Understanding Artificial Ice Operating Temperatures

There is no fixed value for “best” ice operational temperatures. There are some recommended temperature levels that have existed for many years with most still being considered reasonable targets to be met. However, it is important that today’s ice maker understand the science and variables that exist in each facility. Understanding the variables will allow you to better comprehend the challenges you may be facing in your building.

The following information is shared as a quick overview to the subject and should allow the reader to better understand the variables that can impact many of the temperatures we are to discuss.

Definitions

Humidity

Moisture, dampness in the air.

Relative Humidity (RH)

Ratio of water vapour in air to the maximum amount or water vapour that the air could hold at a given temperature and pressure.

Wet Bulb Thermometer

Thermometer with a wet wick around its bulb. Cooling effect of evaporation (and heating effect of condensation on the ice) depends on the amount of moisture (relative humidity) of air.

Dew Point

Temperature at which air reaches 100% relative humidity (saturation) and the vapour begins to condense to a liquid.

Sublimation

Changing directly from solid to gas without becoming a liquid, as with Dry Ice.

In ice arenas, sublimation can take place when the relative humidity is too low. This leaves a rough and granular surface on the ice rink.

Air/ice interface

When the air above the ice sheet has a dew point temperature higher than the ice surface temperature, moisture from the air will condense on the ice surface making it frosty and adding to the cooling demand.

Air Conditioning (HVAC)

The process of cooling, heating, moisture control and distribution of air in a controlled manner.

Factors affecting Ice Temperatures and Conditions

Geographical location

An arena in the north or far south will generally have better conditions for ice due to outside conditions when compared to a rink nearer the equator. Outside air temperature will impact indoor ice conditions. In the same context, winter ice and summer ice in both locations will have similar challenges.

Age, design and maintenance of the facility

Older buildings often lack today’s equipment capabilities and will often struggle due to wear and deterioration of the refrigeration and mechanical systems. The design of the building may also challenge indoor temperatures. Building envelope must be as air tight as possible. Conventional design for normal heated buildings will result in years of grief and significant added costs for the rink operator. Poorly placed structural beams or mechanical ducts can impact on air flow and contribute to poor ice conditions. A lack of ongoing maintenance to pipes, pumps, air/fluid filters cooling water and refrigerants can cause the system to work harder and longer thus not allowing the ice to freeze properly.

Indoor temperatures and humidity levels

These will vary based on building design and use. A building that sits empty with no use can fairly easily be controlled with the correct equipment. Turning on the lights, allowing people in while adding resurfacing water will all contribute to rising indoor air temperature and humidity requiring more from the mechanical systems.

Air Conditioning Design

The largest factor effecting ice temperatures and refrigeration plant loads is the condition of the air above the ice and the method of air distribution. Many facilities have conventional air jet distribution systems and conventional air conditioning equipment. The difference between this approach and a purpose designed ice surface air conditioning system can mean up to 50% addition to the refrigeration demand.

Outdoor weather conditions

This can challenge ice conditions and the ice making and ventilating equipment in several ways. A building that has all the best equipment can be put to the test when 500 people come in to the building during a rain downpour and their clothes are wet. This moisture will be released along with the energy they exert based on the excitement of the event.

Further, fresh air must be circulated throughout the building. The air being drawn into the building, if left untreated through a quality HVAC system, will cause the ice maker grief. Warm and cold outside air will contribute to different ice conditions unless interior conditions are carefully and strictly controlled by well designed ventilation equipment.

Secondary refrigerant temperatures

The setting and controlling of the secondary refrigerant temperatures can dictate the ice temperature. Some systems do not have adequate or have poorly operating refrigeration systems that just do not shut off, thus never meeting the set temperature level. This temperature is recorded in the refrigeration room as “supply and return” temperatures.

Ice temperatures

Temperature readings measure how cold the ice is. These readings can be taken in the concrete or sand slab, in the ice through a probe that is frozen into the ice sheet, or on top of the ice though an infra-red system. Each method will vary in temperature reading but may give the same ice conditions. A temperature taken in the concrete slab or in the ice sheet will be colder when compared to a surface reading, so the ice maker must understand the insulation factor of the concrete and ice and how it affects the interpretation of the reading. Infrared measurement has proven to be the most reliable and accurate method of measuring ice temperature.

Common operational mistakes

- A facility setting slab or return brine temperatures at the beginning of the season and never adjusting them throughout the year and then wondering why ice conditions change as the seasons change and different events occur. Many of the settings we are about to share are set as start targets, when in fact an ice maker may need to be setting the equipment to meet these targets at the end of the event, not the beginning as ice conditions may deteriorate as the event goes on.

- Simple operational attitudes such as door openings can significantly impact indoor air humidity and temperature. Too many operators leave large entrance doors open for no reason or use the wrong size door for simple operational tasks as they believe opening the ice resurfacer doors to accept deliveries is easier than a general facility entrance/exit door.

Most arenas require 3-4 hours of refrigeration run time to change the ice temperature by 1-3 degrees. Again, this can be impacted by all the variables we have discussed.

What are the Best Temperatures?

The sliding coefficient between a skate blade and the ice surface are at its best at exactly -2.2°C. When there are warmer ice temperatures the skate blade cuts deeper, while at colder temperatures friction is also increased due to frost formation on the surface.

The constantly changing internal external heat loads on the ice surface cause the temperature on the ice to vary from ideal levels. An ice technician’s true skill is the synergy between the "art" of "making ice" with the ice-resurfacer and the science of understanding and controlling ice temperatures! Too many rely on pre-set controls and then wonder why they have poor ice conditions at some events.

In North America, a community arena strives to be between 10-18°C [50 - 65°F] dry-bulb and 40-50% relative humidity, or a dew point of 0-4 °C [32 - 40°F] While this is the ideal condition for best ice, it is clearly not obtainable in shopping malls, large multi use buildings and for ice

facilities in the south without substantial and special HVAC equipment. However, targeting a dew point of 4 to 10°C [40-50°F] is possible and far more important than lower dry bulb temperatures. E.g. At 24°C [75°F] a relative humidity of 45% equates to a dew point of 11°C.

Normal Ice Surface Target Temperatures

• Hockey: -5.5 to -4.5 [22 - 24°F]

• Public Skating: -4.5 to -3.5 [24 - 26°F]

• Other Ice Sports: -4.5 to -3.5 [24 - 26°F]

• Figure Skating: -4.5 to -3 [24 - 27°F]

• Speed Skating (short track): -7 to -6 [19 - 21°F]

• Ice Maintenance (and overnight tempering): -3 to -2 [27 - 28°F]

• Professional curling: -4.4 to -3.3 [24 - 26°F]

with a facility temperature of 5°C [40°F] 1.5M [5 ft.] above the sheet and a relative humidity of 65%.

Professional Ice Arenas are looking for the air conditions in the facility to be maintained between 16°C - 18°C with 40 - 44%RH and a surface temperature of -5.5°C to -4.5°C at game’s end.

Secondary Refrigerant Temperatures

Some ice makers believe that they can control ice temperature by setting the secondary refrigerant temperatures. While his is not impossible, this is not the best approach to maintaining good quality ice conditions.

In properly air conditioned sports facilities;

- Typical secondary refrigerant supply temperature is –8 to -10°C [17.5 – 14°F]

- Typical secondary refrigerant return temperature is -6 to -8°C [21 – 17°F]

In properly air conditioned shopping mall type facilities;

- Typical secondary refrigerant supply temperature is –9 to -11°C [15.5 - 12°F]

- Typical secondary refrigerant return temperature is -7 to -9°C [19 – 15.5°F]

Other Points to Consider

Some facility managers have discovered that how skates are sharpened can impact ice quality. Trying to determine why ice damage is occurring should include skate sharpening “hollows” as part of an ice technician’s investigation. A 16mm hollow will have less of an impact when compared to a 10mm hollow.

The introduction of harder stainless steel blades has also contributed to an ice maker's challenges.

Ice blankets used at night can have a major benefit in warmer facilities such as shopping malls. When a simple blanket covers the ice the cooling load can be reduced by up to 50% by eliminating convective (air & humidity) loads. The thickness or insulating value of the blanket has only a very small effect on it’s effectiveness. It’s main benefit is to stop air moving over the ice.

Conclusion

A “caution” is given to all this information. Before undertaking any adjustments the ice technician must first understand exactly what they are about to adjust!

- Never consider new adjustments prior to or during significant facility events.

- Record in detail all adjustments and the result of the adjustments for future references or corrective action.

SubCool Engineering has sound, practical knowledge on variables that affect ice making. It’s understood that outside temperatures, inside temperatures and humidity, type of ice activity, number of spectators, spectator heating and cooling, all play a factor in maintaining optimum artificial ice conditions! However, owners must be committed to applying these skills in the workplace. Having a strong theoretical understanding but failing to apply the knowledge gives no return on training investment.

SubCool Engineering is always happy assist you in better understanding this information while helping you create and maintain an exceptional sheet of ice.

Temperature Adjusting Energy Notes

Each Degree C that you raise the ice temperature reduces the load on the refrigeration plant by 3 to 4 per cent. The higher the ice temperature, the lower the potential for heat transfer.

Increasing the ice temperature during times that there is to be no use (8+hours) has several benefits. This saves energy and also “tempers” the ice making it more durable. Tempering results in less ruts and chips which requires less maintenance.

Additional Information and Resources to this Document

Ontario Recreation Facilities Association Inc. (ORFA) - Understanding Artificial Ice Operating Temperatures

http://www.customicerinks.com. http://www.cimcorefrigeration.com

http://www.saskpower.com/pubs/energy_management.shtml

CETC Varennes (NRC) Factsheet on Controlling Ice Temperature (utilizing energy conservation methods)

http://cetcvarennes.nrcan.gc.ca/fichier.php/codectec/En/2003-066-6/2003-066-6f.pdf

Disclaimer

The information contained in this reference material is distributed as a guide only; it is generally current to the best of our knowledge, having been compiled from sources believed to be reliable and to represent the best current opinion on the subject. No warranty, guarantee or

representation is made by CTC as to the absolute correctness or sufficiency of any representation contained in this reference material and CTC assumes no responsibility in connection therewith; nor can it be assumed that all acceptable safety and health measures are contained in this reference material, or that other or additional measures may not be required in particular or exceptional conditions or circumstances. Reference to companies and products are not intended as an endorsement of any kind.