Geothermal design inputs
Geothermal Loop Design Software: What Inputs Matter Before Drilling
Direct answer: geothermal loop design software is useful only when the inputs are real: room or block loads, ground temperature, soil or rock assumptions, EWT targets, equipment flow, pipe size and material, antifreeze concentration, header layout, pressure drop, and pump head. The software does not prove the drilling plan by itself. It tests a design model before the field work starts.
LoopLink public help files are one example of how design programs organize these assumptions. The important point for a homeowner or technician is not the brand name of the tool. It is whether the design inputs are documented well enough for the installer, driller, and service technician to agree on what the loop is supposed to do.
Definitions That Matter
Load
The heating or cooling rate the building needs at design conditions. Residential loads should come from an accepted load calculation process, not from square feet alone.
EWT
Entering water temperature at the heat pump. Loop design uses minimum and maximum EWT targets because equipment capacity, COP, EER, and loop length all depend on water temperature.
GHEX
The ground heat exchanger: the buried or submerged loop that exchanges heat with earth or water.
Head Loss
The resistance the pump must overcome through heat pump, valves, pipe, headers, fittings, and the loop field at the design flow.
Inputs To Confirm Before Drilling
| Input | Why it matters | What to check |
|---|---|---|
| Heating and cooling loads | The loop is sized to move heat into or out of the ground for the actual building demand. | Manual J or other accepted load output, design conditions, and zone assumptions. |
| Equipment schedule | Heat pump capacity, required flow, pressure drop, and rated performance change with operating conditions. | Selected model data and published rating context where applicable. |
| EWT targets | Lower heating EWT or higher cooling EWT can reduce loop length but changes equipment operation. | Minimum and maximum EWT used in the model and why they were chosen. |
| Ground assumptions | Soil, rock, moisture, groundwater, grout, and deep-earth temperature affect bore length and spacing. | Local logs, site survey, test data when needed, and conservative assumptions when unknown. |
| Pipe and fluid | Pipe diameter, DR, material, antifreeze, and fluid properties affect heat transfer and pressure drop. | Material standard, fusion method, fluid type, concentration, and compatibility. |
| Hydraulic layout | Flow paths, headers, fittings, and distance to the mechanical room determine pump head and purge needs. | Critical path, header sizing, flow splits, and flushing plan. |
Decision Logic
- Start with building loads and selected indoor equipment.
- Set design EWT targets and equipment flow requirements.
- Choose a loop type and draft a bore, trench, pond, or hybrid layout that fits the site.
- Assign pipe material, diameter, DR, antifreeze, and fluid properties.
- Calculate bore or trench length and then calculate the hydraulic critical path.
- Revise the design if pump head, flow balance, flushing velocity, pressure rating, or field layout is not workable.
Worked Example
Example only: a design calls for 12 gpm through the ground loop and uses four parallel flow paths. The starting split is 3 gpm per path before header losses and balancing details are checked. If the designer changes to three flow paths, each path sees 4 gpm. That may improve or harm the final design depending on pipe size, velocity, head loss, heat transfer, and purge requirements.
system flow = sum of active parallel flow paths
gpm per path = system gpm / number of parallel pathsField Checklist
- Document the load source and date.
- Record selected heat pump model, rated conditions, and design flow.
- List minimum and maximum EWT used in the model.
- Confirm loop type, bore or trench count, depth or length, spacing, and layout.
- Confirm pipe material, pipe size, DR, fittings, joining method, and pressure rating boundary.
- Record antifreeze type, concentration target, and fluid property assumptions.
- Show pressure drop and pump head through the critical path.
- Show flushing and purging assumptions for every branch.
Safety And Professional Boundary
Loop design is not a guess from tonnage. It crosses HVAC load calculation, drilling, hydronics, pressure-rated pipe, antifreeze handling, electrical service, and local code. A homeowner should not pressure-test, fuse pipe, alter antifreeze, or re-pump a loop based only on a web page.
When To Call Hartzell’s
Call when a proposed geothermal job has a design report but the inputs are unclear, when an existing loop has low-flow symptoms, or when a loop needs a professional review before drilling or equipment replacement.
Related geothermal pages
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 PRO help home – Public LoopLink PRO design workflow: loads, operating temperatures, flow, loopfield alternatives, head loss, and pump/control selection.
- LoopLink RLC zone help – Inputs for peak heating/cooling load, thermostat setpoints, sensible heat factor, and budgetary-load warning.
- LoopLink PRO zone group help – Flow analysis modes, design flow, EWT inputs, fluid type, temperature, and concentration context.
- ACCA Manual J residential load calculation – Residential load calculation boundary before loop design and equipment selection.
- IGSHPA standards page – Current CSA/ANSI/IGSHPA C448:2025 standard status and current standard boundary.
- 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.
FAQ
Does this page say Hartzell has a software relationship?
No. This page explains the inputs any serious geothermal loop design workflow needs. No software relationship is implied.
Can loop design software replace field measurements?
No. It can compare assumptions, but the design still depends on verified loads, site conditions, code requirements, and field execution.
What should a homeowner ask for before drilling?
Ask what loads, ground assumptions, EWT targets, pipe, fluid, header, pressure-drop, and pump-head assumptions were used.