Bosch Buderus SB625WS, Installation Instructions Manual

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Glossary | 49
6 720 805 218 (2013/02) SB625WS/SB745WS
12 Glossary
Appearance
The appearance of water depends on the presence of sediment, in
suspension or in colloidal form, and on the presence of dissolved
substances that create easily identifiable conditions like turbidity,
colouration or foaming. These substances can lead to limescale, sludge,
corrosion, abrasion, microbial growth and foaming.
Their presence in a heating system indicates either that the filling water
has not been sufficiently purified and has been topped up, or that there
are problems inside the circuit, (such as corrosion, leaks, etc.). It is
essential to identify the source of any such impurities so that the correct
remedial action can be taken.
Temperature
The temperature reached at different points in a heating circuit is
extremely important, since it determines whether phenomena like
limescale, corrosion and microbial growth will occur and how quickly
they will develop. Temperature must be accurately specified at all stages
of the system design process, and must be checked carefully as soon as
any malfunctioning is detected.
pH
The pH value, referred to 77 °F (25°C), expresses how acidic or basic a
solution is, in a scale from 0 to 14.
• 0 defines maximum acidity
• 7 defines neutrality
• 14 defines maximum basicity
pH is a fundamental parameter in evaluating how corrosive system water
might be. It also represents an extremely important factor in the
development of limescale, corrosion and microbial growth. Generally
speaking, any pH value lower than the range specified in the
Characteristics of filling and refilling water section can cause generalized
corrosion, while any pH higher than that range can lead to limescale,
sludge and corrosion.
Fixed residues at 180 °F – Electrical conductivity
Fixed residue offers a direct measurement by weight of the quantity of
salts contained in a sample of water evaporated at 180 °F.
Since the electrical conductivity of a water based solution depends
largely on its salt content, electrical conductivity is often taken as an
alternative measurement to fixed residue. Since conductivity is also
influenced by temperature, any measurement taken with a conductivity
meter must be referred to 77 °F (25°C). Conductivity is expressed in
microsiemens per centimetre (

S/cm).
As a practical means of measurement, it is assumed that fixed residue
(expressed in mg/kg) corresponds to about 2/3 of the corresponding
conductivity measurement (in

S/cm).
A high salt content can cause limescale, corrosion and sludge, and can
also point to design errors or poor operating practices (e.g. insufficient
bleeding) of the heating system or water treatment system.
Hardness
The total hardness of a water sample is an expression of the sum total of
all the calcium and magnesium salts dissolved in it. The temporary
hardness value expresses the sum total only of calcium and magnesium
bicarbonates. Hardness is expressed in mg/kg of CaCO3 or in degrees
‘French’ (1°fr = 10 mg/kg CaCO3).
The use of hard water without suitable treatment can lead to the
formation of limescale.
Alkalinity
M-alkalinity or total alkalinity represents the sum total of all alkaline salts
(bicarbonates, carbonates, hydrates and alkaline phosphates) present
in a water sample. P-alkalinity or phenolphthalein alkalinity expresses
the content of hydrates and half the carbonates. The phenolphthalein
alkalinity of naturally occurring water is normally zero. Alkalinity is
expressed in mg/kg of CaCO3.
High P-alkalinity values can lead to increases in pH, and are generally
caused by inadequate venting and bleeding.
Iron
Free iron in a water circuit can lead to sludge and/or secondary forms of
corrosion. If the iron content of the raw water supply exceeds the
established limits, suitable pretreatment must be provided. Iron found
in system water as the result of corrosion points to the fact that the
heating system or the treatment system is not being operated properly.
Copper
Copper content is expressed in mg/kg of Cu.
The presence of copper in system water can cause dangerous localized
corrosion. Copper is seldom found in any appreciable quantity in raw
water.
If it is detected, it is therefore the result of corrosive processes inside the
heating circuit.
It may only be necessary to measure the copper content of the water if
the system contains copper components which might be corroding.
Chlorides and sulphates
These values are expressed in mg/kg of Cl and SO4, respectively.
Since the system filling water is considered to be drinkable, no specific
limits are laid down for chloride and sulphate content. These salts can
nevertheless cause corrosion if they come into contact with certain
metals (certain stainless steels in the case of chlorides and copper in the
case of sulphates).
Microbial growth
A wide range of algae, fungus, mould and bacteria species can live and
breed inside heating circuits. These microbes not only form living
colonies of organisms but also cause corrosion and bad smells when
they die and decompose.
Microbial growth
In this context, the term ‘microbial’ refers to any form of organic life
normally classified as algae, fungi, moulds and bacteria.
Their growth is fed by light, heat, sludge and accidental pollution.
Perhaps the most dangerous microbes for a heating system are
autotrophic bacteria (e.g. ferrobacteria and sulphate reducing
bacteria). These are one of the direct causes of localized corrosion.
Microbial growth can be prevented by using suitable biocides.
This document only defines the intrinsic characteristics
of water used in heating systems in order to identify
suitable treatments. Failure to do so can lead to a wide
range of problems.