Utilisation of Ambient Air and Shallow Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 425

brine circuit (ground-coupled heat pump and vertical probe) - consists of 30 %
propylene-glycol and 70 % water. Due to their relatively high surface require-
ment, ground collectors are only used for comparatively low heat capacity lev-
els (in general smaller than 20 kW). Therefore only the systems SFH-I, SFH-II
and SFH-III can be operated as heat source systems with ground collectors. For
the compound system of domestic hot water generation and space heating SPFs
of 3.43 (SFH-I), 3.65 (SFH-II) and 3.85 (SFH-III) can be achieved.
− Ground-coupled heat pumps with direct evaporation (GD). For the assumed
systems with direct evaporation, copper tubes with a plastic coating are sunk at
a depth of 1.2 m on a layer of sand. Due to the similarly large surfaces re-
quired, heat pump systems for the supply tasks SFH-I, SFH-II and SFH-III are
analysed. The refrigerant R407a serves as the heat carrier from the collector to
the heat pump. The annual work rates of these systems are at 3.76 (SFH-I),
4.00 (SFH-II) and 4.20 (SFH-III).
− Vertical ground probe with brine circuit (GP). At an assumed heat withdrawal
capacity of 50 W per m ground probe, ground probe lengths of 2 x 60 m (SFH-
II), 3 x 90 m (SFH-III) and 12 x 75 m (MFH) can be derived for the systems
under review. The HDPE probes are designed as double-U-tubes and installed
in boreholes that are afterwards filled with a suspension of bentonite, cement
and water. The SPFs for domestic hot water generation and space heating are at
3.59 (SFH-II), 3.77 (SFH-III) and 3.73 (MFH).
− Ground water wells (GW). For the systems SFH-II, SFH-III and MFH, produc-
tion and injection wells that are 20 m deep each are excavated. The lining and
walling of the boreholes is done correspondingly. The extracted groundwater
that serves as a heat carrier is discharged via injection well into the ground
again after heat withdrawal by the heat pump. The SPFs are at 3.95 (SFH-II),
4.20 (SFH-III) and 4.15 (MFH).
In order to be able to give an estimate of the costs involved in supplying low-
temperature heat with the heat pump systems defined above, investment and
operation costs plus the specific heat generation costs for the reference systems
defined in Table 9.7 will be presented below. Due to the location-specific geo-
logical conditions (e.g. condition of the ground, heat conductivity of the subsoil,
distance of the groundwater conductor from the top edge of the terrain) significant
differences in the design of the heat source system and thus in the cost structure of
the compound system can occur. Additionally, the costs for electrical energy and
the connection of the heat pump to the public electricity grid are widely dispersed
depending on the respective conditions of the local utility. The costs discussed in
the following can therefore only show a certain scale and average reference val-
ues. In individual cases and depending on the local framework conditions, lower
but also higher heat generation costs can be possible.
Investments. The amount of specific investments into heat pump systems is
largely determined by the applied technology and the size of the system. In gen-
eral, the specific costs decrease with an increase in system size. This is mainly