13.11 Additional function for DHW heating
In solar thermal systems with DHW storage, we recommend heating
the preheating cylinder and the preheating stage in dual mode DHW
cylinders to ≥ 60 °C once a day (regardless of the cylinder volume).
13.12 Connecting the DHW circulation and automatic thermostatic mixing valve
To ensure trouble-free functioning of the solar thermal system, it is
important that, in the DHW cylinder, areas with cold water are availa-
ble to receive the solar energy. These areas must not be reached by
the DHW circulation return. The DHW circulation connection in the
DHW cylinder must therefore be used (see following diagram).
DHW with temperatures in excess of 60 °C can cause scalding. To
limit the temperature to 60 °C, install a mixing device, e.g. an auto-
matic thermostatic mixing valve (see page 92). If the maximum set
temperature is exceeded, the valve mixes cold water into the DHW
as it is drawn off.
If the automatic thermostatic mixing valve is used in conjunction with
a DHW circulation pipe, a bypass line is required between the DHW
circulation inlet on the DHW cylinder and the cold water inlet on the
mixing valve. To avoid recirculation, a check valve should be instal-
led (see following diagram).
A
DHW circulation pump
B
Automatic thermostatic mixing valve
C
Check valve
D
DHW circulation return in summer
Line required to prevent excessive temperatures in summer
E
DHW circulation return in winter
Flow temperature max. 60 ºC.
F
Automatic thermostatic mixing valve inlet
Pipe runs as short as possible, as these receive no flow in win-
ter.
Note
Viessmann offers a thermostatic DHW circulation set as an acces-
sory (see page 92).
Information regarding design and operation
(cont.)
VITOSOL
VIESMANN
137
5822 440 GB
13
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