Environmental Engineering Reference
In-Depth Information
For houses with a low energy standard, the space can be smaller. Depending on
the quality of the ground, the withdrawn heat capacities vary between 10 and
40 W/m
2
(Table 9.3). This enables a heat generation of approximately 360 MJ per
square metre ground during the heating period.
Series connection
A
A
Trench
system
Parallel connection
Shaft
Trench
B
B
Section A-A
Section B-B
Filling
Ground
Fig. 9.8
Installation pattern of horizontal ground-coupled heat exchanger (see /9-4/)
A significant reduction in the space required can also be achieved by the instal-
lation pattern of a trench collector also shown in Fig. 9.8. According to this con-
cept, the heat transfer tubes are installed at the side walls of a trench with a depth
of approximately 2.5 m and a breadth 3.0 m. The required length of the trench de-
pends on the quality of the soil and the heating capacity of the heat pump. A spe-
cific trench length of 2 m per kW heating capacity can be taken as a guide value
/9-5/.
Table 9.3
Mean withdrawn heat capacities from the soil (see VDI 4640, sheet 2)
Type of soil Withdrawn heat capacity
Dry, sandy soil 10 - 15 W/m
2
Humid, sandy soil 15 - 20 W/m
2
Dry loamy soil 20 - 25 W/m
2
Humid loamy soil 25 - 30 W/m
2
Water saturated sand/gravel 30 - 40 W/m
2
A further attempt to reduce the required space is to install the tubes spirally.
There are two main possible designs of spiral collectors, which are mainly built in
North America. The fundamental disadvantage of such collectors is that
ventilation problems can occur.
−
For the slinky or cunette collector /9-6/ a roll of commercially available plastic
tube is laid out on the floor of a broad trench and stretched to the sides (verti-
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