The geothermal well field was installed under
the existing parking lot and consists of more than 6,500 feet of vertical
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
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.
The new rink features a state-of-the-art floor design.
DEMOLITION AND NEW RINK FLOOR
The 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.
The heart of the new installation is the GeoExchange ground source heat pump system.
GEOEXCHANGE GROUND SOURCE HEAT PUMP SYSTEM
The 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
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
DEHUMIDIFICATION AIR HANDLING UNIT FOR TORREY ARENA
The 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
DEHUMIDIFICATION UNIT FOR RITSCHE ARENA
The 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 RETROFIT
A 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 SYSTEM
The 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.
This 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.