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Cooling Tower: Capacity Control
When you visit a customer site, check if the cooling towers are operating at a fixed motor speed, and if they are designed to make the individual chillers operate in sequence. In such an arrangement, when some chillers are not running, the corresponding cooling towers will also not run.
You can save energy and lower the cooling tower approach temperature by running all the cooling tower fans at reduced power. This can be achieved by adding VSDs to the fan motors. VSDs allow multiple cooling towers with multiple fans to run at a reduced speed. Running all the fans at a reduced speed consumes lesser energy compared to running fewer fans at full speed. The low cooling tower approach temperature helps to improve the efficiency of the chiller, which translates into energy savings—both in the cooling tower and in the chiller.
This improvement measure is only applicable for condenser pipes with matrix/common header configuration, and is not applicable for pipe configuration of one cooling tower to one chiller.
An example on how much energy can be saved with this strategy is illustrated on the next slide.
- Are the cooling towers operating at fixed motor speed and serving individual chillers?
- Install Variable Speed Drive (VSD).
- Operate all cooling towers at lower fan speed
Saves energy and ensures occupant comfort:
- Operating all cooling towers at lower speed consumes less energy, increases the total airflow, and lowers the cooling tower approach temperature.
- Chillers operate more efficiently.
- Are the cooling towers single-cell or multi-cell?
- Are the cooling towers currently operating ‘round-the-clock?’
Energy Saving Calculation for Capacity Control
A site has five chillers and five cooling towers. Only three chillers and three cooling towers need to operate. Each of the cooling tower fan delivers 120,000cfm and consumes 25kW.
By how much can the total fan power consumption be improved if all the fans are operated at a reduced speed?