Condenser Water Management: The Forgotten Side of Chiller Plant Optimization Strategies
August 8, 2015 | Rom Smolinski, Mechanical Engineer
A chiller plant is a large, complex machine that runs at a high voltage: typically an industrial level voltage of around 480. Naturally, owners seek to optimize the chiller plant’s energy usage to the greatest degree possible. Yet many systems’ optimization strategies overlook significant opportunities to reduce power consumption.
In order to understand how you can get the most energy-efficient performance out of a chiller system, it’s useful to consider how it works.
How it works
In general, a chiller plant functions like the building’s AC, but on a larger, more complex scale. The plant is located in a large building that contains chillers and other components like water pumps and pipes, heat exchangers, cooling towers, and other mechanisms that work together to provide a supply of cold water, which is routed in turn through a building such as a hospital.
At the target building, the cold water then goes to components usually known as air handlers, which use the water to chill the air and reduce humidity. The air handlers then push the chilled air out at high pressure into the building’s ductwork, and from there to the spaces themselves.
The motors at the chiller plant are quite large, ranging from 100 to 1000 horsepower. This is typically where optimization efforts are concentrated, using variable frequency drives (or VFDs) on the pumps and fans. The VFDs take electricity that comes in at a constant voltage and adjust it so that the motor can change speed efficiently.
Because the chiller uses 70% of the system’s power, this is where most people focus their attention. But another part of the system bears consideration: the condenser.
Optimizing the condenser
The condenser pushes heat outside to a cooling tower or towers, made in different sizes to correspond with the chiller.
The condenser also features large pumps. In some larger facilities, the motors in cooling towers range from 75 to 125 horsepower, and a system might include multiple towers. These mechanisms must scale to push the necessary volume of water back and forth between the outside and the chiller.
So while the condenser uses less power overall, it’s still a significant source of energy expenditure. In fact, very few facilities use VFDs on their condenser pumps, whereas this is standard practice on the chiller itself.
Why? It is a simple matter of misperception. Because the condenser pump is the smallest motor in the system, people imagine there is little return in optimizing it. But this is simply untrue – particularly as a system gets larger, the savings swiftly accrue.
The primary challenge in optimizing the condenser is to reduce power consumption of these pumps and fans, while not increasing the chiller’s power. In order to achieve this, work with your chiller manufacturer to get good information from them, making certain that your programming and building automation take all of this information into account. It is possible to reduce chiller energy consumption at the same time. When properly prepared for, a thoughtful and comprehensive chiller and condenser optimization can reduce energy costs tremendously over time.