By: Brendan Lenko, P.E. It was early in the 1970's in an old Quonset hut type building in and amusement park in Rye N.Y. where American inventor Cal MacCracken was testing another brilliant invention - making ice without a refrigerated floor but with 20 F cold stratified air circulated above a big pond of water. To contain the air near the floor, Cal created a 3' high crawl space with folding chairs and plywood above the hopeful ice surface. Well, it worked. After several days of testing and ice making Cal began removing the plywood to strap on his skates and enjoy his newly made ice. But as Cal began skating through the 20 F air he quickly noticed that the ice was starting to melt from the top down. To Cal's surprise, he was losing his ice and did not know why. Although he was a brilliant and accomplished engineer with many accolades including developing some of the earliest space suits for NASA, co-developer of the combustion chamber in GE's first Jet Engine, and the inventor of the "Roll-O-Grill" hot dog roller found in most ball parks (and hockey rink's) today, Cal could not figure our why this ice was melting so fast below his feet. And on this bright sunny day, Cal was mystified. Cal wandered about the ice surface in this metal Quonset hut and could not figure out how the ice was melting with the air temperature still holding at 20 F. Some type of heat is needed to melt ice this fast and he did not know where it was coming from.....Until he looked up!! Back to Top ------------------------- Calvin MacCracken only needed to do a few quick calculations to determine that approximately 100 tons of invisible radiation was causing his ice to melt. It was coming from the hot inside metal roof of the Quonset hut and radiating down to the 20 F ice surface. With a few more calculations Cal demonstrated that even a typical rink would be exposed to a radiant heat load of about 30 tons. Cal proceeded to develop and patent the very first low emisssivity ceilings. Today, Low Emissivity Ceilings can be found in approximately 2000 ice rinks world wide. Although this may seem to be a large number, it is still a relatively new technology since most have been installed in the last 15 years. The strong uptake of low emissivity ceilings in ice rinks is no coincidence. When designed and properly installed, they provide tremendous energy savings with paybacks in the range of 1-3 years as well as many other valuable benefits to an ice rink. Unfortunately, if not supplied and installed by experienced contractors, they can also result in some undesirable problems and conditions. Many people are aware of the technology and accept that it works to save energy. While, others are interested in knowing more about such a magic technology before they can accept it. There are certainly some misconceptions in the market which tend to clutter the true facts. The most important thing to know is that low emissivity ceilings can be successfully applied in almost any rink, and owners, managers and operators should attempt to educate themselves with all of the potential benefits this technology before they decide to install any type of roof or ceiling material in an ice rink. Back to Top Background There are three types of heat transfer which contribute to the overall heat load on an ice surface. They are conduction, convection and radiation. Conduction occurs when heat travels through a solid substance such as along a spoon in a hot cup of coffee. This occurs in an ice rink when heat travels through the ground, floor or boards and warms the ice. Convection occurs when heat transfers from a fluid to a solid or from a solid to a fluid. In an ice rink this occurs when air moves above the ice surface and warms the ice. Radiation heat transfer occurs between two surfaces that are not touching each other, independent of the temperature of the space between them. When two surfaces are exposed to each other, heat actually travels from one surface to the other regardless of the temperature of the air between them. If one surface is warmer than the other, there will be a net heat transfer from the warmer surface to the colder surface. For example, the sun is much warmer than the earth and even though the space between the sun and earth is very cold, the sun still heats up the earth every day by radiation. The same thing occurs in every ice rink, although to a lesser degree. The inside ceiling of an ice rink is usually 40-100 F. This is because heat from lights, skaters, equipment, heaters and others all warm the air in the rink which rises and warms the inside ceiling surface. The outside sun will also warm the roof and inside ceiling. Then, because the ice surface is usually between 18 and 28 F, a temperature difference occurs between the ceiling and the ice. The result is a net radiation heat transfer to the ice. Although it is a small amount of radiation compared to the sun's radiation, the radiant heat load in a ice rink typically represents 25-40% of the overall refrigeration load. Low emissivity ceilings specifically deal with the radiant part of the heat load. In most community ice rinks, the radiant heat load is the single largest heat source the refrigeration system must remove to keep the ice at its desired temperature. For example a typical heat load might be 65 refrigeration tons on an average day in June. The radiant part of this load is likely between16-27 tons. The magnitude of the radiant heat load depends on several things. They are the temperatures of each surface, the area of each surface, the geometry or exposure of each surface to the other, and a special material surface property called emissivity. Back to Top Emissivity is best defined as the ability of a surface to radiate heat. Materials which radiate the maximum amount of heat possible have an emissivity of 1.0. Most building construction materials such as wood, plastic liners, paint finishes and others typically have high emissivities of 0.90 to 0.95. This means that the inside ceiling surface of most ice rinks will emit 90-95% of their maximum heat radiation. Low emissivity ceilings however have emissivities of 0.03. Thus, the installation of a low emissivity ceiling will reduce the radiation from the ceiling to 3% of its maximum value. This represents a reduction of the radiant heat load by about 95% and a reduction of the overall refrigeration heat load by 23-38%. Insert figure #1. Low "E" Ceilings The common material in all true low emissivity ceilings is a polished aluminum surface. Only polished aluminum type surfaces have emissivities of 0.03. In most cases this aluminum foil material is laminated to either a vinyl, polypropylene, or fibreglass backing for strength. The main differences between these materials is their ability to resist punctures from flying pucks and of course their costs. To work properly in an ice rink, the low emissive surface (polished aluminum) must point down to the ice. Although the low emissivity material will still be as warm or warmer than before, the low emissivity of the side facing the ice will prevent the heat from radiating to the ice. If the foil is facing up, then some high emissivity surface will be facing the ice and will allow the ceiling heat to radiate to the ice. Low emissivity materials do not need an "R" value to work. Because they are barriers to radiation heat transfer, the "R" values which are associated with conductive heat transfer, are not needed. The conductive heat transfer through the roof or ceiling does not directly impact the ice. Although they may still work as low emissivity ceilings, the "R" value is not necessary and in some cases causes other problems in the ice rink. For example, having too much insulation in an ice rink creates the "freezer effect". Too much insulation has a tendency to make the entire ice rink cold like a freezer, where the air temperature and ice temperature can all be below 32 F. Rather, although we all want cold ice 22-26F, users prefer slightly moderate 50-60F space temperatures for comfort. Next, with extremely cold inside temperatures including wall and ceiling surface temperatures, there is a much greater chance for condensation to occur - especially when moisture loads occur in the rink. Care should always be taken to ensure that ice rinks are not over insulated and properly dehumidified. An ice rink expert, familiar with the thermodynamics and building properties of ice rinks should always be consulted prior to installing additional insulation or building membranes. Back to Top Energy Savings Many case studies and reports have documented the energy savings achieved with the installation of low emissivity ceilings. A review of the energy and dollar savings would show that rinks in northern climates (northern USA & Canada) typically save $800-1200/month in winter months and $1000-1500/month in summer months (based on electrical charges of between $0.045-0.075 / kWh). The greater savings in the summer months is due to the warmer inside ceiling temperatures and high radiant heat loads in warm weather. Therefore, rinks which operate ice for 10-12 months per year achieve significantly better results owing to the greater savings in the warmest months of the year. Similarly, rinks in moderate and southern climates save significantly more energy and dollars. Monthly energy savings of $1200-$1700 are not uncommon. Southern located ice rinks typically save the most energy and money because the radiant heat loads are high for the entire operating season. Depending on the space conditioning parameters, annual energy savings can be as high as $20,000, but typically in the range $14,000 - $18,000. Energy savings also vary with the type and geometry of ice rink structure. Parobolic shaped roofs often save the most energy because the radiant heat actually focuses on the ice surface. Rinks with lower ceiling heights also tend to save more energy because of the close exposure of the ceiling to the ice. Although rinks with high ceilings tend to have slightly warmer inside ceiling temperatures, energy savings can vary as a result of the distant exposure to the ice. Rinks with large quantity of wood beams have also been known to produce variable energy savings results. This is mostly due to the fact that the solid wood beams themselves radiate heat directly to the ice surface as well as reflect their heat off of the low "E" ceiling and down to the ice surface. Although energy savings sometimes vary, it is the good payback, however which make low emissivity ceilings an automatic choice for almost any rink operating ice more than 7-8 months per year. With a typical installed cost of approximately $25,000, financial payback times are almost always in the 1-2.5 year range. Back to Top Application Considerations For any low emissivity ceiling to work effectively, the foil surface must face the ice. If a non-foil surface faces the ice, it will radiate heat to the ice just as any other building material will and there will be little if any energy savings. The low emissivity ceiling should also cover a ceiling area which is at least 5-10' wider than the ice surface. This is because radiation occurs at more than just a 90 deg angle. Since the bulk of the radiation effect is within 30 deg of perpendicular some coverage outside of the rink is necessary. Further, if some areas outside the rink are warm and well exposed to the ice a soft ice spot or soft side could occur in the rink if it is not covered with low emissivity material. An air space between the low emissivity material and the inside ceiling is generally recommended but not absolutely necessary in all installations. In cold weather, the air space acts as a thermal break between cold outside conditions and the inside of the rink. If the low emissivity ceiling is in contact with a cold roof member, condensation could form on the inside of the ceiling which would start to make the low emissivity ceiling wet. When it becomes wet, it radiates heat just as if it were not there anyway, and energy savings would be reduced. Back to Top In warm conditions, the air space gives the unradiated ceiling heat a place to be stored since it is no longer radiated to the ice. If however, there is no air space between the low emissivity material and the insulation, it is still usually acceptable since the insulation is composed of many air spaces anyway. Because in warm climates, there is little concern for problems due to cold surfaces, the air space can usually be eliminated with no serious side effects. Low emissivity ceilings can also improve the lighting in an ice rink. With a light reflectance of 0.85, the silver finish of a low emissivity ceiling will result in a lighting improvement when installed in buildings with ceiling light reflectances less than 0.85. Typically arenas with any ceiling color other than white will result in lighting improvement with the installation of a low "E" ceiling. The results are even more noticeable if the original ceiling is of wood or dark painted finish. From a dehumidification point of view, low emissivity ceilings can help reduce ceiling condensation but they should never be installed in place of dehumidification equipment. Low "E" ceilings will certainly help reduce ceiling condensation by warming the inside ceiling ( ie. storing unradiated heat at the inside roof deck) and keeping it above dew point, but they will not totally eliminated the need for dehumidification. Back to Top Low emissivity ceilings prevent radiation heat transfer to the ice. They also reduce the radiant heat transfer to the rest of the rink as well. As such, the installation of a low emissivity ceiling will inherently cause the rink to be slightly colder. This means that the ice rink heating system could actually operate slightly more to compensate for the reduction in ceiling heat. The definitive answer to this question specifically depends on how the rink is heated and how the heating system is controlled. For example, if there are radiant heaters which are manually operated, there may be no noticeable difference in the amount of time the heat operates. If however, the heating system operates according to a space thermostat located within approximately 10 feet of the ice floor, then it may operate more to keep the space at its set point. Any additional space heating however, will be more than offset by the refrigeration energy savings associated with the low emissivity ceiling. If, however space heating is still a concern, a rink heat load analysis should be conducted by an ice rink professional to determine the overall effect of the low emissivity ceiling. From an aesthetic point of view, low emissivity ceilings have often been credited for both brightening up and enhancing the look of an ice rink. When installed at the roof deck in an ice rink, they often highlight the fine architectural characteristics of the beam or truss structure. In fact, most rinks look much better after the low emissivity ceilings have been installed. As long as they are professionally installed, it does not matter whether they are installed above the beams at the roof deck, suspended between the beams or attached to the bottom of the beams. (see attached photos) Low emissivity ceilings should always improve the look of the rink. One important concern however, is that of flying pucks. If a low emissivity ceiling is installed below the 30' level in a hockey rink which hosts high caliber hockey, flying pucks can sometimes puncture or simply wrinkle the low emissivity ceiling. When installed at or below 30' in height, horizontal protective netting should also be installed below the ceiling to protect it. It need only be installed 6-12" below the ceiling, but horizontal netting will keep the ceiling looking new for a long time. Back to Top Low emissivity ceilings can also help reduce the maintenance in your ice rink. Where facilities often clean or paint their overhead beams on a regular basis, low emissivity ceilings can cover up unsightly beams or simply prevent paint chips from falling on the ice. If rust is a concern, a low emissivity ceiling can be installed below metal beams and help keep them warmer and dryer, reducing rust formation. Low "E" ceilings have also been credited with drying out water laden fibreglass insulation in ice rinks. When retrofitted below wet fibreglass/plastic liner installations, the low emissivity ceilings retain heat which helps dry out the insulation and render it effective again. 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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