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Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp.
Data subject to change
Applications Manual
test of the well. This data normally includes pumping water
level at 3 different ow rates and the pre-test static water
level. From this it is possible to calculate the pumping level
at a wide range of ows and to use this data in design
steps.
6.6 Groundwater Well Pumps
Open-loop systems typically use
submersible
type well
pumps equipped for the most part with nominal 3,600 rpm
motors. As a result, they are able to produce a higher ow
per unit diameter than line shaft pumps which typically
operate at speeds of 1,800 rpm or less. The higher speed
of the submersible also results in a greater susceptibility
to erosion if signi cant sand is produced from the well.
Submersibles are somewhat more sensitive to voltage
variation than surface motors and adequate voltage
(allowing for any drop in wiring to the well and down well)
should be veri ed.
Calculating the
head
for a well pump involves some
different issues than a similar calculation for a circulating
pump. There are 3 main components to the total head: lift,
surface losses and injection head.
Lift
is composed of the static water level plus the
drawdown at the design rate. Its name derives from the
fact that this is the vertical distance the water must be
“lifted” by the pump to get it to the surface. Data to
determine these values comes from the ow test of the
Fig. 28 Production well to system connection
well serving the system (preferred) or from information on
nearby wells. Also included in the lift is the friction loss
in the pump column (between the pump and the ground
surface) which is usually on the order of 1 to 3 ft.
Surface losses
are those associated with the piping from
the well to the structure and equipment (heat exchanger,
etc.) and piping from the structure to the disposal point.
Unless there are signi cant elevation considerations or
distances involved, surface losses normally amount to less
than 40 ft. assuming a 5 PSI loss in the heat exchanger.
The type of disposal can have an impact on the total pump
head. In surface discharge applications, often a pressure
sustaining valve is used to maintain a small (less than 5
PSI) back pressure on the system to keep it full of water.
For
injection head
, the impact may result in added pump
head (if a positive pressure is required at the surface) or
reduced pump head (if the water level in the well remains
below ground surface). Key components in the connection
of the production well to the system are shown (Fig. 28).
Not shown in this diagram is a pump column check valve
which would be located at the base of the column near
the bowl assembly. The check valve maintains the column
full of water and in doing so prevents damaging reverse
thrust on start up. Submersible motors are equipped with
a thrust bearing to resist the down thrust developed in
normal operation. When starting with an empty column,
a pump can exert a temporary up thrust on the motor
which if encountered often enough can result in premature
failure of the motor. To prevent this, submersibles should
be equipped with a column check valve.
