Design Tips
On an indirect refrigeration system a choice must be made between the type of secondary coolant that you select. Both Calcium Chloride and glycol have been successfully used over the years and there are applications where both secondary coolants have an advantage. To a much lesser degree other heat transfer mediums such as methyl alcohol have also been utilized in the ice rink industry.
In regards to energy efficiency, Calcium Chloride is the better choice. Its heat transfer coefficient is much better than glycol. This fact equates to smaller, less expensive chillers for the same heat transfer. The heat transfer in the floor piping system is also better. Due to the superior heat transfer characteristics, the brine pump can be smaller and the required pump horsepower and corresponding energy consumption is reduced with calcium chloride.
Calcium chloride is highly corrosive when not maintained properly. With proper system design and operation it is still the best choice for most ice rink applications. The system components must be selected specifically for the Calcium Chloride. Typically chillers are made out of carbon steel or cuper-nickle. Brine pump shafts and butterfly valve stems should be made out of stainless steel.
With a system utilizing Calcium Chloride, it is imperative that the system is kept full at all times and no air is allowed to come in contact with the internal components. A high-grade environmentally friendly rust inhibitor must be used to ensure equipment longevity. It is good practice to carry out routine in house brine tests to monitor brine strength and pH on a semi annual basis and to request a lab report once a year.
In systems that are occasionally emptied and filled such as a portable system, glycol can be a very good choice. Glycol will reduce the effects of corrosion in systems that are occasionally opened to the air. It is still important to use good quality inhibited glycol such as Dow SR-1 and to ensure that annual lab samples are taken to verify the integrity of the solution.
On floors with end headers, the 1" pipe permits higher glycol flow rates at lower pressure drops. This results in reduced temperature drops across the grid, faster temperature recovery, and superior temperature control. Better ice surface conditions are maintained during varying conditions. Equivalent flow rates can be achieved with the ½" mat style system if side headers are installed but this will result in over 400% more mechanical joints and the corresponding potential for leaks.
The lower pressure drops in the large pipe system will result in reduced horsepower requirements per gallon of pumped glycol.
When the 1" pipes are imbedded in the cement floor this design provides a very large thermal mass, which keeps temperature swings to a minimum further improving ice consistency.
The larger 1" pipes are less susceptible to fouling or blockage by foreign objects and have less than ½ the mechanical connections reducing the chance of leaks.
The 1" pipes when imbedded in cement require no further handling and do not deteriorate as rapidly as the ½" pipes that are rolled and unrolled over the years.
In order to provide sufficient pipe protection for the mat style system it is normal to operate with a thicker ice surface than is required with a cement floor.
A cement floor is easier to monitor ice thickness by drilling tap holes on a weekly basis. Consistent ice thickness means consistent ice temperature and reduced operating costs.
Set up and take down time is eliminated with the cement floor versus the mat style system that must be rolled up and put away if the ice is removed.
There are good reasons for installing both sand floors and cement floors in an ice skating facility. Hopefully the following should make your decision easier.
Sand floors are utilized to reduce the initial cost of an ice surface. A sand floor is generally used in a year round ice facility but can be installed in a seasonal facility with some precautions to prevent unwanted traffic on the piping system during the off season.
A sand floor reduces the flexibility of the facility in that no off-season activities can be held directly on top of the sand. An ice covering can be used to facilitate light activities on top of the ice, but there is not enough support for rodeos, tractor pulls etc. If for some reason the building must be sold, a sand floor will reduce the buildings usefulness and resale value.
A cement floor for an NHL size ice rink will cost between $50,000.00 and $125,000.00 more than a sand floor depending on the floor strength, proximity of material, and a good super-flat contractor. A cement floor increases the flexibility of the facility in that dances, bingo's, and trade shows can be held in the off season. With a properly engineered floor, a circus or other heavy event can be held as well. As with a sand floor, the ice surface can be covered for non-ice events while the ice is in place.
In order to prevent puncturing the cooling pipes, additional care and attention is required during the initial stages of ice making with a sand floor. Before applying the first water, you must ensure that all of the pipes are in their chairs and the sand has been dressed out to its normal operating level.
In order to maintain a crisp, clean, efficient ice surface all arenas should have the ice periodically removed to purge the buildup of solids and old paint that is deposited over time. On a sand floor the residue tends to cake on the sand surface and can only removed by replacing the surface sand. This residue is easily washed away on a cement floor.
A cement floor is much easier to make ice on, especially with less experienced personnel. A sand floor requires gently misting the sand surface while avoiding puncturing the pipes until there is an ice layer thick enough to walk on and eventually drive a Zamboni on. When installed properly, a cement floor always ensures a precisely level surface to form the ice base. A sand floor can deviate over the years with use.
It is advisable to maintain 1 3/4" to 2 1/2" of ice on a sand floor to reduce the chance of puncturing pipe during ice events. Cement floors only require 1 ¼" of ice for safe use. Periodically measuring the ice surface thickness by drilling holes (ice taps) is much easier with a cement floor. With a sand floor added attention must be taken to ensure that no pipes are punctured while edging or re-surfacing. This special care is not necessary on a cement floor.
Once the ice is in place, there can be a small amount of difference in energy consumption between a sand floor and a cement floor. The same amount of BTU's will enter the ice surface regardless of the style of floor. A well-designed cement floor will typically have 1" of cement cover and 1" of ice cover above the cooling pipes. A sand floor will typically have 2" of ice cover above the pipes. Ice has a K value of 1.3 and cement has a K value of 0.54. The K value is the rate a substance conducts heat with a higher K value conducting heat faster than a low K value. So, theoretically the cement floor would have to operate a little colder than the sand floor for the same amount of heat to be exchanged. However, in reality, many sand floors usually develop small hills and valleys over the years, which requires the ice level to be kept thicker in many areas, which reduces the efficiency.
Whichever way you choose to build your ice skating facility, rest assured that with proper care and attention a great ice surface can be maintained on either a sand floor or a cement floor.
If you can control the humidity in your facility you are one very large step towards creating the ideal ice skating environment.
Humidity enters an ice rink with incoming ventilation air, the opening of doors, from the use of showers, and through the normal respiration of the people within the building.
If your facility is in a cold environment such as Winnipeg, Manitoba the incoming air can easily be 00F and 50% relative humidity during a typical winter day. If this entering cold air is warmed up to 400 F the humidity will now fall to less than 20% because warm air has the ability to hold more moisture. This lower humidity level poses little problem to the proper operation of the facility.
However if your facility is in Los Angeles, California the incoming air could easily be 650 F with a relative humidity of 65%. If this entering warm air is reduced to 500 F inside the skating rink the humidity will skyrocket to 100% relative humidity because the cold air will not hold as much moisture. At this point there is only one place for the water vapour to go, it condenses into water droplets and the problems begin.
Just as a boiling kettle deposits moisture on a cold window on a winter's day, airborne moisture in an ice rink will also deposit on cold surfaces, and of course the coldest spot is very likely the ice surface itself. When this happens, the ice will cloud over, losing its desired sheen and will start to become sluggish to skate on. The glass around the ice surface will also fog over, obstructing the view of the audience.
In addition to the aesthetic inconveniences caused by excessive humidity the condensing moisture releases a tremendous amount of heat into the ice surface that must be removed at the expense of operating the refrigeration equipment longer than would normally be required. Condensation can permeate your building insulation, drastically reducing its effectiveness and of greater consequence, structural steel will start to rust and wood will start to rot, further reducing the integrity of your facility.
In addition to the aesthetic inconveniences caused by excessive humidity the condensing moisture releases a tremendous amount of heat into the ice surface that must be removed at the expense of operating the refrigeration equipment longer than would normally be required. Condensation can permeate your building insulation, drastically reducing its effectiveness and of greater consequence, structural steel will start to rust and wood will start to rot, further reducing the integrity of your facility.
Luckily, with proper design, humidity can be controlled effectively and efficiently. The two commonly used styles of dehumidification systems are the mechanical dehumidifier and the desiccant dehumidifier.
The floor surface is occasionally constructed entirely with sand but this limits the use of the facility. More commonly the floor consists of a 5" or 6" cement pad reinforced with Rebar.
The brine is supplied to the floor via 6" to 10" headers. The headers are constructed of PVC or steel. The headers feed an in-floor-cooling grid consisting of 1" polyethylene or steel pipe spaced on 3" to 4" centers.
The cooling floor brine is usually a calcium chloride solution mixed to a freeze point of -5 to -10 deg. F. The pH should be maintained at a level of 7.5 to 8.5 The brine should be tested annually by a lab regularly engaged in testing arena brine samples.
The rejected waste heat from the refrigeration plant typically provides the heat source for the heating floor but boilers or electric resistance heaters are occasionally used as well.
The heated calcium is usually supplied to the heating floor via 4" brine mains. The mains in turn feed a 1" polyethylene grid spaced on 12" to 24" centers The heating floor is positioned approximately 1' under the cooling floor and is separated by insulation and a vapour barrier.
The heating floor brine should be kept at a freeze point of 10-15 deg. F. The pH should be maintained at a level of 7.5 to 8.5 The brine should be tested annually by a lab regularly engaged in testing arena samples.