Technical data

66 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
6.1.5 Domestic hot water preparation with heat pumps
Table 6.3: Design aid for combination and domestic hot water cylinders
6.1.5 Country-specific requirements Germany: German Technical and Scientific
Association for Gas and Water (DVGW) - worksheet W 551
The DVGW worksheet W 551 describes measures for reducing
the growth of legionella bacteria in domestic water systems. A
distinction is made between small systems (detached and semi-
detached houses) and large systems (all other systems with cyl-
inder volumes larger than 400 litres and pipe volumes larger
than 3 l between the cylinders and the extraction points).
For small systems, a standard temperature setting of 60 °C is
recommended on the domestic hot water preparation equipment.
Operating temperatures under 50 °C should always be avoided.
When using low-temperature heat pumps, the reheating in the
domestic hot water cylinder should take place via a supplemen-
tary electric heater for economic reasons.
The water at the domestic hot water outlet, for example, must be
heated to a minimum of 60 °C for large systems. If the design of
the heat pumps is correct, these temperatures can also be
achieved with medium-temperature heat pumps. In bivalent sys-
tems, the domestic hot water preparation should be carried out
by the second heat generator.
Switzerland: SVGW data sheet TPW:
Legionella in domestic water installations –
What has to be taken into account?
This data sheet discusses where problems with legionella bacte-
ria in domestic water could arise and the available options for ef-
fectively reducing the risk of infection.
NOTE
Installation of a flange heater is generally recommended to enable heat-
ing to temperatures of over 60 °C. Electric reheating can be time-control-
led by the controller according to the application and/or customer re-
quirements.
6.1.6 Hydraulic connection of domestic hot water cylinders
Connecting the combination cylinder PWD 750
The following drawing shows the domestic hot water preparation
via a combination cylinder PWD 750 with circulation line. In nor-
mal tapping operation, a part of the domestic water is fed over
the heat exchanger of the PWD 750 and heated up. The domes-
tic hot water set temperature is regulated via the built-in thermo-
stat-controlled three-way valve. When the circulation pump is
activated, part of the water is fed into the top right heat ex-
changer via the bypass and heated up there. The thermostat-
controlled three-way valve then mixes the heated water into the
circulation pipe until the desired temperature is reached.
NOTE
In contrast to the PWD 750, the heat exchangers are arranged in a line one
above the other in the combination cylinders PWD 900 and PWD 1250.
This must be taken into account in the hydraulic integration of the cylin-
ders.
Fig. 6.4: Integration of the circulation return in the cold water inlet of the ther-
mostat mixer
Water-to-water heat pumps
Heat pump Volume in litres
Heat exchange surface
in m²
Cylinder Charge pump M18
WI 10TU 300 3.2 WWSP 332 UP 60
WI 14TU 300 3.2 WWSP 332 UP 60
WI 18TE 400 4.2 WWSP 880 UP 80
WI 22TE 500 5.7 WWSP 900 UP 70-32
WI 27TE 500 5.7 WWSP 900 UP 70-32
WI 50TU
500 5.7 WWSP 900
UP 70-32
800 8 WWSP 885S
WI 100TU 2 x 500 11.4 2 x WWSP 900 7.5 m³/h
Water-to-water heat pumps 230V
Heat pump Volume in litres
Heat exchange surface
in m²
Cylinder Charge pump M18
WI 9ME / WI 14ME 300 3.2 WWSP 332 / PWS 332 UP 60
Pipe lengths with a 3 l volume
Copper pipe ∅ x mm Pipe length / m
10 x 1.0 60.0
12 x 1.0 38.0
15 x 1.0 22.5
18 x 1.0 14.9
22 x 1.0 9.5
28 x 1.0 5.7
28 x 1.5 6.1
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