Getting Technical
During the 1970s chromium, in its most active and toxic
hexavalent form [Cr6] was progressively banned. Suddenly,
cooling water treatment became much more expensive.
Corrosion inhibitors based on zinc could handle corrosive water
reasonably well, but no product could replace chromium as both
a wide-spectrum bactericide and an algaecide. Then zinc was
banned, leaving the water treatment industry with only far more
costly non-toxic phosphate corrosion inhibitors which also had
the disadvantage of being nutrients for bacteria requiring much
higher biocide dosing levels. To avoid these highly escalated
costs of treatment, the use of softened supply water to cooling
water circuits was virtually universally discontinued. However,
using unsoftened supply water immediately introduced scaling
problems which rapidly became the number one cooling water
problem until the early 1980s.
Prior to the Internet it often took a while for new technical
changes to be implemented in South Africa. By September in
1984 the large companies which had invested huge amounts of
money and effort into researching and developing anti-scaling
polymer chemicals were able to supply some of their new
products locally.
These new anti-scaling chemicals for use in unsoftened
supply water were the biggest single technical change which had
occurred so far in chemical cooling water treatment programmes
www.hvacronline.co.za
worldwide and their costs were also far higher which not
surprisingly generated widespread customer resistance.
Technical developments and changes in air conditioning
plants since 1984 have been far-reaching involving in particular,
computerised applications, pollution and electrical grid energy
demand reduction. The Montreal Protocol was signed in 1987
and continues to influence air conditioning, for example, no
more new R22 installations. A fairly recent phenomenon is
proliferation of data centres requiring substantial air chilling
air conditioning plants, not for people but for the computers
themselves. In 1984, energy savings were low priority and
sustainable energy use was virtually unheard of. The term ‘load-
shedding’ only came into use about 25 years later and although
it is still used almost exclusively in regard to electrical grid
power supply it is also gradually being applied to other non-grid
electrical generating installations.
There were no heat recovery systems designed into the plants
like there are today including desiccant type energy wheels.
Variable speed drives for water circulating pumps were available
but expensive. Capacity controls other than basic on/off systems
comprised thermostatically operated airflow restrictors on the
suction side of centrifugal fans. Current air conditioning plants
are indeed vastly more sophisticated in respect of programmable
automated controls. Generally, there are also additional water
RACA Journal I April 2020
57