Technical data

www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 37
Brine-to-water heat pump 3.2.3
3.2.1 Installation depth
In cold regions, the ground temperature at a depth of 1 m can
drop to freezing point even without heat being extracted. The
minimum temperature at a depth of 2 m is approx. 5 °C. This
temperature rises with increasing depth, although the heat flow
from the Earth's surface decreases. Therefore, if the collectors
are laid at too great a depth, it cannot be guaranteed that any ice
will thaw in the spring. Thus, the installation depth should be ap-
prox. 0.2 to 0.3 m beneath the maximum frost line. For most re-
gions, this is between 1.0 and 1.5 m.
ATTENTION!
For installing ground collectors in trenches, a pipe depth of 1.25 m
should not be exceeded in order to ensure lateral protection. Risk of
spillage!
3.2.2 Clearance
When determining the clearance d
a
between pipe runs, care
must be taken to ensure that the ice radii which form around the
pipe coils have melted sufficiently, after a frost period, to allow
precipitation to drain, thus preventing waterlogging.
The recommended installation clearance is between 0.5 and
0.8 m, depending on the ground conditions and the climatic re-
gion.
 The longer the maximum duration of the frost period, the
greater the installation clearance and the required area
should be.
 In the case of poor ground thermal conduction (i.e. sand),
the installation clearance should be reduced (with a compa-
rable horizontal surface), thereby increasing the total pipe
lengths.
NOTE
In cold regions with standard outside temperature below -14 °C (e.g.
south Germany), an installation clearance of approx. 0.8 m is required.
In warmer regions with standard outside temperatures of -12 °C and
higher, the installation clearance can be reduced to approx. 0.6 m.
3.2.3 Collector surface and pipe length
In ground which is free of stones, PE-100 pipes can be used. In
ground which contains stones, the use of cross-linked pipes
made of Polyethylene, e.g. PE-X... with an external diameter of
32 mm is recommended due to their higher impact strength.
The area required for a horizontally-installed ground collector de-
pends on the following factors:
 Refrigerating capacity of the heat pump
 Ground type and ground humidity content and climatic re-
gion
 Maximum duration of the frost period
NOTE
In low mountain range locations in heights of approx. 900 m to 1000 m
above sea level, the abstraction capacities are very low and the use of
ground heat collectors is not recommended.
NOTE
Chapt. 3.2.6 on page 41 gives standard values for dimensioning ground
heat collectors.
1. Step: Heat output of the heat pump as calculated in the
design point (e.g. B0/W35)
2. Step: Calculation of the refrigeration capacity by deduct-
ing the electric power consumption in the design of
the heat output.
3. Step: Select specific abstraction capacity depending on
the ground type from Table 3.2
Table 3.3: Specific abstraction capacities
4. Step: Calculation of the required pipe length
0
=
HP
- P
el
Example:
SI 14TU
HP
= Heat output of the heat pump
13.9 kW
P
el
=
Electr. power consumption of the heat
pump as calculated in the design point
2.78 kW
0
=
Refrigerating or abstraction capacity
of the heat pump from the ground as
calculated in the design point
11.12 kW
4
4
4
4
Ground type Specific abstraction capacity
for 1,800hrs
Dry, non-cohesive ground
(sand)
approx. 10 W/m
Loam / silt approx. 19 W/m
Sandy clay approx. 21 W/m
Refrigerating capacity from the second step = 11.12kW
Ground type loam / silt
Pipe length L = 11120 W / 19 W/m = 585.3 m
=> 6circuits of 100 m are selected