Geothermal Pre-feasibility Tool Glossary Methodology and Assumptions Resources Help

Definitions were drawn from Department of Design and Construction's Geothermal Heat Pump Manual. Closed loop system Type of geothermal heat pump system that circulates water with an antifreeze solution in a network of closed piping installed in the group. Coefficient of performance Ratio of the heat extracted to the energy consumed in the process. Ground coupling Arrangement of piping and fluid handling equipment designed to exchange heat with the earth's interior. Geothermal (ground source) heat pumps Heating and cooling devices that take advantage of the relatively constant temperature of the earth's interior, using it as a source or sink for heat. When cooling, heat is extracted from the building and dissipated into the earth; when heating, heat is extracted from the earth and pumped into the space. Ground thermal capacity Based on geological conditions, the thermal energy available from the lot. The capacity varies depending on the system utilized (open loop, closed loop, or standing column well). Heat Exchangers Device for transferring thermal energy from one fluid to another. Heat pump Device used for heating and cooling, which operates by moving heat from a cooler to a warmer location and vice versa, by extracting heat from the air, water, or earth. Heating, ventilation and air conditioning (HVAC) Hybrid systems A system which uses a condensing boiler and/or a cooling tower to supplement the geothermal system Open loop system Type of geothermal heat pump system that uses ground water pumped from a supply well to transfer heat and returns the water to the ground through diffusion wells. Simple payback period The period of time required to recoup the funds expended in an investment. The calculation is determined by the initial cost divided by the annual savings, and is not a full life cycle cost analysis. Standing column well system Type of geothermal heat pump system that also uses ground water, but relies on smaller amounts inside a very deep well to exchange heat with the surrounding bedrock.

The Geothermal Pre-screening Feasibility tool assesses both technical and economic feasibility to make recommendations. The methodology and associated assumptions used to determine feasibility are described below. Words in bold can be found in the Glossary page. Technical feasibility Technical feasibility is dependent on a lot's geological and hydrogeological properties, the ground thermal capacity for the geothermal system, and the building's heating and cooling needs. We analyzed geological and hydrogeological data sourced from the U.S. Geological Survey to screen where in New York City the three types of geothermal ground source heat pump systems (closed loop, open loop, and standing column well) were viable, based on depth to bedrock and depth to groundwater data. Assessing thermal capacity We determined ground thermal capacity, or the thermal energy available for use through the application of each system, for each building lot where geological and hydrogeological conditions were favorable. This process included the following steps: Developed unit ground thermal capacities for the three main types of geothermal heat pump systems (standing column wells, closed loop, and open loop) using hydrogeological and geological mapping data from the U.S. Geological Survey. The system for determining capacities for each of the systems is included in the full report. Calculated the area available for the installation of geothermal systems for each building lot by using available building footprints and lot data, including individual block and lot size, and building footprint and square footage data from Primary Land Use Tax Lot Output. Using the unit ground thermal capacity and available land area calculated from 1 and 2, calculated the estimated thermal capacity for the three systems for all building lots in New York City. Assessing outdoor areas Geothermal systems are feasible if there is sufficient outdoor area to install the wells, and therefore thermal capacity to meet or exceed the building's peak and annual heating and cooling loads. We assessed whether outdoor area was sufficient using the following steps: Developed estimates of building annual heating and cooling loads based on building size, type, and age. Compared ground thermal capacity with building requirements to determine if sufficient capacity is available, and if annual heating/cooling loads are sufficiently balanced. To maintain optimal system performance over an extended life cycle, it is essential that the heating and cooling loads off-set each other to maintain constant sub-surface temperatures on a year-to-year basis. Evaluated the potential of hybrid systems to achieve balance if heating and cooling loads are not sufficiently similar. Economic feasibility After deeming sites to be technically feasible for the installation of a geothermal system, those sites were evaluated for economic feasibility using the following assumptions: Assumed the building was planning a full heating/cooling system upgrade. Assumed typical heating and cooling systems based on current standards and codes. (These building baseline systems are considered representative of typical buildings in New York City.) Assumed the building baselines were developed to estimate energy consumption and installation costs for standard systems, and applied to all buildings. Assumed energy consumption and installation costs were developed and applied to all buildings where these systems were feasible. Price comparisons were completed based on energy savings with the geothermal system, comparative maintenance costs, a carbon credit as defined within Local Law 6 of 2016, and anticipated installation costs. Comparative incremental simple payback periods based on the calculations and assumptions described above were determined for replacing with geothermal versus typical systems. For City facilities, a general recommendation was provided based on these findings. For more information, please refer to the full report.