Viessmann VITODENS 242-F Technical Manual page 73

Design information
(cont.)
Expansion vessel and heat sink in the return
The steam can propagate in the flow and return.
A
B
P
C
D
E
A Collector
B Safety valve
C Vitodens
D Heat sink
E Expansion vessel
The difference between the steam production capacity of the collector
array and the heat loss of the pipework to the point where the dia-
phragm expansion vessel is connected to the heat sink results in the
required residual cooling capacity.
Note
The SOLSEC program is available at www.viessmann.com for calcu-
lating the residual cooling capacity and the sizing of 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, heat sinks
Output at 75/65 °C in W
Stagnation heat sink
– Type 21
Pre-cooling vessel
Expansion vessel
The expansion vessel can be calculated once the steam range 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 + V )·Df
mag kol drohr e fv
VITODENS
Expansion vessel and heat sink in the flow
The steam can propagate only in the flow.
D
E
Conventional radiators the capacity of which is determined as 115 K
are assumed as the heat sink. To make things clearer, the heating
output is given as 75/65 °C in the program.
Note
On account of the expected high surface temperatures, Viessmann
stagnation heat sinks (see technical guide Vitosol) are equipped with
a plate that receives no flow, as protection against accidental contact.
Provide protection against accidental contact when using commercial
radiators. In addition, the connections must be diffusion-proof.
Cooling capacity during stagnation
in W
482
—
V Rated volume of the expansion vessel in l
mag
V Liquid content of the collectors in l
kol
V Content of the pipework subject to steam loads in l
drohr
(calculated from the steam range and the pipework content per
m pipe length)
V Increase in the volume of the heat transfer medium in its liquid
e
state in l
V = V · β
e a
V System volume (content of the collectors, the heat
a
exchanger and the pipework)
β Expansion factor
β = 0.13 for Viessmann heat transfer medium from -20 to
120 ºC
A
B
P
C
Liquid content in l
964
450
VIESMANN
6
12
73