Refrigeration Systems keep NHL arenas on ice

July 27, 2000
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Figure 1. Refrigeration load for an ice arena.
A full-size hockey arena floor is normally 200 by 85 ft; Olympic-size hockey floor, 200 by 100 ft; curling sheets are 14 by 146 ft, but are usually laid out at 15 by 150 ft. The refrigeration load (Figure 1) can range from 45 to 300 tons for an arena.

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-in. cement pad reinforced with Rebar.

The brine is supplied to the floor via 6- to 10-in. headers. The headers are constructed of PVC or steel. The headers feed an in-floor-cooling grid consisting of 1-in. polyethylene or steel pipe spaced on 3- to 4-in. centers.

The cooling floor brine is usually a calcium chloride solution mixed to a freeze point of -5° to -10°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-in. brine mains. The mains, in turn, feed a 1-in. polyethylene grid spaced on 12- to 24-in. centers. The heating floor is positioned approximately 1 ft under the cooling floor and is separated by insulation and a vapor barrier.

The heating floor brine should be kept at a freeze point of 10° to 15°. 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.

Figure 2. A direct refrigeration system.

Direct refrigeration system

A direct refrigeration system (Figure 2) circulates refrigerant in a piping system imbedded directly in the rink floor. This format has been used for a small number of refrigeration systems throughout the United States but rarely in Canada.

The direct refrigeration system is more efficient than an indirect system, but the increased exposure to refrigerant leaks has decreased its popularity.

Some outdoor refrigeration systems have employed ammonia as the refrigerant, but the norm has been R-22 or one of the newer, “ozone-friendly” alternatives.

The piping configurations vary with the manufacturers. A very common configuration was 1/2-in. steel tubing on 4-in. centers. There have been a lot of problems with leaks on this format over the years, so recently there has been a trend towards using larger-diameter schedule 40 pipe in an effort to minimize leaks.

The low-pressure liquid refrigerant is pumped from a recirculation vessel to a supply header at one end of the arena. From the header, the refrigerant enters individual circuits and passes through the cooling floor grid, where it picks up heat. A portion of the liquid refrigerant will evaporate as it absorbs heat.

The liquid/gas mixture arrives in the return header and then returns to the recirculation vessel. The heat-laden refrigerant vapor separates in the recirculation vessel and is drawn in by the compressors, where its pressure is increased. The compressed gas enters the condenser, where it gives up heat and turns into a high-pressure, medium-temperature liquid and drains into the receiver.

From the receiver, the high-pressure liquid refrigerant passes through a solenoid valve controlled by a level control in the recirculation vessel. The high-pressure liquid is reduced in pressure by an expansion device and enters the recirculation vessel as a low-temperature liquid capable of absorbing heat again.

A pump can convey the refrigerant or it can be pushed through the system utilizing high-pressure gas from the discharge side of the system. This method incorporates additional valving to eliminate the possibility of dumping excess high-pressure gas into the low-pressure side of the system.

Heat reclaim

The entire refrigeration process is devoted to removing heat from one area and disposing of it outdoors at the condenser. Since a great deal of heat is conveyed by the refrigeration system and a lot of power is consumed to operate the electric motors, it makes sense to make efficient use of the waste heat.

Before a lot of money is being spent to reclaim heat, you must first identify a good use for the heat. Remember that the colder it is outside, the less heat will be available for reclaim. Will the heat be available when you most need it?

Do not use recovered heat as the sole heat source for an occupied area. If, for some reason the plant is shut down or only running a minimal amount of time, it could cause severe difficulties in cold weather.

The installation of a heat-reclaim system must make economic sense. For example, if you require only a minimal amount of heat for hot water on rare occasions, it would be better to install a small electric or gas hot water heater.

If a heat-reclaim device is to be used for domestic hot water, it must be double-walled and vented to prevent contamination of town water in the event of a leak.

Some good uses of heat reclaim are:

  • Underfloor heating;

  • Zamboni water heating;

  • Domestic hot water heating;

  • Swimming pool heating;

  • Fresh air makeup preheat; and

  • Snow melt pit.

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