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Roseville Skating Center and City Hall Feasibility Study September 23, 2007 integrated system adds significant amounts of thermal energy to the system that can be transferred to other campus buildings. The integration of the two refrigeration systems in the campus buildings with the heating, ventilation, air conditioning and water heating systems in the buildings is accomplished by connecting the mechanical equipment to a common, fluid based system that can store thermal energy. In practical terms this is accomplished by making two basic changes to the mechanical heating, cooling and refrigeration systems in the buildings. The first change is to convert or replace refrigeration and air conditioning systems that reject thermal energy to the outdoor air (via cooling towers and air cooled condensers), to a fluid based system connected to a GHX that is designed to store thermal energy in the ground around the buildings. The second change is to replace gas burning appliances (gas boilers, roof-mounted gas furnaces, gas water heaters, etc.) to fluid based equipment designed to extract thermal energy from a GHX buried in the ground around the buildings. By connecting equipment that provides heating, cooling and refrigeration that often operates simultaneously, to a common GHX, it is possible to transfer energy easily and efficiently from one building to another. And since the ground can store large amounts of thermal energy by simply increasing in temperature a few degrees, or release large amounts of energy by cooling a few degrees, temporary energy imbalances are easily addressed. The GHX operates much like a bank account. When there is excess thermal energy that is not required immediately it can be deposited into a thermal energy savings account. When heating is needed in a building and no thermal energy is available from the refrigeration systems, it is possible to dip into the energy savings account. 5.1. Thermal Energy Storage: Ground Heat Exchanger (GHX) The earth has an enormous capacity to store low grade thermal energy. This is accomplished simply by burying a heat exchanger in the earth around the buildings on the campus. A heat exchanger can be built by burying high-density polyethylene (HDPE) pipe in the ground. HDPE pipe can be buried either in a horizontal trench at a depth of 5' to $', or in vertical boreholes drilled to a depth of 150' to 400'. The ambient ground temperature in Minneapolis is approximately 4i°F. When more thermal energy is removed from the ice surface in the ice Arena than can be used in the Ice Arena / Banquet Hall, the refrigeration system can be designed to warm fluid that is circulated through the GHX. When the fluid is warmer than the surrounding ground temperature, heat is dissipated to the ground, while the fluid is cooled by the 47°�' earth. As more thermal energy is dissipated to the GHX, the ground graduallywarms creating a large mass of warm ground. Geo-Xergy Systems Page 14 of 33