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Potential Gains and Application Concerns… We’re pumped about Variable Primary-Flow Pumping.

Variable Primary-Flow Pumping (VPFP) is a type of pumping design used in centralized chilled/hot water systems. It is a method of controlling the flow rate of water through the pipes to match the building's cooling/heating load and maintain a comfortable temperature, while minimizing energy consumption. In both chilled and hot water VPFP systems, the water pump varies its speed to meet the demand of the system; without the use of additional primary pumps to maintain flow to the plant equipment.

This allows the system to operate more efficiently by reducing the amount of energy needed. To achieve this, flow meters and a bypass valve are utilized to control a minimum flow rate through the equipment. VPFP water systems include a differential pressure sensor within the piping network. The sensors communicate with the control system to adjust the pump's speed and maintain a pressure differential setpoint. By maintaining differential pressure, the flow rate varies based on the building's cooling/heating demand, not only through the building but also through the plant equipment, reducing the amount of energy consumed by the pumps.

Overall, VPFP systems offer energy savings compared to fixed-speed pumping systems or traditional variable primary-constant secondary systems, regardless of the building's cooling/heating demand. The use of VPFP can help to reduce the amount of energy needed to circulate water through the building's cooling/heating system, making it a popular choice for large commercial buildings with centralized water systems.

What are the Pros of Variable Primary-Flow Pumping (VPFP)?

  • Energy savings: VPFP systems can reduce the energy consumption of the pump by adjusting the flow rate to match the building's cooling or heating load, reducing the need for the pump to run at full capacity at all times.

  • Lower First Cost: The eliminations of dedicated primary pumps result in less equipment to be purchased, installed and powered.

  • Improved efficiency: By maintaining a constant differential pressure, VPFP systems can reduce the pressure drop caused by pipes, valves, and other components in the system, improving the overall efficiency of the system.

  • Improved control: VPFP systems may provide greater control over the flow rate of water through the pipes, allowing for more precise matching of the building's cooling or heating load and maintaining a more consistent temperature. This is due to the requirement of flow meters and the elimination of 3-way control valves. In general, these systems can maximize the temperature differentials across the buildings, especially when paired with pressure independent control valves.

  • Lower maintenance costs: VPFP systems typically require less maintenance than traditional fixed-speed pumping systems, or their variable primary-constant secondary counterparts, as they experience less wear and tear due to the reduced need for the pump to run at full capacity all the time. They also require less equipment to be installed.

  • Longer lifespan: VPFP systems can extend the lifespan of the pump and other components in the system by reducing the amount of stress placed on them due to the reduced need for the pump to run at full capacity all the time.

  • Smaller Installation Footprint: One set of pumps are required for the entire system as opposed to primary and secondary pumps.

  • Higher Levels of Redundancy: Using manifolded pumps and plant equipment, any combination may be isolated and serviced.

What are the Cons of Variable Primary-Flow Pumping (VPFP)?

  • Control Commissioning: VPFP systems are more complex than traditional pumping systems, and as a result, they can be more difficult to design and commission correctly. It is not uncommon for control technicians to trip equipment on low flow alarms as the minimum flow controls are not properly calibrated.

  • Limited turndown capability: VPFP systems may not be able to operate effectively at very low flow rates, which can limit their turndown capability and require additional pumping systems to be installed to handle low-flow conditions.

  • Compatibility issues: VPFP systems may not be compatible with all types of building heating and cooling systems, and may require additional design considerations to ensure compatibility.

Final thoughts on Variable Primary-Flow Pumping (VPFP):

VPFP systems offer several advantages. However, they can require higher levels of calibration. To ensure the successful implementation and operation of a VPFP system, careful consideration of pipe sizing, pump selection, control system calibration, and compatibility issues is essential. Additionally, proper maintenance is required to ensure the sensors, controls, and software are working correctly. Overall, VPFP systems can provide significant energy savings and improved efficiency, making them an attractive option for large commercial buildings. However, careful planning and design, as well as diligent maintenance, are necessary to fully realize these benefits.

After living through many projects suffering from improperly commissioned variable primary flow systems, Design Management Group has developed turn-key control solutions to help implement energy saving strategies such as Variable Primary Control to new and existing plants. Contact Us to find out how we are Building Systems, Smarter...


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