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Case Studies: Dubuque County Courthouse


Dubuque County Courthouse – Dubuque, Iowa

38,000-square-foot, five-story, 105-year-old structure listed on the National Register of Historic Places

Geothermal heat pump system:

  • 106-ton Mammoth brand.
  • 100 console-type water source heat pumps sized from ¾ to four tons each.
  • COPs of 3.88 and EERs ranging from 17.7 to 22.6.

Geothermal loop system:

  • Open loop well at 94 feet deep.
  • 350 gallon-per-minute capacity.
  • Variable speed drive on well pump.

Annual energy costs:

First-year savings to taxpayers was $6,000 in natural gas, $3,000 in water and $2,000 in electricity.

At a glance:

  • Former boiler and cooling tower heap pump system provided existing piping to each console, minimizing disruption of building and occupants.
  • Building now has increased comfort with simultaneous heating and cooling – critical in Iowa’s volatile spring and fall weather.
  • New system uses only 10 percent of the old, gaining valuable floor space in a historic building.
  • Maintenance needs were reduced considerably, allowing staff spread time at other county facilities.

System performance report:

GeoExchange System Monitored Performance: Dubuque County Courthouse – Final Report by CDH Energy
[PDF format – 20 pages, 393KB]


Steven Ulstad Architects – Dubuque, Iowa


Gilmor & Doyle, Ltd. – Waterloo, Iowa


Giesler Brothers – Dubuque, Iowa


Alfa-Laval plate heat exchangerMammoth console unit