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no longer possible, cooling methods (such as huge refrigeration
plants) must be employed to allow the workforce to move and
work in the underground environment.
While there are local experts on a mine who are well-versed
in ventilation design, consultancies are often employed to
design HVAC systems for mines to consider the ‘what ifs’.
And this part is important as a mine is complex and changes
constantly. The ore body in one area may be bigger or smaller
than expected, the grades may be better or worse than
predicted, the ore body may be depleted or may be affected by
various intrusions or faults and the location of the development
changes as a result, or the mining method may change. There
are many variables and upsets to consider and the designer
must juggle these variables and come up with short, medium-
and long-term plans to provide cooling. Working with the
mine personnel to establish and understand their needs,
development and production rates is crucial.
The Chamber of Mines has developed sound guidelines
for mining companies and design engineers to build, maintain
and inspect ventilation systems. Indeed, South Africa is often
considered a centre of excellence when it comes to keeping
mines cool and optimising energy use.
When it comes to applicable regulations, the mining industry
is certainly regulated and policed. I cannot even begin to mention
which regulations are more important than others. Suffice to
say that it is so tightly controlled that the mines have their own
version of the Occupational Health and Safety Act, which is the
Mines Health and Safety Act, governing every aspect of mining.
There are several options available to the mine HVAC
designer: surface plants (for bulk-air cooling and chilled water
production), underground plants (for cooling generation closer to
the production areas) and surface ice plants. The three different
strategies are employed as they become viable at different
mining-production depths. Surface plants may become less
viable as the depth of the mine increases and pumping costs
of chilled water needing to be sent underground becomes
prohibitive. Underground plants can reduce pumping costs but
given the high ambient in which their cooling towers must work,
the efficiencies of these plants are lower. At greater depths still,
ice generation by surface plants has proved to be cost-effective
(lower efficiency of the refrigeration plant vs greatly reduced
pumping cost). As a mine evolves over a period, the mine
would often start with one technology and change to another
as operating costs of another, more favourable technology,
becomes beneficial.
HOW DOES AN OWNER CHOOSE THE BEST
PRODUCT AND SYSTEM?
It really depends on the requirements. They may need surface
cooling (in other words, generation of chilled water on
www.hvacronline.co.za
surface), underground cooling (generation of chilled water in
the underground working environment) or something more
exotic like ice. Correct equipment selection is key. Single-stage
centrifugal chillers deliver optimal performance for bulk air
cooling. Screw chillers deliver the best performance for sending
water underground. Understanding the conditions that your
chiller will work under allows equipment suppliers, like AHI
Carrier, to optimise the equipment that we would provide for
these installations.
There are several new innovations in the mining HVAC
environment. Chiller technology is evolving, and equipment is
getting more efficient. Reducing operating costs, by maximising
the equipment efficiencies, would warm any mine owner or
investor’s heart.
An important decision when it comes to efficiency is
certainly the correct initial selection of equipment. Equipment
arrangement, however, is where operating costs can be
leveraged. Chillers may be arranged in various configurations
to reduce operating costs. There are, of course, many savings
possible when you start to consider pumping, and given the high
cost of pumping, this is an important focus area. Some mines
employ thermal storage to maximise time-of-use savings. This
can take the shape of surface ice dams or large underground
dams to reduce pumping during peak tariff times. The latter is
complex however and requires careful design and management.
WATER QUALITY AND TREATMENT
Water used in cooling towers needs good treatment to protect
the components and heat-transfer surfaces making up the
cooling system. Water treatment is also vital to avoid the
proliferation of harmful bacteria, including legionella, in the
recirculating water.
According to Lizzie Myburgh, water-treatment manager
of Baltimore Aircoil, a company that develops, manufactures
and distributes evaporative or hybrid cooling, one of the most
common mistakes made when designing and installing a mine
HVAC system is not taking water quality into consideration.
Water is used as a cooling medium in cooling systems and
it absorbs heat in the liquid phase (heat exchangers), rises in
temperature and then disposes of the heat by evaporation
(cooling towers) and drops in temperature. The water itself
does not cause any problems; but being the universal solvent, it
harbours several unwanted guests. These contaminants may be
brought in with the municipal water supply or scrubbed out of the
air stream used to assist evaporation. Depending on the material
of construction of the cooling tower the water-quality control
limits indicate the limit the cooling tower can run at before scale
and corrosion start forming on the heat-transfer surfaces.
Continued on page 45
RACA Journal I January 2020
43