Sizing The Expansion Vessel - Viessmann VITOFLEX 300-UF Technical Manual

Design information
Heating water buffer cylinder
D
More than 1 heating water buffer cylinder as low loss header
E
(5 sensors)
Heating water buffer cylinder 2
F
Heating water buffer cylinder 1
G
Low loss header
H
Possible with large water volume in mains
TS131
L
(2 pce from Vitoflex 300-UF, 720 kW)
Design recommendation
Trade name
9
Rated heating output
Boiler circuit
Thermally activated safety valve TS-131
Required water flow rate at 2.5 bar
Cylinder capacity
Supply line ZLg
Supply line ZLv
Drain line ALv
Safety valve type SV 68 M
Safety line SL

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 to be installed is subject to the heating system specification
and should be checked in each case.
Quick selection table for calculating the vessel size V
Safety valve bar
p
sv
Pre-charge bar
pressure
System vol- litre
ume V
A
Selection example
Conditions:
p = 3 bar (response pressure of the safety valve)
sv
H = 13 m (static head of the system)
Q = 18 kW (rated heating output of the heat source)
v = 8.5 l/kW (specific water capacity)
Panel radiators 90/70°C
V = 1000 l (volume of buffer cylinder)
PH
Conversion factors for alternative flow temperatures other than 90 °C
Flow temperature °C
Conversion factor
Divide the vessel size found in accordance with the above tables by the conversion factor.
Viesmann
90
(cont.)
kW
pce
l/h
l
R
R
R
R
n
3.0
1.0 1.5 1.8
220 — —
340 200 —
510 320 200
840 440 260
1050 540 330
1470 760 460
2100 1090 660
2630 1360 820
3150 1630 990
4200 2180 1320
5250 2720 1650
6300 3260 1980
8400 4350 2640
10500 5440 3300
50 55 60
3.03 2.50 2.13
Additional heat generator controlled with a max. retaining
M
valve for
- Oil/gas boiler
- Electric heater
With additional heat generator, dual mode
P
- Oil, gas, electric
M20 Boiler circuit pump
Y20 Boiler mixer
KW Cold water supply min. 2.5 bar, max. 3.5 bar
Vitoflex 300-UF
390 530
DN 80 DN 80
1 1
1637 2224
3200 4300
¾ ¾
¾ ¾
¾ ¾
1¼ 1½
DN 50 DN 65
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 + 1000
V
A
n
V = 18 kW x 8.5 l/kW + 1000 l
A
= 1153 l
litre
25
If possible, when calculating the gas pre-charge pressure, select a
35
supplement of 0.2 bar:
50
p ≥ H/10 + 0.2 bar
80
0
p ≥ (13/10 + 0.2 bar) = 1.5 bar
100
0
140
From the table:
200
With p = 3 bar, p = 1.5 bar, V
250
sv 0
V = 250 l (for V max. 1360 l)
300
n A
400
Selected:
500
1 x diaphragm expansion vessel N 250 (from Vitoset pricelist)
600
800
■ All details relate to a flow temperature of 90 °C.
1000
■ The tables have allowed for a hydraulic seal to DIN 4807-2.
Recommendation:
■ 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 installa-
tions: p ≥ 1.5 bar
0
■ Set the fill or 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
65 70 75
1.82 1.59 1.39 1.24
720 950
DN 100 DN 125
2 2
3020 3986
5800 7600
1 1
¾ ¾
¾ ¾
1½ 2x 1½
DN 80 2x DN 65
= 1153 l
A
80 85 90
1.11 1.00 0.90
VITOFLEX 300-UF
1250
DN 125
2
5246
10000
1¼
¾
¾
2x 1½
2x DN 80
95 100
0.82