It’s easy to talk about the potential of power and energy loggers (PELs), how they help track energy usage, highlight inefficiencies, and save costs. But how do they perform in real-world conditions? Julian Grant, General Manager at Chauvin Arnoux UK, shares practical insights which were revealed during an 11-day energy monitoring session at a secondary school in Kent.
Most organisations and businesses are used to working with tight budgets, but schools are probably dealing with some of the tightest ones out there. So, it’s crucial to get the most out of every (£) pound they spend. And since energy bills take up a large chunk of their budget, focusing on energy efficiency becomes a top priority.
That’s why we partnered with a secondary school of 700 students to carry out an in-depth energy audit. The goal? To identify opportunities for improving efficiency and cutting costs.
The school’s governors were keen to take action, so we decided to install a Chauvin Arnoux three-phase power and energy logger at the school’s main incoming supply. This would give us the data we needed to spot areas where savings could be achieved.
This innovative data logger uses flexible current transformers, clamp-on connections, and a magnetic base for quick and easy mounting. Thanks to its design, it was installed with minimal disruption. The device was left in place for eleven days, capturing a complete set of data from both school days and weekends
The results were both insightful and practical. One of the key findings was a significant imbalance in phase currents, as shown in Figure 1. The peak current on one phase reached 219.2 A, compared to 172.8 A on the second phase and 150.3 A on the third, which highlights a clear issue with how the school’s loads — mostly single-phase are unevenly distributed across the phases. This is undesirable as imbalance increases the current in the neutral conductor and can result in excessive heating. Current imbalance can also lead to local voltage imbalance at various points in the installation, which may affect the efficient operation of three-phase loads like motors.
Figure 1
Also notable was the high level of harmonics in the supply system. As seen in Figure 2, the third and fifth harmonics were particularly high. Given the growing numbers of ‘electronic’ loads in today’s schools, it’s not surprising. Personal computers, office equipment and LED lighting tend to introduce third harmonics, while uninterruptible power supplies (UPSs) and servers are a common source of fifth harmonics. That said, harmonics can still pose a risk as they may cause unexpected heating in neutral conductors and can interfere with the proper functioning of electronic equipment.
Figure 2
Perhaps the most surprising discovery from the logged data can be seen in Figure 1. As would be expected, peak current usage occurs during regular school hours when the building is occupied. But what really stood out was that even during evenings and weekends, when the school was closed, around 30 A per phase were still being drawn. While some of this probably relates to things like emergency lighting and is therefore unavoidable, the overall figure was unexpectedly high.
The school then investigated this out-of-hours consumption and found that the portable electric space heaters, which were being used to supplement the poorly performing HVAC system in part of the school, were often being left on during the night and at the weekend.
This turned out to be a classic example of a quick, zero-cost energy saving opportunity. The solution? Simply encouraging teachers to be more mindful about switching off heaters at the end of the day.
One final parameter that was carefully evaluated during the monitoring period was power factor, but this was found to be good at all times, with little opportunity for further improvement. This was probably because the school had few inductive loads, and those were balanced out by capacitive loads such as LED lighting. But in other settings, including other schools, the situation might be very different. That’s why it’s always important to pay close attention to power factor results during any energy monitoring exercise.
Moreover, this data logging activity delivered clear, actionable recommendations that promise significant benefits moving forward.
Switching off portable heaters outside of school hours has already been put into action, though it’s only a temporary fix. In the long term, far greater energy savings are expected by upgrading the school’s HVAC system. The goal is to improve overall efficiency to the point where portable heaters are no longer needed at all. There may be other unnecessary out-of-hours energy loads too like lights and computers left on when no one’s around. The school can further investigate and consider simple solutions, such as occupancy sensors for lighting and timed switches to automatically power down computers at the end of the day.
Next, high levels of harmonics certainly need to be addressed. It would be beneficial to identify the individual sources and, where necessary, fit filters. The result will be cleaner supplies, reduced cable heating and longer equipment life.
Lastly, the school can look at redistributing single-phase loads on the power system to provide better balance between phases. Again, this would reduce heating in neutral conductors, and help ensure that any three-phase loads on the system operate efficiently.
Monitoring power quality and usage at the school in Kent turned out to be a straightforward and low-cost exercise that had zero impact on day-to-day operations. What it did deliver, however, was a wealth of valuable insights that will help the school use electricity more efficiently and cut down on energy costs. So, to answer the question raised at the start: are power and energy loggers useful in real-world settings? Absolutely. They’re an incredibly effective for identifying energy-saving opportunities. https://cauk.tv/
This article appeared in the May 2025 issue of Energy Manager magazine. Subscribe here.