lower energy consumption, and reduce the total cost of ownership.
Technical features of the cooling system
- Cooling capacity: 2 × 745 kW
- Motor speed with frequency inverter: up to 4500 rpm
- Secondary refrigerant: calcium chloride
- Secondary refrigerant temperature in/out: -9/-12 °C
- Refrigerant: Ammonia (R717)
- Evaporation temperature: -14.5 °C
- Condensation temperature: 30.0 °C