Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 35
Brine-to-water heat pump 3.1.3
3.1.2 Drying out buildings
When a house is being built, large quantities of water are nor-
mally 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 de-
signed 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 compressor runt-
imes 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 down to -14°C to -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%.
A mixture of water and antifreeze is used as a heat transfer me-
dium to achieve a lower freezing point. Ethanediol (ethylene gly-
col) is used as antifreeze in the majority of systems in Germany,
Austria and Switzerland. Due to the material used in the brine ac-
cessories, the more environmentally-friendly ethylene- and pro-
pylene glycol can be used in Dimplex heat pumps without corro-
sion inhibitors.
Table 3.1: Approved antifreeze
NOTE
The output data of the heat pumps is recorded with ethylene glycol (25%).
Propylene glycol and ethyl alcohol can also be used, but we currently
have no measurements for the impact on output and coefficient of per-
formance.
The following antifreeze is not approved due to lack of long-term
experience:
"Thermera", which is manufactured with a betaine base and
is controversy with regard to environmental aspects
"Tyfo-Spezial without corrosion inhibitors.", as this anti-
freeze contains non-ferrous metals (e.g. copper)
"Tyfo Spezial with corrosion inhibitors", as this antifreeze
has not been officially approved by our suppliers and is so
aggressive, that it causes corrosion on the paneling in the
event of leaks.
ATTENTION!
No claim is made that this list is complete
Fig. 3.1: Freezing curve of a monoethylene glycol/water mixtures in relation
to the concentration
Pressure protection
Brine temperatures between approx. -5°C and +20°C can occur
when heat is exclusively extracted from the ground. These fluc-
tuations in temperature result in a change in volume of approx.
0.8 to 1% of the total volume of the system. In order to keep the
operating pressure constant, an expansion vessel with a primary
pressure of 0.5 bar and a maximum operating pressure of 3 bar
is necessary.
ATTENTION!
For protection against overflowing, a tested membrane safety valve
should be installed. The air outlet pipe of the safety valve must, according
to DIN EN 12828, end in a collecting basin. To monitor pressure, a
pressure gauge with minimum and maximum pressure designation is
necessary.
Filling the system
The system should always be filled in the following order.
Mix the required concentration of antifreeze and water in an
external container.
Check the antifreeze/water concentration with an antifreeze
tester for ethylene glycol.
Fill the brine circuit (at least 2 bar to a maximum of 2.5 bar)
De-aerate the system (install a micro-bubble separator)
ATTENTION!
Even following lengthy operation of the brine circulating pump, filling the
brine circuit with water and then adding antifreeze does not create a
homogenous mixture. The unmixed water column freezes in the
evaporator and destroys the heat pump!
Name Synonym
Chemical
formula
Eethanediol Ethylene glycol C2H6O2
1,2 propanediol Propylene glycol C3H8O2
Ethanol Ethyl alcohol C2H5OH
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