Version Nr. 1-1 - 31.08.2017
Doc. Nr. 992125210
4 / 14
4. Technical information
Air - water heat exchangers are intended as complementary accessories to large industrial equipment
which include a motor-operated fan or blower together with a cooling heat exchanger. These may also
include an electric heater. The fan or blower is intended to recirculate air and allow heat exchange.
The heat exchanger is designed for chilled water or anti-freeze/corrosion inhibitor mixed water from a
separate source.
The cooling function may be controlled by an on-board or remote controller or thermostat, a
thermostatically controlled valve or an electrically controlled valve. Heating function, when installed is
provided by an electrical heating element. The unit seals the cabinet which ensures that the clean air
inside does not come into contact with the ambient air which may well be dirty or polluted. The unit is
fit for purpose within the rated/declared ambient conditions (e.g. dusty and oily air or high air
temperatures between 34°F and 162°F), also indicating the rated allowable ingress and environment.
Water quality
To ensure the maximum lifetime of an air-water heat exchangers, it is important to supply cooling
water in conformity with the VGB Cooling Water Guidelines (VGB-R 455 P). The cooling water used
must be soft enough to avoid scale deposits, but should not be too soft as this would corrode the heat
exchanger. Where the cooling water is cooled for reuse, part of the water has to be changed with fresh
water to prevent the concentration of hardness and salt content which makes the water more
corrosive.
The main impurities and possible methods of eliminating them are given in the table below:
Pollution of the water
Method of elimination
Mechanical impurities (dp > 0.079in)
Filtration of the water
Excessive hardness
Softening of the water by ion
exchange
Moderate content of mechanical impurities
and hardness formers
Addition of dispersants or stabilisers
Moderate content of chemical impurities
Addition of passivators and inhibitors
Biological impurities (bacteria and algae)
Addition of biocides
When the water is re-cooled, it is recommended that the water condition is maintained as close as
possible to the following list of hydrological data:
Hydrological data
pH-values
7 - 8.5
Carbonate hardness
>3 <8
°dH
Free carbon dioxide
0.4673 - 0.8763
gr/gal
Associated carbon dioxide
0.4673 - 0.8763
gr/gal
Aggressive carbon dioxide
0
gr/gal
Sulphides
free
gr/gal
Oxygen
< 0.5842
gr/gal
Chloride ions
< 2.921
gr/gal
Sulphate ions
< 14.6
gr/gal
Nitrates and nitrites
< 0.5842
gr/gal
COB
< 0.4089
gr/gal
Ammonia
< 0.2921
gr/gal
Iron
< 0.01168
gr/gal
Manganese
< 0.01168
gr/gal
Conductivity
< 2200
µS/cm
Solid residue from evaporation
< 29.21
gr/gal
