Last month’s column (Pumps & Systems, October 2014) described the collection of data when assessing a system with no control. In this column, the plant operating data will be used to determine a baseline of how much energy is used for the process. Personnel and outside experts can then look for ways to improve the system and minimize costs. Assessments are based on the idea that a system was originally designed to meet a specific set of requirements, but during the design process, several unknowns were incorporated. Once a plant is operating, the unknown design factors become known, and the system can be improved. This column explains how to perform the baseline calculations and develop the energy cost balance sheet to determine how energy is used by the system.
First of Two Parts
11/10/2014
Figure 1. The batch tank fill piping system fills the 60,000-gallon batch tanks before starting a three-hour batch process. (Graphics courtesy of the author)
The data collected during the assessment will be used during the calculations. This information is presented in Tables 1 and 2.
Table 1. The operating data collected during the assessment when filling BT-04 and the minimum flow recirculation (updated—see Author’s Note)
Table 2. The operating data collected during the assessment when filling BT-01 and the minimum flow recirculation (updated—see Author’s Note)
The first step is to determine how much energy is consumed to operate the system. Power consumed and cost for the power can then be determined. Each item in the system will be considered in different operating modes.
Author’s Note: It was discovered that the motor current values presented in the October 2014 column were in error. Tables 1 and 2 have been corrected in this column to reflect the accurate motor current data. This error was discovered when cross validating the results.