How to Perform a Geothermal Conversion

Geothermal systems leverage the earth’s consistent underground temperatures for heating and cooling. These systems provide long-term heating and cooling solutions requiring relatively low maintenance due to the stability of underground equipment. While geothermal systems can vary in size, type, and scale, there are processes common to any geothermal conversion. Though institutions often hire consultants to manage these projects, the following is a high-level overview of the steps they will take.

Step 1: Perform an Initial Site Analysis

An initial site analysis will determine the energy available at the site and the feasibility of installing a geothermal system. The following actions are part of a proper analysis:

Assess site details by gathering site maps, geological surveys, and reporting on any previous site assessments

Perform relevant geotechnical tests such soil thermal conductivity testing to determine how well the heat will transfer to and from the earth

Drill a test well, also known as a geothermal test borehole or thermal response test, to evaluate soil and rock composition, ground temperature profile, thermal conductivity, and groundwater presence and moisture content, as well as help size the system correctly

Evaluate available space to install an underground geothermal field, e.g., soccer fields, parking lots, etc.

Explore options for vertical and horizontal loops, considering benefits and challenges associated with various construction methods, such as drilling direction

Step 2: Evaluate Existing HVAC Systems

Existing building HVAC systems often rely on high-temperature (e.g., 350ºF) hot water or steam heat distribution in a closed loop system throughout a building to provide radiant heat. These systems frequently operate using gas- or oil-fired boilers.

Alternatively, geothermal systems use electricity-powered heat pumps to transfer thermal energy from underground loops to building heating and cooling systems. A fluid, such as a water and antifreeze mixture, will circulate through underground loops. These loops either absorb heat from a building to underground to cool a space or transfer heat from the ground into the building to heat it. Geothermal systems use forced-air systems (ductwork) to push heated or cooled air throughout a space.

Geothermal systems use lower supply water temperatures, so buildings with high-temp steam or hot water distribution may need retrofits. An evaluation of your existing HVAC system should therefore include the following:

• Review existing equipment fuel sources (e.g., gas, electric, oil)
• Assess opportunities to electrify existing HVAC equipment 
• Evaluate temperature impacts from lowering supply temperatures 
• Assess current electrical service capacity and future needs 

Step 3: Identify and Implement Load-Reduction Strategies

Before replacing any equipment within a building, establish whether you have any opportunities to reduce load and right-size a geothermal system. You’ll need to do the following:

• Record a baseline of existing energy usage, energy costs, and carbon emissions for buildings under consideration for geothermal conversion
• Assess existing building systems, their ages, and potential energy-efficiency measures and/or load-reduction strategies
• Identify energy-saving measures prior to or concurrent with implementing a geothermal system to potentially reduce the overall system or geothermal field size 
• Evaluate models of energy, emissions, and cost impacts from load reduction and energy-efficiency measures to compare against the baseline 
• Implement above measures

Step 4: Design the Geothermal System

This process involves selecting the appropriate geothermal system type based on past and projected energy loads and physical constraints. Consider implementing changes in phases to align with your institution’s budget (or funding or financing capacity), greenhouse gas emissions goals, and campus growth. A reputable contractor experienced in borehole installation in the local area can help you prevent avoidable mistakes. You may want to ask a consultant to help you prepare robust bidding requirements in selecting a contractor for system design.

Your drilling contractor will:

• Reassess the cooling and heating load profiles after implementing energy-saving measures 
• Evaluate additional needs for campus expansion or program changes 
• Determine additional capacity required through other equipment types to supplement the bore field capacity and/or balance thermal rejection or extraction over the years 
• Project financial impacts of the implementation strategy 
• Identify potential for additional integration of geothermal capacity within structural foundations in future construction
• Design a system that accounts for regulatory requirements at the local, state, and federal levels, including requirements for drilling and excavation, or environmental concerns related to drilling or soil disturbance

Step 5: Explore Available Incentives and Funding

Before committing to a geothermal conversion, you’ll want to explore all available funding, financing, and incentives. It may be beneficial to identify funding options early on in this process and continue to monitor their availability, as that may influence your institution’s appetite for investing in a geothermal conversion. You’ll want to do the following:

• Research current incentives offered through utilities and government sources for geothermal systems 
• Quantify incentives available based on the initial analysis and preliminary sizing of the system  
• Complete a life-cycle cost analysis (LCCA) that incorporate incentives, financing mechanisms, and available funding for the proposed system to assist with decision-making, evaluating and comparing options by calculating the total cost of ownership (TCO) or net present value (NPV)

Planning and Next Steps

Thinking ahead, any upcoming major building renovations or new buildings are good opportunities to continue decarbonizing your campus. These buildings should be able to accept supply and return temperatures from the geothermal system. Make a plan to connect stand-alone buildings as appropriate based on the heating and cooling load profiles for each building to ensure thermal load balance.

While electrifying an existing building or multiple buildings through a geothermal retrofit can be a lengthy and disruptive process, a geothermal system can operate reliably for more than 50 years and is one of the most energy efficient and cost-effective solutions for decarbonization.

Resources

• District Energy Strategies
• Storage Strategies
• Renewable Energy Strategies
• GHG Emissions Reduction Audits [PDF]
• Case studies: Skidmore College, Bard College, University at Albany