Calculator Inputs
Plotly Graph
The chart compares annual energy use and estimated monthly operating cost distribution.
Example Data Table
| Scenario | Heating Load (BTU/h) | Cooling Load (BTU/h) | COP | EER | Loop Type | Estimated Tons |
|---|---|---|---|---|---|---|
| Small Office | 36,000 | 30,000 | 4.1 | 17 | Vertical Bore | 3.5 |
| Retail Unit | 60,000 | 54,000 | 4.3 | 19 | Horizontal Trench | 5.5 |
| Residential Large Home | 48,000 | 42,000 | 4.2 | 18 | Vertical Bore | 4.5 |
Formula Used
Design Heating Load = Peak Heating Load × Safety Factor
Design Cooling Load = Peak Cooling Load × Safety Factor
Required Tons = Design Load ÷ 12,000
Heating kW = (Design Heating Load × 0.00029307107) ÷ COP
Cooling kW = Design Cooling Load ÷ EER ÷ 1000
Annual kWh = Compressor kW × Operating Hours + Pump Energy + Auxiliary Heat
Annual Cost = Total Annual kWh × Electricity Rate
Loop Length = Selected Tons × Loop Factor × Safety Factor
Loop factors in this calculator are planning values. They help with early sizing studies, but final geothermal design should consider soil conductivity, bore spacing, groundwater conditions, and local design standards.
How to Use This Calculator
- Enter the building peak heating and cooling loads.
- Provide expected seasonal operating hours.
- Enter heating COP, cooling EER, and electricity rate.
- Select the intended ground loop arrangement.
- Add pump and auxiliary heat assumptions.
- Submit the form to view equipment size, loop length, energy use, and annual operating cost.
- Use the chart and exported reports for planning discussions.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates geothermal equipment size, loop length, compressor demand, seasonal energy use, and annual operating cost using user-entered engineering assumptions.
2. Is the loop length final for construction?
No. It is a planning estimate only. Final loop design needs site-specific thermal conductivity, drilling depth limits, trench layout, groundwater behavior, and local code review.
3. Why are COP and EER both needed?
COP models heating efficiency, while EER models cooling efficiency. A geothermal system performs differently in heating and cooling modes, so both values improve the estimate.
4. What safety factor should I use?
Many early-stage studies use 1.05 to 1.15. Higher values provide more margin, but oversizing may raise cost and reduce operating efficiency.
5. How is unit size selected?
The calculator converts design load into tons and rounds up to the nearest half-ton. It selects the larger of heating or cooling demand.
6. Does the calculator include pump energy?
Yes. Pump wattage is converted into seasonal electrical use and added to heating and cooling energy totals for a more realistic estimate.
7. Can I use this for residential and commercial projects?
Yes. It works for both early residential and commercial assessments, provided the entered loads, efficiencies, and operating hours are reasonable.
8. Why might real operating cost differ?
Actual cost depends on weather variation, thermostat settings, part-load performance, circulation design, auxiliary heat use, tariff structures, and maintenance conditions.