Environmental Engineering Reference
In-Depth Information
are a sufficient dimensioning and a flow temperature of the heat utilisation sys-
tems that is as low as possible (e.g. 35 °C for floor heating).
−
Heating rate. Depending on the electricity generation technology it is based on
and the SPF of the heat pump system, currently achievable heating rates are be-
tween 1.1 and 1.8.
The dependence of the COP on the temperature difference between the heat
source and the heat sink is thus a main characteristic of heat pump systems. Fig.
9.20 shows the characteristic curves that are currently achievable in operation
when utilising heat pumps withdrawing the energy from the ambient air or the
near surface ground.
Accordingly, e.g. an air-coupled heat pump at an annual mean temperature of
the heat source at currently 0 °C has a COP of approximately 3. In comparison, a
ground-coupled heat pump achieves a COP of around 4.5 under the same circum-
stances. This is one of the reasons for the increasing installation of heat pumps for
shallow geothermal energy use. The importance of air-coupled systems is gradu-
ally declining in Central Europe.
5.5
5
Heat source ground
4.5
4
3.5
3
Heat source air
2.5
2
-5
-2.5
0
2.5
5
Heat source temperature in °C
Fig. 9.20
COPs of heat pumps for low-temperature heating systems withdrawing heat from
ambient air and near-surface ground
Heat regime in near-surface ground.
Artificial withdrawal and/or discharging
heat into the near-surface ground leads to a disturbance of the heat regime in the
ground. Therefore the heat deficit or the excess heat have to be balanced by heat
transfer. Meanwhile this is mainly ensured by the system itself for systems with an
approximately balanced energy balance in the subsoil (e.g. heat pumps for heating
and cooling purposes). For ground-coupled heat pump systems with an exclusive
heat withdrawal from the near-surface ground this does not apply. The heat deficit
has to be balanced by the natural ambient heat flow (i.e. mainly consists of solar
energy and the geothermal energy of the deep subsoil).
Through measurements from a system and by extrapolating using numeric
simulation it becomes obvious that ground-coupled heat pumps can be run con-
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