Quick Reference Guide - Page 10
Checking water volume and initial pressure of expansion vessel
The expansion vessel of the Hydro Unit has a capacity of 12 litres. The initial pressure of the expansion vessel is 0.1 MPa (1 bar). The suggested initial water charge is 0.2MPa (2 bar).
The pressure of the safety valve is 0.3 MPa (3 bar).
Verify whether the capacity of the expansion vessel is sufficient using the following expression. If the volume is insufficient, install an appropriate external expansion vessel.
V
<12 L > 12 L
Action
Internal Expansion Vessel Size OK
Internal Expansion Vessel Size too small. Install appropriate external expansion vessel
V:Necessary total vessel capacity (L)
Ɛ: | Water expansion coefficient at average hot water temperature |
Vs: | Total water volume in the closed system (Do not include Hot Water Cylinder) |
P1: | System pressure at tank setting position (Mpa_abs*). |
| (Pipe inner pressure during pump operation before heating device operates = water supply |
| pressure) |
P2: | Maximum pressure used during operation at tank setting position (MPa_abs*). |
| (= safety valve setting pressure) |
*The absolute pressure value (abs.) is obtained by adding the atmospheric pressure (0.1 MPa (1 bar)) to the gauge pressure.
Water temperature and expansion coefficient (Ɛ)
Hot water temperature | Expansion rate |
(°C) | (Ɛ) |
0 | 0.0002 |
4 | 0.0000 |
5 | 0.0000 |
10 | 0.0003 |
15 | 0.0008 |
20 | 0.0017 |
25 | 0.0029 |
30 | 0.0043 |
35 | 0.0050 |
40 | 0.0078 |
45 | 0.0100 |
Water temperature and expansion coefficient (Ɛ)
Hot water temperature | Expansion rate |
(°C) | (Ɛ) |
50 | 0.0121 |
55 | 0.0145 |
60 | 0.0171 |
65 | 0.0198 |
70 | 0.0229 |
75 | 0.0258 |
80 | 0.0292 |
85 | 0.0324 |
90 | 0.0961 |
95 | 0.0967 |
- | - |
Example
Maximum Hot Water temperature: 55°C, initial
water charge: 0.2MPa and system volume: 200 L.
The calculated Vessel capacity (V) is 11.6 L:-
11.6 | = | 0.0145 | x | 200 | |
1 | - | (0.2+0.1) | |||
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| (0.3+0.1) | |||
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In this case V < 12 L therefore the internal expansion vessel is sufficient.
There is no need to install an external expansion vessel.