Evaluating the Parts: Building an Energy Cost Balance Sheet for Each Item

In last month’s article an Energy Cost Balance Sheet was created for the piping system shown in Figure 1. We saw how to calculate the cost of operation for the centrifugal pump using the manufacturer’s pump curve. Many of the details of the remaining equipment were left for future articles. This month we will see how to perform the detailed cost calculation for the other items in the system.

Figure 1 shows the operating data from the installed plant instrumentation. We’ll use this operating data along with the manufacturer’s equipment data sheets to calculate the differential pressure and flow rate through each item. With that information, the cost of electrical power, and the annual cost of operation we can calculate the annual operating cost and energy usage for each item in the system’s Energy Cost Balance Sheet.

Figure 1 – The operating data from installed plant instrumentation along with elevations of selected tanks and equipment.

To calculate the operating cost of an item in the system, we must determine its head loss and corresponding flow rate. Since there is insufficient installed instrumentation to determine these values, they must be calculated using data from the equipment manufacturers.