Utilisation of Ambient Air and Shallow Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 415

Floor heating system

Cold

Heating control, ambient
temperature regulated

water

C ompressor

Duplex-store
for domestic hot water

Expansion valve
Brine/water-heat pump including
circulation pumps and control devices

Ground-coupled

heat exchanger

Fig. 9.15 Heat pump heating system with ground-coupled heat exchanger (see /9-1/)

Heat pump systems for heating and cooling purposes. Ground-coupled heat
pumps cannot only be used for heating, but also for space cooling purposes, as the
operation of heat pumps can generally be reversed. Heat is then transferred from
the building into the ground. Through the double use of this cost-intensive system
component in the ground, such systems for heating and cooling operate at com-
paratively reasonable costs. In the case of vertical probes, hollow spaces can occur
around the tube due to water vapour diffusion away from the tube because of the
heat transfer into the ground. This has to be avoided by adequate backfilling of the
tube.
Under Central European climatic conditions it is also possible to achieve space
cooling without operating the heat pump as a refrigerating aggregate (i.e. by using
cooling ceilings or convectors and the cooled brine from the ground), if the cool-
ing demand is low. Fig. 9.16 therefore shows three possible types of operation of
ground-coupled heat pumps with direct cooling.
− In winter, the heat pump is in charge of heating. This generates low tempera-
tures (or a deficit in heat) at the heat pump evaporator. The subsoil cools down
(heat mode in Fig. 9.16).
− During transition time or - for suitably designed systems with a cooling capac-
ity that is not too high - during the entire cooling period, heat from the building
can be transferred to the ground in line with the natural temperature difference
between ground and cooling device. Thus the building is cooled (direct cool-
ing; refrigeration mode 1 in Fig. 9.16). The temperature of the heat carrier can
exceed the original temperature of the ground. This is possible as long as it is
low enough to still ensure the required cooling of the building. In most cases, a
dehumidification of the intake air is not possible for direct cooling
(refrigeration mode 1), as only at the beginning of the cooling period the
temperature is guaranteed to sink below the defrosting temperature between 14