Flow That Follows Demand

The Setup

A 30,000 ft² university academic building in Canada relies entirely on a geothermal heat pump system for heating and cooling. Built in 2010, the facility uses water-to-air heat pumps connected to a horizontal ground heat exchanger (GHX) beneath the parking lot adjacent to the building. A 10 HP circulation pump equipped with a variable frequency drive (VFD) provides flow through the ground loop.

A Well-Performing Geothermal System

Ensure^® monitoring since July 2025 shows a geothermal system that is meeting building loads while maintaining stable loop temperatures throughout the year.

Ground loop flow varies with seasonal demand, reaching peak rates of approximately:

• 150 GPM during summer cooling
• 125 GPM during winter heating

The VFD allows the pumping system to adjust flow as conditions change, helping the building maintain comfort while avoiding unnecessary pumping energy during lower-load periods.

Performance Benchmark

A common benchmark for geothermal pumping performance is pump horsepower per 100 tons of installed heat pump capacity:

This building has 150 tons of installed heat pump capacity served by a 10 HP circulation pump, resulting in = 6.7 HP per 100 tons

Based on installed equipment, this gives the system a B rating.

But because the pump is equipped with a VFD, it operates below full speed for much of the year as building loads vary. Since pump power decreases dramatically as speed is reduced, this allows the system to operate at A-level performance for much of the year while maintaining occupant comfort and efficient heat pump operation.

The Benefit of Variable Flow

Variable-speed pumping is one of the most effective ways to optimize a geothermal system. By matching flow to building demand, the system can:

• Reduce pumping energy consumption
• Lower operating costs
• Maintain stable heat pump performance
• Improve overall system efficiency

Takeaway

This project demonstrates a successful geothermal project. By allowing flow to follow demand, the VFD helps the system deliver reliable heating and cooling while minimizing pumping energy.

In geothermal systems, efficient operation isn't about maximizing flow, it's about delivering the right flow at the right time.