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13.9 Ventilation
At points in the system that are at high risk from steam or in roof
installations, only use air separators with manual air vent valves,
which require regular manual venting. This is particularly necessary
after filling.
Correct ventilation of the solar circuit is a prerequisite for trouble-free
and efficient operation of the solar thermal system. Air in the solar
circuit generates noise and puts at risk the reliable flow through the
collectors or through individual array sections. In addition it can lead
to accelerated oxidation of organic heat transfer media (e.g. com-
mercially available mixtures of water and glycol).
Air vent valves are used to vent air from the solar circuit:
■ Manual air vent valve
■ Automatic air vent valve
– Quick-action air vent valve
– Air separator
For the construction and specification of air vent valves, see chapter
"Installation accessories".
The air vent valves are installed in the solar flow line at an accessi-
ble point in the installation room upstream of the heat exchanger
inlet.
P
A
A
Air vent valve, built into Solar-Divicon
When setting up and connecting larger collector arrays, the ventila-
tion characteristics of the system can be optimised by flow lines
joined above the collectors. This prevents air bubbles from causing
flow problems in individual collectors in partial arrays linked in paral-
lel.
In systems higher than 25 m above the air vent valve, air bubbles
that form in the collectors are dispersed again as a result of the high
pressure increase. In such cases, we recommend using vacuum
deaerator systems.
13.10 Safety equipment
Stagnation in solar thermal systems
All safety equipment in a solar thermal system must be designed for
stagnation. If, during insolation on the collector array, heat can no
longer be transferred within the system, the solar circuit pump stops
and the solar thermal system goes into stagnation. Longer system
idle times, e.g. due to faults or incorrect operation, can never be
completely ruled out. This results in a rise in temperature up to the
maximum collector temperature. Energy yield and loss are then the
same.
Requirements:
■ The solar thermal system must not be damaged by stagnation.
■ The solar thermal system must not pose any risk during stagna-
tion.
■ Following stagnation, the solar thermal system must automatically
return to operation.
■ Collectors and pipework must be engineered for the temperatures
expected during stagnation.
Information regarding design and operation
(cont.)
132
VIESMANN
VITOSOL
13
5822 440 GB