Applications Manual Bosch Geothermal Heat Pumps | 37
Bosch Thermotechnology Corp.
Data subject to change
6.1 Open-Loop Geothermal Heat Pump
System Water Quantity
While open-loop systems operate with groundwater that
is typically constant in temperature throughout the year,
the quantity of water that is pumped will in uence the
temperatures that the geothermal heat pump experiences.
Bosch geothermal heat pumps used for open-loop systems
need differing amounts of water depending on the size
of the unit and the Bosch equipment speci cations. The
water requirement of a speci c model is usually expressed
in Gallons per Minute (GPM) and is listed in the Bosch
speci cations for that unit. The groundwater well should
be large enough to supply the water needed by the
geothermal heat pump in addition to the domestic water
requirements.
Generally, an open-loop geothermal heat pump system
will use approximately 1-½ to 3 gallons per minute (GPM)
per ton of cooling capacity. This equates to 2,160 to 4,320
gallons per day for a typical 3 ton geothermal heat pump
unit, depending on the equipment ef ciency and the
amount of cooling or heating necessary. A groundwater
well that may need to supply all the water needs for a
home including the Bosch geothermal heat pump system
may require a yield of 20-30 GPM to meet the peak ow
requirements.
Groundwater occurs below the surface at depths where all
the open spaces in the soil, sediment, or rock are
Well
Area of influence
Cone of depression
Aquifer
Groundwater flow
Aquifer
Evaporation
Water table
Condensation
Precipitation
Recharge or
infiltration
Runoff
Groundwater flow
Discharge area
Water Cycle
Fig. 21 Water cycle
Courtesy of National Ground Water Association
completely lled with water. All groundwater, whether
from a shallow well or a deep well, originates and is
replenished by precipitation.
Groundwater is provided through a normal water cycle in
nature (Fig 21).
The typical minimum water ow or GPM for open-loop
systems is often based on entering water temperature
(EWT) as follows:
f 1.5 GPM when water temperature is above 50ºF
f 2.0 GPM when water temperature is below 49 ºF
In order for a Bosch geothermal heat pump system to
operate at its speci ed heating and cooling capacity and
ef ciency, the proper groundwater ow rate through
the water-to-refrigerant coaxial heat exchanger must be
maintained. The groundwater aquifer, source well, and
pumping system must be able to supply the required ow
rate.
During the winter heating cycle, the open-loop geothermal
heat pump system operates by extracting heat from the
groundwater, and transferring it to the structure. During
the summer cooling cycle, heat is transferred away from
the structure by the groundwater.
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