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General
Information on cold water
8
Information on cold water
8.1
General
Different variants of fresh water modules and heat
exchangers
In general, there are two major points to consider for
drinking water heating via plate heat exchangers:
•
Calcification:
This depends on the water hardness specified in
degrees of German hardness (°dH).
•
Corrosion of the plate heat exchanger:
This depends on the water quality, especially the
conductance.
This is why ETA offers two versions of fresh water
modules or replacement heat exchangers. The
inexpensive standard solution with stainless steel
plates connected by copper solder, as well as the
somewhat more expensive special solution with
stainless steel plates connected by stainless steel
brazing solder ("INOX" heat exchanger).
If you have the fresh water module with the
"standard heat exchanger" but are not sure
whether this can keep up with the demands of your
drinking water, then you can operate the fresh water
module normally, of course. If the heat exchanger
actually develops leaks due to copper corrosion, you
can exchange it at any time for the special solution with
stainless steel brazing solder. This heat exchanger is
also offered individually by ETA.
Ask your heating technician
We recommend that you take advantage of the heating
technician's experience. He or she will know whether
you must pre-treat your drinking water and which
procedure is best suited to the drinking water in your
region.
8.2
Calcification
Increasing water hardness increases the risk of
calcification
Irrespective of the type of drinking water heater, we
recommend installing a water softener from a water
hardness of 14°dH and above. With our fresh water
module, damage caused by calcification is not of great
concern since an inexpensive replacement heat
exchanger from ETA can be replaced by the heating
engineer in a few easy steps. For machines like coffee
makers, washing machines, dishwashers ... the
damage from calcification is often associated with high
costs, or the devices may even become irreparable.
Due to the fact that 1 litre of water contains about
18 mg of calcium for each °dH, the risk of calcifi-
cation increases with increasing water hardness. One
litre of water with 10° dH therefore contains around
180 mg calcium, at 20° dH about 360 mg.
The calcification risk also increases when the hot
water temperature is set above 55 °C or when
circulation pumps are operated for 24 hours (in other
words practically all the time). In these cases, the
provided protective measures against excessive calci-
fication, such as reducing the primary temperature
(see functionality of the fresh water module),
circulation breaks or its deactivation and optimised
connection arrangement of the ETA fresh water
module, are unable to cope.
The heat exchangers offered by ETA do not
exhibit any differences in terms of calcification.
They only differ in terms of corrosion resistance.
8.3
Corrosion
The electrical conductance is crucial for possible
copper corrosion
What is important for potential copper corrosion of the
solder connections of the individual plates is the
electrical conductance. How well water conducts
current is determined with the conductance meter. This
can only measure how well all conductive minerals in
the water conduct together. The conductance of
individual materials cannot be determined. So this
overall hardness determines the conductance.
Basically, water with a lower conductance has a lower
overall hardness. Water with higher conductance is
correspondingly harder. However, it is not possible to
calculate the hardness from the conductance with a
precise formula, or vice versa.
A rule of thumb is: per °dH the conductance of tap
water increases by at least 35 μS/cm.
Due to the content of sodium, chloride and sulphate in
different tap waters differing widely, the conductance
can be pushed up sharply. For example: tap water with
an overall hardness of: 17° dH and a conductance of
over 700 μS/cm exists. So the rule of thumb can only
be applied to a limited extent for tap water. However, it
is helpful in making a rough estimation without precise
water tests.
In general, copper soldered heat exchangers with
a conductance of less than 500 μS/cm are very
corrosion-resistant. At 500-1000 μS/cm, corrosion
