This Month’s Topic – Some Control Schemes to Save Energy
We will discuss VFDs (Variable Frequency Drives) in variable flow applications and smarter controls for ventilation systems. There are no text book guarantees for percent reduction in energy usage for most schemes. Each application is different and requires individual analysis before realistic cost justifications can be developed.
VFDs in Variable Flow Applications
VFDs can be applied to variable flow/torque applications such as centrifugal blowers, fans, and pumps; where flow is directly proportional to motor speed. Many times, the motors in these applications are running too fast. Energy reductions can be achieved by reducing the motor speed with a VFD, either in an open-loop or preferably a closed-loop system. In a typical application a 50% reduction in speed results in an 80% reduction in power. There are other noteworthy points. Some VFD manufacturers offer analog inputs and PID functions so that no-frill closed-loop control can be performed without additional devices. Constant torque applications like conveyors, positive displacement pumps and compressors can achieve energy savings from slower operating speeds using a VFD. The VFD’s soft-start function helps reduce mechanical wear by facilitating a smooth start-up. Running at lower speeds will also reduce system noise, vibration and heat. Finally, the state of Pennsylvania has a rebate program for manufacturers who install VFDs in their facilities – PA Act 129. Drives are rebated at $30 per horsepower, so the hurdle for cost justification is much lower. Hurry though, Act 129 Phase II starts in June and ends when the money runs out! There are some Phase I funds remaining, but it ends on May 31, 2013.
Smarter Ventilation Controls
In many manufacturing plants, ventilation systems are turned on and then forgotten. This can result in excessive motor operating costs, undesirable loss of building heat in the heating season, undesirable intake of hotter outside air in the cooling season, and can contribute to extreme conditions for employees and processes. Consider some low-cost controls schemes that can be integrated to your existing equipment – schemes that monitor inside and outside air temperature readings to cycle fans, have automatic summer and winter operating modes, and are password protected. You may be surprised at all the benefits of smarter ventilation controls.