In Rockford, Ill., the owners of a new 12-business strip mall approved a plan for a network of water-to-air geothermal systems piped to a large main serving as a “thoroughfare.” Each system would be able to pull and deposit British-thermal-unit-rich fluids as needed. With a total capacity of 90 tons, the project called for an extensive geothermal-exchange field.



“The geo-exchange field takes up the entire parking lot,” Ryan Kerry, part owner of Great Lakes Geothermal, the drilling subcontractor, said.


“Boreholes for the Rockford mall average 250 ft in depth,” Kerry said. “We would normally go deeper, but we kept hitting gravel. Most likely, it's loose conglomerate from an old, now-dormant underground river bed.”




“Illinois state code mandates that all geothermal boreholes are grouted,” Kerry said.


On the Inside


“Initially, we considered having a primary pumping system with continuous flow through all the wells and all the units, but later discarded the idea, even though we knew there'd be greater overall system efficiency if we circulated fluids that way,” Bill Sprague, project manager for Area Mechanical, said. “But the owner of the building insisted on having the ability to split up the utility bills. A primary pumping arrangement would have allowed for only one power meter.

“There's a total of eight circuits, each comprised of eight 2-in. geothermal loops,” Jeff Hurst, geothermal product manager for Connor Co., Area Mechanical's geothermal-equipment supplier, said. “These are connected, or fused together, in the geo-exchange field.”


“Once the circuits reach the building, they join a 4-in. main, or header, that all the units individually draw from,” Hurst explained. “It's not a continuously running body of fluid. Fluids circulate only when there's a call for Btus.”

To ensure heating and cooling costs are distributed fairly, each shop has its own flow center. The flow center is wired to the tenant's power meter. Each tenant simply pays for its energy use.

“The pump arrangement we ended up using gives each tenant the ability to monitor their own energy use, hopefully making them a little more energy-wise,” Sprague said. “That was the building owner's intent, and it appears that it's worked very well.”


The average flow rate for the restaurant's 7 tons of heating and cooling systems is 3 gpm per ton.










“We must meet the minimum need of 2 fps when flushing, as recommended by IGSHPA (International Ground Source Heat Pump Association),” Project Manager Bill Sprague said. “But with commercial systems, where larger pipes are used, we often need a larger motor and pump to meet the volume we need to push through larger pipes. Our 7-hp unit is well-suited for that.

“Once we were called in to push debris out of a large geo-exchange field that we weren't involved with,” Sprague continued. “They couldn't move the sand and grit out of it with a standard-sized flushing unit. We cranked up our 7-hp unit and got the job done. There were gallons of stuff in the pipe that didn't belong in there.”



“We usually double it to be safe,” Sprague said.