Geothermal Ground-Source Heat Pump (GSHP

HVAC & Geothermal Engineering: Ground-Source Heat Pump Principles

Geothermal (Ground-Source) Heat Pumps (GSHPs) leverage the steady year-round thermal mass of the earth as a heat source in winter and heat sink in summer:

• Coefficient of Performance (COP): Measures heat delivered per unit of electrical energy consumed means the heat pump delivers 4.0 units of thermal energy for every 1.0 unit of electricity purchased—equivalent to 400% thermal efficiency).

• Ground-Source vs. Air-Source Heat Pumps (ASHPs): Air-source heat pumps suffer steep COP degradation during sub-zero winter freeze events because outdoor air is cold; ground-source loops maintain constant 50°F entering water temperatures, sustaining peak 4.0+ COP regardless of blizzards.

• Carnot Thermodynamic Second Law: The theoretical maximum efficiency of any refrigeration cycle is governed by the Carnot limit); minimizing the temperature lift between the ground loop and indoor supply ducting maximizes real-world system COP.

How to Use This Calculator

Enter your Geothermal Heat Pump Capacity (Tons) (e.g. 4.0 (1 Ton = 12,000 BTU/hr = 3.517 kW)), Rated Heating Coefficient of Performance (COP) (e.g. 4.2 (Typical ground-source: 3.5 to 5.0)), Rated Cooling Energy Efficiency Ratio (EER in BTU/Wh) (e.g. 22 (Typical ground-source: 18 to 28 EER)), Ground Loop Entering Water Temperature (°F) (e.g. 50 (Constant earth temp: 45°F to 55°F)), Indoor Heating Setpoint Temperature (°F) (e.g. 70), Annual Space Heating Demand (MMBTU/Year) (e.g. 65 (Typical home: 50 to 90 MMBTU/year)), Electricity Utility Rate (/kWh) (e.g. 0.14), and Baseline Heating System Being Replaced — choose from Standard Natural Gas Furnace (80% AFUE @ 1.30/therm), Heating Oil Boiler (85% AFUE @ 3.80/gallon), Propane Furnace (85% AFUE @ 2.90/gallon). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Ground-Source Heat Pump (GSHP) Thermodynamics \& Efficiency equations:

Carnot Maximum COP = T_indoor, KT_indoor, K - T_ground, K (T_K = (T_F - 32) × (5) / (9) + 273.15)

Second Law Exergy Efficiency (\%) = ((Rated COP) / (Carnot COP)) × 100\%

Annual Electricity Consumed (kWh) = (Annual Heating Load (MMBTU) × 1,000,000) / (3,412.14 × Rated COP)

Annual Geothermal Heating Cost = Annual kWh × Electricity Rate (\/kWh)

Annual Cost Savings = Baseline Heating Fuel Cost - Annual Geothermal Cost

Worked Example

For example, heating a home with a \ using a 4.0-ton GSHP with a heating \ and \ electricity rate against an 80% natural gas baseline): The geothermal system consumes costing \634.98/year). The baseline gas furnace requires 812.5 therms costing \1,056.25/year. The geothermal heat pump saves \421.27/year (39.9% reduction) while running at 37.7% Second Law Carnot efficiency.

Understanding Your Result

Evaluate your result in the context of your specific use case and relevant industry standards or reference values. A single calculated result is a starting point — test two to three scenarios to understand how sensitive the outcome is to your key input assumptions. For high-stakes decisions, verify your result against a secondary source or subject-matter expert before acting.