Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 61
Domestic hot water preparation with heat pumps 6.1.2
6 Domestic hot water preparation with heat pumps
6.1 Heating domestic hot water with the heat pumps for heating purposes
The heat pump manager regulates both space heating as well as
the preparation of domestic hot water (see chapter on regula-
tion). The system for heating domestic hot water using the heat
pump should be set up parallel to the system for space heating,
because a different domestic hot water temperature is normally
required for domestic hot water preparation than for space heat-
ing. The return sensor should be installed in the common return
of the heating system and the domestic hot water heating system
(see chapter on integration).
6.1.1 Requirements placed on the domestic hot water cylinder
The standard continuous power ratings specified by the different
cylinder manufacturers are not suitable criteria for selecting a cyl-
inder for heat pump operation. The following criteria must be
taken into consideration when selecting a cylinder: the size of the
heat exchanger area, the construction and the layout of the heat
exchanger in the cylinder, the continuous power rating, the flow
rate and the installation position of the thermostat or sensor.
The following criteria must be taken into
consideration:
Heating up stationary domestic hot water (covering water
level losses - static state).
The heat output of the heat pump at the maximum heat
source temperature (e.g. air +35 °C) must also be transfera-
ble at a cylinder temperature of +45 °C.
The cylinder temperature is lowered when a circulation pipe
is used. The circulation pump should be time-controlled.
It must be possible to tap the required amount of domestic
hot water even during shut-off times without the heat pump
having to reheat.
Selective reheating using a flange heater is only possible in
combination with a temperature sensor.
ATTENTION!
On systems where the domestic hot water preparation takes place via the
glycol circuit, the glycol can be prevented from coming into contact with
drinking water using suitable measures. These measures include using
food-safe glycol (e.g. propylene glycol) or using double-walled safety
heat exchangers.
6.1.2 Domestic hot water cylinder for heat pumps for heating purposes
Domestic hot water cylinders are used to heat the water for san-
itary facilities. The heating takes place indirectly via an installed
pipe coil with heating water or combo tanks directly into the
finned tube heat exchangers according to the flow principle.
Design
The tanks are manufactured in a cylindrical design according to
DIN 4753 Part 1. The heating surface consists of a welded, coil-
shaped bent pipe or a finned tube heat exchanger with direct do-
mestic hot water preparation. All connections lead out from one
side of the cylinder.
Corrosion protection
According to DIN 4753 Part 3, the entire interior surface of the
cylinders is protected by an approved enamel coating. This
enamelling is applied in a special process, and guarantees relia-
ble corrosion protection in combination with the magnesium
anode which is fitted as an accessory.
According to the specifications of the German Technical and Sci-
entific Association for Gas and Water (DVGW), the magnesium
anode should be initially inspected by after-sales service after 2
years of use and then at regular intervals. It should be replaced
according to need. Depending on the quality of the domestic
water (conductivity), it is advisable to have the reactive anode in-
spected in shorter intervals.
The anode (33 mm) should be replaced once it has reduced in
size to a diameter of 10-15 mm.
The stray current anode (Correx anode) is also available as an
alternative to the magnesium anode. It is connected directly to a
voltage source and is therefore maintenance-free.
Water hardness
Domestic water contains varying amounts of lime depending on
its source. Hard water contains a large amount of lime. There are
different water hardness levels which, in Germany, are meas-
ured in degrees of hardness (°dH).
“French degrees of hardness” are used in Switzerland. These
correspond to
If electric flange heaters are used for general reheating to tem-
peratures over 50 °C, we recommend the installation of a descal-
ing system for water if the water supply has hardness level III
with a hardness of > 14 °d.H. (hard and very hard water) or
more.
Commissioning
Ensure that the water supply is turned on and the cylinder is filled
before commissioning. The initial filling and commissioning must
be carried out by an authorised specialist company. The entire
system, including all factory-assembled components (e.g. flange
lid) should be inspected to ensure that everything is working
properly and that there is no leakage.
Hardness level
soft
= less that 1.5 millimoles of calcium carbonate
per litre (equivalent to 8.4 °dH)
Hardness level
medium
= From 1.5 to 2.5 millimoles of calcium carbon-
ate per litre (equivalent to 8.4 to 14 °dH)
Hardness level
hard
= more than 2.5 millimol calcium carbonate per
litre (equivalent to more than 14 °dH)
1° d.H. = 1.79° fr.H.
1° fr.H. = 0.56° d.H.