Utilisation of Ambient Air and Shallow Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 413

lubricants used so far. Additionally, the filling amount can be reduced signifi-
cantly in comparison with the semi-halogenated chlorofluorocarbon R22. The re-
quired amounts for small systems up to 10 kW are at only around 1 kg. Due to the
combustibility of the refrigerants R290 and R1270, special security measures have
to be taken in line with the filling amount. They can generally be realised without
problems in practice. For larger systems mainly R134a is currently used as the
substitute refrigerant.
9.2.4 Overall systems
Heat source systems (Chapter 9.2.1 and 9.2.2) and heat pumps (Chapter 9.2.3) are
integrated into overall systems that enable the utilisation of ambient air or shallow
geothermal heat as end and useful energy respectively. Therefore firstly typical
system configurations for characteristic applications are described. Afterwards
system aspects of such overall systems will be discussed.
System configurations. In the following, a heating system with exhaust air heat
recovery and exhaust-air to inlet-air heat pump, with a ground-coupled heat pump
and a heat pump system for heating and cooling purposes will be introduced as
typical overall system configurations.
Heating systems with exhaust-air to inlet-air heat pump. Over the last few years,
exhaust-air to inlet-air heat pumps have been especially developed for houses with
a very low heating energy demand and controlled ventilation systems. Not only do
they cover the entire demand for space heating energy by heating up the inlet air,
but can also cover the domestic hot water demand to a large extent. Fig. 9.14
shows exemplary such a heat pump unit. The inlet air is heated further by the heat
pump condenser after exhaust air heat recovery. The evaporator is allocated in the
exhaust air duct after the exhaust air heat recovery heat exchanger. In order to re-
duce icing of the evaporator on the exhaust air side, one option is to position a
ground-coupled heat exchanger between ambient air and the exhaust air heat re-
covery heat exchanger. Thus the exhaust air in the heat exchanger cannot cool
down so much. The way the cooling fans are allocated enables their exhaust heat
to contribute to the heating process (i.e. in the exhaust air duct before the heat ex-
changer of the exhaust air heat recovery and after the condenser in the intake air
duct). If enough heating energy is available for the house, the heat pump switches
to the condenser of the domestic hot water generation system. Furthermore, an
additional thermal solar system can be used to generate domestic hot water. Dur-
ing cold and cloudy periods in winter, an electric immersed heater is available as a
back-up for the domestic hot water supply. Such heat pump systems can achieve
SPFs of up to 3.5 /9-15/.