We couldn’t have the Beijing Olympics without snow machines. But at what cost ?

sydney: Snow machines have harnessed the laws of thermodynamics to paint the slopes of Beijing white for this year’s Winter Olympics.

Beijing may seem like a strange place for winter games. The city receives almost no annual snowfall and has an average temperature of just below 0 degrees Celsius even during the winter month of February.

Chinese authorities have used more than 350 snow cannons to prepare the courses for athletes around the world. This practice has become more common in recent Winter Olympics, with the Sochi and Pyeongchang games relying on 80% and 98% artificial snow respectively.

But isn’t all that artificial snow terribly expensive? If you own an air conditioner and keep half an eye on your energy bill, you expect snowmaking to be extremely energy-intensive. The uninitiated might think of snow machines as giant freezers with fans attached, consuming cities’ electricity to chill entire mountainsides.

That’s not really the case. Efficient machines in suitable climates (like Beijing’s) can use as little as 1.5 kilowatt hours per cubic meter of snow produced. In Beijing’s climate, you could cover a Sydney apartment with a few centimeters of snow with the same energy that air conditioning would use in an hour.

But that does not mean that there is no environmental cost. More on that later.

How do snowmobiles work?

Artificial snow is not a chemical trick. The slopes of this year’s event are covered in pure frozen water.

Basically, snow machines work using a clever thermodynamic feat, taking advantage of the natural cooling that occurs as water evaporates. And because their cooling power comes from evaporation, they can operate in relatively warm temperatures, down to 1 degree Celsius (provided the humidity is low enough).

Here’s how it works. The snow machines expel a fine mist of water into the cold, dry atmosphere. Some of the water in each droplet evaporates quickly, carrying away the heat and lowering the temperature of the rest of the droplet below its freezing point. This process is known as evaporative cooling and is the same mechanism that cools us down when we sweat.

Since the loss of energy needed to form ice in this process is due to evaporation, snow machines do not have to expend energy to freeze water. They only need energy to power the fans and compressors that disperse the water droplets.

However, as any Winter Olympian will tell you, snow is more than frozen water. And snowmobiles must produce powder coverage worthy of the greatest athletes in the world.

They achieve this by using a nucleator, which is basically any substance that facilitates the formation of an ice crystal. Without it, the droplets in the fog would end up as supercooled water and clump together into large droplets before freezing. This would create undesirably dense, icy snow.

Nucleators can be chemical or biological, but in Beijing no such aid is used. Instead, tiny ice crystals are used as nucleators. These nucleating ice crystals themselves are formed by even more thermodynamic manipulation, in which pressurized water is forced through a nozzle, rapidly reducing the pressure and breaking it into tiny droplets.

When the pressure of a gas drops rapidly, its temperature also drops, which is why deodorant from a pressurized spray can feel cold. In this case, the sudden drop in temperature cools the atomized water well below 0 degrees Celsius, rapidly freezing it into the ice crystals of the nucleator.

In the final stage of the snowmaking process, these ice crystals mix with the water mist and are propelled into the air, causing the water to freeze and fall as artificial snow. Propulsion is achieved either by the use of compressed air, in the case of snow lances, or by blower-type machines with large fans.

The snow that forms in this process is not quite the same as real snow, as artificial snow forms quickly from liquid droplets, instead of slowly forming from water vapour. Therefore, the shape of artificial snow particles is different from that of natural snow. The former has no nice monocrystalline structures, only tiny (polycrystalline) snowballs.

The issue of sustainability

As our climate warms and weather conditions change, we are becoming increasingly dependent on artificial snow to meet the demands of vacationers and sports enthusiasts.

These Winter Olympics are the first to rely 100% on fake snow. And although artificial snowmaking is not as catastrophic for the environment as it seems at first glance, it is not without its drawbacks.

First, artificial snow is made up of water, which is undeniably an essential resource. The International Olympic Committee (IOC) sustainability report for this year’s games estimates that the city of Zhangjiakou, the epicenter of the Beijing Games, will use 730,000 m of surface water for snowmaking alone (nearly 300 Olympic size swimming pools).

The amount of water used throughout the Beijing area will be much greater (although there will be significant efforts to recover snowmelt and avoid using excessive amounts of potable water to make snow) .

Second, in warmer climates, chemical additives are needed to help snow form and stay frozen. And although these are not actively toxic, there are still doubts about their safety.

Finally, snow cannons produce a lot of snow. Early Chinese media reports claimed that only 200,000 m of water would be needed to make snow. But the IOC’s pre-match report says that figure is over 800,000m.

Depending on the figure used, the density of snow created and the amount of water lost through evaporation, the total amount of snow produced can vary from 0.5 to 3 million cubic meters. So, although the machines produce snow efficiently, the total energy consumption is still high.

According to the IOC, in Beijing, this demand for electricity is met by 100% sustainable production. This is encouraging and will hopefully help accelerate the global adoption of environmentally friendly technologies. (The conversation)

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