Viessmann VITODENS 242-F Technical Manual page 70

Design information
■ Steam spread is less than the pipe run in the solar circuit (flow
and return) between solar collector and expansion vessel:
The steam cannot reach the expansion vessel in the event of stag-
nation. The displaced volume (solar collector array and pipework
filled with steam) must be taken into account when sizing the
expansion vessel.
■ Steam spread is greater than the pipe run in the solar circuit (flow
and return) between solar collector and expansion vessel:
Include a cooling line (heat sink) in the design, to protect the
expansion vessel diaphragms against thermal overload (see dia-
grams below). Steam condenses in this cooling line and reduces
the temperature of the liquefied heat transfer medium to below
70 °C.
Expansion vessel and heat sink in the return
The steam can spread through the flow and return.
A
B
P
D
5
E
A Solar collector
B Safety valve
C Vitodens
D Heat sink
E Expansion vessel
The necessary residual cooling capacity is determined from the dif-
ferential between the steam-producing power of the solar collector
array and the heat dissipation of the pipework up to the connection
point for the expansion vessel and the heat sink.
Note
The SOLSEC program is available at www.viessmann.com for calcu-
lating the residual cooling capacity and sizing the heat sink.
This program offers three suggestions for implementation:
■ Sufficiently long, uninsulated pipework branching to the expansion
vessel
■ A sufficiently large pre-cooling vessel, in relation to the cooling
capacity
■ A correctly sized heat sink
Specification for heat sinks
Stagnation heat sink
– Type 21
Pre-cooling vessel
VIESMANN
70
(cont.)
C
Output at 75/65 °C in W
Expansion vessel and heat sink in the flow
The steam can only spread through the flow.
A
B
P
C
For the heat sink, standard radiators with an output calculated at 115
K are assumed. For greater clarity, the program indicates the heating
output at 75/65 °C.
Note
Due to the expected high surface temperatures, Viessmann stagna-
tion heat sinks (see Vitosol technical guide) are equipped with a
plate that receives no flow, for protection against accidental contact.
If commercially available radiators are used, protection against acci-
dental contact must be provided. In addition, the connections must
be diffusion-proof.
Cooling capacity during stagnation
in W
482
—
D
E
Liquid content in l
964
450
VITODENS
12