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� <br />��k _ � , _ �, � � <br />Oct. 18, 2004 <br />Item: 4. <br />Department Approval Manager Approval Agenda Section <br />Item Description: " `� � <br />Update and Options regarding Problems with the Refrigera- <br />tion Sys�em at the John Rose Minnesota OVAL <br />I. Background <br />A. The Basic System. <br />The concrete surface of the OVAL is refrigerated to maintain ice approximately <br />4 months of the year. It does this through a chiller vessel. The chiller is an <br />800 ton unit that uses ammonia to cool a saltwater solution called brine. The <br />brine is cooled by circulating it through approximately 800 hundred carbon <br />steel tubes within the chiller vessel that are surrounded by ammonia. Each <br />tube is roughly 28 feetlong and one inch in diameter. The walls of the steel <br />tubes are rather thin to allow the ammonia to chill the brine circulating <br />through each tube. There are approximately 20,000 gallons of brine within <br />the system. <br />Once the brine is chilled to approximately 10° within the steel tubes within the <br />chiller vessel, the chilled brine is pumped through plastic pipes to the concrete <br />floor of the OVAL. The surface of the OVAL floor is approximately 110,000 <br />square feet. The OVAL floor is the largest outdoor sheet of refrigerated ice in <br />the world. There are over 80 miles of plastic pipe embedded within the concrete <br />floor of the OVAL that distribute the chilled brine to stabilize the temperature <br />of the concrete floor and, hence, the ice above. <br />B. The Problem $v What Has Been Done. <br />The John Rose Minnesota OVAL has operated for 11 years. Beginning last <br />year, we started experiencing pressure losses within the OVAL's chiller vessel. <br />The pressure problem was significant enough that, on June 14, 2004, staff <br />asked the City Council to approve a competitively bid contract with Gartner Re- <br />frigeration. This contract was to open up the chiller vessel, identify the source <br />or sources of the pressure leaks, and to repair the system. The Council ap- <br />proved this contract for approximately $80,000. <br />Work under that contract has gone on for the last four months. Both ends of <br />the chiller vessel were removed. To the extent possible, corrosion was removed <br />from chiller tubes and support manifolds. (The steel tubes were inspected and <br />cleaned in place; due to the number and length of the tubes, and the way they <br />