Geothermal Pump Head Calculator

Determine total ground loop circulation GPM, Darcy-Weisbach friction head loss (ft of head), antifreeze viscosity penalties, and circulator pumping power watts per ton.

Total Capacity (Tons)

Loop Flow Rate per Ton

Antifreeze Mixture

Lowest Loop Entering Temp

Parallel Circuit Loops

Bore Loop Pipe Size

Single Circuit Loop Length (Both Legs + Header)

Total Loop Circulator Head Loss

28.4 Ft Head

Total Circulation: 15.0 GPM (3.75 GPM/circuit)

Reynolds Number (Re)

2,850 Re

Turbulent flow (> 2500)

Pumping Power

145 Watts

29 Watts / ton

Pressure Drop in PSI: 12.3 psi

Fluid Velocity in 3/4" HDPE: 2.08 ft/sec

Recommended Pump Module: Dual ECM High-Efficiency (e.g. Magna3 / UP 26-99)

Reynolds number exceeds 2,500 threshold, guaranteeing turbulent heat exchange without excessive pumping penalty.

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Geothermal Loop Hydraulics & Circulator Pumping Optimization

A properly engineered ground loop circulator pumping system must balance two competing thermodynamic priorities: maintaining turbulent flow (Reynolds number $Re > 2,500$) inside the HDPE pipes for efficient convective heat transfer into the fluid, while minimizing pumping parasitic power so circulator electricity does not degrade overall heat pump system COP.

Fluid Friction & Viscosity Factors

Flow Rate Standard:
Nominal flow rate is typically 3.0 GPM per ton (0.054 L/s per kW) across the coaxial water-to-refrigerant heat exchanger.
Propylene Glycol Viscosity Penalty:
At 30°F (-1°C), a 20% propylene glycol mixture is significantly more viscous than water, nearly doubling pipe friction head loss compared to pure summer water.
Darcy-Weisbach Head Loss Equation:
h_f (ft) = f × (L / D) × [ V² / 2g ]
Pumping Power Efficiency Metric:
Best practice ASHRAE guidelines target less than 50 to 75 Watts of circulator pumping power per ton of system capacity.

Frequently Asked Questions

Why is turbulent flow (Re > 2,500) critical in geothermal loops?

Laminar flow causes a stagnant boundary layer of fluid against the inner pipe wall, acting as thermal insulation. Turbulent flow vigorously mixes the fluid, maximizing heat exchange with the ground.

How does propylene glycol affect geothermal pump head loss?

At cold winter operating temperatures (around 30°F), a 20% propylene glycol antifreeze mixture has more than double the kinematic viscosity of water, substantially increasing system friction head.

What is an efficient pumping power benchmark for geothermal systems?

ASHRAE guidelines recommend designing circulator pumping systems to consume less than 50 to 75 Watts per ton of installed heat pump capacity.