Marley
/
MH
Fluid Cooler
/
Engineering Data: Freeze Prevention
9
Fluid Cooler Coil
When the ambient temperature falls below 32°F, heat
loss from the coil 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 45°F 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
45°F, 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 32°F,
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
marleyct.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 tower
and all exposed pipework at shutdown.
Electric Basin Heaters
Marley offers an automatic basin water heater system,
consisting of the following components:
• Stainless steel electric immersion heater(s).
Threaded couplings are provided in the side of
the collection basin.
• NEMA 4 enclosure containing:
Magnetic contactor to energize heater.
Transformer to convert power supply to 24 volts
for control circuit.
Solid state circuit board for temperature and
low-water cutoff.
The enclosure may be mounted on the side of the
fluid cooler.
• Control probe in the collection basin to monitor
water temperature and level.
• Heat tracing for recirculating water pump.
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 tower 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 GPM
and on the volume of water contained in the piping
system to and from the tower. 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.
CAUTION
Freezing ambient conditions could cause significant
damage to the heat exchanger coil of the MH Fluid
Cooler. To avoid possible damage, it is imperative to
provide for adequate freeze protection.
MULTICHILL Refrigeration Products
SPX Cooling Technologies - Marley Cooling Towers
Cooke Industries - Phone: +64-9-579 2185 Fax: +64-9-579 2181 Email: [email protected] Web: www.cookeindustries.co.nz
