28
Charging of Geothermal Heating Systems
Problems and Issues, Incorrect Brine Concentration
Flushing
Problems
Various problems can occur when
charging a geothermal heating sys-
tem with antifreeze which can result
in the reduced capacity of the system
or even a total system failure. The
most common problems are as fol-
lows:
Dirt in the circuit
Drilling companies generally strive to
fill only clean water into geothermal
heating systems. However, careless-
ness during the installation and
connection can result in dirt and sand
getting into the probes. This dirt can
damage the circulating pump or the
evaporator of the heat exchanger.
Insufficiently mixed brine solu-
tion
If the correctly calculated antifreeze
volume is charged directly as a
concentrate without the appropriate
mixing device, individual probes may
jam or become completely discon-
nected due to the viscosity of the
concentrate. Water, without the re-
quired glycol content, circulates in the
remaining probes, which can freeze
during the commissioning of the heat
pump and destroy its evaporator.
Incorrect brine concentration
In some cases, the detected glycol
concentration differed greatly from the
calculation. This was mostly due to a
lack of the proper equipment to pre-
pare the mixture correctly. If the con-
centration is too high, the heat pump's
capacity is reduced and works less
efficiently. The heat pump may also
overheat. An insufficient concentra-
tion (<20%) may cause corrosion and
frost damage.
Correctly charging the GHS
with the help of a mixing tank,
mixing equipment with filter
All of the problems listed above
can be avoided by properly charging
the GHS circuit. The right equipment
can make all the difference as well.
Use a mixing and charging tank to
charge the GHS circuit according to
the following requirements:
-
clean mixture
-
correct concentration
-
homogeneous mixture
Flushing
Use filtered potable water and pres-
sure to flush first the circulating pump
of the GHS circuit and the evaporator
and remove pollutants such as weld-
ing beads, small stones, and dirt.
After closing a valve in the heat pump
circuit, each circuit of the GHS is
flushed in succession. A pressure of
2 bar is used to flush a 140 m long
ø 32 mm probe for 6 minutes as
depicted below.
Min. flushing
time for 32 mm probes
10
9
8
7
6
5
4
3
2
1
0
0
50
100
150 200
Probe length
D
u
ra
ti
o
n
i
n
m
in
u
te
s
2 bar pressure
3 bar pressure
Charging hose
C
Exces pressure
2,5 bar
Mixing
tank
120 l
Jet pump e. .g.
Grundfos
max. 5 m
3
/h
max. 5 bar
Geothermal probe
Brine-circulating pump
Heat pump
Expansion vessel
geothermal probe circuit
Discharging hose
filter
