Significant gains in energy efficiency have been elusive for heat transfer systems that use high-volume air-movement systems such as cooling towers, chillers and evaporative coolers. Although much attention has been given to improving fan and blade airfoil designs used in high-volume air-movement systems, such efforts have provided only marginal efficiency increases. Further, most fans have a limited operating range in which they can provide optimum performance.
One out-of-the-box approach can help fan users realize efficiency gains of 25 percent or more. In addition to using the latest fan and airfoil designs, system variables such as power, fan speed and blade pitch angle must be adjusted and managed constantly in real time against the backdrop of the changing system operating conditions. A smart air-movement system (SAMS) using modern electronic controls can be a key part of energy-efficient large-volume air-movement systems. Beyond managing system efficiency, a SAMS can monitor system health and indicate potential problems or failures before they occur.
Integrated ControlThe foundation of a SAMS is integrated control. Just five to seven years ago, integrated controls were scarce and expensive. However, like personal technology, significant advances have occurred in just a few years.
For instance, consider the development of cellular phones. A large attaché case was once needed to carry all of the individual devices that are packed into today’s prevailing smartphones. While personal digital assistants (PDAs) and cell phones were in widespread use five years ago, the data on a PDA typically had to be manually re-entered on the user’s cell phone. And, if a telephone number or other contact information changed, the user had to manually update all the individual places the information was stored.
Industrial controls suffered from similar problems. A cooling tower diverter had its own control. Fan operation also relied on a separate temperature reference. There was no single point of control based on the process variables that actually determined how the equipment should operate.
In the intervening years, for both cell phones and cooling tower controls, the electronics industry has evolved. For personal technology devices, this has produced today’s smartphones. For cooling tower controls, integrated yet more affordable components are available to replace electromechanical control systems of the past. Today’s embedded controls are affordable and reliable. What’s more, they are specifically designed and programmed to manage the equipment with respect to the operating environment, desired results and energy savings.
Streamlined PerformanceIn a way, a lifetime of system experience with the respective operating environment is encoded within the firmware (program) that is embedded into a specific-use computer. For example, in a heat exchanger with a large air-movement system, the pitch of a fan blade can be adjusted to operate in concert with the motor’s alternating-current (AC) drive. Energy savings with respect to environmental conditions thus can be optimized in real time without operator intervention.
Another example is evaporative coolers. Many industrial, pharmaceutical and commercial applications rely on these devices to deliver consistent heat rejection. While most would agree that process cooling occurs in a dynamic environment, primary components of an evaporative cooler are not configured to operate efficiently in varying conditions. Many evaporative coolers installed today still have single-speed pumps and fans that are regulated from disjointed controls, while the processes that depend on these evaporative coolers have become ever more precise. The scenario is like trying to get a modern jet aircraft off the ground fitted with engines of 50 years ago. Flaps, which are moveable wing surfaces, were once limited to what a pilot could crank down prior to takeoff and crank up once airborne. Conversely, modern aircraft can vary and control wing surfaces to create lift efficiently throughout the flight envelope. With the advent of AC drives and variable frequency drives (VFDs), ordinary fans based on decades-old airfoils designed by the National Advisory Committee for Aeronautics are now confronted with operating in a dynamic environment.
Likewise, cooling tower fans are pitched to run at one or two speeds. Fortunately, like modern avionics (aircraft electronics), today’s embedded controls are capable of economically and automatically adjusting fan blade pitch along with pumps, valves and auxiliary equipment operation. In addition, advances in fan or fill engineering are easily incorporated for fully integrated control.
The Bottom LineThe cost benefit of using integrated controls can be significant. For example, a chilled water plant in which a 100-hp pump was managed by an integrated control with a data feedback loop from a chiller and its cooling tower resulted in power savings exceeding 50 percent for the pump. Over the 15-year projected life of the equipment, nearly $70,000 of savings is expected. A payback on the investment occurred in 11 months.
In many cases, even greater energy savings over a broad range of operating conditions can be achieved by using fans with optimized airfoils and automatic adjustable pitch in combination with a VFD. Again, the payback is typically achieved in months, not years.
By using a SAMS with integrated controls, large-volume air-movement systems can be managed precisely relative to environmental and process conditions. The potential for energy savings and overall system control is substantial.