# Model-Based Assessment of Energy Efficiency in Industrial Pump Systems: A Case Study Approach
## 2 Case Study on Water-Cooling System: Operation, Data Collection, and Efficiency Modelling
### On-Site Measurements of the Existing VSDP  
A frequent obstacle to improving energy efficiency in industrial environments is the absence of comprehensive and reliable historical data on energy usage. In our scenario, the data at hand include the pump flow and pressure for the active VSDP, the specific VSDP being used, and the set point frequency of the converter, with a sample point taken every 10 min throughout the year. However, as there are no data on the electrical input power for the VSDPs, it is not possible to calculate the energy consumption directly. To solve this problem, we first measured the pump flow rate, pump pressure, and electrical input power at several stationary operating points (OPs) over a wide operating  
Figure 1: Schematic representation of the central water-cooling system with a description of the marked positions. Figure 2: Existing VSDP in the central WCS (**left**) and VSDP schematic (**right**). range. These measurements allowed us to develop an efficiency model for the VSDPs, which was then used to estimate the total annual energy consumption based on the historical data. To ensure accurate measurements without disrupting the industrial process, we took advantage of the redundant WCS design. The measurement equipment was installed on the inactive VSDP and the system was then switched to this pump for testing. Hydraulic parameters were measured using a differential pressure meter (DP-4000, Klay Instruments, Dwingeloo, The Netherlands) and an ultrasonic flow meter (Fluxus ADM 6725, Flexim, Emerson, Vantaa, Finland), with data recorded on an Allemmo 2890-9 (Ahlborn, Holzkirchen, Germany). Electrical input power was measured with a power analyser (PPA5530, Newtons4 th, Leicester, UK) and data were recorded directly to a laptop using PPALoG software (v. 3.2). Data synchronisation between the recording devices was performed manually. As it was not feasible to carry out measurements several times a year in order to record realistic low loads in winter and high loads in summer, we decided to carry out the measurements in mid-June. During this period, the demand for cold water remains moderate, so that the industrial process can tolerate short-term deviations from the hydraulic parameters predicted in the WCS. To obtain measurements under operating conditions other than those of the running industrial process, we scheduled ten-minute intervals in which the WCS was deliberately interrupted--either subcooled or superheated--depending on whether we wanted to measure the pump's performance at high or low load. After each measurement interval, additional time was required to normalise the WCS back to the required operating condition. This minimised the impact of these sub-optimal cooling conditions on the industrial process. Multiple measurement periods were required to collect data on the desired OPs. Different OPs and therefore different cooling water requirements were simulated by adjusting the frequency set points and the valve openings on the pressure side of the pump. Each pipe is equipped with throttle valves located both upstream (on the suction side) and downstream (on the discharge side) of the pump (Figure 1), which can be adjusted manually. The valves are otherwise fully open when the pump is in operation. To simulate different operating conditions, three valve positions were tested: fully open, 60% open, and 30% open on the discharge side [41]. These valve positions were combined with four frequency set points (50 Hz, 40 Hz, 30 Hz, and 20 Hz), resulting in twelve different OPs covering a wide operating range. The slip compensation function of the converter ensures that the induction motor (IM) maintains an almost constant speed despite fluctuating hydraulic loads, resulting in speeds of 1500 rpm, 1200 rpm, 900 rpm, and 600 rpm for all practical purposes. The performance of both pumps was measured at identical operating points, yielding nearly identical results.