Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 17
Selection and design of heat pumps 1.3.4.7
1.3.4.4 Design of brine-to-water and water-to-water heat pumps (mono energy operation).
Mono energy brine-to-water or water-to-water heat pump sys-
tems are equipped with a second electrically operated heat gen-
erator, e.g. a buffer tank with an electric heating element. Mono
energy brine-to-water or water-to-water heat pump systems
should only be planned in exceptional circumstances if shut-off
times mean that large quantities of power must be drawn from
the grid or if, on account of the available device range, a heat
pump must be selected which has a considerably larger output in
comparison to the total heat consumption. Mono energy opera-
tion is also particularly suitable for the first heating period if the
building is dried out in autumn or in the winter.
1.3.4.5 Design of air-to-water heat pumps (bivalent operation)
When a system is operated as a bivalent-parallel system (exist-
ing older building), a second heat generator (oil or gas boiler) as-
sists the heat pump from the bivalence point of < 4 °C.
It often makes sense to select a smaller sized heat pump since
the heat pump's percentage of annual heat output fluctuates very
little. A prerequisite is that long-term operation of a bivalent sys-
tem is planned.
For buildings with radiators as a heat distribution system, heating
flow temperatures of 50 °C and more are often permanently re-
quired. In this case, it is often advisable to have an additional bi-
valent alternative operation for heat pumps and boilers, as air-to-
water heat pumps in particular offer significantly better outputs in
higher outside temperatures. In low outside temperatures, the
2nd heat generator takes over the heating of the building.
Fig. 1.5: Coverage ratio of a heat pump in different operating modes
The diagram shows the coverage ratio of a heat pump for the op-
erating modes bivalent-parallel and bivalent-alternative depend-
ing on the heat consumption of the building using an example
building.
NOTE
Experience has shown that, in the case of bivalent systems used in mod-
ernisation projects, the existing oil or gas boiler is taken out of service
after a few years, for a variety of reasons. Therefore, designing should al-
ways be carried out in the same way as the mono energy system (biva-
lence point is approx. -5 °C). At the same time, the buffer tank should also
be integrated into the heat flow.
1.3.4.6 Design of brine-to-water and water-to-water heat pumps (bivalent operation).
The same interrelationships generally apply for bivalent opera-
tion of water-to-water and brine-to-water heat pumps as for air-
to-water heat pumps. However, other dimensioning factors must
be considered depending on the layout of the heat source sys-
tem.
Ask our heat pump system specialists if you have any questions
on this topic.
1.3.4.7 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 decisively increase the humidity in the building's structure.
This increased humidity in the entire structure causes an in-
crease 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.
In the case of brine-to-water heat pumps, this heating element
should then only be activated during the first heating period on
the basis of the brine flow temperature (approx. 0 °C) or on the
basis of the limit temperature (0 °C to 5 °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.
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