Low Loss Header - Viessmann VITODENS 200-W Technical Manual

Design information
(cont.)
Testing the integral expansion vessel or the expansion vessel fit-
ted to the mounting frame
Expansion vessel integrated into the Vitodens 200-W,
Vitodens 222-W and Vitodens 300-W, 13 and 19 kW
Pre-charge 0.75 bar
pressure
Blow-off pres- 2.5 bar
sure
Capacity 10 l
Mounting frame with expansion vessel (accessory for the
Vitodens 300-W, 26 and 35 kW)
Pre-charge 0.75 bar
pressure
Blow-off pres- 2.5 bar
sure
Capacity 18 l
When making the hydraulic connections, check that the size of the
expansion vessel matches the system conditions.
The following steps will enable you to make a rough check.
V = f ((V + V ) A + 2.4)
DEV A K f
V = Volume of the expansion vessel
DEV
f = Expansion factor (= 2 for expansion vessel)
V = System volume
A
V = Boiler water volume
K
A = Heating water expansion factor
f
Example:
System:
■ Vitodens 200-W
■ Boiler water volume 2.4 litres
■ Rated output 26 kW
■ Panel radiators
■ System volume approx. 130 litres
■ Heating system 70/50 ºC
Calculation:
Heating system 70/50 ºC: average water temperature approx. 60 ºC
A = 0.0171
f
V = 2 · ((130 + 2.4)· 0.0171 + 2.4)
DEV

Low loss header

Application
Design rules for system hydraulics:
■ When balancing the low loss header, adjust the flow rate on the
equipment side approx. 10 to 30 % lower than the flow rate on the
system side (reducing the return temperature).
■ The low loss header should be sized for the max. volume flow that
may occur in the overall system.
The low loss header separates the heat source (boiler circuit) from the
downstream heating circuits.
Install a low loss header if the max. flow rate of an individual design is
greater than the corresponding value shown in the "Specification"
table.
For installation designs in conjunction with low loss headers, see
"System examples".
Boiler circuit
The circulation pump in the Vitodens must be able to supply the
required water volume against the (mostly low) pressure drop of the
boiler circuit; the pressure drop of the low loss header is negligible.
Subject to the water volume circulating in the boiler circuit, the respec-
tive residual head may be determined for sizing the internal pipe diam-
eters using the pump diagrams; alternatively the variable speed pump
for the Vitodens 300-W can be adjusted accordingly.
VITODENS
V = 9.32 litres
DEV
Result: The integral expansion vessel (10 litre capacity) is sufficiently
large for this system.
Note
If the integral expansion vessel or the expansion vessel in the mount-
ing frame is inadequate, connect an appropriately sized expansion
vessel to the expansion vessel connector on the Vitodens.
Calculating the heating system volume (approximate values)
1000
800
600
400
200
130
0
5 10 20
Output in kW
A Convector heaters
B Panel radiators
C Radiators
D Underfloor heating
Calculating the expansion factor A
Average water temp. [ºC]
50
60
70
Heating circuit
The central heating pumps to be installed on site must be able to
deliver the water volume in the heating circuits against their pressure
drop; size the pumps accordingly.
Principle of operation
T1 T3
V primary
V secondary
T2 T4
D
C
B
A
30 40 50
f
Expansion factor A
f
0.0121
0.0171
0.0228
VIESMANN
75
6