Unit Accessories; Cold Water Basin Heaters; Remote Sumps; Electric Water Level Control - EVAPCO ESW Series Operation And Maintenance Instruction

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 40°F basin water temperature at a 0°F 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 coils, steam coils or steam injectors.

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 5 and 100 psig. 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 42° F 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.
The best method of capacity control during cold weather operation is the use of a variable frequency drive (VFD). This allows the
closest control of the leaving water temperature by allowing the fan(s) to run at the appropriate speed to closely match the
building load. As the building load decreases, the VFD control system may operate for long periods of time at fan speeds below
50%. Operating a low leaving water temperature and low air velocity through the unit can cause ice to form. It is recommended
that the minimum speed of the VFD be set at 50% of full speed to minimize the potential for ice to form in the unit.
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