Calculating the Feasibility of Geothermal Heating and Cooling Systems
From ASHRAE Journal Newsletter, Aug. 27, 2019
By Mary Kate McGowan, Associate Editor, News
Of the 850,000 lots in New York City, how many can feasibly use geothermal energy? A tool can answer that question.
The Geothermal Screening Webtool was developed for the New York City Mayor’s Office of Sustainability and the Department of Design and Construction to assess the feasibility of geothermal heating and cooling for every lot in all five boroughs. Based on a selected location, building size and installation costs, the tool determines the feasibility of installing geothermal heating and cooling, said Charles Copeland, P.E., Fellow/Life Member ASHRAE.
The tool analyzes three different geothermal systems—closed loop, standing column well and open loop—for implementation compared to conventional HVAC systems. Buildings are sorted into 25 building types based on size and occupancy and other factors. This establishes a baseline for thermal load and the conventional energy consumption, according to a report.
Copeland, president/CEO of Goldman Copeland Associates, said his firm, a local geologist and a Dutch firm created the tool that uses United States Geological Survey maps and other data such as water considerations and cost to determine feasibility.
The objective, non-sponsored tool can be used during a project’s investigation period and provide a simple payback period to guide decisions on cost and feasibility. The tool can alert designers which geothermal system would work best in a lot, and if the lot is suitable for geothermal heating and cooling systems, according to Copeland.
The tool does not guarantee a geothermal system is feasible, and a lot’s geologic conditions are uncertain without drilling. These subsurface geologic conditions can vary from the mapped conditions, which can affect system feasibility, according to the report.
The tool can be used in other places as a “roadmap,” said Copeland.
“Someone could do this approach in many other cities and many other towns,” he said, adding that users outside of New York City would have to add special conditions, area prices and consult with area geologists.
The U.S. Department of Energy has similar technology feasibility and cost analysis tools such as NREL’s System Advisor Model.
How It Works
The screening tool’s purpose is to provide a threshold assessment of the potential for using ground source heat pumps in New York City buildings, according to the report.
The following variables factor into the assessment:
The map allows users to access the following information when they select a lot or building:
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Basic lot/building information including lot size, building indoor area, building footprint and building type for confirmation.
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Geological/technical feasibility of each geothermal system type.
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Depth to bedrock (all boroughs) and depth to groundwater (all boroughs, excluding Manhattan and Bronx).
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Carbon footprint reduction and cost savings with installation of geothermal.
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Simple payback period analysis based on energy savings and initial costs associated with the installation of geothermal, with and without the carbon credit.
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An option to override basic building information including building type, footprint and square footage is also included. The tool re-runs the calculations and provides an output for the new building.
Findings
Copeland said geothermal energy could be a prime energy source alternative that emits less carbon and does not use fossil fuels. This fits into New York City’s commitment to reducing its total greenhouse gas emissions by 80%—relative to 2005 levels—by 2050. New York state is also aiming to reduce greenhouse gas emissions by 40% compared to 1990 levels by 2030.
To meet those goals and the buildings’ heating needs, heat pump technology is being considered as a major way to reduce fossil fuel consumption and associated emissions. In 2016, the NYC Council passed a local law requiring a publicly available online geothermal heat pump screening tool to provide a threshold assessment of the potential use of ground source heat pumps in New York City buildings. The Geothermal Screening Webtool is the result.
So far, the tool has found limited positive results in Manhattan and the Bronx. The building loads often exceed potential capacity accessible using the available outdoor area in these boroughs. Staten Island, Queens and Brooklyn show promising results because outdoor area drilling is more prevalent, and building loads are typically less intense, according to the report.
The tool has deemed most commercial buildings not feasible because of large cooling loads and limited availability outdoor area. The report shows most feasible lots were small multi-family buildings or single-family homes where available outdoor space suffices to meet the buildings’ heating and cooling requirements.