Vertical geothermal design

Vertical Geothermal Borefield Design in Oklahoma: Depth, Spacing, Headers, and Flow

Direct answer: a vertical geothermal borefield in Oklahoma is designed by matching building loads, ground conditions, bore geometry, pipe, grout, EWT targets, flow, pressure drop, and headers. There is no reliable fixed depth per ton. The bore count, depth, spacing, rows, flow paths, antifreeze, and pump head have to work as one system before drilling starts.

For Oklahoma homes and light commercial buildings, the design problem is practical: fit enough heat exchanger into the available site while keeping flow, pressure drop, purge access, and long-term loop temperature within the design boundary. Soil, rock, groundwater, drilling access, utility clearances, and local requirements can change the final layout.

Core Definitions

Bore

A drilled vertical hole that contains the loop piping and grout or other approved fill.

Borefield

The full set of vertical bores, usually arranged by rows, bores per row, center-to-center spacing, and header location.

Flow Path

The route fluid takes through one parallel circuit. Flow per path affects velocity, pressure drop, purge performance, and heat transfer.

Header

The pipe assembly that connects multiple loop circuits to supply and return piping.

Those inputs go into software, and the software is only as good as what you feed it. The inputs to confirm before drilling is the short version.

Design Inputs For Oklahoma Sites

Input	Why it changes the borefield	Field question
Heating and cooling loads	The load decides how much heat must be rejected to or extracted from the ground.	Was the load calculation done for this building and these design conditions?
Deep-earth temperature	The starting ground temperature affects EWT targets and bore length.	What temperature was used and what source supports it?
Formation conductivity	Clay, sand, shale, limestone, moisture, and groundwater can move heat differently.	Was this estimated from logs, local data, or a test?
Bore spacing and rows	Spacing affects thermal interaction, land fit, drilling access, and long-term behavior.	What spacing and row pattern are shown on the design drawing?
Pipe, grout, and fluid	Pipe diameter, material, DR, grout conductivity, and antifreeze affect heat transfer and pressure loss.	Are pipe and fluid assumptions listed in the design report?
Headers and flow	Header length, circuit count, pipe size, and the farthest circuit determine pump head and purge requirements.	Does the design include a critical-path head-loss calculation?

Depth is an output of the load, never a guess. Bore depth, flow, head, and antifreeze is the calculation behind that.

Decision Logic

Confirm the load and selected equipment first.
Set minimum and maximum EWT targets for the loop.
Estimate or measure ground properties and deep-earth temperature.
Lay out bore count, rows, spacing, and available header route.
Choose pipe size, material, DR, grout assumption, and heat-transfer fluid.
Calculate design length and long-term ground-load effect.
Calculate flow per path, header pressure drop, and pump head.
Revise the layout when any thermal, hydraulic, purge, pressure, or code boundary fails.

Worked Example

Example only: a preliminary plan uses 6 vertical bores at 250 ft each. Total drilled heat-exchanger length is 1,500 ft. If the field is arranged as 6 parallel paths and the design flow is 18 gpm, the starting flow split is 3 gpm per path. If pressure drop is too high or purge velocity is not workable, the designer may adjust pipe diameter, header layout, bore series count, or pump selection before the plan is released.

total bore length = number of bores x depth per bore
gpm per flow path = system gpm / parallel flow paths

Header And Flow Checks

The header is not an afterthought. LoopLink PRO public header documentation treats header sizing and head-loss calculation as a separate step for the active ground heat exchanger, and it calls out the need to use the farthest distance for the worst-case circuit. That same principle matters in the field: the pump has to serve the hard path, not just the average path.

Field Checklist

Load report, equipment schedule, and design EWT values are attached to the job file.
Bore count, bore depth, row layout, center-to-center spacing, and drilling access are shown.
Pipe material, pipe size, DR, U-bend material, and joining method are specified.
Grout or fill assumption is documented.
Fluid type and antifreeze concentration target are documented.
Header route, valve access, purge points, and critical-path head loss are shown.
Known utilities, wells, septic, drainage, property boundaries, and local requirements are checked before drilling.

Safety And Professional Boundary

Vertical borefield work involves drilling, pressure-rated pipe, buried utilities, antifreeze, grout, heavy equipment, and electrical pump controls. Design assumptions should be reviewed by qualified geothermal professionals and installed under applicable codes and standards.

When To Call Hartzell’s

Call Hartzell’s when a borefield design is missing load inputs, EWT assumptions, flow paths, header sizing, or pump-head checks, or when an existing vertical loop needs to be evaluated before equipment replacement.

Call Hartzell's about vertical geothermal: 405-375-4822

Related geothermal pages

Geothermal hub Oklahoma loop design fundamentals Loop design software inputs Flow center sizing HDPE loop pipe and fusion

Primary sources used

These sources set the technical context. The page does not replace the model-specific manual, local code, or field measurements for a real job.

LoopLink RLC vertical bore help – Vertical bore inputs: formation conductivity, bore spacing, rows, bores per row, series/parallel flow paths, grout, EWT, and bore depth.
LoopLink PRO SDSU-RR header help – Header sizing, worst-case distance, design-flow and flushing-flow head-loss checks, and purge-velocity context.
LoopLink PRO zone group help – Flow analysis modes, design flow, EWT inputs, fluid type, temperature, and concentration context.
IGSHPA standards page – Current CSA/ANSI/IGSHPA C448:2025 standard status and current standard boundary.
PPI HDPE geothermal piping – Ground heat exchanger pipe material context, HDPE joining methods, and related standards.
PPI TN-55 plastic piping materials for ground source geothermal – Ground loop definitions, flow center context, antifreeze definitions, static water column pressure, pressure loss, and fluid compatibility limits.
U.S. Department of Energy geothermal heat pump overview – General GHP system context and ground-loop heat exchange overview.

FAQ

Is there one correct bore depth per ton in Oklahoma?

No. Bore depth depends on loads, geology, grout, pipe, spacing, EWT targets, flow, long-term ground load balance, and drilling conditions.

Why does bore spacing matter?

Bores that are too close can thermally interact. Spacing also affects header layout, property fit, drilling access, and long-term ground temperature behavior.

Can an existing vertical field be reused?

Sometimes, but only after the loop is identified, pressure checked, purged, flow checked, and compared with the replacement equipment and load assumptions.