16
Subject to technical amendments without notice | 83050700gUK – Translation of the original operating manual | ait-deutschland GmbH
23
Flushing and filling the system
IMPORTANT
The system must be absolutely free from air
before commissioning.
23.1 Water quality
of the fill and additional water in hot water
heating systems according to VDI 2035 Part
I and II
Use of modern, energy-efficient heat pump systems
is becoming increasingly widespread. Their ingenious
technology enables these systems to achieve very
good efficiencies. The decreasing space available for
heat generators has led to the development of compact
units with increasingly smaller cross-sections and high
capacities. This means the complexity of the systems
and the material diversity are also increasing, which
plays an important role especially in their corrosion
behaviour. The heating water not only affects the
efficiency of the system, but also the life of the heat
generator and the heating components of a system.
The guide values of VDI 2035 Part I and Part II must
therefore be complied with as minimum requirements
for proper operation of the systems. Our practical
experience has shown that the safest and most
trouble-free running of the systems is achieved with
so-called low-salt operation.
VDI 2035 Part I gives important information and
recommendations regarding scaling and its prevention
in heating and domestic hot water heating systems.
VDI 2035 Part II primarily deals with the requirements
for reducing heating water corrosion in hot water
heating systems.
Principles of Part I and Part II
The occurrence of scaling and corrosion damage in
hot water heating systems is low, if
●
proper planning and commissioning is carried out
●
the system is closed in corrosion terms
●
adequately dimensioned pressurising is inte-
grated
●
the guide values for the heating water are com-
plied with
●
and regular servicing and maintenance are car-
ried out.
A system log should be kept, in which the relevant
planning data is entered (VDI 2035).
Damage that can occur in case of non-
compliance
●
malfunctions and the failure of components (e.g.
pumps, valves)
●
internal and external leaks (e.g. from heat ex-
changers)
●
cross-section reduction and blockaging of compo-
nents (e.g. heat exchanger, pipes, pumps)
●
Material fatigue
●
gas bubbles and gas cushion formation (cavita-
tion)
● negative effect on heat transfer (formation of coat
-
ings, deposits) and associated noises (e.g. boiling
noises, flow noises)
Limescale – the energy killer
Filling with untreated drinking water inevitably leads
to the precipitation of all calcium as scale. The
consequence: limescale deposits form on the heat
transfer surfaces of the heating. The efficiency falls
and the energy costs rise. A rule of thumb is that 1
millimetre of limescale deposit causes an energy loss
of 10%. In extreme cases it can even cause damage
to the heat exchangers.
Water softening to VDI 2035 – Part I
If the water is softened before the heating is filled, in
accordance with the VDI 2035 guidelines, no scale
can form. This effectively and permanently prevents
limescale deposits and the resulting negative effects
on the entire heating system.
Corrosion – an underestimated problem
VDI 2035, Part II, deals with the problem of corrosion.
Softening the heating water can prove to be
insufficient. The pH value can significantly exceed
the limit of 10. pH values higher than 11 can set in,
which even damage rubber seals. The VDI 2035, Part
1 guidelines are fulfilled, however, VDI 2035, Part 2
suggests a pH value between 8.2 and maximum 10.
If aluminium materials are used, which is the case in
many modern heating systems, a pH value of 8.5 must
not be exceeded, because otherwise there is a threat
of corrosion – and aluminium is attacked without the
presence of oxygen. Therefore, apart from softening
the heating fill and additional water, the heating water
should also be appropriately conditioned. This is the
only way to comply with the VDI 2035 requirements
and the recommendations and installation instructions
of the heat pump manufacturer.
