Viessmann VITODENS 222-F Technical Manual page 62

Design information
Expansion vessel and heat sink in the return
The steam can spread through the flow and return.
A
B
P
D
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.
5
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
Expansion vessel
The expansion vessel can be calculated once the steam spread has
been determined and any heat sinks that may be used have been
taken into consideration.
The required volume is determined by the following factors:
■ Expansion of the heat transfer medium in its liquid state
■ Liquid seal
■ Expected steam volume, taking account of the static head of the
system
■ Pre-charge pressure
V = (V + V + V
dev col dpipe e
VIESMANN
62
(cont.)
C
Output at 75/65 °C in W
+ V )·Df
fv
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
—
V Nominal volume of the expansion vessel in l
dev
V Liquid content of the solar collectors in l
col
V Content of the pipework subject to steam loads in l
dpipe
(Calculated from the steam spread and the pipework content
per m pipe length)
V Increase in the volume of the heat transfer medium in its liq-
e
uid state in l
V = V · β
e a
V System volume (content of the solar collectors, the heat
a
exchanger and the pipework)
β Expansion factor
β = 0.13 for Viessmann heat transfer medium from −20 to
120 °C
D
E
Liquid content in l
964
450
VITODENS
12