Viessmann VITOSOL 200-FM SV2F Design Manual page 88

Design and Operation
Connecting the DHW Circulation and Thermostatic Mixing Valve
Mixing Valve
To ensure trouble-free functioning of the solar thermal
system, it is important that the lower portion of the solar
DHW tank remain cool so that it can receive the solar
energy. The lower portion of the dual coil DHW tank or
the solar pre-heat tank must not under any circumstances
be heated by the DHW circulation pump. It is highly
recommended that the DHW circulation connection be
used when installing Vitocell DHW tanks (see diagram).
To limit the temperature to 140°F (60°C), install a mixing
device, e.g. a thermostatic mixing valve. If the mixing
valves maximum set temperature is exceeded [e.g. 140°F
(60°C)], the valve will mix cold water with hot water,
as it is drawn from the tank. This is very important as
DHW temperatures in excess of 140°F (60°C) can cause
scalding.
- Mixing valve set to 120°F (49°C)
- Tank Temperature
- No DHW being used and the
recirculation pump is operating
- Mixing valve set to 120°F (49°C)
- Tank Temperature
- No DHW being used and the
recirculation pump is operating
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120°F (49°C)
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120°F (49°C)
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DHW Circulation Bypass Line
When a thermostatic mixing valve is used in conjunction
with a DHW circulation pump, a bypass line is required
between the DHW circulation inlet on the Vitocell tank
and the cold water inlet on the mixing valve. To avoid
incorrect circulation, a check valve must be installed
(see page 87).
The bypass line will be used when the storage tank
temperature is at a higher temperature than the DHW
service temperature and there is no DHW being consumed
in the building and the DHW circulation pump is operating.
The bypass line ensures that the DHW supply temperature
is maintained, while not forcing the entire dual coil tank
or the pre-heat tank to be heated by the backup heat
source. This is very important as this reverse circulation
will reduce or eliminate the ability to store solar energy in
the lower portion of the storage tank, or the solar pre-heat
tank. (See diagrams below)
- Mixing valve set to 120°F (49°C)
- Tank Temperature
- DHW is being used and the
recirculation pump is operating
NO BYPASS LINE
- Mixing valve set to 120°F (49°C)
- Tank Temperature
- No DHW is being used and the
recirculation pump is operating
Solar System Design Guide
(continued)
120°F (49°C)
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120°F (49°C)
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