The designed program runs on Microsoft Excel and it is used to calculate energy- and finan-cial savings available in a pumping system, when using variable speed control instead of throttle control. The program operation is illustrated generally in Fig. 2.1, and it’s described more detailed in next chapter.
Input information Evaluation of the pump characterictics
Printing the results and plotting the graphs
Calculation of required shaft power
Evaluation of the motor and drive efficiencies Calculation of the required
electric power Calculation of the energy
consumption
Calculation of economic information
Fig. 2.1 Operation of the program in general.
The program makes the calculations on the basis of user given information about the pump-ing system, economic conditions and flow profile. The required input information is shown in Fig. 2.2.
Fig. 2.2 The input page of the program. Pump nameplate and system information, motor and drive efficien-cies and economic conditions are required for the calculations. The used units of each quantity are marked on the right side of the input field. Flow profile can be read from the file or inputted man-ually by clicking buttons on the bottom of the page. The used decimal separator for input values depends on Excel’s language settings.
All required information about pump, motor and drive should be found in the nameplates or datasheets of devices. The density of the liquid used in a process is usually known. Static head is determined by measuring or assessing the vertical difference of supply and destina-tion reservoirs’ surface levels. Informadestina-tion about current economic condidestina-tions is also re-quired to calculate the available financial savings. Energy price and related CO2 emission
can be inquired from the electric company. The investment cost includes purchase and in-stallation prices of the variable speed drive. Interest rate and inflation can be determined according to their current values. The lifetime of a pumping system is usually considered to be from 15 to 20 years, depending on system and process.
User can input the flow profile manually or with a text file. In the text file, the information must be divided in two columns and separated by commas. In the first column, there must be timestamps, for example in the form “15.1.2014 00:14:28” or “2014-1-15 00:14:28” or
“1/15/2014 12:14:28 PM”. The correct timestamp notation depends on the used language version of Excel because of the built-in date- and time handling functions used in the de-signed program. Intervals between timestamps do not have to remain constant. In the second column, there must be flow rate values in m3/h and used decimal separator is a dot. An ex-ample of a file with properly arranged data is shown in Fig. 2.3. Reading a flow profile from text file is useful, if user has measured flow rate data from a process. If the text file has header lines, the number of them must be entered on the input page.
1.1.2014 00:00:00, 330.50 1.1.2014 11:00:00, 440.33 1.1.2014 12:34:30, 420.48 2.1.2014 01:20:00, 500.00 2.1.2014 15:10:26, 450.11
Timestamp Flow rate in m3/h
Fig. 2.3 The properly arranged process data file. Timestamp and flow rate are separated by comma and dot is used as the decimal separator in flow rate values.
In manual input of the flow profile, information is also entered in two columns. In the first column, utilization time of each flow rate is given in hours and in the second column, flow rate is given in m3/h. Used decimal separator in both values depends on used Excel language version. The manual input is useful especially if user don’t have any measurement data from the process, or the used flow profile in the process is planned to be changed. The manual input page is shown in Fig. 2.4.
Fig. 2.4 The manual input page of the program. The utilization time is given in hours in the first column and the flow rate value is given in m3/h in the second column. After the flow profile is inputted on the field, “Calculate”-button can be clicked to do the calculations. “Clear”-button is used to clear the contents of the table for a new flow profile. Flow profile is automatically filled in the shape of a bell curve from 30 % to 100 % of the pump nominal flow rate. The used decimal separator for input values depends on Excel’s language settings.
The entered flow profile is assumed to be repeated for an entire year, so if there are times when the system is standing still, they should be entered too for more accurate calculations of the annual energy consumption. When all required input data is entered, the program makes the calculations and activates the results page. In the results, information about achievable savings and graphs of pumping system performance and savings potential are shown to the user. The results of the calculations are shown in Fig. 2.5.
Fig. 2.5 The results page of the program. Viability of the variable speed drive investment can be evaluated on the basis of the calculations. The program shows the energy and financial savings achievable by change of the pump control method.
User can draw conclusions about the profitability of the investment in VSD, on the basis of calculated information, which includes energy and financial savings and also a few important economic quantities, which are described in the next chapter.
The program also draws graphs, which describe pump performance and energy savings available with the change of flow control method. These graphs are illustrated in Fig. 2.6.
The pump QH curve illustrates the difference of head losses in the valve and VSD controlled systems. The QP curve compares power consumption of both control methods as a function of flow rate. Histograms are plotted on the basis of given flow profile and QP curves. The upper histogram shows the flow distribution of the process. The lower one shows the achiev-able relative energy savings with the used flow profile.
Fig. 2.6 Graphs of the results page. Pumping system characteristics are illustrated in two graphs on the top, the upper one is QH curve and the lower one is QP curve. Two lower histograms describe the flow rate distribution and savings potential at different flow rates with the given flow profile.
For more detailed information and graphs, user can move to the information page by clicking
“Detailed information”-button on the bottom of the results page. The information page con-tains input information and results of the calculations, QH and QP curves, histograms about flow rate and energy consumption distribution, specific energy and rotational speed curves, total efficiency curves for both control methods, and efficiency curves for all devices sepa-rately in both control methods. It is possible to save the information page by clicking “Save as PDF”-button. Information page also includes the text box for the pump name on the top of the page, and the text box for the user notes on the bottom of the page. The information page is shown in Fig. 2.7.
Fig. 2.7 Part of the information page. Page includes the input information, results of the calculations and different curves and graphs.