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Engineering Data: Freeze Prevention
14
Fluid Cooler Coil
When the ambient temperature falls below 0°C,
heat loss from the coil can be substantial even without
recirculating water flowing over the coil. The process
fluid, without an applied heat load, may be prone to
freezing. There are various methods to protect against
coil freezing.
Ethylene and propylene glycol solutions are the
best means to protect against coil freezing and are
recommended for most installations. The appropriate
concentration of ethylene or propylene glycol should be
determined based on the required protection from low
ambient temperatures.
If the use of an industrial antifreeze solution is not
compatible with the system, another accepted method
of preventing coil freezing is to maintain a sufficient flow
rate and heat load on the process fluid. The fluid exiting
the coil must be maintained at or above 7°C at the full
process flow rate. If the process load does not yield such
a heat load, it may be necessary to apply a supplementary
heat load to the process fluid.
Draining the coil is not considered to be an acceptable
means of protection against freezing. Introducing air to
the interior of the bundle will promote corrosion of the
heat exchanger coil. In an emergency, this alternative can
be used in the event that the process fluid drops below
7°C, the ambient temperature is below freezing and the
coils are not protected with industrial antifreeze.
Cycling of the recirculating water pumps should not be
used to control process flow temperatures. Coils may be
used for seasonal dry operation followed by seasonal wet
operation, but not for frequent cycling of the recirculating
water pump. Such operation may lead to an excessive
scale buildup resulting in a decrease in efficiency.
Fluid Cooling Recirculating Water
When the ambient air temperature falls below 0°C,
the recirculating water within the fluid cooler can freeze.
Marley Technical Report #H-003 “Operating Cooling
Towers in Freezing Weather” describes how to
prevent freezing during operation. Ask your Marley sales
representative for a copy or download a copy at
spxcooling.com.
During shutdown, water collects in the basin and may
freeze solid. You can prevent freezing by adding heat to
the water left in the basin—or, you can drain the fluid
cooler and all exposed pipework at shutdown.
Electric Basin Heaters
An automatic basin water heater system, consisting of
the following components:
CAUTION
Freezing ambient conditions could cause significant
damage to the heat exchanger coil of the MC Fluid
Cooler. To avoid possible damage, it is imperative to
provide for adequate freeze protection.
• Standardweatherproof(IP55)enclosure,rating
depending on model and minimum expected winter
temperature(seetablebelow):
• RatingsareinkWforspecifiedambienttemperature.
For lower ambient temperatures refer to SPX
engineering for advice.
• Standardelectircalsupplyis380/415V3ph(220/240V1
phavailableasextracostoption).
• Heaterhasanintegralthermostat,setpointnominally
3°C but adjustable to suit operating requirements.
The basin heater option is only for freeze protection
of the recirculation water in collection basin. The
basin heater option does not protect the coil during
freezing weather.
Heater components are normally shipped separately
for installation by others.
Indoor Storage Tank
With this type of system, water flows from an indoor
tank and back to the fluid cooler where it is cooled
and recirculated. The water flows by gravity from the
fluid cooler to the tank located in a heated space. At
shutdown, all exposed water drains into the tank where it
is safe from freezing.
The amount of water needed to successfully operate
the system depends on the fluid cooler size and m
3
/hr
and on the volume of water contained in the piping
system to and from the fluid cooler. You must select a
tank large enough to contain those combined volumes—
plus a level sufficient to maintain a flooded suction on
your pump. Control makeup water according to the level
where the tank stabilizes during operation.