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the brine solution will, typically, lower the freezing point of the solution. However, if the calcium chloride content is increased beyond a certain point, the freeze point of the solution will actually go up rather than down. This critical concentration is called the eutectic point and represents the lowest value that a salt solution can be made to freeze at. This value is around -60°F (-50°C). As the concentration of calcium chloride within the water increases, so does the density and specific gravity. In addition, the specific heat and thermal conductance decreases. The term "specific gravity" is most often used when measuring the concentration of salt in water. The specific gravity of a brine is the ratio of the density of the brine to that of water. As such, expressions of specific gravity have no units of measure. Water at 62.4 lb/ft 3 (100 kg/m 3 ) is said to have a specific gravity of 1 at 60°F (16°C) and as calcium chloride is mixed into water, the specific gravity of the solution goes up. The recommended specific gravity of calcium chloride brine solutions for rinks is 1.2 and is measured at 60°F (15.5°C). Such a solution represents a concentration of approximately 22% solution and would yield a freezing point of about -15°F (-26.1°C). If concentration of this solution is allowed to decrease, say by dilution to a specific gravity of 1.186, the freezing point rises to approximately 0°F (-17.7°C). On the other hand, if the strength is increased to 1.24, the freezing point falls to -25°F (-32°C). Although it may seem that there is no considerable problem in keeping a somewhat stronger- than-recommended brine solution, it should be noted that it will increase brine pump horsepower requirements and/or reduce total brine flow and can affect the heat transfer capacity of the brine solution. Adding or Strengthening Brine Should it become necessary to add or strengthen the brine or to add brine treatment to the system after the initial charge, it can be done by creating a suction at the brine pump and then using the two brine charging valves located between the brine shut-off valves and the pump. A suitable brine mixing tank is needed, such as a clean 45 imperial gallon (208 liters) drum. This is used to mix the calcium chloride with the water. A connection near the bottom of the mixing tank is then connected to the brine charging valve adjacent to the pump suction. 30 R INK MAGAZ INE MAy/June 2007 BRINE INHIBITORS Most brine systems use some type of brine inhibitor to help control corrosion. Chromate inhibitor was typically supplied for brine systems until approximately 1990. After this time organic brine inhibitors have been supplied. This inhibitor concentration should be analyzed a minimum of once per year. Organic inhibitors unlike chromate break down in the brine system and create an organic sludge. A bypass filter should be installed as part of the brine system to control the accumu- lation of this sludge in the brine system. GLYCOL SYSTEM Ethylene and propylene glycols are now commonly used in recreation facilities as an alternate to brine solutions. Charging glycol, maintenance, adding or strengthening and control are all similar to that of the brine system. It is also common practice to utilize the bypass filter on a glycol system to control sediment and dirt. Glycol solutions should also be analyzed a minimum of once per year. Freezing points of Aqueous Glycol Solutions An ethylene concentration of 40 percent by weight and a -10ºF (-23.3ºC) tempera- ture are typical for ice rink applications. B R I N E M A I N T E N A N C E B R I N E M A I N T E N A N C E An Indirect Refrigeration system uses brine and ammonia. You can see the brine pumps on the left, the chiller and surge drum in the middle and the compressors on the right. RINK PHOTO

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