Installation Instructions

Water treatment | 13
6 720 805 218 (2016/02)SB625WS/SB745WS
3 Water treatment
The quality of the fill and top-up water is an essential factor for increased
efficiency, functional reliability, long service life and for maintaining the
constant operational condition of a heating system. If the system is filled
with water that has a high calcium hardness, this will be deposited on the
heat exchanger surfaces and will obstruct the transfer of heat to the
heating water.
As a result, the wall temperatures of the stainless steel heat exchanger
surfaces will increase and the thermal stress (loads on the boiler body)
will increase. Water treatment is an essential factor in ensuring trouble
free operation, availability, a long service life and the efficiency of the
heating system.
3.1 Chemical and physical characteristics
The chemical and physical characteristics of heating system water must
be similar to those of drinking water.
A chemical water treatment device is recommended in order to protect
system components as well as an inlet filter to prevent solid particles
from entering the system in suspension and causing corrosion or sludge.
Typical layouts of water treatment systems
Fig. 7 Water treatment for heating installations
[1] Filter
[2] Water softener
[3] Boiler
[4] Chemical treatment unit
Chemical and physical requirements of heating system water
3.2 Central heating system
Possible causes for corrosion and limescale
Typical problems encountered in central heating systems include:
• the breakage of heated surfaces through overheating caused by the
thermal insulation of limescale deposits on the water side
• oxygen corrosion
• deposit corrosion
• stray current corrosion
• diffused and localized acid corrosion.
3.2.1 Limescale deposits
Limescale forms when the calcium and magnesium bicarbonates that
are dissolved in the water at ambient temperature become chemically
transformed when the water is heated.
Calcium bicarbonate forms calcium carbonate, water and carbon
dioxide, while magnesium bicarbonate transforms into magnesium
hydroxide and carbon dioxide.
Calcium bicarbonate Ca(HCO
3
)
2
when temperature is increased:
F. 1 Calcium bicarbonate changes when temperature is increased
Magnesium bicarbonate Mg(HCO
3
)
2
when temperature is increased:
F. 2 Magnesium bicarbonate changes when temperature is
increased
Calcium carbonate and magnesium hydroxide precipitate to form
insoluble deposits that adhere and compact on surfaces to form
limescale, a substance with a high thermal insulating power.
Inside a boiler, limescale forms mainly in areas subject to direct heat and
high temperatures. It is so common to find deposits localized in a few
specific areas, where temperature is the highest. A coating of limescale
NOTICE:
If it proves impossible to treat the heating system water
supply properly because the water charging system is
automatic and uncontrolled, if there are no barriers
installed to prevent water oxygenation, and if the
heating system includes an open expansion vessel, then
the boiler itself must be separated from the heating
system by means of a heat exchanger.
Installation must conform to any and all national, federal,
state and local standards and codes.
Y
6 720 805 218-17.1T
1
32 4
Parameters Unit Heating water
pH 7.5- 9,5
Hardness ppm < 50
Electrical conductivity s/cm < 100
Chlorides mg/l < 10
Sulphides mg/l < 10
Nitrides mg/l < 10
Oxygen in solution mg/l –
Iron (Fe) mg/l < 0.5
Table 7 Requirements of heating system water
NOTICE:
Chemical products used for water treatment must be
compatible with applicable water pollution laws.
Provided they are properly applied, these laws
guarantee the safe functioning of the heating system.
CaCO
3
H
2
OCO
2
++
Mg OH
2
2CO
2
+