Installation manual
72
3
3 Brine-to-Water Heat Pump
3.1 Ground as Heat Source
Temperature range of the earth's surface
at a depth of approx. 1 m +3 to +17°C
Temperature range at greater depths
(approx. 15 m) +8 to +12°C
Operating range of the brine-to-water heat pump -5 to +25°C
Types of operation
Monovalent
Mono energy
Bivalent (alternative, parallel)
Bivalent-renewable
Wall penetration
NOTE
Information for using waste heat from cooling water as a heat source can
be found in Chap. 4.3.2 on p. 129.
3.1.1 Dimensioning information - the ground as heat source
The ground heat exchanger, which serves as a heat source for
the brine-to-water heat pump, should be designed according to
the cooling capacity of the heat pump. This can be calculated
using the heat output minus the electric power consumption of
the heat pump as calculated in the design.
NOTE
A heat pump with a higher COP has, at comparable heat output, less
electrical power consumption and, therefore, higher cooling capacity.
When replacing an older heat pump with a newer model, check
the capacity of the collector and, if necessary, modify it to suit the
new cooling capacity.
Under ground, heat is conveyed almost solely by thermal
conduction, whereby the thermal conductivity increases with
increasing water content. Like the thermal conductivity, the heat
storage capacity is also largely determined by the water content
of the ground. If the water in the ground is frozen, the amount of
energy which can be extracted increases considerably because
the latent heat of water at approx. 0.09 kWh/kg is very high.
Therefore, optimal utilisation of the ground as a heat source is
not impaired if the buried pipe coils freeze.
Dimensioning of the brine circulating pump
The volume flow rate of brine depends upon the output of the
heat pump and is conveyed by the brine circulating pump. The
brine flow rate specified in the device information (Chap. 3.6 on
p. 83) results in a heat source temperature spread of approx. 3K.
In addition to the volume flow rate, the pressure drops in the
brine circulation system and the technical data of the pump
manufacturer should also be taken into consideration. The
pressure drops in pipes connected in series, installed
components and the heat exchangers should be added.
NOTE
The pressure drop of an antifreeze/water mixture (25 %) is 1.5 or 1.7 times
higher than pure water (Fig. 3.2 on p. 73), whereas the capacity of many
circulating pumps sinks by approx. 10 %.
3.1.2 Drying-out of buildings
When a house is being built, large quantities of water are
normally used for mortar, rendering, plaster and wall paper,
which only evaporates very slowly from the building. In addition,
rain can further increase the humidity in the building's structure.
This increased humidity in the entire structure causes an
increase in the heat consumption of the house during the first two
heating periods.
For this reason, buildings should be dried out using specially
designed dehumidifiers. If the heat outputs of the heat pump
have been marginally calculated and the respective building is to
be dried out in autumn or in winter, particularly if brine-to-water
heat pumps are implemented, we recommend installing an
additional heating element to compensate for increased heat
consumption. This should then only be activated during the first
heating period, depending upon the brine flow temperature
(approx. 0°C).
NOTE
In the case of brine-to-water heat pumps, the increased runtimes could
cause the heat source to supercool in turn causing the heat pump to
automatically switch off.
3.1.3 Brine fluid
Brine concentration
Antifreeze should be added to the water on the heat source side
to prevent frost damage to the evaporator of the heat pump.
Frost protection is required between -14°C and -18°C for pipe
coils buried underground, due to the temperatures that may
occur in the refrigerating cycle. A monoethylene glycol-based
antifreeze is used. The brine concentration for installation
underground ranges from 25 % to a maximum of 30 %.
0
=
HP
– P
el
HP
= Heat output of the heat pump
P
el
= Electr. power consumption of the heat pump as
calculated in the design
0
= Refrigerating or abstraction capacity of the heat
pump from the ground as calculated in the design
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