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By: Brendan Lenko, P.E.
For many years there were only two things needed to make a good ice surface. They were water and cold. As long as the water was kept below 32 F, it remained frozen and was sufficient for ice hockey, figure skating or public skating. Users would strap on their skates and as long as they could skate they were happy. There were no concerns for hardness, speed, snow, or friction. Whether it was indoors with a refrigerated slab or outdoors in a natural ice surface, the ice was made from water and cold - not much else.
Today, the same ingredients are still needed to make ice, but science has entered the ice rink industry and demonstrated that ice too can be improved with new technology. New products, techniques and expertise have all contributed to the quality of ice. Ice makers can now make fast ice for speed skating, hard ice for hockey, soft ice for figure skating or controlled ice for curling.
One of the most important ingredients to making a quality sheet of ice is temperature. It is a proven fact that colder ice is harder and warmer ice is softer. That is why hockey players generally prefer colder ice and figure skaters prefer warmer ice. But just how cold should the ice be for hockey? Or how warm should it be for figure skating? Or for that matter curling?
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There have been various documents written about what the ice temperature should be for different activities. Unfortunately, just knowing what the temperature should be is not enough. The most important thing is that we can control the ice to these temperatures and keep them there throughout the entire event.
The ideal temperature for a given ice activity will vary with the quality of water used for ice making. Generally, the more dissolved solids in the source water, the colder it will have to be to achieve a certain hardness. Given a typical concentration of dissolved solids of say 300-400 ppm, the following general guidelines can be used.
Table #1 - Typical Ice Surface Temperatures for Different Ice Activities
| ACTIVITY | ICE TEMP |
| Competitive Adult Hockey | 22 F |
| Figure Skating | 25 F |
| Curling | 23 F |
| Youth Hockey | 24 F |
| Mite/Tyke Hockey | 26 F |
| Public Skating | 28 F |
| IceMaintenance | 28 F |
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To say an ice temperature of 22 F is good for hockey, is still not enough. This is because the temperature on the ice surface is not the same as the ice below. In general, the ice gets warmer the further it is away from the refrigerant pipes in the sand or concrete. For example, with ice 1.25" thick, the surface of the ice might be 22.0. F while the bottom part of the ice might be 19.5 F (i.e. at the ice/concrete interface). So it really depends on where the temperature is measured. The temperatures in Table #1 are ice surface temperatures. You will have to operate colder temperatures than Table #1 if your ice measurements are taken in the concrete or ice/concrete interface.
For example, if the temperature is measured in the concrete slab, the actual ice surface temperature could be up to 3-8 F higher than this. If it is measured with a sensor imbedded in the ice, the surface could be up to 1-5 F warmer.
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It follows then that the thicker the ice is the greater will be the temperature difference between the surface and the ice below. In our example, to achieve an ice surface temperature
of 22.0 F given 2" thick ice, a temperature of 18.0 F is required at the ice/concrete interface below.
The following table shows the required temperature at the ice/concrete interface to achieve a 22 F ice surface temperature for various ice thickness'.
Table #2- Required Temperature at Ice/Concrete Interface to Achieve 22 F Ice Surface Temperature for Varying Ice Thickness
| Desired Ice
Surface Temp deg F |
22.0 | 22.0 | 22.0 | 22.0 | 22.0 | 22.0 | 22.0 | 22.0 |
| Ice Thickness | ¾" | 1" | 1¼" | 1½" | 1¾" | 2" | 2¼" | 2½" |
| Required
Temperature at Ice/Concrete Interface deg F |
20.5 | 20.0 | 19.5 | 19.0 | 18.5 | 18.0 | 17.5 | 17.0 |
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If you are NOT measuring your ice temperature at the surface, you may NOT be getting the ice surface temperature you think.
It only seems obvious then that if we skate on the ice surface, we should measure the ice surface temperature. Of course imbedding a thermometer or sensor in the ice surface is impractical since the skaters would cut into it. So how can we measure the ice surface temperature?
One technology has now been used successfully to measure ice surface temperatures in hundreds of rinks world wide. It is called an infrared sensor. It measures the ice surface temperature without even touching the ice. This device senses the heat that is naturally radiated from ice and then using specific ice properties, it converts the heat to a temperature reading for the ice surface. It is typically mounted or hung above the ice from a beam or score clock and pointed down at the ice.
Infrared sensors have been used in industry for many years. It has only been in the last 3-4 years that they have been successfully applied to ice rinks. The author has actually designed and installed over 150 infrared ice temperature monitoring and control systems in ice rinks all over the world. Today, these infrared sensors are the best method of measuring the ice surface temperature on an ongoing basis.
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With infrared sensors to measure the actual ice surface temperature, there is no confusion or guesswork as to what the true ice temperature is. Regardless of the ice thickness, or heat load on the ice, we can use infrared sensors to tell us the ice surface temperature at any time.
But now that we know what our ice surface temperatures really are using infrared sensors, and having identified the best temperatures for the various ice activities, how do we get the ice to that temperature and keep it there?
Traditionally, refrigeration companies have installed the same controls into ice rinks that they install for other refrigeration processes. These controls are designed to maintain the temperature of the brine, glycol or direct refrigerant that is pumped from the refrigeration system to the process. In an ice rink, the process is the rink floor. So, using a brine or glycol thermostat, the refrigeration equipment maintains the temperature of the brine or glycol passing under the ice. Then as long as the thermostat was set low enough, the ice would remain frozen.
But, as we have just seen, the actual ice surface temperature is not the same as the brine, concrete, sand or even the ice below. So, by maintaining the brine temperature with a brine thermostat, it does not provide for very good ice temperature control. The same argument holds true when using a thermostat that sense concrete or sand temperature, suction pressure, or even ice temperature below the ice surface. They are all indirect methods for trying to control the actual ice surface temperature.
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The problem becomes much more pronounced when we consider the varying heat loads on the ice. That is, for a given brine temperature, the ice surface temperature will fluctuate as the heat loads on the ice fluctuate. As the heat loads on the ice increase such as on a busy warm afternoon, the ice surface temperature must increase as well. Conversely, on a cold winter night with the lights off and doors closed, the heat load is less and the ice temperature will actually become colder than usual. As a matter of fact, the ice surface temperature can be as much as 2 F - 20 F warmer than the brine temperature depending on the heat load.
The main reason this occurs is because a temperature gradient is required in the floor to remove more heat through the floor. The more heat removed, the larger the temperature gradient must be. Moreover, if the brine or slab temperature is fixed below the ice, as the heat load changes the ice surface temperature must adjust according to the heat load to achieve the required temperature gradient. So, the heat load on the ice will vary from day to night and summer to winter, and if a brine or slab thermostat is used for control, the ice temperature will also be varying from day to night and summer to winter.
Figure #3 - Typical Ice Surface Temperature Variations with a Fixed Brine Temperature
Figure #3 shows how the ice surface temperature will fluctuate as the day progresses and the heat loads on the ice increase. At night, the heat load is reduced and the ice surface temperature decreases. Later in the day, the heat load on the ice has increased and the ice surface temperature will increase accordingly. Notice in this case there was almost a 10 F swing in ice surface temperature through the day. This is certainly not indicative of good hockey ice. With this method of temperature control it is virtually impossible to control the ice surface temperature accurately.
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The preferred method of ice temperature control is to control the refrigeration equipment according to the actual, ice surface temperature with an Infrared Controller. Such a system constantly monitors the ice surface temperature with an infrared sensor and as the ice temperature starts to rise, it activates more cooling through the refrigeration system. Conversely, as the ice temperature starts to drop below the ice temperature set point, the controller turns off refrigeration capacity. Then, as the heat loads fluctuate on the ice, the required temperature gradient is achieved by allowing the brine temperature to fluctuate. The net effect is an ice surface temperature that is maintained to within +/- 0.5 deg F.
In addition, when there is a sudden increase in the heat load, as is the case of a resurfacer flood, the infrared controller will detect it first since it monitors the ice surface. With a brine or slab thermostat, there would be a "thermal lag" or time delay before the controls can respond to the heat load. With an infrared controller, the response is almost instant so the refrigeration equipment can stay on top of the heat load.
A more advanced variation of this control developed by the author, is a way to predict how fast the ice is warming up or cooling down so that infrared ice controller and refrigeration equipment can actually stay ahead of the fluctuations in heat load. In several instances, this type of control has actually maintained the ice to within +/- 0.2 F.
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Now, if we want soft 25 F ice for figure skating, we can simply dial it into our infrared controller and the control system will keep the ice surface temperature at 25 +/- 0.5 F. The figure skaters will find it much easier to land their jumps on the soft ice and control their moves during practice. It will help reduce the holes and chipping that occurs when the jumps are made, so ice maintenance is also reduced.
Next, hockey players will be able to skate on fast 22 F ice without the sluggish feel of soft ice even when the heat loads are the greatest say at the end of a Over Time game. The infrared sensor and controller will continue to maintain the 22 F for as long as the game lasts or until it is programmed for a different temperature.
As well, with ice at 23.0 F and using the predictive control method, curlers will be able to throw the same weight from the first rock to the last without the warming of the ice to slow their stones down in the last few ends of a draw. No only will the ice be more consistent, but the curling competition will be more competitive.
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Of course all of this sounds quite simple. But there has been quite a bit of technical design development to this method of control. Although the technology is readily available today, it must still be designed and applied to each specific ice rink properly to achieve the desired results. For example, some infrared sensors can be bought off the shelf, but they must be designed for low temperature ice applications to work in an ice rink. They must also be able to avoid or filter out the temperature fluctuations that occur when skaters pass under them. We can not have the refrigeration system turning on and off each time a skater passes under the infrared sensor.
When designed properly, an infrared ice temperature control system can not only improve ice quality, but they can also generate a great deal of energy savings. The energy savings comes two ways. First, it will prevent the ice temperature from getting colder than necessary, as is the case with brine thermostats at night. Instead of the ice getting down past 20 F at night as in Figure #3, the controller will maintain the desired set point (i.e. 22 F ). This will effectively require less refrigeration and thus save energy. Second, the controller provides a means of setting the ice temperature up even higher at night when the ice is not in use. This again will require less refrigeration work and generates more energy savings. In fact, many infrared controllers have been known to pay for themselves in under two years.
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Setting the temperature up at night has other benefits as well. By setting the ice surface temperature up to 28 F for several hours at a time, it naturally relaxes the built up stresses in the ice that cause ice to be brittle and chippy. It actually "tempers" the ice just as heat tempers steel. The net effect is a tougher and more durable ice surface with less deep ruts and chips. This in itself can justify the use of an infrared controller. We have all seen the puck jump off a players stick at a critical moment in the game. An Infrared Ice Temperature Controller can help prevent the chippy ice that causes some of these problems and save valuable energy at the same time.
Of course there are several precautions which should be taken when selecting an infrared controller and changing the method of ice temperature and refrigeration control in your ice rink. Here are a few guidelines.
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1. Training - Ensure that your installation comes with adequate training of your rink personnel. This is the single most important factor in obtaining a successful product. The rink staff must be able to set the temperature program on the controller. If they are unable to use it, it might as well not be there. It is recommended that a follow up training session be made 1-2 months after the original installation. This will be an effective refresher for the rink staff .
2. Refrigeration Expertise - Because an Infrared Controller will effectively change the way the refrigeration equipment will operate, ensure that it is designed and installed by qualified refrigeration personnel that have experience in refrigeration controls. An error in the control design can not only create bad ice but be dangerous to everyone in the rink.
3. Experience - Some projects are more difficult than others. Ensure that your infrared controller comes from a company with sufficient experience using this technology. If you are paying for the equipment, you should not suffer with an inexperienced contractor.
4. Energy Conservation - The amount of energy savings achieved with an infrared controller depend greatly on how it is programmed and set up. If incorrectly programmed, controllers can actually cost more money than they save. Ensure your installation contractor has sufficient energy conservation expertise to avoid these problems.
5. Ice Rink Expertise - Infrared Controllers also change the way your ice rink operates. A company with experience in ice rink operations, scheduling and ice programming is best suited to understand the challenges faced by your ice rink. For example, in some cases it is better to keep the ice colder for figure skating so that it is cold enough for the next hockey ice rental.
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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.