Sizing The Solar Expansion Vessel - Viessmann VITOCAL Series Technical Manual

Design information
To prevent thermal shocks inside the solar circuit, the operation of
the solar thermal system will be interrupted at collector temperatures
> 120 °C (collector protection).
Solar DHW heating
The solar circuit pump starts and the DHW cylinder is heated up if
the temperature differential between the collector temperature sen-
sor and the cylinder temperature sensor (in the solar circuit return) is
greater than the start temperature differential set at the solar control
unit.
The heat pump will be prevented from heating the cylinder if the tem-
perature at the cylinder temperature sensor (in the DHW cylinder,
top) exceeds the set value selected at the heat pump control unit.
The solar thermal system heats the cylinder to the set value selected
at the solar control unit.
Note
■ Hydraulic connection: See www.viessmann-schemes.com.
■ Aperture area that can be connected: See the "Vitosol" technical
guide.
Solar central heating backup
The solar circuit pump and the circulation pump for cylinder heating
start if the temperature differential between the collector temperature
sensor and the cylinder temperature sensor (solar) is greater than
the start temperature differential selected at the heat pump control
unit. The heating water buffer cylinder is heated.

Sizing the solar expansion vessel

Solar expansion vessel
Design and function
With shut-off valve and fixings
A Heat transfer medium
B Nitrogen charge
C Nitrogen buffer
D Minimum safety seal 3 l
E Safety seal
F Delivered condition (pre-charge pressure 4.5 bar, 0.45 MPa)
G Solar thermal system filled, without heat effect
H At maximum pressure and the highest heat transfer medium
temperature
Expansion vessel Part no.
A
B
VITOCAL
(cont.)
Capacity Pre-charge
pressure
l
7248241 18
7248242 25
7248243 40
7248244 50
7248245 80
Heating stops when the temperature differential between the collec-
tor temperature sensor and the cylinder temperature sensor (solar)
is less than half the hysteresis (standard: 6 K) or if the actual tem-
perature captured by the lower cylinder temperature sensor corre-
sponds to the selected set temperature.
See also the "Vitosol" technical guide.
Solar swimming pool heating
See "Vitosol" technical guide.
Solar control unit
Solar control module, type SM1 (accessories): See page 145.
Note
The Solar-Divicon (part no. Z017690) also includes a solar control
module: SDIO/SM1A electronics module
See Viessmann pricelist, register 13.
A solar expansion vessel is a sealed vessel where the gas space
(nitrogen charge) is separated from the space containing liquid (heat
transfer medium) by a diaphragm and the pre-charge pressure is
subject to the system height.
Specification
a
Ø a b
bar (MPa) mm
4.5 (0.45) 280
4.5 (0.45) 280
4.5 (0.45) 354
4.5 (0.45) 409
4.5 (0.45) 480
a
Connection Weight
mm
370 R ¾
490 R ¾
520 R ¾
505 R 1
566 R 1
VIESMANN
7
kg
7.5
9.1
9.9
12.3
18.4
129