The State Capitol Building of Oklahoma is a historic building, with approximately 400,000 square feet of floor area and six floors. It was initially cooled by window air conditioning units and unitary air conditioners and heated by steam from a steam generator located near the building.
A ground heat exchanger was installed inside a 300-foot diameter traffic circle and consists of 373 vertical boreholes, each 256 feet deep. Up to six loops were attached to each header pipe, which were connected into 12 underground gathering pits.
Supply and return line from the field run under the traffic circle through an existing steam tunnel. Fluid from this field is circulated to 325 heat pumps located throughout the State Capitol building.
Two 125-horsepower pumps operating as a primary and stand by arrangement are capable of producing 2,200 gallons per minute each at full flow. These pumps circulate fluid through the ground heat exchanger and the installed heat pumps. There are no intermediate heat exchangers separating the ground heat exchanger fluid from the heat pump fluid.
A cooling tower was installed to reduce the installation cost and waste excess heat that is not being used. Ground heat exchanger costs average $5.30 per foot, which does not include the steam pipe from the field to the Capitol building. Drilling of the ground heat exchanger field, using a single drilling machine, took a crew of three persons approximately six months.