Water Treatment - Data Aire DAPA-2.5 Installation, Operation & Maintenance Manual

Water Treatment

If impurities are not controlled, they can cause sludge or biological fouling. Simple blowdown
(discharging a small portion of the recirculating water to a drain) may be adequate to control scale and
corrosion on sites with good quality makeup water, but it does not control biological contaminants such
as Legionella. Chapter 49 of the ASHRAE Handbook—HVAC Applications covers water treatment in
more detail. Specific recommendations on water treatment can be obtained from water treatment
suppliers.
6.2.3.1
Scale treatment
In daily use, scale accumulates at the water side of heat exchangers therefore regular scale treatment
is a must.
Variations in water quality from place to place and variations in applications of plate heat exchangers
make it difficult to define in simple terms the water quality requirements for minimum maintenance. It is
important to ensure the right water quality and reduce scale by establishing the requirements for local
conditions or utilizing specialist water treatment companies.
The following should be paid attention to in daily maintenance.
6.2.3.2
Undissolved solids (turbid water)
If undissolved solids and other fibers are in the water, the channels of the condenser are easily blocked.
Fibrous debris cannot pass the heat exchanger and must be disposed of. To reduce undissolved solids
blocking the condenser, granules should be kept smaller than 0.8 mm and is recommended to fit a 40
to 70 mesh strainer. Regular maintenance of this unit is required to ensure continued performance.
6.2.3.3
Dissolved products
Under certain circumstance crystallized deposits of calcium and magnesium ion in the water will attach
to the condenser surface and scale. The higher the concentration of Ca2+ and Mg+ and the water
temperature, the greater the possibility of scale formation. Thick scale will not only gravely affect heat
transfer capability but even block the channels. As a result, never use this kind of water directly and
always carry out water treatment beforehand.
6.2.3.4
Cleaning
Although cleaning of in situ condensers is a difficult process, it may be necessary in extreme
circumstances. Fouling of a condenser can be corrected by chemical cleaning, reverse flushing or a
combination of both. Both procedures will require temporarily disconnecting the condenser on the water
side and preforming these procedures. Reverse flushing in situ is the simplest option and may be the
only treatment necessary if fouling is predominantly caused by sedimentation. If however, scaling has
occurred, chemical cleaning will be necessary. This should be performed using a weak acid cleaning
liquid pumped through the heat exchanger in reverse flow direction at approximately twice the normal
flow rate. Remember that the cleaning acid should be circulated in reverse flow for usually 24 hours. At
the completion of the cleaning process, it is important that the condenser be flushed with clean water
for at least 30 minutes.
63