Technical data
104 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
8.6.1 Integration of the heat pump in the heating system
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 tempera-
ture level required by the heating system. They are not used for
bridging shut-off times (see Chapt. 8.6.3 on page 104).
In heavily-constructed buildings and for the use of panel heating
systems in general the sluggishness of the heating system com-
pensates for possible shut-off times.
Heat pump manager timer functions offer the possibility to com-
pensate for set shut-off times through programmed raises.
NOTE
The recommended capacity of the buffer tank connected in series is ap-
proximately 10% of the heating water flow rate of the heat pump per hour.
A volume of approximately 8% is sufficient for heat pumps with two per-
formance levels. However, it should not exceed 30 % of the heating water
flow rate per hour.
Overdimensioned buffer tanks lead to longer compressor run-
times. 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.
8.6.1 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 man-
ager. 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 rate 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 con-
nected in series. This increase in circulated heating water vol-
umes result in longer runtimes and an improved average effi-
ciency over the whole year (seasonal performance factor).
NOTE
The buffer tank connected in series increases the circulated heating
water volume and guarantees the operational safety even when only indi-
vidual rooms require heating.
8.6.2 Heating systems without individual room control
If brine-to-water or water-to-water heat pumps are used in sys-
tems 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 pe-
riods 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 equalisa-
tion.
8.6.3 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 recom-
mended to be installed for the use of heat pumps and in combi-
nation 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) ac-
cording to need. This mixer regulation is activated when the sec-
ond heat generator is called during a shut-off time. The electric
heating element should be set to approx. 80 to 90°C.
The technical data for the different buffer tanks is listed below.
Type PSP buffer tanks are built-under buffer tanks with sheet
steel casing, i.e. the relevant heat pump can be installed directly
on the buffer tank. PSW tanks are floor-mounted buffer tanks
with a foil covering.
Fig. 8.18: Heating operation with constantly-regulated buffer tank
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