ASHRAE Journal - August 2022 - 43

TECHNICAL FEATURE
After determining system types, a comparison between
energy costs for geothermal and conventional systems
was developed. Only the portions of the heating and
cooling load that were impacted by system type were
considered in this portion of the study. Pump and fan
peak energy consumption was determined based on
ASHRAE standards for all cases, and weather bin data
analysis was applied to determine annual consumption.
For compressor energy consumption, the conventional
case refl ected effi ciency penalties in the summer for
the relatively hot heat transfer fl uid. In building types
where heat pumps were used as a baseline, this was partially
offset by effi ciency gains from the hot heat transfer
fl uid in the winter. Boiler consumption was based on
an assumed average condensing boiler effi ciency level
of 90%. While this relatively high effi ciency may not be
consistently achievable in practice, it was deemed logical
to assume that a building considering conversion to
a geothermal system would be optimally run with either
upgrade. Boiler consumption was also calculated based
on weather bin data.
Economic Feasibility
After development of the energy consumption analysis
for the various building types, this data was applied to
the actual buildings to determine economic feasibility
of the geothermal systems. Tables based on the weather
bin data analysis summarized the energy consumption
per 1,000 ft2 (93 m2) for the various building types, for
both conventional and geothermal systems. This information
was then imported into the master building
table and individualized for buildings based on type and
square footage. Where the master building table called
for a hybrid system, energy consumption was prorated
between the conventional and geothermal system types
per the requirements of the hybrid system. Energy savings
from the geothermal system were thus determined
for each system in terms of both energy (Btus) and cost.
A further cost savings was then attributed to the geothermal
system based on the carbon credit as established by
New York City. Output includes the payback period with
and without the carbon credit.
Installation costs were estimated, based on tons for
cooling equipment (including geothermal systems),
horsepower for pumps and kBtu for boilers. These
assumptions are all based on prior work and rules of
thumb. Actual costs vary considerably for each site and
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A U G U S T 2 0 2 2 ashrae.o rg ASHRAE JOURNAL
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should be extensively reviewed during an individualized
feasibility study before any decisions are implemented.
An incremental payback period is then determined
by comparing the cost of the conventional system to the
cost of the geothermal system and dividing by the energy
savings. If the incremental payback is less than 12 years,
a recommendation is made to move forward with the
feasibility study; if less than 25 years, a recommendation
is made to consider the study. Otherwise, it is not recommended
to take the next step.
Conclusion
The potential for far greater use of geothermal energy
should be fully explored. The New York City geothermal
screening tool, which pioneered the process, and
Westchester GeoPossibilities, which now demonstrates
replicability of that initial tool, are at the forefront of
geothermal energy exploration. Understanding the role
of these tools is key to applying this renewable energy
resource to its fullest and best use.
Desiccant and Energy Recovery wheels
available in standard and custom sizes.
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ASHRAE Journal - August 2022

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