Installation manual
180
8.5
8.5 Buffer Tank
A buffer tank connected in series is recommended for heat pump
heating systems to ensure the minimum runtime of the heat
pump of 6 minutes for all operating statuses.
Air-to-water heat pumps with defrosting by reverse circulation
extract the energy required for defrosting from the heating
system. In air-to-water heat pumps, a buffer tank connected in
series must be installed in the flow in which the immersion heater
is screwed into in mono energy systems to ensure defrosting.
NOTE
During the start-up of a air-to-water heat pump, the heating water must be
pre-heated to the lower operating limit of at least 18°C to ensure
defrosting.
ATTENTION!
An electric heating element which is fitted in a buffer tank must - as a heat
generator - be protected by fuse according to EN 12828. It must also be
additionally equipped with an expansion vessel that cannot be shut off as
well as with a type-tested safety valve.
When implementing brine-to-water or water-to-water heat
pumps, the buffer tank can be installed in the flow or, in a purely
monovalent mode of operation, even in the return flow.
Buffer tanks connected in series are operated on the
temperature level required by the heating system. They are not
used for bridging shut-off times (see Chap. 8.5.3 on p. 180).
In heavily-constructed buildings and for the use of panel heating
systems in general the sluggishness of the heating system
compensates for possible shut-off times.
Heat pump manager timer functions offer the possibility to
compensate for set shut-off times through programmed raises.
NOTE
The recommended capacity of the buffer tank connected in series is
approximately 10% of the heating water flow of the heat pump per hour.
A volume of approximately 8% is sufficient for heat pumps with two
performance levels. However, it should not exceed 30 % of the heating
water flow per hour.
Overdimensioned buffer tanks lead to longer compressor
runtimes. In heat pumps with two performance levels this may
lead to the unnecessary switching on of the second compressor.
ATTENTION!
Buffer tanks are not enamelled and, for this reason, should never be used
for heating water for domestic use. Buffer tanks should be installed
within the thermal envelope of the building in a completely frost-free
location.
8.5.1 Heating systems with individual room control
With individual room control the required room temperature can
be adjusted without changing the settings of the heat pump
manager. If the room set temperature set at the room
temperature controller is exceeded, the actuators close so that
the heating water no longer flows through the overheated rooms.
If individual heating circuits are closed and the volume flow is
thus reduced, part of the heating water flow flows through the
overflow valve or the differential pressureless manifold. This
causes the return temperature to rise and the heat pump to be
switched off.
In systems with buffer tanks connected in series the heat pump
switches off before all rooms have been sufficiently supplied. A
renewed start-up of the heat pump is prevented on account of
the utility requirement that a heat pump may only be switched on
up to three times per hour.
In the case of systems equipped with a buffer tank, the increase
in the return temperature is delayed due to the flow through the
tank. No increased system temperatures arise if the tank is
connected in series. This increase in circulated heating water
volumes result in longer runtimes and an improved average
efficiency over the whole year (annual performance factor).
NOTE
The buffer tank connected in series increases the circulated heating
water volume and guarantees the operational safety even when only
individual rooms require heating.
8.5.2 Heating systems without individual room control
If brine-to-water or water-to-water heat pumps are used in
systems without any controllers in the individual rooms, the
buffer tank can be omitted if the individual heating circuits are
sufficiently dimensioned so that minimum compressor runtime of
approx. 6 minutes is also ensured in interseasonal transition
periods with low heat consumption.
NOTE
If there is no individual room control in the living quarters, a more or less
consistent temperature level is reached within the thermal envelope of
the building. The heating of individual rooms on a higher temperature
level (e.g. bathroom) can partly be achieved through a hydraulic
equalisation.
8.5.3 Buffer tank for bridging shut-off times
An additional buffer tank, equipped with a second heat generator
and acting as a constantly-regulated buffer tank, is
recommended for installed for the use of heat pumps and in
combination with radiators in lightly-constructed buildings (due to
small tank capacities). The buffer tank is heated up in
combination with the special program heat generator 2 (heat
pump manager) according to need. This mixer regulation is
activated when the second heat generator is called during a shut-
off time. The electric heating element should be set to approx. 80
to 90°C.
Fig. 8.9: Heating operation with constantly-regulated buffer tank
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