By: Brendan Lenko, P.E. Recently, many questions have arisen about the suitability and effectiveness of water purification for making ice in hockey rinks. Many hockey facilities especially at the professional level are experiencing a wide array of problems associated with such systems as reverse osmosis and deionization. This report explains many of the problems associated with water purification and offers solutions and recommendations for proper water treatment and ice making practices. What Is Good Ice? Before we discuss the problems with ice, we must first define what good ice is, including the properties of ice that are desirable for good hockey ice and the properties which are not desirable. In general there are five main qualities of ice, which can have an effect on the performance of the player and the game. They are: 1. Chippiness 2. Smoothness of Ice 3. Friction of the Ice 4. Softness or Hardness 5. Quality and Quantity of Snow Although all of the five are related in one way or another, they will each be explained separately. Back to Top Chippiness Chippiness is the most easily understood property of ice and often the most critical. Chippiness can be defined in the ice rink field as the ability for ice to break apart in large chunks. Chips usually occur when a player cuts sharply, stops or heavily impacts the ice so as to break it leaving the resultant snow in large granules. It is a problem because the puck no longer glides freely about the ice. In fact, when the puck impacts an ice chip, it will often cause the puck to bounce or jump making it more difficult for the players to control the puck and especially pass the puck. When the more skilled players can no longer make use of their skill on such a chippy ice surface, the quality of ice effectively levels the playing field, making lesser skilled players more competitive with players having more skill. In more technical terms, chippiness is caused when ice is formed in a long uniform grain pattern leaving the ice in a brittle condition. Because ice fractures along its grain boundaries the longer the grain formations, the greater the chances of large fractures in the ice. Longer grain formations in ice make it chippy ice. Further, because ice is actually a high temperature material (like many metals), long grain formations possess high energy levels. These energy levels cause high stresses in the ice structure making it more likely for large fractures to occur. This problem can be treated in a similar manner to that of metals. Just like metals can be made tougher and more ductile by tempering, so it is with ice. Tempering a sheet of ice actually relaxes the built up stresses and helps prevent the chippy ice. Where long ice grains cause brittleness, shorter crystals with a greater concentration of molecular dislocations can be much less brittle and less chippy. When ice grains are more inter-twined and less uniform, it is more difficult for them to break apart in large chunks. The formation of the ice grains is dependent on water quality. Purified water (such as than produced by deionization) will naturally create longer ice grains. This is because the pure water will permit fewer molecular dislocations in the ice structure allowing ice grains to form in long uniformed patterns. Ice formed from pure water will naturally create longer ice grains because there are less foreign molecules present to cause the molecular dislocations. To prevent the chippy ice, there must be some foreign molecules present in the water to impede long grain growth and cause the ice grains to grow in various directions with less uniformity. Although chippy ice can still be tempered to relax the internal stresses, it should still be noted that the ice will originate in a brittle condition, especially if it is made with extremely purified water. Unfortunately, (for reasons to follow) this does not necessarily mean that unpurified city water will make better ice. Secondly, the formation of ice grains is dependent on the freezing rate of the water itself. The faster the water freezes, the longer the ice grains will be and the larger the internal stresses ice will have. This is evident in new or "green" ice where freshly laid water has been frozen too quickly. New ice is typically brittle for this reason. It generally needs time to be tempered or cured before it becomes good ice. Fortunately, proper ice tempering and ice temperature control can help reform or relax long ice grain formations and prevent brittle, chippy ice. (see Ice Tempering). Lastly, causing the ice to quickly drop several degrees in temperature can also create brittleness or chippiness. A more gradual decline in temperature is preferred. This is also discussed in Ice Tempering. A recommended water treatment system for preventing brittle ice is identified in this report. Refer to the Discussion section for more details. Back to Top Smoothness of Ice In general when warm water is laid on the ice it should always level out and freeze in a flat manner creating a smooth ice finish. There is one phenomena especially related with deionization in which this does not happen. The term "Beading" is used to describe what occurs when freshly laid pure water freezes in a bumpy, inconsistent fashion, similar to how water sits on a newly washed car. The difference is that the water actually freezes in this beaded form. Also called "Squirrelly Ice", the main reason it occurs is because of the high surface tension (cohesion) of chemically pure water. "Squirrelly Ice" is a serious problem with water purification systems because it can occur without warning and can be much more detrimental than the worst chippy ice. Not only will pucks jump and bounce, but the skaters themselves can actually be effected by the funny bumps and ridges in the ice. In simplified terms, surface tension is the thing that holds a water droplet together. When the surface tension is higher, the water molecules will want to stick to each other more than sticking to the existing ice. This surface tension is effectively a cohesive force in the water that will actually make the water layer stand up higher and prevent it from spreading evenly or flat. When the water freezes in this position, it results in a bumpy and uneven surface. The high surface tension that causes "Squirrelly Ice" is directly associated with water purity. As the water becomes more pure, the surface tension and adhesive forces increase. Figure #1 shows the capillary rise (a measure of surface tension) of pure distilled water verses basic tap water. Notice that the capillary rise and surface tension also increases as the water gets colder. There is no question that high surface tension and "Squirrelly Ice" will result from water purification systems based on common deionization or reverse osmosis. See Discussion section for details of how to prevent "Squirrelly Ice" when using water purification. Back to Top Ice Friction Friction on an ice surface is a measure of the force, which opposes the motion of either a skater or puck. The lower the friction (coefficient of friction), the easier it will be for a skater to glide on the ice, the faster a puck will slide on the ice and the less work will be required to propel the skater on the ice. It is definitely a proven fact that the presence of impurities in water increases the friction of ice. So, removing the impurities in water by water purification will certainly reduce the friction and make the ice faster. That is, skaters can glide easier and skate faster on ice made from either deionization or reverse osmosis water purification systems. In fact, there are many studies and reports that will confirm this. Puck movement on the other hand is not necessarily improved with water purification. The main reason for this can be seen in how a puck slides on the ice compared to how a skate blade cuts and slides on the ice. The difference between the two is basically how the snow developed effects the puck more so than it effects the skate blade. This is because skaters have hundreds times more mass and much less ice contact area than a puck. So, a smaller imperfection in the ice may have a relatively larger effect on a puck. Players too will agree that consistent puck movement is more important than reduced skating friction. It is for this reason that pure water alone is not necessarily the answer to having good ice. Further, frictional measurements should be made on ice with some snow coating since most of a hockey event is played on a snow covered ice surface. The way in which the snow can effect the puck is simple. If the snow sticks to the ice it will increase the ice friction enough to effect the puck's movement. If it does not stick to the ice, the puck should be able to glide through the snow smoothly without being effected. For example, light, fluffy, dry snow that does not stick to the ice is most desirable because the puck will often glide through it. Heavy or wet snow which does stick to the ice has more of a sand paper effect on the puck with the tendency of slowing it down or effecting its movement. The main thing to understand in a discussion of ice friction is that although water purification systems reduce ice friction to improve skating conditions, good consistent puck movement is commonly considered more important than skate friction. Any water treatment system for hockey ice should also address puck movement as a result of the type snow developed. A more detailed discussion of this in the Quantity and Quality of Snow section. Back to Top Quality and Quantity of Snow Produced Good ice can also be measured by the type and amount of snow produced. There are various different types of snow developed in a hockey rink and it is particularly important to understand why some snow sticks to ice and why some does not. Warm ice (26-32F) in a humid environment will often produce relatively wet sticky snow regardless of what type of water is used. Because this type of sticky snow depends heavily on humidity control as well as ice and air temperature control it will not be expanded on further in this report on water quality. Snow can also become sticky and adhere to ice as a result of flood water quality. Where pure water was found to be very cohesive (sticking to itself), snow and small ice particles and chips made for pure water tend to be very adhesive (stick to one another). That is, snow made from pure water usually wants to stick to the ice. This process is called "sintering". It was first proven by Faraday in the mid 1800's. Faraday found that "if two pieces of ice are placed in contact they will unite together even when the surrounding temperature is such as to keep them in a thawing state", (Hobbs, 1974). So, if the snow sticks to the ice, the actual ice surface will become slightly rough and demonstrate a greater friction (coefficient of friction) on the puck. This is certainly an undesirable quality of ice. This "sintering" of snow to ice has been found to be more prevalent with ice made from pure water. For reasons to follow, the problem gets worse as the water gets purer. Consider fairly pure water but with some dissolved solids (TDS). As this water is laid to freeze the impurities will naturally work their way to the surface because the pure part of the water will always freeze first on the bottom. The ice is left fairly pure below but with a small concentration of dissolved solids (impurities) on top. It is this top ice which is cut up as snow during play. As such, the snow is inherently made of some impurities. And, it is these impurities which act as a buffer between the ice and snow to help prevent the sintering from occurring. So, water with some TDS will have a lesser tendency to cause the snow to stick to the ice and consequently allow the puck to glide through the snow. Conversely, purified water will not possess any buffer and actually worsen the sintering and snow friction. It can be concluded then that purified water in the case of puck movement does not necessarily reduce the friction or help the puck to slide better. In fact it can do just the opposite by helping the snow to stick to the ice raising its friction. Snow friction by sintering is also heavily dependent on the humidity of the air over the ice surface. Good humidity control in the arena environment is one of the most effective ways of preventing the snow from effecting the puck movement by sintering. Back to Top Ice Hardness Hard ice is another desirable quality in hockey ice as long as it occurs without chippiness. The harder the ice is the less deeply the skate cuts will be and the less snow will be developed. Further, the harder the ice is, the less the mechanical friction will be on the skaters since the blades will not cut in as deeply. Mechanical friction should not be confused with the sliding friction that occurs in surface to surface contact. Mechanical friction is the part associated with the deformation and cutting of the ice. It has been proven and advertised many times over that ice made from pure water will be harder, denser and bond better than ice made from untreated city water. For reasons already stated the ice grains formed with pure water would not be interrupted with molecules of other dissolved solids. The lack of a high concentration dissolved solids will allow the water molecules compact themselves to form a denser ice sheet. The key in this freezing process is to freeze the water without allowing it to create chippy or brittle ice. Back to Top DISCUSSION The information presented here has identified the causes of various problems associated with making ice using water purification techniques such as reverse osmosis and deionization. It has also identified some of the positive characteristics of ice made with purified water. The challenge then is to develop an optimum water treatment system which will provide the positive characteristics of ice made from pure water and eliminate the negative side effects that are also associated with using pure water to make ice. The optimum water treatment system must still be able to produce pure water to maintain the hardness and low coefficient of friction for the skaters. The merits of using purified water should not all be lost just because of the side effects. Therefore, an optimum water treatment system should also be able to: 1. Prevent the chippiness caused by purified water, 2. Reduce the surface tension of the water which causes "Squirrelly Ice", and 3. Eliminate the snow "sintering" commonly associated with water purification. One particular water treatment method has already been developed and tested to provide the optimum conditions listed above. The system is a reverse osmosis based water purification system that selectively leaves certain ingredients in the water, which prevent the occurrences of "Squirrelly Ice" and chippiness as well as sintering of the snow to the ice. To address chippiness, certain elements are left in the purified water to cause the necessary molecular dislocations needed to prevent the ice grains from forming in the patterns associated with brittle, chippy ice. The ice remains hard and fast, but left with toughness and durability necessary for high caliber hockey. Another element, which is kept in the purified water stream effectively, eliminates the high surface tension that causes "Squirrelly Ice". As such, the water does not develop any bumpiness or ridges in it. It freezes in a smooth and flat configuration just as it should. Lastly, an adjustable water purity capability allows the operator to choose and adjust how pure the water should be for his particular facility. This capability naturally provides a buffer which reduces the chances of snow sticking to the ice sheet (sintering) and causing a friction effect on the puck movement. The system, developed by the writer is truly an optimum in water purification for ice rinks. Water alone however will not guarantee perfect ice results. There are several other factors that must all be done properly to achieve the best ice conditions. Back to Top Ice Temperature Control The most effective means for proper ice temperature control is by monitoring and controlling from the actual ice surface temperature. An infrared-based ice surface temperature sensor can be employed and integrated with the controls for the primary and secondary refrigeration equipment. Systems, which control the ice temperature indirectly using the brine or slab temperatures, are naturally allowing unnecessary swings in the ice temperature to occur. An infrared ice surface temperature sensor is the only device which can identify a heat load just as it hits the ice and deal with it accordingly and without delay. Back to Top Ice Tempering Every ice surface requires some tempering to help prevent even the mildest form of chippiness. Regular ice tempering will help relax the stresses in the ice and help prevent brittleness and chippiness from occurring. Tempering will allow the ice grains to expand and contract to reform in more desirable patterns, which prevent brittleness. There are several ways to properly temper an ice surface. 1. Apply two or three hot floods with the resurfacer back to back in a short period of time. The hot water will refreeze slowly allowing the ice grains to form gradually prevent long grains from forming. 2. Warm the ice up to 28-30F for several hours at a time (i.e.6-12 hours). The time spent at a higher temperature will relieve the ice of built up stresses developed in past freezing cycles. 3. Warm the ice up to 28F and down to 24F several times in a day (Pulsing). This process will also help work out any built up stresses in the ice grains. 4. Organize one or two large and active skating events where the entire ice sheet gets heavily skated on. And, follow the skate with one or two good hot floods. Back to Top Building Heat Load Control The temperature of the ice itself can be significantly improved by preparing the operating conditions inside the facility ahead of any major event. Things such as space temperature and humidity, as well as forced air movement and ventilation can be critical to the success of any important ice event. Adjusting building air handling equipment ahead of time can certainly help prevent localized warming and softening of the ice as well as reduce the huge convective heat load on the ice. Controlling the heat loads is often used when ice temperature control from the actual ice surface temperature is unavailable. A through understanding of ice temperature control and the effect of heat loads are definitely necessities for any rink operator planning a successful ice event. Back to Top Ice Maintenance A comprehensive ice maintenance program is also a must in the effort to consistently achieve professional caliber ice. All of the ice maintenance and refrigeration staff must be fully aware of all the building parameters that could effect the ice and be able to deal with them accordingly. Arena staff should also understand how the refrigeration system and equipment operate and be able to safely change various setting as necessary. The ice maintenance staff must be able to identify a problem ahead of time and be able to resolve it before it becomes critical. Proper communication is also essential among ice maintenance staff. The necessary information must be passed from one shift to another otherwise valuable ice preparation and planning could all be lost. Lastly, there should be a regular dialog between the icemakers and the refrigeration personnel. As we have seen, the rate of refrigeration and freezing, and ice temperature control all effect the quality of ice just as much as the ice making & maintenance processes themselves. Back to Top About the Author: Brendan Lenko, P.E. is a professional engineer and President of Energy Ice. Through his career, he has been involved in hundreds of low emissivity ceiling projects through out the world in consulting, design, energy analysis and project management capacities. His experience includes projects in countries such as Japan, Russia, Finland, Sweden, Norway, Denmark, Switzerland, Germany, Indonesia, as well as Canada and the USA. If you have questions relating to low emissivity ceilings, ice temperature controls or just energy conservation & engineering in ice rinks in general, you can reach him in Canada at 905-632-8840. |
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