While systems efficiency isn’t a new term in the industry, it is one of increasing importance. Driven by government regulations, like the Department of Energy’s (DOE) Energy Conservation Standards for Pumps, and the industry’s demand for efficient pump selection, there is a growing emphasis on specifying system solutions that reduce energy consumption and operational costs. Part Load Efficiency Value (PLEV), a new pump selection criteria, helps HVAC system designers select pumps that maximize efficiencies and minimize energy costs.
What Is PLEV?
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 adopted from the Integrated Part Load Value (IPLV) performance calculation that was developed as part of AHRI 550/590-1998. At Bell & Gossett, we’ve adapted the formula for centrifugal pumps used in HVAC systems and updated our ESP-PLUS online selection software to include it.
Why Is It Important?
General industry practice is to select a pump based on a system’s design load, or the maximum capacity of the system. With this selection process, the pump system efficiency is typically measured at 100 percent capacity. However, the system only operates at that level roughly one percent of the time in a given year.
This is one of the reasons why many systems today operate inefficiently. Oversizing pumps is costly — it increases the system’s operation, maintenance and capital costs. Studies have shown that 30 to 50 percent of the energy consumed by pump systems could be saved through equipment or control system changes.
How Can You Use It?
PLEV, and our specially designed selection software, gives system designers the information they need to select pumps that meet and exceed the highest part load value for a given pump selection.
Intelligent 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. Our term for these efficiency ranges is Efficiency Islands.
An Efficiency Island is an area on the performance curve where the pump operates as widely and as deeply as possible within a preferred operating range. Newer centrifugal pump designs, like those in our e-Series, use cutting-edge computational fluid dynamics technology to sustain higher levels of efficiency over a wider range of operating conditions, resulting in energy savings.
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 applying the PLEV/IPLV load profile specifications will ensure a fair apples-to-apples comparison among pump manufacturers.
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.
PLEV is a pump selection criteria that provides a clearer understanding of a pump at partial flow rates and gauges its operational performance within a hydronic system. When engineers use PLEV to select pumps, they will help ensure maximum operational performance at part load conditions and lower energy costs.
For more information, visit bellgossett.com.