Utilisation of Ambient Air and Shallow Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 432

Hydraulic changes in the subsoil caused by groundwater withdrawal. The with-
drawal of groundwater and the ensuing discharge leads to a lowering of the
groundwater level around the production well and a rise in the groundwater level
around the injection well. This leads to an adjustment of the flow that is limited to
a certain area.
Noise effects. Negative effects for the environment have often occurred due to
high sound power levels of systems in the past. Compared to earlier system gen-
erations, significant reductions in sound radiation have been achieved for new
systems in the market. Heat pumps with a heating capacity around 10 kW some-
times achieve a sound intensity of below 45 dB(A). Thus sound emissions are
practically not a problem nowadays.
Effects caused by boreholes. Harmful situations for the groundwater occur if the
borehole is insufficiently sealed off from the top edge of the terrain. This can lead
to water-contaminating substances seeping in from the surface of the earth /9-22/.
If sinking and completion of the boreholes is done professionally, such aspects
practically do not occur.
The groundwater flow conditions can be influenced in a negative way if devel-
opment drillings (e.g. for vertical ground probes) sink through two or several
groundwater levels with different levels of pressure without control. The hydrau-
lic contact of various groundwater layers is undesirable, particularly if one of the
layers contains highly mineral or contaminated groundwater. By including a bar-
rage, possible harmful effects can be largely avoided /9-22/.
Malfunction. Accidents in the context of heat pump utilisation can occur if the
materials sunk into the subsoil corrode easily and cannot withstand the stress. The
materials used for vertical ground probes, for example, have to be able to with-
stand the pressures during deep drillings and not tear easily. So far no tube frac-
tures have occurred for PE-tubes, for instance, at depths up to around 150 m /9-
22/.
The extent of the environmental effects caused by the heat pump, and the heat
source part involved, that occur in the case of an accident depend on the types of
refrigerant and antifreeze compound that are used. Antifreeze additives that are
currently used most are ethylene-glycol and propylene-glycol - both in the hazard
1 class for water. The environmental effects that can, for instance, be caused by
leakage, are generally small. The same is true for heat pump working media for
direct evaporation, as the used refrigerants - with the exception of ammonia - are
either not harmful for water or can only cause very little damage. Experiments
with R290 as the refrigerant have shown that only relatively small, temporary
hazardous effects occur for soil and groundwater. They are also very limited to a
certain area /9-23/. New developments with CO 2 heat pipes are definitely not haz-
ardous for the water.