Temperature independent snow production – what exists today?

The goal with this research project – mapping what exist today and how this can be improved – was to create a base for further work on energy efficient and environmentally friendly snow production. The reliability of natural snow, and the number of days it is possible to produce snow with traditional snow production equipment is decreasing due to the warmer climate. This results in increased use of temperature independent snow production equipment, and making this equipment more efficient is important for reducing the energy consumption.

Temperature dependent snow production

About 90% of all ski resorts produce artificial snow, and many resorts rely solely on artificial snow for parts of the winter season. Traditional temperature dependent snow production is based on nozzles spraying water droplets that freeze in the cold air.  This method requires temperatures of -2 °C or colder.  The lower the temperature is, the more efficient the production equipment is.  Artificial snow produced in this way has a density about four times higher than natural snow, which make it more durable.

Temperature independent snow production

Several ski resorts around the World have already installed temperature independent snow production equipment. This snow is produced by creating small ice particles/grains, and can be done in several ways. Flake ice, plate ice, scraped ice-slurry and vacuum ice are some of the methods, with flake ice being the most common.

Flake ice: Flake ice is produced by applying water to the surface of a cooled drum or tube.  The ice is normally removed by scaping, and will fall down as dry sub-cooled flakes.  The flake ice machines typically operate with temperatures at -20 to -25 °C, which is lower than the other methods. This makes the method more energy demanding, but gives a high yield.

Plate ice: In plate ice machines a water film runs across cooled vertical plates and freezes on the plate surface.  The temperature inside the plates is normally at -7 to -21 °C.  The ice is removed by warming up the plates in a defrosting cycle, such that the ice plates fall into a crusher. Plate ice machines normally have higher energy efficiency than flake ice machines due to the higher temperature on the cold side.

Scraped ice-slurry: This is today the most used method for producing ice-slurry (a mix of small ice particles and cold water).  The process consists of water being cooled down or frozen on a surface, then scraped off with a rod or similar.  This creates a slurry, that can be separated further to wet snow. By using salt, it is possible to make this into a consistency close to dry snow.  The energy efficiency with this method is better than both plate ice and flake ice, since the operating temperatures are close to 0 °C.

Vacuum-ice: This is the most effective method of producing ice-slurry.  The technique consists of lowering the pressure inside a chamber such that the water freezes and ice-slurry is created.  These systems can be made in a large size, and are more energy efficient than the other methods mentioned above.  It is also possible to operate these systems using heat, such that for example excess municipal heat or heat from other industry can be used.

Potential improvements

Cooling systems are normally measured by their COP (coefficient of performance) which is a ratio of useful cooling provided to work (energy) required. Higher COPs equate to higher efficiency, lower energy (power) consumption and thus lower operating costs.  Carnot-COP says something about how much an ideal machine can deliver, and approximately 50% of Carnot-COP is normally achievable.  In the figure below, different existing temperature independent systems are drawn in a diagram with 50% Carnot-COP shown as a line.  The distance from the different systems to the line illustrates the potential improvements.  The figure shows that the energy efficiency of all the systems can be significantly improved.

Figure 1: COP vs. condenser temperature for the different snowmakers. Ice production technology is stated and capacity in m3/24 hrs as well as the condenser temperature/temperature lift is given inside the parenthesis (capacity m3/24 hrs – condenser temperature/temperature lift ℃)

Conclusion

Temperature independent snow production is a possible method for securing snow in above freezing temperatures.  Today’s systems require lots of electricity, and are therefore expensive to operate.  As an example, a temperature independent system will use approximately 22.8 kWh per m3 produced snow, while temperature dependent snow lances use approximately 1,42 kWh per m3.  The research project also showed that there are large differences between the different systems, and that they all can be significantly improved.

This research is part of the project “Snow for the future”. The research report was published in 2017. Author and contact person is Stian Trædal (stian.tradal@sintef.no)

Framework for evaluating snow production technologies

This research work is presenting an estimation of the total environmental foot print for temperature independent and temperature dependent (snow lances/snow fans) technologies.  The model is a further development of an Excel-based model used for general planning of snow production.  The method for calculation includes greenhouse gas emission from consumption of electricity and heat, leaks from refrigerants, production of materials and transport of snow, as well as reduction of emission through export of excess heat.

The model is demonstrated through calculation of examples from the Granåsen ski arena in Trondheim, Norway (the venue for the 2025 Nordic World Skiing Championship), and will be further used to evaluate different snow production methods and their environmental impact, specifically greenhouse gas emissions.

Theme

The calculation of the total environmental impact for a specific snow production technology includes (in this project) five contributions as shown in the figure: 1) CO2 intensity to consumed electricity, 2) CO2 intensity to consumed heat, 3) leaks of refrigerants, 4) Production of materials, and 5) transportation of snow

The calculations are based on the CO2 intensity for the electricity mix for the mid-Norway region, the consumption of electricity for temperature dependent snow production (traditional snow making), calculation of daily CO2 emission from electricity consumption for both temperature independent and temperature dependent snow production, in addition to calculations of emission related to transportation in cases of off-site snow production.

The developed model and its possibilities have been demonstrated through examples from the Granåsen ski venue.  Five different scenarios, one being today’s situation, and where low, normal and high CO2 intensity for electricity was given as input to the different scenarios.   

Conclusion

The results show that by exporting excess heat from snow production to a local external user or by using excess heat for heat-driven snow production at an external location, the CO2 emission will be reduced compared with normal operations at the venue.

This research is part of the project “Snow for the future”. The research report was published in 2020. Author is Vidar Torarin Skjervold. Contact person is Ole Marius Moen (ole.moen@sintef.no)