Enhancing Efficiency in Water Distribution: Replacing Pressure Relief Valves with VFD-Based Automatic Pressure Control 

Intended Audience: Electrical Appliance Engineers, Water Utility Professionals, Facility Managers 

Overview: In a water distribution system, constant pressure was being maintained using pressure relief valves (PRVs), which divert excess water back to storage tanks. While effective, this method forces pumps to operate at full load continuously, leading to energy inefficiencies and increased wear. This case study explores the implementation of a Variable Frequency Drive (VFD) system, integrated with a pressure transducer, to maintain consistent pressure dynamically resulting in significant energy savings and a rapid return on investment. The installation resulted in payback in just 6 months. 

Description of System: The facility’s process water distribution system comprises two 15 kW (20 hp) pumps configured in a duty/standby arrangement supplying raw water. Each pump is capable of exceeding peak flow demands. Previously, system pressure was regulated by a PRV that redirected surplus water to the storage tank, causing the active pump to operate at full capacity regardless of actual demand. 

Description of Intervention: A VFD was installed to modulate pump speed based on real-time pressure readings from a transducer installed in the distribution main. This setup allows the system to maintain constant pressure under varying flow conditions without the need for a PRV, enabling automatic and energy-efficient control. 

See Table 1 below: 

Table 1: Summary of Results 

Summary of Results: Energy Efficiency: The VFD reduces pump speed during low-demand periods, significantly lowering energy consumption. 

• Reduced Maintenance: Eliminating the PRV reduces mechanical complexity and associated maintenance costs. 

• Extended Equipment Life: Lower operating speeds reduce bearing loads and shaft deflection, enhancing the longevity of seals and bearings. 

Rapid Payback: The system achieved full return on investment within six months of installation. (Refer to Table 1 for a detailed cost-benefit analysis.) 

Conclusion: Variable Frequency Drive (VFD) control is well-suited for pumping systems with variable flow demands and where pressure losses are primarily due to pipe friction. In cases where a pump is determined to be oversized after commissioning—particularly in constant demand applications—impeller trimming should be considered as a practical and cost-effective optimization. 

Written by:
Members of the Committee, 1^st Edition 
Published In: Pump Life Cycle Cost: A Guide to LCC Analysis for Pumping Systems, 2^nd Edition 
Year of Publication: 2021 
Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems – 2nd Edition – Pumps.org

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