Debunking Geothermal Heating and Cooling System Myths

Co-written with Dave Hermantin

An emerging technology that can help many companies, governments, and cities reach their decarbonization goals may be right beneath their feet. Electrification is key for deep decarbonization of buildings to tackle substantial energy and emission reductions. According to the Department of Energy, space heating and cooling for residential and commercial buildings combined accounts for one-fourth of a building's energy consumption. Substituting fossil fuel heating and cooling systems (such as oil and natural gas) with electric and clean energy technologies can substantially cut carbon emissions and health risks.

Enter Geothermal Energy Systems

Heating and cooling from geothermal energy is not a novel technology. It's becoming a critical component and an urban solution in the building electrification race to achieve carbon-free operations. Oil and natural gas boilers are beginning to be phased out due to their hefty carbon emissions and negative indoor air quality concerns. Geothermal systems are a feasible solution to replace their fossil fuel counterparts to supply a building's heating and cooling baseload needs efficiently. Thanks to innovative technologies, geothermal can be installed in dense urban environments.

Geothermal systems are effective, valuable, and powerful because they can be applied to most building types almost anywhere in the country. Depending on geographic location, starting from 20 feet and even over 500 feet, the Earth's surface temperature from absorbed solar radiation is a constant 50-60°F all year round. Geothermal systems leverage this constant temperature to heat and cool buildings by extracting heat from the ground in the winter and dumping heat in the summer.

Specifically, Closed loop geothermal systems use high-density polyethylene (HDPE) pipes drilled deep underground to circulate a mixture of water and a safe, food-grade antifreeze to collect and transfer heat or from the building.

Although 55°F may sound cold to heat your building, it is much warmer than the 20-30°F temperatures in a northeastern winter. Geothermal heat pumps boost the 55°F from the ground to a comfortable indoor temperature of 65-70°F for heating. In the summer, indoor heat is removed from the building and rejected to the ground. Coldwater is then circulated back to the heat pump to provide cool air to the building.

Geothermal technologies efficiently heat and cool buildings by utilizing a regenerative resource of the Earth's ground temperature. Paired with a clean energy source to power the heat pumps, geothermal is a reliable, efficient, and significantly carbon-free heating and cooling mechanism.

From a life cycle GHG emission perspective, it is important to note that no renewable energy is completely carbon-free. Compared to current fossil fuel power production, the life cycle GHG emissions from renewable energy systems are still substantially lower. Implementing clean energy technology now greatly reduces our current GHG emissions.

The life cycle GHG emission and social and environmental impacts are essential considerations for any energy technology. In particular, Geothermal is gaining traction due to the unique and emerging technology in commercial and institutional applications.

Distinguished geothermal industry engineer and expert Dave Hermantin, Vice President of Engineering of Brightcore Energy, helps me discuss three common misconceptions and concerns about geothermal systems.

1. Structural Concerns

Underground installations automatically raise questions about a mechanical system's structural integrity. However, geothermal systems are extremely robust to withstand the underground elements. The HDPE pipes used as the geothermal ground heat exchangers are warrantied for 50 to 65 years and have an expected life of 100 years! In addition to these pipes' sturdiness, all of the geothermal equipment is either underground or inside of the building, which protects the system components from extreme weather-related events and solar radiation. These can be the worst enemies to any mechanical equipment.

Housing equipment inside the building improves system efficiency and longevity and reduces maintenance. Outside units undergo degradations and malfunctions from weather exposure. By design, geothermal is a resilient heating and cooling system that can be critical in regions experiencing the worst effects of climate change. Overall, geothermal heat pumps have a 25 year expected useful life, which is 10 years longer than an air source heat pump!

2. Environmental Health & Safety Concerns

Unlike Closed loop systems that contain the heat-conveying fluid within the pipes and are independent of the surrounding environment, open loop systems and Standing Column Well systems directly use groundwater for heat extraction and heat rejection. High-quality groundwater is required for open loop systems to work efficiently and without complications. For example, New York City's groundwater quality is generally poor for open loop systems. It requires specialized materials and measures (such as filters and valves) to protect the geothermal system from untreated groundwater elements. Closed loop geothermal systems eliminate the need for extensive maintenance measures while not disturbing essential underground water systems.

The quantity and use of refrigerants also vary by electric heating and cooling systems. Refrigerants are materials of historical environmental concern with notable Global Warming Potential (GWP) and their effect on the ozone. Heat pumps use refrigerants for heat conversion, but geothermal systems minimize and centralize the refrigerants to the heat pump itself. The refrigerant isolated in one geothermal system component makes it simple to dispose of and replace at the end of the heat pump life.

For comparison, Variable Refrigerant Flow (VRF) systems are electric systems that use a heat pump to circulate refrigerants to heat and cool buildings. Conventional HVAC systems use water or air. With VRF, a large volume of refrigerant is circulated in a network of pipes throughout the building, which can cause health and environmental concerns. Any leakage is typically difficult to identify, which increases these risks.

3. Sustainability Concerns

The building sector is against the clock for decarbonizing its carbon footprint as climate change impacts are becoming more imminent. Cities are fueling this race with local regulation to incentivize a swift transition to fossil-free operating systems. For example, New York City is one city leading the effort, with Local Law 97 taking effect in 2020. Buildings over 25,000 sqft will start facing penalties if they exceed their carbon intensity limits for the compliance period starting in 2024.

The primary method to reducing a building's carbon footprint is replacing on-site combustion systems (such as oil and natural gas) with electric-based systems (such as air source and geothermal heat pumps). Yet, the New York City and Westchester County grid has a GHG emissions factor of 596.4 lbsCO2/MWh, with non-renewable accounting for 99.1% of the fuel mix for electricity generation. Highly efficient HVAC systems can significantly reduce source GHG emissions from the grid by using less electricity.

Although VRF, air source, and geothermal (ground source) heat pumps are powered by electricity, geothermal systems reach significantly higher efficiencies (300%-600%!) and need less energy to run.