Technical data

44 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
3.3.3 Brine-to-water heat pump
Fig. 3.13 on page 44 shows a cross section through a double U
pipe of the type normally used for heat pumps.
For this type of heat exchanger, a bore hole must first be drilled
with a radius of r
1
. Four heat exchanger pipes and a back-fill pipe
are inserted, and the borehole is then back-filled with a cement/
bentonite mixture. The heat exchanger fluid flows downwards in
two of the pipes and flows upwards again in the other two. The
pipes are connected at the lower end with a borehole head, cre-
ating a closed-loop heat exchanger circuit.
Fig. 3.13: Cross section of a double U pipe with back-fill pipe
NOTE
When using brine circuit equipment or heat pumps with an integrated
brine circulating pump, the pressure drops of the borehole heat ex-
changer must be determined and compared with the free compression of
the brine circulating pump. To avoid unnecessarily high pressure drops,
DN 40 pipes should be used for borehole heat exchanger depths of more
than 80 m.
3.3.3 Filling ground heat exchangers
Just like ground heat collectors, ground heat exchangers are
generally filled with a glycol solution with a concentration of 25 -
30 %. This ensures that brine inlet temperatures of - 5°C can be
easily achieved in the heat pump. The glycol portion protects the
heat pump from freezing.
In some cases, however, it may be necessary to operate the
ground heat exchanger with pure water without antifreeze. In this
case, the brine inlet temperature must not fall below 0 °C, as the
water could freeze in the brine pipe, which would cause damage
to the pipe. A number of different points must therefore be taken
into account when operating ground heat exchangers with water:
 A water-to-water heat pump is used instead of a brine-to-
water heat pump
 The minimum brine outlet temperature must not be lower
than 4 °C in this case
 The transmission capacity of the heat exchanger reduces as
a result of the higher temperatures. The number of heat ex-
changers required approximately doubles compared to a
ground heat exchanger with water/glycol.
3.4 Additional heat source systems for ground heat usage
As an alternative to ground heat collectors, other types of heat
source systems are offered, such as geothermal baskets, trench
collectors, energy poles, coil collectors etc..
These heat source systems must be designed in accordance
with the manufacturer or supplier instructions. The manufacturer
must guarantee the long-term functioning of the system based on
the following data:
 Minimum permissible brine temperature
 Refrigerating capacity and brine flow rate of the installed
heat pump
 Annual operating hours of the heat pump
Additionally, the following information should be made available:
 Pressure drop with specified brine flow rate for designing the
brine circulating pump
 Possible impact on the vegetation
 Installation requirements
NOTE
Experience shows that the abstraction capacities of classic ground heat
collectors only differ slightly from other systems, since the energy stored
in 1m
3
of ground is limited at 50 to 70 kWh/a.
Possible optimisation of the abstraction capacities depend first
and foremost on the climate conditions and the ground type, and
not on the type of heat source system.
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