In the late 90s, I used Excel to develop a simple graphical system that showed the variable speed performance of a pump based upon its published 60-hz H/Q curve. I have modified it to model several different pumping applications, and four different versions are on my website today. Although they can be useful tools, they are limited to 60-hz data and units of GPM, feet and HP. Because of these limitations, I have received a number of requests from our readers to develop an international version. VPSA50 is the result of several, fairly simple modifications to one of those versions. It is designed for 50-hz data and uses the affinity laws to calculate the lower speed H/Q points and the input power required for each. It also allows the use of any unit of measure.
Figure 1
Figure 1 is a screen shot of the data entry tab of VSPA50. Entering the data requested in Step 1 automatically formats the chart title, the x/y axis values and the data label values. Step 2 collects the H/Q data for the 50-hz performance curve used to compute the lower frequency curves. Step 3 allows the entry of an optional system curve. Finally, in Step 4, the power required for each 50-hz H/Q point is entered in the units defined in Step 1. This information is used to produce data labels that show the power requirement for the H/Q points on each of the curves. Detailed instructions can be found below the data entry portion of this screen.
Figure 2
Figure 2 is the chart produced from the data entered in Figure 1. The title and units of measure are automatically placed in their proper position and the scale of the x and y axes are proportioned to the H/Q data entered. Although all frequency points between 50-hz and 25-hz are calculated, only the major ones (in 5-hz increments) are displayed on the graph. Each is color coded and identified in the legend box. The data labels on each of the H/Q curves show the power required at that point. The optional system curve, plotted in red, shows the actual variable speed performance at each intersection with the frequency curves.
I also developed a 60-hz version for those who may need to use international units of measure when evaluating 60-hz pumps. VSPA50 and VPSA60 are available for download at the "Variable Speed Pumping" section of my website. Both require Microsoft Excel. Please give them a try and send me your feedback.