Appendix; Selection Example; Sizing The Expansion Vessel - Viessmann VITOLIGNO 200-S Technical Manual

Appendix

7.1 Sizing the expansion vessel

In accordance with EN 12828, water heating systems must be equip-
ped with a diaphragm expansion vessel. The size of the expansion
vessel is subject to the heating system specification and should be
checked in each case.

Selection example

Given:
p = 3 bar (response pressure of the safety valve)
sv
H = 13 m (static head of the system)
Q = 30 kW (rated heating output of the heat source)
v = 8.5 l/kW (specific water capacity)
Panel radiators 90/70°C
V = 2000 l (volume of buffer cylinder)
PH
The specific water capacity v was determined as follows:
■ Radiators: 13.5 l/kW
■ Panel radiators: 8.5 l/kW
■ Underfloor heating system: 20 l/kW
Calculation:
V = Q x v + V
A PH
V = 30 kW x 8.5 l/kW + 2000 l
A
= 1255 l
If possible, when calculating the gas pre-charge pressure, select a
supplement of 0.2 bar:
p ≥ H/10 + 0.2 bar
0
p ≥ (13/10 + 0.2 bar) = 1.5 bar
0
Conversion factor for flow temperatures other than 90 °C
Flow temperature °C
Conversion factor 3.03
Divide the vessel size found in accordance with the above tables by the conversion factor.
VITOLIGNO 200-S
50 55 60 65
2.50 2.13 1.82
Quick selection table for calculating the vessel size V
Safety valve bar
p
sv
Pre-charge bar
pressure
System vol- litre
ume V
A
1050
1470
2100
2630
3150
4200
5250
From the table:
With p = 3 bar, p = 1.5 bar, V
sv 0 A
V = 250 l (for V max. 1360 l)
n A
Selected:
2 x diaphragm expansion vessel N 250 (from Vitoset pricelist)
■ All details relate to a flow temperature of 90 °C.
■ The tables have allowed for a hydraulic seal to DIN 4807-2.
Recommendations:
■ Select a sufficiently high safety valve response pressure:
p ≥ p + 1.5 bar
sv 0
■ For circulation pumps, due to the inlet pressure required, select at
least 0.3 bar above the pre-charge pressure even for attic/roofspace
installations: p ≥ 1.5 bar
0
■ Set the fill/starting pressure on the water side of vented systems in
their cold state at least 0.3 bar above the pre-charge pressure:
p ≥ p + 0.3 bar
F 0
70 75 80
1.59 1.39 1.24 1.11
n
3.0
1.0 1.5 1.8
220 — —
340 200 —
510 320 200
840 440 260
540 330
760 460
1090 660
1360 820
1630 990
2180 1320
2720 1650
= 1255 l
85 90 95
1.00 0.90
VIESMANN
V
n
litre
25
35
50
80
100
140
200
250
300
400
500
100
0.82
7
75