Bosch Geothermal Heat Pumps Applications Manual page 41

Applications Manual
Pressure regulating valves are often used to increase or
decrease water ow through the geothermal heat pump
in response to refrigerant pressure. In some cases more
water may be required in heating than in cooling, or vice
versa. With the Bosch geothermal heat pumps, these
valves are not required. However, if installed, a pair of
valves is required for proper operation, one for cooling
(direct acting) and another for heating (indirect acting). A
refrigerant tap is provided in the refrigerant line located
between the reversing valve and the water-to-refrigerant
coaxial heat exchanger for proper monitoring of the
refrigerant pressures.
A bladder type expansion tank should be sized to provide
at least one minute continuous run time of the pump
using its drawdown capacity rating to prevent pump short
cycling. When using a single groundwater well to supply
both domestic and geothermal heat pump water, care
must be taken to insure that the groundwater well can
provide suf cient ow for both.
In well water applications, a slow closing solenoid valve
must be used to prevent water hammer. Solenoid valves
should have a 24 VAC coil and be connected across Y1 and
C1 on the interface board for all Bosch equipment. Assure
that the VA draw of the solenoid valve, if used, does not
exceed the contact rating of the thermostat.
Bosch Thermotechnology Corp.
Bosch Geothermal Heat Pumps | 41
6.3 Open-Loop Geothermal Heat Pump
System Water Disposal
The circulated groundwater from the Bosch open-loop
geothermal heat pump system, with only its temperature
changed requires disposal. The discharge water from the
Bosch geothermal heat pump is not contaminated in any
manner and can be disposed of in various ways depending
on local building codes (i.e. discharge well, dry well, storm
sewer, drain eld, stream or pond, etc.) Most local codes
do not allow the use of a sanitary sewer for disposal.
Always consult your local building and zoning department
to insure compliance in your area.
Disposal can be accomplished by both surface and sub-
surface methods. During severe cold outbreaks, the pumps
may require constant use. The largest volumes of water
will be produced during the coldest part of winter. The
disposal method must be compatible with the volume of
water that will be discharged and must be able to handle
the extreme weather conditions. During the spring and
fall, the volume of water required will be reduced. Because
of the expense involved in the construction of a second
(return) well, the installer may prefer surface or near
surface disposal methods. However, many situations will
not allow these methods.
Surface disposal is generally the easiest method for
disposing of the used groundwater from the Bosch
open-loop geothermal heat pump system. The disposal
locations can include on-site or off-site ponds, streams
and other bodies of water. Each disposal method poses
some environmental and operational disadvantages. The
used water may be diverted to a surface water body, such
as a lake or stream; however, this action may require a
local permit for the discharge. The method of conveyance
must be secure to avoid problems with erosion and
sedimentation, which can impact the stream or lake.
Additional problems may occur in the winter because of
freezing conditions.
Long-term impacts to groundwater levels are possible if
discharge exceeds recharge. Water may be channeled to a
private, on-site collection basin where it in ltrates into the
ground. This type of disposal is generally successful only
where the basin bottom is composed of highly permeable
sands and gravels. Otherwise, in ltration tends to be too
slow; periodic maintenance must be done to clean the
basin. Along with silting, microbial and bacterial plugging
are the chief causes of the permeability reduction. Basins
also require large areas of property. Disposal to a private
basin would not require a permit.
Another possibility is to discharge water into a storm
sewer with permission from the municipality. This option
is generally precluded by limited access to the sewer.
Also, this method does not recharge the local aquifer.
Disposal to sanitary sewers is typically prohibited because
of local ordinances. Such discharges can lower a sewage
treatment plant ef ciency, thereby raising operating costs.
Data subject to change