8
/ Freeze Prevention /
When the ambient air temperature falls below 0°C, the
water in a cooling tower 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 from our
website.
Water collects in the cold water basin during shutdowns,
and may freeze solid. You can prevent freezing by adding
heat to the water left in the tower. Or, you can drain the tower
and all exposed piping at shutdown.
■
Electric Basin Heaters
Provide an electric immersion heater for each cell of the
tower to prevent freezing of water in the collection basin
during periods of shutdown. The rod type heater is installed
in the side of the cold water basin.
Each heater will include an integral thermostat, set
point nominally 4°C but adjustable to suit local operating
requirements.
Any exposed piping that is still filled with water at
shutdown —including the makeup water line—should be
electrically traced and insulated (by others).
1. Required kw is the amount of heat needed to ma4.5°C basin
water temperature at the indicated ambient air temperature.
2. Tank heaters shown are 220 volts, single-phase.
3. Component heaters shown are 400 volts, three-phase.
Options or special heater selections may add several weeks to
delivery.
4. Heaters do not operate continuously. Heaters cycle on and off
automatically as basin water temperature dictates.
5. Contact your Marley sales representative for selections appropriate
for other ambient conditions than those shown here.
■
Indoor Tank Method
In this type of system, water flows from an indoor tank,
through the load system, and back to the tower, where it is
cooled. The cooled water flows by gravity from the tower to
the tank located in a heated space. At shutdown, all exposed
water drains into the tank, where it is safe from freezing.
The table on page 9 lists typical drain-down capacities
for all Aquatower models. Although we do not produce
tanks, many of our representatives offer tanks supplied by
reputable manufacturers.
The amount of water needed to successfully operate
the system depends on the tower size, flow and 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.
You should always use a bottom outlet for this type of
piping system. The following table lists the flow capacities for
bottom outlets.
Basin Heater Selection
Tower
Model
-12°C Ambient
-25°C Ambient
Tank Heater
Component
Heater
Tank Heater
Component
Heater
490A
2 kW
3 kW
2 kW
3 kW
490B
2 kW
3 kW
2 kW
3 kW
492A
2 kW
3 kW
2 kW
3 kW
492B
2 kW
3 kW
2 kW
3 kW
493A
2 kW
3 kW
3 kW
3 kW
493B
2 kW
3 kW
3 kW
3 kW
494A
2 kW
3 kW
4 kW
3 kW
494B
2 kW
3 kW
4 kW
3 kW
494C
2 kW
3 kW
4 kW
3 kW
495A
3 kW
3 kW
6 kW
4.5 kW
495B
3 kW
3 kW
6 kW
4.5 kW
496A
3 kW
4.5 kW
6 kW
6 kW
496B
3 kW
4.5 kW
6 kW
6 kW