Should All Motors Have VFDs to Save Energy?
Anyone working in energy management is likely familiar with Variable Frequency Drives (VFDs), also referred to as Variable Speed Drives (VSDs). VFD technology allows facilities to save significant energy by throttling back AC motors and pumps to somewhere between 0-100% of nameplate capacity when the load or work needed to be performed does not call for the full force of a particular motor or pump.
As the price in VFD technology has dropped since its invention in the 1980s, it can be tempting for building managers to install the drives on all pumps, motors, and fans throughout their facilities. However, building managers should consider several factors when contemplating VFDs for their equipment. Some things to consider when evaluating VFD opportunity:
Pump & motor run times
Cost of additional equipment to correct power factor or electrical noise filtering
Lower pump maintenance costs and longer pump life
Maintenance costs of VFDs
Applicable utility rebates
Variable Frequency Drives (VFDs)
Additionally, it is important to consider the impacts that installing a VFD on a particular motor will have on other systems and motors in a system. Building equipment and industrial facilities are complicated, intertwined ecosystems that operate most efficiently and effectively when building operations are coordinated. This ensures that good, intended causes – such as adding VFDs to motors – do not cause unwanted effects. Therefore, it is also important to fully understand how systems interact before installing VFD technology. Having a modern and properly sequenced Building Automation System (BAS) or Building Energy Management System (BEMS) can greatly assist with the system coordination. Here are some things to consider when evaluating VFD opportunities in your facility from Doty and Turner’s Energy Management Handbook:
Reducing airflow can compromise indoor air quality and reduce filtration system effectiveness, leading to required air changes per hour not being met
Modifying supply air flow can compromise the HVAC design pressurization; return air flow may need to be modified to maintain the correct pressurization
Increasing pressure in duct work may compromise the duct work integrity
Reducing flow rates and temperatures in duct work may cause electrical duct heaters to overheat, causing trips or fire hazards
Exhaust flows could be compromised, causing a health hazard, particularly in dust collectors or flume hood systems
Excessive velocity reductions in steam, chilled water, or hot water systems could cause sedimentary build-up or air binding
Chillers operate at lower efficiency as they are run at lower speeds. Reducing water-flow through chillers to match demand can significantly reduce chiller efficiency and potentially off-set energy savings
Understanding how all your equipment interacts can be a daunting task. The first step in evaluating any energy efficiency project is to understand how much and where energy is being consumed. Improv Engineers can assist your facility team in collecting accurate and detailed data on your equipment by deploying our easy-to-use meters. Our experienced energy engineering team with decades of experience is ready to assist you today.