Critical to understanding VFDs is understanding the science which provides us the opportunity to use this amazing technology to save significant energy. When using VFD’s in pumping application, the Affinity Laws described below are used to describe the relationship between hydraulic characteristics and rotational speed of centrifugal pumps.
The Affinity Law’s state: “ The change in power varies by the cube of the change in speed. In this case, twice the speed requires eight times the power.”
It is understanding this Law which results in the huge power and financial savings when using VFD’s in pumping application. In many instances of flow or pressure control, the application does not need to run at full speed, hence a reduction offers significant opportunities for energy savings with little or no reduction in process output.
Variable Frequency operation allows for the most efficient and energy saving option for AC Motors. Using VFDs on AC motors allows them to run at the ‘optimum’ Frequency to ensure the lowest energy usage level. In other words, VFD’s have the ability to adjust the speed of electric motors to match the actual or ‘real’ demand of the application. When FWs Intelligent Inverter Solution is optimised for the motor and application, energy savings of between 30 to 70 per cent are typically achieved.
The electricity required to operate 1 x 15kW 3pH AC motor 24 hours a day over a year creates on average an estimated 141.40 tonnes of CO2e (Carbon emissions) being released into the atmosphere. FWs solution is estimated to reduce these emissions to roughly 70 tonnes of carbon per annum. This is a saving of approximately 70 tonnes of carbon emissions every year just on one of these motors. Applying this technology has the potential to make a significant contribution towards reducing emissions, cutting carbon Tax costs, and the effect on the environment.
Clients are encouraged to do their own calculations based on their current & predicted costs associated with Carbon and within the Carbon Tax Scheme. These savings should only be seen as a by-product of applying FW solutions and FW does not factor these additional benefits into the estimated savings.
AC motors typically consume more than 50 per cent of the energy used to power a building. As compared with other types of loads, the induction motor has a relatively poor power factor, causing higher line currents, which causes additional heat in line cables and transformers. The Majority of electricity providers put limits on the loss & load factor associated with low Power Factor generated by their customers, who have to pay a penalty if their Power Factor falls below certain limits, which can range from 0.8 to 0.97.
The power factor is especially low in cases where the motor is over-sized for the given application and therefore, running lightly loaded. This is extremely common in commercial buildings, as the majority are designed with motors built to meet peak demand, e.g, the hottest summer day of the year. However given the extremely high cost of power in Australia, this over-engineering now accounts for significant costs to clients, and can sometimes attribute more than $20,000 per annum in potential savings.
The LS iS7 VFD which is utilised in the FW Units has inbuilt Power Factor correction through an inbuilt DC reactor, which greatly improves the losses and associated costs of having a low Power Factor. In some cases, the reductions in kWh consumption due to PF correction (with motors operating at 100%) have been up to an 18% saving.
In addition to reducing the motor’s electricity consumption costs, it is important to note that further savings can be attributed to operating the motor at reduced loads using FWs Solution. Decreasing the motor’s constant maximal output can greatly reduce harmful wear & tear on mechanical functions, potentially decreasing maintenance and replacement costs, and ultimately prolonging the motor’s efficiency and longevity. Data obtained through independent engineer’s reports show that the pump’s bearing temperatures are less than half when using FW’s VFD Solution. Most motors operating at a single speed run at extremely high bearing temperature which contributes to their high failure rate.
The FW Solution also provides added layers of protection for the pump motor through the built in functions of the Variable Frequency Drive. These automatic functions include a drive trip mechanism that protects against over-voltage, under-voltage, over-current, drive over-temperature, motor over-temperature, I/O phase loss, I/O mis-wiring, overload, external device fault 1.2, loss of speed command, hardware fault, communication error and CPU error.