29
Charging of Geothermal Heating Systems
Charging with Antifreeze
Correctly Charging a Geothermal Heating System Circuit
Charging with antifreeze
After flushing, the entire geothermal
heating system circuit is to be filled
with clean tap water. Follow the steps
below to prepare the required
concentration of antifreeze with a
100% concentrate. For example:
The required antifreeze concentration
is 25% (ideal range is 25-30%) with a
140-m Duplex® ø 32 mm geothermal
probe. (Content per meter = 4 pipes x
10 dm, length x 0.13 dm,
inner radius
2
x
π
= 2.12 l/m)
Correctly Charging a Geother-
mal Heating System in 14 Steps
1. Flush the GHS circuit as de
scribed on page 18.
2. Calculate the probe volume acc.
to table above. One geothermal
probe (geothermal probe ø 32
mm) has 2.12 l/m content per
meter. This yields the following
geothermal probe content for our
example:
140 m x 2.12 l/m = 296.8 liters
(297 l). Do not forget the content
of the connection lines up to the
heat pump, 30 liters in our exam-
ple. This results in a total system
content of 297 30 liters
= 327 liters.
3. Required volume of 100%
antifreeze concentrate:
25% of 327 liters = 82 liters.
4. Close the slide valves to the heat
pump. Remove the drain hose
from the tank and place in drain.
5. Open the slide valves of the
GHS – if several probes have
been installed, one slide valve
after the other is opened during
charging.
6. Fill the mixing tank with an ap-
prox. mixture of 1:1 of antifreeze
concentrate and fresh water.
Depending on tank size, not all of
the 82 liters of concentrate will fit
into the tank (see calculation,
no. 3).
7. Switch the feed pump on.
As soon as the tank begins to
empty, continuously fill in the
remaining antifreeze concentrate
and additional fresh water into
the mixing tank at a ratio of ap-
prox. 1:1. Make sure that always
at least 40 liters of mixed reserve
remains in the tank. Volume
markers can be attached to the
edge of the tank as an aid.
8. The feed pump is allowed to run
until the entire antifreeze
mixture – except for the 40 liters
reserve – are filled in and then is
switched off at once. Excess tap
water drains from the drain hose
into the drain.
9. Now insert the drain hose into the
tank, turn the feed pump back on,
and allow it to run until glycol and
water are thoroughly mixed. This
takes about 6-8 times as
long as it takes for flushing (see
diagram, item flushing).
10. Close charging valves at drain
hose and then those at the
geothermal heating system
distributor. The excess pressure
valve (2.5 bar) routes the excess
mixture back into the tank. Shut
off feed pump. About 40 liters
remain in the tank. Some of the
mixture was absorbed by the
expansion of the geothermal
heating system.
11. In case of relatively long geother-
mal heating systems and insuffi-
ciently mixed mixture, the excess
pressure valve at the tank is
triggered and intensifies the
mixing.
12. If several geothermal probes are
combined into one system, the
second, third, etc. geothermal
probes are first flushed and then
charged individually.
13. Once all the probes are charged,
the evaporator and the brine cir-
culating pump must be charged
next. All slide valves to the geo-
thermal heating systems are
closed for this purpose and the
slide valves to the evaporator are
opened. The remaining mixture is
now carefully pumped via the
slide valve at the filling hose.
Allow water in the circuit to es-
cape via the drain hose. As soon
as the glycol mixture emerges as
the drain hose (color change),
close the corresponding valve
and allow the pump pressure to
charge the expansion vessel (2.5
bar). Then close the valve at the
filling hose. The system is now
charged with the correct concen-
tration and correct operating
pressure without introducing pol-
lutants to the system.
14. Now carry out a pressure test.
This test should be performed
over an extended period to avoid
the hassle of finding leaks later
on. Note: Antifreeze mixtures are
more likely to result in leaks earli-
er than water alone!
The brine circuit is to be charged with
a charging pressure of 1 bar
(diaphragm-type expansion vessel
initial pressure) + 0.3 bar as brine
header = total of 1.3 bar.
The temperature difference during
this operation should not exceed 4 K
between sole inlet and outlet.
Probe diameter
Content per meter
25 mm
1,31 l/m
32 mm
2,12 l/m
40 mm
3,34 l/m
