Sequence Of Operation For Two Fan Units With Two Speed Motors During Peak Load; Variable Frequency Drives; Sequence Of Operations / Guidelines For Multi-Fan Units With A Vfd During Peak Load - EVAPCO ATC-E Operation And Maintenance Instruction

Sequence of Operation for Two Cell Units with Two Speed Motors during Peak Load
For eco-ATWE, see Sage
1. Both fan motors off – Pump running on one cell.
2. Both fan motors off – Pump running on both cells.
3. One fan motor on low speed, one fan motor off – Pump running on both cells.
4. Both fan motors on low speed – Pump running on both cells.
5. One fan motor on high speed, one fan motor on low speed – Pump running on both cells.
6. Both fan motors on full speed – Pump running on both cells.

Variable Frequency Drives

The use of a variable frequency drive (VFD) provides the most precise method of capacity control. A VFD is a device that converts
a fixed AC voltage and frequency into an adjustable AC voltage and frequency used to control the speed of an AC motor. By
adjusting the voltage and frequency, the AC induction motor can operate at many different speeds.
The use of VFD technology can benefit the life of the mechanical components with fewer and smoother motor starts and built-in
motor diagnostics. VFD technology has particular benefit on evaporative cooling units operating in cold climates where airflow can
be modulated to minimize icing and reversed at low speed for de-icing cycles. Applications using a VFD for capacity control must
also use an inverter duty motor built in compliance with NEMA standard MG-1. This is an available option from EVAPCO.
NOTE: VFD's should not be used on pump motors. The pumps are designed to be operated at full speed and are not intended to
be used as capacity control.
The type of motor, manufacturer of the VFD, motor lead lengths (between the motor and the VFD), conduit runs and grounding can
dramatically affect the response and life of the motor. Select a high quality VFD that is compatible with the fan motor(s) in the
EVAPCO unit(s). Many variables in the VFD configuration and installation can affect motor and VFD performance. Two particularly
important parameters to consider when choosing and installing a VFD are switching frequency and the distance between the motor
and VFD often referred to as lead length. Consult the VFD manufacturerʼs recommendations for proper installation and
configuration. The motor lead length restrictions can vary with the vendor. Regardless of motor supplier, minimizing lead length
between the motor and drive is good practice.

Sequence of Operations / Guidelines for Multi-fan Units with a VFD during Peak Load

For eco-WE, see Sage
1. Both fan motors off – Pump running on one cell.
2. Both fan motors off – Pump running on both cells.
3. Both VFDs turn on at the manufacturerʼs recommended minimum operating speed (20-25%) – Pump running on both cells.
4. Both VFDs speed up uniformly (they should be synchronized on start-up) – Pump running on both cells.
5. Both VFDs are on full speed – Pump running on both cells.
Note: the VFDs need to have a pre-set shutoff to prevent water temperatures from becoming too cold and to prevent the drive
from trying to turn the fan at near zero speed. Operating below 25% of motor speed achieves very little return in fan energy
savings and capacity control. Check with your VFD supplier if operating below 25% is possible.
For more details on the use of variable frequency drives, please download a copy of EVAPCOʼs Engineering Bulletin 39 from
www.evapco.com.
2 /Sage 3 control Panel O&M
2 /Sage 3 control Panel O&M
Operation and Maintenance Instructions
15