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In response to industry demand for the most efficient pump selection, Bell & Gossett (B&G) introduced a new pump selection criteria called Part Load Efficiency Value (PLEV) to help HVAC system designers select pumps that maximize efficiencies while reducing energy costs.
PLEV is a calculation that represents the efficiency of a centrifugal pump at partial flow rates, and can be used to gauge true pump performance within a hydronic system. It is derived from the Integrated Part Load Value (IPLV) performance calculation developed as part of AHRI 550/590-1998 that describes equipment efficiency while operating at various capacities of a chiller system. B&G engineers have adapted the formula for centrifugal pumps used in HVAC systems and updated the company’s ESP-PLUS online selection software with the PLEV selection criteria.
B&G is the first to offer a specification formula to help system designers select pumps based on real-world system demands. General industry practice is to make pump selections based on a system’s design load, or the maximum capacity of the system. With this approach, the pump system efficiency is typically measured at 100 percent capacity, even though the system normally only operates at that level 1 percent of the time.
How to use PLEV
PLEV selection criteria and specially designed selection software offer system designers the tools they need to meet and exceed efficiency requirements.
Pump Selection
When using PLEV for pump specification, it’s crucial for system designers to choose pumps that operate at the highest efficiencies across the largest segment of the pump curve. B&G’s term for these efficiency ranges is Efficiency Islands. An Efficiency Island is an envelope on the performance curve where the pump operates as widely and as deeply as possible within the preferred operating range. Newer pump designs, like B&G’s e-Series of centrifugal pumps, use cutting-edge computational fluid dynamics technology to sustain higher levels of efficiency over a broader range of operating conditions. In addition, using high-efficiency pumps with properly applied variable speed controls will result in significant energy savings for a given hydronic system.
Comparing Pumps
PLEV can also be used to accurately compare pumps from different manufacturers to identify overall operational efficiency. The 30 percent TDH, or calculated minimum control head within the equipment schedule along with specifications, will ensure a fair comparison among manufacturers.
Benefits of PLEV
With a growing emphasis on decreasing energy consumption driven by government regulation, The PLEV formula is an indispensable tool. The calculation can be used to:
Provide the most accurate specification of a centrifugal pump at partial flow rates
Help to eliminate oversizing often associated with system design – a common, yet often unnecessary practice that increases operation, maintenance and capital costs
Gauge true pump performance within a hydronic system
Maximize operational performance while reducing energy use and operating costs
Proper system design is critical in increasing pump reliability and overall system performance. By matching equipment more precisely to actual system demands, pumps will use less power and require less maintenance, lowering life-cycle costs and extending equipment life.
