Operating a Submersible Pump Without a VFD: Feasibility and Benefits
While modern installations often utilize Variable Frequency Drives (VFDs) for submersible pumps, it is still possible to operate these pumps without them, especially when dealing with single-phase motors. In this article, we explore the feasibility and benefits of operating a submersible pump without a VFD, and when the use of a VFD might be more advantageous.
Background on Single-Phase Motors in Submersible Pumps
Until recently, many residential wells relied on single-phase 120 or 240-volt induction motors for their submersible pumps. These motors could start every time the system pressure dropped below a set point, manually stopping when the pressure resumed to a high set point value. This setup, however, often required a large enough holding tank to ensure the motor pump could operate without short-cycling and causing frequent starts and stops.
The Role of a Holding Tank
The holding tank size was critical to ensuring a long-lasting motor pump. Insufficiently sized holding tanks could result in frequent short-cycling, which could lead to premature wear and tear on the motor. To mitigate this issue, a large holding tank was typically installed to reduce the frequency of pump starts, extending the life of the motor.
Advantages of Using a VFD
Despite not being mandatory, the use of a VFD offers several advantages:
1. Built-in Soft Start: Most VFDs provide a built-in soft start feature, which helps to minimize the inrush current and noise during startup. This is particularly beneficial in areas with weak electricity, where it can help reduce light flickering and overall electrical stress.
2. Efficiency and Self-Starting Capability: VFDs enable the use of 3-phase electrical motors, which are generally more energy-efficient and can self-start without the need for a complex starting circuit. This makes the system simpler and more robust, as the motor can start and stop without additional complexity.
3. Smaller Buffer Tank: Operating a VFD allows for the use of a smaller buffer tank without the risk of short cycling the pump motor. The VFD controller monitors the water demand and runs the pump accordingly, maintaining pressure at the desired set point. This means the pump can run continuously as long as there is a significant demand for water, reducing unnecessary cycles and extending the pump's lifespan.
Personal Experience with a VFD-Driven Pump
I operate a 3HP VFD-driven pump, and my system is set at 60 PSI. When the pump is in operation, there is hardly any noticeable drop in pressure or any type of pressure cycle. This consistency is particularly beneficial during activities like showers, where the mix of hot and cold water remains constant, even without a pressure-balancing shower valve.
On my system, the water holding tank is merely 1.5 US gallons, significantly smaller than the tanks typically required for non-VFD setups. A 3HP pump can supply a substantial amount of water, more than any household would need, making it an efficient and practical solution.
Conclusion
While you can operate a submersible pump without a VFD, the advantages of using a VFD make it a more practical and efficient choice. Whether you opt for a VFD or not depends on your specific needs and the setup of your system. For those interested in energy efficiency, reduced maintenance, and simplified operation, a VFD can greatly enhance the performance of a submersible pump.