Unit Accessories; Cold Water Basin Heaters; Remote Sumps; Electric Water Level Control - EVAPCO ATC-E Operation And Maintenance Instruction Manual

Operation and Maintenance Instructions

Unit Accessories

The appropriate accessories to prevent or minimize ice formation during cold weather operation are relatively simple and
inexpensive . These accessories include cold water basin heaters, the use of a remote sump, electric water level control and
vibration cut out switches . Each of these optional accessories ensures that the cooler or condenser will function properly during
cold weather operation .

Cold Water Basin Heaters

Optional basin heaters can be furnished with the unit to prevent the water from freezing in the basin when the unit is idle
during low ambient conditions . The basin heaters are designed to maintain 4-5°C basin water temperature at a -18°C,
-28°C or -40°C ambient temperature . The heaters are only energized when the recirculating pumps are off and no water is
flowing over the heat exchanger coil . As long as there is a heat load and water is flowing over the heat exchanger coil, the
heaters do not need to operate . Other types of basin heaters to consider would include: hot water or steam coils .

Remote Sumps

A remote sump located in an indoor heated space is an excellent way to prevent freezing in the cold water basin during
idle or no load conditions because the basin and associated piping will drain by gravity whenever the recirculating pump
is idle . EVAPCO units built for remote sump operation do not include recirculating water pumps .

Electric Water Level Control

Optional electric water level control packages can be furnished to replace the standard mechanical float and valve
assembly . The makeup water pressure for electronic water level control should be maintained between 35 and 700 kPa .
The electric water level control eliminates the freezing problems experienced by the mechanical float . In addition, it provides
accurate control of the basin water level and does not require field adjustment even under varying load conditions . Please
note: the standpipe assembly, make up piping and solenoid valve must be heat traced and insulated to prevent them from
freezing .

Vibration Cut Out Switches

During severe cold weather conditions, ice can form on the fans of cooling towers causing excessive vibration . The
optional vibration switch shuts the fan off avoiding potential damage to or failure of the drive system .

Capacity Control Methods for Cold Weather Operation

Induced draft and forced draft coolers or condensers require separate guidelines for capacity control during cold weather
operation .
The sequence of control for a unit operating at low ambient conditions is much the same as a cooler or condenser operating under
summer conditions provided that the ambient temperature is above freezing . When the ambient temperatures are below freezing,
additional precautions must be taken to avoid the potential for damaging ice formation .
The most effective way to avoid ice formation in and on a closed circuit cooler or condenser during the winter is to run the
unit DRY . In dry operation, the recirculation pump is turned off, the basin drained, and air passes over the coil . Instead of
using evaporative cooling to cool the process fluid or condense the refrigerant, sensible heat transfer is utilized, so there is no
recirculation water to freeze . If this method will be used on a forced draft unit, be sure to verify that the motor and drives have
been properly sized to handle the reduction in static pressure experienced when the spray water is turned off .
It is very important to maintain close control of the cooler or condenser during winter operation . EVAPCO recommends that
an absolute MINIMUM leaving water temperature of 6°C must be maintained for cooler applications . The higher the leaving
temperature from the cooler or condenser, the lower the potential for ice formation .

Induced Draft Unit Capacity Control

The simplest method of capacity control is cycling the fan motor on and off in response to the leaving fluid temperature
of the cooler or condenser . However, this method of control results in larger temperature differentials and longer periods
of down time . During extremely low ambient conditions, the moist air may condense and freeze on the fan drive system .
Therefore, fans must be cycled during extremely low ambient conditions to avoid long periods of idle time when water is
flowing over the coil . The number of start/stop cycles must be limited to no more than six per hour .
A better method of control is the use of two-speed fan motors . This allows an additional step of capacity control . This
additional step reduces the water temperature differential, and therefore, the amount of time the fans are off . In addition,
two-speed motors provide savings in energy costs, since the cooler or condenser has the potential to operate on low
speed for the reduced load requirements .
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