ASHRAE Journal - August 2022 - 42

TECHNICAL FEATURE
TABLE 3 Building type breakdown.
BUILDING TYPE
C1
Commercial, Post-1980 > 7 Stories
C2 Commercial, Post-1980 up to 7 Stories
C3
Commercial, Post-War > 7 Stories
C4 Commercial, Post-War up to 7 Stories
C5
Commercial, Pre-War > 7 Stories
C6 Commercial, Pre-War up to 7 Stories
C7 Commercial, Very Large, > 500,000 ft2
Hospital and Health Facilities
Institutional General
K-12 Schools
Religious
University
BUILDING DESCRIPTION BUILDING TYPE
MF1
MF2
MF3
MF4
MF5
MF6
MF7
IN1
IN2
IN3
IN4
IN5
NYCHA
BUILDING DESCRIPTION
Multifamily, Post-1980 > 7 Stories
Multifamily, Post-1980 up to 7 Stories
Multifamily, Post-War > 7 Stories
Multifamily, Post-War up to 7 Stories
Multifamily, Pre-War > 7 Stories
Multifamily, Pre-War up to 7 Stories
Multifamily, Very Large
New York City Housing Authority
SF1 1 -4 Family, Free Standing Wood Frame
SF2
W1
W2
W3
" technically suitable. " Technical suitability criteria vary
by system type.
All three systems can be used with supplemental heat
rejection provided by cooling towers or supplemental
heat supplied by condensing boilers; both can be used
in conjunction when peak heating and cooling loads are
not quite met by the geothermal capacity or where the
heating-cooling balance is greater than acceptable. For
the purposes of this tool, it was assumed that if the heating-cooling
balance was greater than 30%, then a hybrid
system was necessary. After a more precise site-specific
feasibility study is completed, it may be necessary to use
a hybrid system even with a closer balance. This would
increase system cost but potentially remain economical
in some cases.
Geology and Underground Conditions
As part of an ongoing mapping project, USGS compiled
geological data from relevant New York City agencies
into a preliminary geographic information system (GIS)
database that was used in the screening tool. The data
provided by USGS were for depth to bedrock and depth
to groundwater. Note that New York City and many other
locations in the country may have protected aquifers
that cannot be accessed with geothermal wells. Depth
to bedrock was used, along with depth to groundwater,
to delineate the geologic suitability of standing column
wells (SCWs). Depth to groundwater was also one of
the criteria used for the open loop system. In general,
open loop systems may not be an option for many
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ASHRAE JOURNAL ashrae.o rg
A U G UST 2022
1 -4 Family, Row House, Masonry
Warehouse/Factory > 3 Stories
Warehouse/Factory up to 3 Stories
Transportation, Garages, and Utilities
installations, given the sediment and
particulates that they may contain.
Finally, during the next (more
detailed) investigation and feasibility
phase, all underground conditions
must be thoroughly evaluated,
including potential pipes, electrical
services, and underground tunnels.
We also recommend that a grouted
(±2 in. [51 mm]) test well be dug,
which can be up to 500 ft (152 m)
deep depending on location. That test
well will help ascertain the potential
heat transfer of the interior surfaces.
Energy Consumption
Where geothermal systems were
found to be geologically feasible, follow-up calculations
determined economic viability. To enable a generalization
of New York City buildings into the very few categories
in Table 3, it was necessary to make several assumptions
in the development of this tool. The first assumption
was that any building considering upgrading to a
geothermal system was already committed to upgrading
heating and cooling equipment to a code-compliant
and centralized system. The cost of the installation
would never be justified by payback period alone unless
considered incrementally against the installation of an
alternative conventional centralized system.
From this assumption, a baseline for each building
type considered the conventional system most likely to
be installed. Commercial buildings were assumed to
operate with cooling towers and packaged water-cooled
AC units, and natural gas-fired condensing boilers
or district steam for heating. Institutional sites were
assumed to primarily use cooling towers and packaged
water-cooled AC units as well as condensing boilers,
except schools, which were assumed to have packaged
air-cooled units and standard boilers. High-rise residential
buildings were assumed to have cooling towers
and heat pumps, while low-rise residential buildings
were assumed to have split-system AC units and condensing
boilers. Single-family homes were assumed
to have split-system AC units and condensing boilers.
Warehouses are typically heating-only facilities and
were disqualified based on heating-cooling balance
issues.
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