When nature doesn't cooperate by providing natural snow, snowmakers take over. Given water, electric or diesel energy, and temperatures below 32°F (0°C) snowmakers can provide snow.
Basically, snow is small particles of ice. So, the really old way of making snow, and the way they still do in the tropics and for special events, is to grind up blocks of ice. However, this is very expensive and labor intensive for larger scale requirements, so, if possible, machines that convert water into snow directly and on site are used.
These snowmaking machines make snow by breaking water into small particles, cooling the water by causing them to move through cold air, nucleating the water particles and distributing the resulting snow on a surface. Why don't people just sprinkle water to make snow? Water is a unique material, it expands when it freezes and it has high heat of fusion, thus your ice cubes float and last a long time. Heat of fusion means that one can cool a pound of water say from 65°F (18.3°C) to 64°F (17.8°C) or 34°F (1.1°C) to 33°F (.6°C) by removing 1 BTU. But to convert one pound of liquid water at 32°F (0°C) from a liquid to one pound of ice at 32°F (0°C) requires the removal of 144 BTUs. In summary, a large amount of heat removal (cooling) is required in snowmaking. Also, water can be cooled well below 32°F (0°C) and still stay a liquid unless it is nucleated. This phenomenon is called supercooling.
So a snowmaking machine (a) breaks the water into small particles, (b) cools the water to 32°F (0°C), (c) removes the heat of fusion, and (d) nucleates. Snowmaking requires relatively large quantities of water, for example, to cover an area of 200 feet (61 meters) by 200 feet (61 meters) with 6 inches (15 centimeters) of snow, one would need 20,000 cubic feet (566 cubic meters) of snow or 1,000 cubic feet (283 cubic meters) of water. This is 82,000 gallons (310,000 liters) of water or 11 truck tankers full. Thus, an excellent water supply is needed and the water pressure should be at least 100 PSI (pounds per square inch) (7 Bar) or 230 feet TDH (total dynamic head).
Many ski areas can convert over 5,000 gallons (18,900 liters) per minute of water into snow. This is 20 tons per minute or 1,250 tons per hour. Or stated another way, a truckload every minute. Snowmaking, while usually used at ski areas, is also used for frost protection on construction projects, freeze protection of crops, automotive and aircraft testing, and sewage disposal. There are over thirty snowmaking companies around the world. SMI® is one of the largest companies dedicated primarily to snowmaking.
Ever wonder why a fresh snowfall seems so peaceful? One reason is that freshly fallen snow muffles sound. Air pockets get trapped between flakes as they land, and the air pockets help absorb sound.
Snowflakes form in much the same way raindrops form. Water vapor freezes onto microscopic bits of dust, salt or other nuclei creating tiny ice crystals. Winds throw the crystals up and down in the clouds, causing them to merge with others or grow with the help of super cooled water droplets.
Not all cold places have lots of snow. Air that is too cold contains little or no moisture and snowflakes cannot form. Snowflakes are much more common in the northern United States than at the North Pole!
A blizzard is the most dangerous type of snowfall. Winds must be at 35 miles per hour (56 kph) at temperatures below 20°F (-7°C). These conditions cause the snow to whip around and significantly lower visibility.
Due to gravity, our atmosphere has weight. About a ton of air is pressing down on you all the time, but you don’t feel it. That’s because the same air pressure surrounds and supports you. Air pressure is measured with a barometer. When air is cold and dry, it weighs more (high pressure), so the barometer is higher in fair weather. When air is wet, it actually weighs less (low pressure), so the barometer is lower when it is raining. Changing barometric readings indicate a change in weather. A falling barometer indicates a change in weather. A falling barometer indicates precipitation is rising. A rising barometer means clear skies are on the way. In snowmaking, generally a clear cold night creates the best conditions for optimal production on high pressure nights.
The temperature air would have to be cooled in order for saturation to occur. The dew point temperature assumes there is no change in air pressure or moisture content of the air.
Wet bulb temperature
The lowest temperature that can be obtained by evaporating water into the air at constant pressure. The name comes from the technique of putting a wet cloth over the bulb of a mercury thermometer and then blowing air over the cloth until the water evaporates. Since evaporation takes up heat, the thermometer will cool to a lower temperature than a thermometer with dry bulb at the same place and time. Wet bulb temperatures can be used along with the dry bulb temperature to calculate dew point or relative humidity.
Our industry prefers to use the term “machine made snow” when describing the snow produced as it is actual snow. We do not like to use the term “artificial snow” as it is not fake or imitation snow. The product produced uses mainly water and some compressed air to help freeze water droplets into snow. Machine made snow typically has no dendrite arms due to the short hang time and is more like small aggregate material.
Snow is typically produced in piles and stored in piles to allow the water droplets time to thoroughly freeze. Some snow is only frozen like an egg shell and it takes time to freeze 100% the total droplet. So most resorts prefer to leave snow in piles for 8 to 10 hours before pushing them out.
However, snow can also be produced that is very dry and totally frozen within seconds of leaving the snowgun. So snow can be made that is skied on during production.
There are generally two primary snowmaking snowgun technologies commercially purchased today – fan and stick/lance. The concept of using nucleation to help freeze the majority water spray still applies to both technologies.
Fan snowguns use propeller driven ducted fans to help throw the snow and provide hang time for mixing and freezing. Fans are known for long snow projection and throw, high capacity in all weather conditions, low wind sensitivity and overall performance. Fans can be portable or fixed position on towers and swing arms. Stick/lance snowguns are generally tower mounted with either 6 meter or 9 meter mast heights. This extra height allows some hang time via gravity. These snowguns have limited throw and are very sensitive to the wind.
Both technologies are popular today. The fans are more popular in area with marginal weather conditions and wider slopes. The sticks are more common in colder climates with narrow slopes. Both types are offered with manual and automatic control options.
SmartSnow is a software and controls package that operates and acts as the brain for a snowmaking system. Input variables like weather, water temperature, snow quality, water pressure help determine the snowgun adjustment to achieve the desired snow quality selected. The entire system can be operated via computer, tablet or smartphone.
SmartSnow has been in development for over 20 years and provides excellent energy and resource management along with provided resorts with comparative data.
Wet bulb condition factors on both ambient temperature and relative humidity to help define the coldest condition a water droplet can obtain. It is related to the temperature reading on a thermometer when its mercury bulb is moistened. This reading is typically colder than the actual dry temperature. So humidity plays a great role in droplet freezing along with the temperature. The colder and drier the conditions, the more effective snowmaking becomes.