Perham High School

GEOptimize Inc was retained by Ottertail Power Company to develop the energy modelling, ground heat exchanger (GHX) optimization strategy, and design review for the proposed 100,000–120,000 ft² Perham High School. A detailed 8,760-hour Trane Trace energy model was created and iteratively refined with the architectural and mechanical design team to accurately represent ventilation control strategies, kitchen make-up air requirements, occupancy schedules, and system performance. The resulting load profiles were used to evaluate GHX sizing and long-term entering water temperature stability using GLD modelling, with local geology defined through Minnesota Department of Health well logs and a thermal conductivity test from the adjacent elementary school. The analysis demonstrated how ventilation control, distribution temperature reset, and system efficiency directly affect annual ground loads and heat pump performance.

Multiple design iterations were assessed to balance annual heat rejection and extraction, reduce peak loads, and minimize borehole length while maintaining a minimum entering fluid temperature of approximately 32°F over a 10-year simulation period. Integration of an auxiliary boiler to serve a portion of the peak heating load significantly improved thermal balance and enabled a reduction in total borehole from approximately 62,400 ft to 48,000 ft—about a 23% decrease in GHX size and cost—while still allowing the geothermal system to provide roughly 98% of the annual heating energy. The review also developed detailed recommendations for borehole depth and spacing, reverse-return header configuration, purging and flushing requirements, Reynolds number targets for turbulent flow, pumping efficiency, geothermal vault location, and control sequences that accommodate interruptible utility power without compromising system performance.