Geothermal System Design Principles Flashcards

What is the recommended minimum flow rate per ton of capacity for a residential closed-loop geothermal system using water as the heat transfer fluid?

Answer: 1.5–3.0 GPM per ton

IGSHPA and equipment manufacturers recommend 1.5–3.0 GPM per ton to ensure adequate heat transfer and turbulent flow in the ground loop.

A geothermal loop filled with 20% propylene glycol solution will have a freeze point of approximately:

Answer: 15°F (-9°C)

A 20% propylene glycol solution has a freeze protection point of approximately 15°F (-9°C), providing a safety margin below typical minimum EWT targets.

In a two-stage or variable-speed compressor geothermal heat pump, what design advantage does variable capacity provide for residential systems?

Answer: Better matches part-load demand, improving seasonal efficiency and comfort

Variable-capacity compressors modulate output to match the actual building load, reducing short-cycling and improving the system's seasonal COP and humidity control.

Which loop configuration is most appropriate for a residential site with limited land area but access to deep drilling?

Answer: Vertical closed-loop boreholes

Vertical closed-loop boreholes require a small surface footprint because heat exchange length is achieved by drilling deep rather than spreading horizontally.

What is the purpose of a 'header' in a closed-loop geothermal bore field?

Answer: It connects multiple parallel borehole loops to a common supply and return manifold

The header manifold connects individual borehole U-tubes in parallel, balancing flow distribution across the bore field and reducing total pressure drop.

According to IGSHPA guidelines, what is the maximum allowable pressure drop recommended across a residential geothermal ground loop to minimize pump energy?

Answer: 4 ft WC per 100 ft of pipe

IGSHPA recommends limiting friction loss to approximately 4 ft of water column per 100 ft of pipe to keep circulating pump power within an energy-efficient range.

A designer is evaluating a pond loop for a residential system. What minimum pond volume (in acre-feet) per ton of system capacity is generally recommended?

Answer: 1.5 acre-ft per ton

Approximately 1.5 acre-feet of pond volume per ton of heating/cooling capacity is the commonly cited minimum to provide adequate thermal mass and recovery.