The effects of poor pool water chemistry on
the heating systems that
serve aquatic facilities can
be devastating. Regardless of pool
size, improper pool chemistry can
lead to unhealthy bathing conditions,
inefficient operation, and damaged
heating system components.
Unhealthy water conditions are a
concern all of their own, so I’d like to
address the two main problems related
to pool heating equipment: calcium
(scale) deposits and corrosion.
Drop a penny into a pool and leave
it there for a while. What happens? It
starts to stain the surface around it.
The copper begins to corrode. Most
of the heating components in a pool
heating system are manufactured with
copper. Heat exchangers are often
copper or cupronickel. Balancing pool
water correctly reduces the damage
done by the pool water.
The first thing we do when we arrive
at a customer’s pool is test the source
water and the pool water. This gives us
a profile of the water, showing where
challenges may be present.
The proper way to add treatment chemicals to a body of water that doesn’t feature mechanical injection is to dilute the chemical with water first, then distribute it throughout the pool as evenly as possible.
What are the total dissolved solids?
How much calcium is in the water
(hardness), how much sanitizer, is
it within balance (LSI, or Langelier
Saturation Index)? Unbalanced water
will always try to find balance, and the
first thing it will attack are the metals it comes in direct contact with. Pool
surface finishes are also subject to
deterioration. Most of the metals
exposed to pool water are in the
mechanical system.
The softest metals are the most
susceptible to corrosion, and can
generally be found in the heat
exchangers of the heating appliances,
whether these be the direct-fired heat
exchangers of the pool heating units
themselves, or in a water-to-water
heat exchanger installed to isolate
pool water from the water within a
boiler. We’ve seen water so aggressive
that new pool heaters are completely
destroyed within two years.
Hard water, which is a common
issue, generally has higher total
dissolved solids (TDS). This is a
separate issue from corrosive water,
but just as large a concern. Water with
a high TDS typically contains a high
level of calcium, though other minerals
can certainly be present. Mineral
deposits — also known as scale —
are unsightly and can develop on any
surface in contact with pool water. But no surface scales over as quickly as a
heat exchanger.
When hard water comes in
contact with the hot surface of the
heat exchanger, the calcium or other
minerals fall out of solution and adhere
to the metal of the heat exchanger. This
creates a number of challenges.
As scale builds up on the heat
transfer surfaces, it insulates the water
from the heat exchanger, reducing
heat transfer and lowering efficiency.
Because the heat exchanger is no longer
rejecting heat to the water effectively,
the unit may short cycle (turn on and
off quickly). This only lowers efficiency
further and creates excess wear and tear
on the heating appliance. Scale buildup
also clogs the channels within a heat
exchanger, reducing the flow rate. This
further lowers efficiency and creates
greater pumping resistance, increasing
electric consumption and overworking
the system pumps.
Heat exchangers are most susceptible to corrosion, whether they be the direct-fired heat exchangers of the pool heating units themselves, or in a water-to-water heat exchanger installed to isolate pool water from the water within a boiler.
Proper Chemical Treatment
There are many factors to consider
when balancing pool water, even when
the chemical water profile is known.
For example, water temperature has
a major effect on LSI. Chemicals in
80 degrees Fahrenheit pool water
will react differently than in 102
degrees Fahrenheit spa water. As
temperature increases, so does the
rate of corrosion. Doing the math
longhand is extremely difficult, with so
many variables and so many different
chemicals.
To simplify the process, we use the
Orenda Calculator app, by Orenda
Technologies. Once you’ve received
your water quality test results, you
input the values, and the app provides
a solution for which chemicals to use
and how much, based on the volume
of the pool and temperature of the
water.
Even with that knowledge, however,
mistakes can still occur while
introducing chemicals to the pool.
We’ve regularly found that people
maintaining small pools (residential
or commercial) tend to dump
treatment chemicals directly into the
pool skimmer. This mainlines the
chemical through the pumps and heat
exchangers, meaning that un-diluted
chemical comes in direct contact with
the components most susceptible
to corrosion. Imagine a highly acidic
compound flowing through the heat
exchanger. These chemicals can be
super corrosive when not properly
diluted.
The proper way to add treatment
chemicals to a body of water that
doesn’t feature mechanical injection
is to dilute the chemical with water
first, then distribute it throughout the
pool as evenly as possible. If it’s not
diluted first, the chemicals — which
are generally heavier than water —
can sink to the bottom of the pool
and get sucked into the main drains,
which achieves the same bad result as
dumping chemicals into the skimmer.
Incorrectly adding chemicals is
possible even in large commercial
applications where properly calibrated
mechanical chemical injection is
installed. Most injection systems are
installed between the effluent side of
the heat exchanger and the pool. This
is fine, but we’ve often found that the installer failed to provide a check valve
between the heat exchanger and the
point of injection. If the pumps are
turned off and suction is somehow
created, the concentrated treatment
chemicals can be drawn back into the
heat exchanger, causing damage.
There’s no shortcut to water
balancing and chemical treatment.
It takes time and knowledge. It’s
also extremely important to follow
the manual when installing any pool
equipment, whether that be a heater,
chemical injection equipment or
pumps. The manufacturers of pool
heaters always list water quality
parameters that must be followed
to ensure their warranties. They do
so because water quality and proper
installation is critical.
Pool surface finishes are at greater risk of premature deterioration when exposed to unbalanced pool water, potentially causing the need for costly resurfacing.
Tom Soukup is the principal of Patriot Water
Works Co. with over 20 years as a hydronic
designer and installer. He specializes in high efficiency and green technology and brings his
expertise to custom commercial work, pool
heating, and agricultural projects.
Reach him at [email protected].
This article first appeared in the September 2023 issue of AQUA Magazine — the top resource for retailers, builders and service pros in the pool and spa industry. Subscriptions to the print magazine are free to all industry professionals. Click here to subscribe.