ASHRAE Journal - August 2022 - 38

TECHNICAL FEATURE
by the tool are based on a feasibility analysis
of three different ground coupling systems
(closed loop, standing column well and open
loop) on every building lot. Building owners
and their engineers can choose the location of
their building on a web-based map to provide
them with a simple payback period to guide
them in a decision to fully review project cost,
savings and feasibility.
Note that the New York City tool is limited by
the wide variety of actual building stock and,
therefore, cannot be taken as a guarantee that
a geothermal system is feasible. In addition,
subsurface geologic conditions beneath a BBL
are uncertain without actual drilling and can
vary from the inferred mapped conditions,
affecting system feasibility.
TABLE 1 Summary of preliminary payback periods for various types of loops.
BOROUGH
PAYBACK
PERIOD
Manhattan < 12 Years
< 25 Years
≥ 25 Years
CLOSED LOOP STANDING COLUMN WELL
20%
0%
438
33,846
Bronx < 12 Years 68,908
< 25 Years
≥ 25 Years
2,103
18,674
Brooklyn < 12 Years 203,626
< 25 Years
4,322
≥ 25 Years 68,872
Queens < 12 Years 267,253
< 25 Years
Staten
Island
Geological and Technical Suitability
Each lot first underwent a " geologic suitability "
test to determine which of the geothermal
systems was suitable based on the underlying geologic
conditions, using hydrogeological and geological mapping
data from USGS. Then, for each geologically suitable
geothermal system, a " technical suitability " was
determined, which varies by system type and includes
depth to bedrock (DTB), depth to groundwater (DTW),
presence and depth of any restricted aquifers and (for
open loop systems only) whether the lot has a minimum
outdoor area and size, depending on the heating and
cooling demand.
The assumptions for geologic and technical suitability
are summarized in Table 2, along with the default depths
for wells and loops used in the tool.
Screening Tool Functionality Assumptions and Conditions
All analyses completed as a part of developing a tool
were exported to a web-based map for public access.
The map enables users to select any lot or building in the
jurisdiction for accessing the following information:
1. Basic lot and building information including lot
size, building indoor area, building footprint and building
type for confirmation.
2. Geological and technical feasibility of each geothermal
system type.
3. Depth to bedrock and/or depth to groundwater
(avoiding protected aquifers).
38
ASHRAE JOURNAL ashrae.o rg
A U G UST 2022
11,407
≥ 25 Years 45,508
< 12 Years 111,904
< 25 Years
1% 10,286
79% 32,400
77%
2%
74%
2%
6,227
21% 83,458
3,106
25% 273,803
82%
4%
3,601
14% 320,567
90%
≥ 25 Years 11,885
11
0% 51,356
10% 72,422
24%
73
6
OPEN LOOP
# OF LOTS % OF LOTS # OF LOTS % OF LOTS # OF LOTS % OF LOTS
8,402
76% 42,607
0%
7%
0%
0%
365
4
93% 89,316
0% 69,788
176
1%
99% 206,945
0% 200,703
43
1%
99% 123,422
0% 51,708
41%
59% 72,081
100%
0%
0%
100%
25%
0%
75%
62%
0%
38%
42%
0%
58%
4. Carbon footprint reduction and cost savings with
installation of geothermal.
5. Simple payback period analysis, based on energy
savings and initial costs associated with installation of
geothermal-with and without a carbon credit.
6. An additional option to override basic building information
including building type, footprint and square
footage; the tool reruns the calculations and provides an
output for the new building.
7. In addition to enabling users to assess existing
buildings for geothermal, a function is available to
enable users to investigate the possibility of installing
geothermal systems with new construction for any lot or
combination of lots.
8. All findings are preliminary and should not be
taken as a guarantee that a full study will determine
installation of a geothermal study to be feasible.
Several caveats must be applied to the results. First, all
space not occupied by the building was assumed to be
available and accessible for the installation of the geothermal
system; this may not always be the case. Further
evaluation may be necessary to ensure that the land is
not archaeologically significant, protected marshland or
contaminated. Additionally, critical New York City infrastructure
such as water tunnels, shafts and appurtenant
facilities are regulated by the New York City Department
of Environmental Protection, which is in the process of
http://ashrae.org
ASHRAE Journal - August 2022

Table of Contents for the Digital Edition of ASHRAE Journal - August 2022
