Geothermal System Cuts Gas, Electric Usage for Athletic Center
February 2, 2009
In a time of tight budgets and soaring energy costs, the St. Cloud (Minn.) Municipal Athletic Center (MAC) found a way to go green and save taxpayer dollars in the process. With the installation of a new GeoExchange system, the MAC is using the earth to maintain the arena ice and heat the facility, saving electricity and gas as well as reducing greenhouse gas emissions.
This project originated after the 2007 Fall Minnesota Ice Arena Manager’s Association meeting where Harris Companies presented information on improving energy efficiency in ice arenas. Following that presentation, Todd Bissett, St. Cloud MAC arena manager, asked for a follow-up visit.
The MAC has two arenas. One is original to the facility and was installed in 1972 (Torrey Arena); the other is part of the 1997 addition (Ritsche Arena). The 1972 arena was in poor condition, needed repair, and was not operating efficiently. In addition, the original arena floor was built using galvanized piping that circulated brine through the floor causing severe degradation in heat transfer and effectiveness. The MAC staff felt that they could justify a chiller replacement with energy savings, but did not think the floor could be replaced due to budget constraints.
Harris Companies met with the arena staff and conducted a preliminary review of the facility and found that the project, including the new floor, would be feasible. The final contract was approved by the City Council and signed in early June 2008. The new floor was installed and skating resumed in late September 2008, while the remainder of the project was completed in November 2008.
The MAC staff has a new arena floor in the Torrey Arena, a high efficiency TRAK International GeoExchange (ground source heat pump) “chiller plant”, a new Web-enabled and integrated building automation system (BAS) installed by Harris Controls, and improved system operation. The MAC team, the city of St. Cloud, and the citizens of St. Cloud now have a high-performance “green” arena that will reduce gas usage by 95 percent and electric usage by 30 percent. Nearly 4 million gallons of water usage will be eliminated along with the yearly elimination of 300,000 pounds of greenhouse gases.
DEMOLITION AND NEW RINK FLOORThe first phase of the project involved the demolition of the Torrey arena floor, the chiller room, pumps, and evaporative condenser.
The new rink was designed using a state-of-the-art floor design that maximizes heat transfer to create a high quality skating surface while using substantially less energy. The new floor utilizes a below-grade thermal storage buffer to create thermal storage capacity, sustain consistent glycol temperatures, and minimize the risk of ice loss related to a loss of cooling.
The floor contains three circuits to provide only the amount of flow needed to maintain ice quality, saving cooling capacity and pump energy. The floor is constructed using high-density polyethylene pipe (HDPE) that was installed using fusion welding to create a seamless piping assembly that is resistant to leaks and friction loss. The floor contains more than 19 miles of 1-inch HDPE and more than 600 feet of 6-inch HDPE pipe. Added insulation under the thermal storage buffer, around the header, and along the sideboards prevents loss of capacity to the surrounding areas.
GEOEXCHANGE GROUND SOURCE HEAT PUMP SYSTEMThe heart of the new installation is the TRAK International GeoExchange ground source heat pump system. The system has four 60-ton heat pumps dedicated to the source loop providing 12-15°F chilled glycol for the arena floors and two 60-ton heat pumps dedicated to the load loop that provides 145°F hot water that is integrated into the existing hot water and domestic hot water systems.
The system was custom designed by TRAK to meet the needs of both ice rinks. The Ritsche Arena (1997) Vilter flooded chiller system was left in place, but tied into the new TRAK system so that it could remain as a back-up system and provide additional capacity if needed during peak load conditions. During construction of the project, the new Torrey Arena floor was initially cooled using the Ritsche Arena Vilter chiller system.
The TRAK heat pumps were custom built by Midwest Fabrication and Supply of Zumbrota, Minn., for this application. The heat pumps are high efficiency industrial grade heat pumps that are designed for the specific facility where they will be installed. They include on-board direct digital controls and electronic expansion valves.
The geothermal well field was installed under the existing parking lot and consists of more than 6,500 feet of vertical boreholes.
The circulating pumps were installed with variable frequency drives to allow reduced flow through the circulating loops.
A fluid cooler was added to the system to allow for additional heat rejection and free cooling during cold winter months when it is possible to circulate chilled glycol through the fluid cooler and eliminate the need for mechanical cooling.
DEHUMIDIFICATION AIR HANDLING UNIT FOR TORREY ARENAThe existing dehumidification unit for Torrey Arena was retrofitted in the field to convert the existing refrigerant and hot water coils to chilled water and hot water coils. In addition, a new high efficiency motor and variable frequency drive were installed. The unit uses excess cooling from the rink floor supply and waste heat to efficiently maintain rink humidity levels.
DEHUMIDIFICATION UNIT FOR RITSCHE ARENAThe Ritsche Arena used a Fresh Air Systems (FAS) dehumidification unit that contained a desiccant wheel that was recharged by heat generated from a 750,000 Btu natural gas hot water boiler in the unit. The hot loop piping was extended to this unit in order to use waste heat generated from maintaining the ice to recharge the desiccant wheel.
HEAT RECOVERY AIR HANDLING UNIT RETROFITA heat recovery air handling unit for the Torrey Arena that had used hot refrigerant gas from the chiller was converted to use hot water that is heated with waste heat from the TRAK heat pump plant.
BUILDING AUTOMATION SYSTEMThe Torrey Arena was built in 1972 with pneumatic controls for the temperature control system. Several years ago, the pneumatic control system was abandoned and replaced with stand-alone electric controls. Most of the valves and actuators were retrofitted in some way, but several were left without any control and remained that way until this project was completed. Ritsche Arena was built in 1997 and used electro-mechanical controls for the Vilter chiller plant and KMC Controls direct digital controls (DDC) for the arena temperature control.
This project replaced all of the stand-alone controls in the Torrey Arena, and integrated both the existing KMC Controls in the Ritsche Arena and the new KMC Controls for the TRAK heat pump plant and Vilter plant into one system. The project also included the addition of CO2 sensors for the Torrey Arena make-up air units so that they only operate and ventilate when the building occupancy requires additional outdoor air.
The BAS uses a Web-enabled graphical user interface to allow the arena staff to monitor the system, adjust schedules, and operate the building from anywhere Internet access is available. The BAS includes energy management functions to monitor and control the arenas’ energy use in the facility.
ELECTRICAL UPGRADEThis project included modernizing the existing electrical supply to accommodate the new equipment. In addition, updates to the secondary feeders were needed to meet current electrical code.
Publication date: 02/02/2009