Malfunctioning inlet guide vanes causing operational issues
GPM, a leading organisation in the industry, has achieved significant benefits following an upgrade of their Air Handling Units (AHUs). The upgrade involved replacing Inlet Guide Vanes (IGVs) with Variable Frequency Drives (VFDs), a move that has resulted in substantial energy savings and improved airflow control.
Benefits of the Upgrade
The implementation of VFDs has brought about several advantages. Firstly, the energy efficiency has seen a significant boost. Unlike IGVs that restrict flow by creating pressure drop and mechanical resistance, VFDs control the motor speed directly. This means the fan runs only as fast as needed to meet demand, resulting in a reduction of energy use.
Secondly, the improved airflow control is another key benefit. VFDs can adjust fan speed dynamically based on real-time demand or pressure feedback, enabling precise control of airflow and static pressure. This avoids over-blown or starved airflow conditions typical with IGVs.
Thirdly, the reduced noise and vibration are noticeable improvements. Operating fans at variable speeds reduces turbulent airflow and associated noise compared to throttling flow with IGVs, which can cause swirl and turbulence downstream of the vanes.
Lastly, the lower mechanical wear is a significant advantage. VFDs enable soft-start and soft-stop capabilities, reducing mechanical stress on fan components compared to sudden starts/stops or constant full-speed operation with IGVs.
The Process of Replacement
The upgrade process was carried out in five stages. First, IGVs were removed from the fan assembly, removing the fixed mechanical restriction in the airflow path. Next, a Variable Frequency Drive was installed to replace the fixed speed drive of the AHU fan motor, enabling variable speed operation. Static pressure sensors were then installed in the ductwork or AHU to provide feedback signals to the VFD controller for precise airflow or pressure control.
The VFD was then programmed to adjust fan speed based on sensor inputs to maintain desired static pressure or airflow, rather than relying on fixed speed with vane modulation. Finally, system performance was tested for airflow capacity, static pressure, noise levels, and energy consumption under various operating conditions to validate improvements.
Supporting Details
Guide vanes like IGVs are effective in reducing swirl and turbulence right after the impeller, but they act as fixed mechanical restrictions that cause pressure loss and increase energy use. On the other hand, VFDs, combined with electronically commutated motors or standard motors, allow the fan's speed to be smoothly varied, which tends to reduce both noise and energy consumption because power is proportional to the cube of speed.
Retrofits allow the implementation of duct static pressure control schemes with VFD-driven fans, enabling maintenance of stable airflow with minimum power usage, compared to pressure-independent modulation with IGVs. Beyond energy savings, VFDs aid in reducing acoustic emissions by reducing turbulent airflow and enabling softer mechanical operation through speed control and avoiding “stall” conditions sometimes aggravated by IGVs.
The Role of Cimetrics
Cimetrics recommended the use of VFDs over IGVs to achieve savings and better airflow control. They provided technical guidance and coordinated activities between GPM staff and the controls vendor. Furthermore, they assisted GPM in securing utility incentives worth $6,300. The upgrade and the secured incentives have helped reduce energy costs, and the annual maintenance costs have also been reduced going forward.
In summary, the replacement of IGVs with VFDs in AHUs shifts airflow control from mechanical throttling to electronic speed modulation, yielding energy savings, enhanced airflow precision, quieter operation, and reduced wear. The process involves IGV removal, VFD and sensor installation, and control optimization.
Data-and-cloud-computing technologies played a crucial role in the success of GPM's Air Handling Unit (AHU) upgrade. The organization utilized advanced software to analyze the performance of the AHU functions, such as energy consumption and airflow control, before and after the upgrade, driving informed decisions and continuous improvement.
Moreover, leveraging technology enabled GPM to optimize the usage of the Variable Frequency Drives (VFDs), ensuring that the fans ran as efficiently as possible at all times, leading to significant energy savings and improved airflow control.
