Analyze Your Snowmaking Equipment

In general, the first question anyone asks about snowmaking is, “How much does it cost?” It is impossible to answer this question specifically, or even approximately. Capital investment will depend on the features of the specific ski area:

1. Area to be covered.
2. Depth of snow required.
3. Availability and location of water and electrical power.
4. Technical characteristics of the guns.
5. Climatological conditions at the area.
6. Possibility of future expansion.

All these factors must be established as accurately as possible, and then each one must be interrelated with all the others so they can be correlated technically and economically into a practical and efficient system. Of course, the problems with any system increase directly with the size of the system.

Compressed Air

One of the most important components, and certainly the most expensive, in any snowmaking system is the air compressor. It is essential that an adequate supply of clean, dry air be available at all times. How much air is required will depend on several variables:

1. Area to be covered.
2. Depth of snow required.
3. Time in which the snow is required.
4. Efficiency of the gun.
5. Climatological conditions.

Because the air system is the most expensive component in the investment, air capacity must be minimized without reducing overall effectiveness of the system.

Consider the effect that each of these variables has on the air requirement:

1. The effect of the area to be covered is obvious. An increase in area will require an increase in air capacity, in direct proportion.

2. Snow depth is also directly proportional to the air required. Generally these two variables, area and depth, are combined to determine the volume of snow required. For example, if one foot of snow is required over one acre of land, these two are combined in a unit known as one acre-foot. On the other hand, if six inches of snow are required over four acres, these two are combined to yield two acre-feet.

3. The time required to produce the volume of snow is inversely proportional to the air requirement. For example, if 50 acre-feet of snow could be made in 36 hours with 2400 c.f.m. of compressed air, it is conceivable only 1800 c.f.m. would be needed to manufacture this snow in 50 hours.

4. & 5. Efficiency of the gun must be considered in conjunction with the climatological conditions. However, this relationship between gun efficiency/climatological conditions and the air capacity is hard to define. Each gun has a different relationship, expressed as an efficiency constant, and this constant has a directly proportional relationship to air capacity. All these variables can be correlated in a mathematical relationship to estimate air capacity.

Air capacity (c.f.m.) =
Volume (acre-ft.) ×
Efficiency Constant
Time (hours)

This relationship establishes how many c.f.m. of air are required to produce any given amount of snow in acre-feet per hour.

Other aspects of the air system that should not be overlooked relative to overall cost are:

1. Aftercoolers: It is generally good design to provide aftercooling, regardless of the nature of the compressed air generation. The aftercooler will not only cool the air, but remove moisture from the air before it enters the piping system.
2. Moisture separators: In conjunction with the aftercooler, a moisture separator could be used to maximize moisture removal. Moreover, highly automated systems being designed today require instrument air for automatic control, making clean, dry air even more important.
3. Diesel or Electric: This question is complicated, however, several articles have been published on the relative merits of renting diesel-driven portable compressors versus purchasing stationary electric compressors. The operator should be aware of the advantages and disadvantages of both before making a decision. In the end, the decision must be based on dollars and cents, including capital investment, operation costs, maintenance costs, installation costs and availability.

Water Supply

The other major component of any snowmaking system is water. Water requirements, like air requirements, depend on several variables:

1. The air requirement that has been established.
2. Efficiency of the gun.
3. The cooling requirements of other equipment in the system.

All these variables are directly proportional to the amount of water required. Again, the most difficult variable to correlate is the efficiency of the gun. Naturally, the manufacturer emphasizes the ability of his gun to handle more water per unit volume of air. However, it is easy to be misled by biased manufacturers. The best way is to compare several guns under identical operating conditions. This is not easy; however it can be done, and where possible, it should be done so the correct water capacity is chosen for the specific gun.

Once the volumetric water requirement is established, the energy characteristics of the pumping equipment to suit the topographical features of the area must be specified. The ski area operator is usually confused by the terms “head” and “pressure.” Both express the energy given to the water by the pump, so they can be related and are actually interchangeable. To convert p.s.i. of pressure to feet of head, multiply the pressure by 2.31. For example, a pump that delivers 100 p.s.i. will pump water to the top of a hill 231 feet high. But the water pressure at the top of the hill will be the same as it was on the suction side of the pump. Another way of looking at this is that a pipe full of water 231 feet high would register 100 p.s.i. on a pressure gauge mounted at the bottom of the pipe. To have 100 p.s.i. at the top of a 231-foot hill, a pump must deliver 200 p.s.i. of pressure, or 462 feet of head. In all these examples, losses due to line friction have been ignored, but they must be considered in the actual design of a piping system. Other factors in the design of a pumping system are:

1. Where two pumps are required, should they be in series or parallel?
2. The safety relief system on the pump discharge should be carefully designed and, where possible, discharge from this system should be recycled.
3. If size and scope warrant the cost, automatic control valves should be used in the water discharge line. This makes control of water flow more accurate throughout the system.

Electrical Requirements

Based on compressor and water pump requirements, electrical power needs can be determined. The ski area operator or his consultant must work closely with the local utility company in this area. Once it is established that adequate power is available, over and above the power required to run existing systems such as lifts and electric lighting, specific electrical requirements for each component should be reviewed to determine the best operating voltage. Generally speaking, the most desirable voltage is 440 volts. However, in installations where extremely large power requirements are needed, wiring, disconnects, starters, etc. might make it more economical to use at higher voltages. For example, at 440 volts the electrical components carry about half the current that they would require at 220 volts and, obviously, lower amperage equipment is less expensive.

When power requirements are calculated for any snowmaking system, it is important to consider future expansion. Although the cost of a 150 kilovolt-ampere (kv.a.) transformer is greater than a 100 kv.a. transformer, it would be substantially less expensive to buy a 150 kv.a. transformer now than to install a 100 kv.a. transformer now and a 50 kv.a. transformer later.

Piping System

In conventional snowmaking, there are two basic piping systems: one to transport air, the other to transport water from the general control area up the slope to the point where snow is made.

There are many alternatives for air and water piping, and there is no general rule for all installations. The system designer must be familiar with the general layout of the area. For example, he must know ski traffic patterns and other general topographical characteristics. Other factors are: the use of surface piping as opposed to underground; type of materials in the piping system; size and weight of pipe to optimize the relationship between initial capital investment and subsequent operational costs; where surface piping is used, the effect of expansion and contraction on the material; in underground systems, the effect of electro-galvanic corrosion on the materials.

Buried systems are preferable to surface systems, if they can be economically installed. Installation costs can skyrocket where ledgerock makes it necessary to dynamite the slope to reach levels below frost. There are well-designed, self-draining valves available which make it virtually impossible for larger pipes to freeze up because of water accumulation in riser piping. However, the designer must be sure to use one of the better systems or water accumulation will occur. By burying a pipe, it is unnecessary to have loop systems. In a surface system, a loop system is essential to insure that water is continuously flowing to prevent freezing. With a loop system, it is important to have an experienced supervisor in the pump and compressor area to maintain continuous control of the entire snowmaking operation. The buried system eliminates many freezing problems and has aesthetic advantages too.

There are basically three types of piping — aluminum, galvanized and steel pipe. Aluminum is light and costs less, however it requires some type of manual air-tight couplings which can cause problems if not used precisely as designed. Generally speaking, aluminum pipe should never be used in buried systems, because of electrolytic corrosion by soil acids. Steel pipe is preferred in buried systems primarily because it is much more resistant to this electrolytic corrosion, and a well-installed welded steel piping system, buried below the frost line poses few problems with expansion and contraction. In surface systems, expansion depends on three variables — the coefficient of thermal expansion of the material, length of the line, and the temperature differential between the pipe and the environment. For example, 100 feet of aluminum pipe exposed to the average parameters of a snowmaking system will have an expansion/contraction value of 3-5 inches. This factor must be considered in designing a surface system.

The schedule and size of pipe must be considered together. For any specific pipe schedule, allowable working pressure of the pipe decreases as the size of the pipe increases. Often piping systems are designed using the theoretical burst pressure, which is not safe.

Pipe sizing, which in turn affects the installation cost, depends on two variables — volumetric flow passing through the pipe and the length of the pipe. Pipe that is too small will result in extreme friction loss and inadequate pressure. In this situation, effective operation of the system will require additional pump or compressor horsepower, which in turn results in additional operating costs. On the other hand, if pipe is too large, initial capital cost will be unduly high. The effect of pipe size on pressure loss can best be exemplified in an example. Assume that 500 U.S. g.p.m. of water are being pumped through a 1000-foot length of pipe. The pressure drop due to friction for 3-inch, 4-inch, and 5-inch pipe would be 378 p.s.i., 101 p.s.i. and 34 p.s.i. respectively. The designer must evaluate the relative cost saving for smaller pipe sizes versus the additional capital costs associated with horsepower requirements (and subsequent operational costs). Moreover, these cost comparisons must be compared with the extra cost of the larger pipe size to determine which particular installation will produce optimum conditions.

The Gun

There are many guns on the market today and the best unit can only be determined by careful evaluation of the area’s climatological data and the type of use the system has been designed for. For example, that part of the system that provides initial cover would be best served by a gun that can handle large volumes of water. On the other hand, those areas where “patching” is required would be