By Chad Edmondson, J.M. Pleasants and Norm Hall, R.L. Deppmann
In our last blog post, we introduced the PLEV, or Part Load Efficiency Value from Bell & Gossett. This week we look at some selections and how to use PLEV.
PLEV was created to give a weighted average of the pump efficiency for the HVAC and plumbing industry. This new efficiency average gives the engineer or designer an efficiency that is most likely a better representation of the actual efficiency of a variable volume system.
Using ESP-PLUS for Energy Analysis
Let’s use an example to show how the PLEV may be used as part of the selection criteria. Assume we have a heat pump system with a pumping requirement of 800 GPM at 100 feet of head in a variable volume, variable speed application. Using the Bell & Gossett ESP-PLUS pump selection program, our selection is shown below.
Notice the traditional duty point efficiency column. The selection is sorted by this column when it first appears. The 1510-5EB with a 30 HP motor is a nice selection. If the pump ran at design flow and head all the time, then the efficiency would be 82.42%. But this is a variable speed, variable volume pump so the efficiency of that selection using the PLEV load profile is only 73.01%.
Part load efficiency is what we should use in any system energy analysis software as the average efficiency.
Let’s click on the Pump PLEV column and re-sort to see what the most efficient pump will be during variable speed operation.
Once we sort on PLEV we see different selections. The most efficient pump for this application is a 3500 RPM selection. The choice, if we choose a 1770 RPM selection, is the e-1510-4GC with a PLEV of 77.43%.
Visit the B&G site to get a password for the ESP-PLUS selection program.
Next week we will look at these selections and question why we might consider a selection with less efficiency as our choice to schedule and recommend to our client.