Reduce Energy Costs by Measuring Power Quality

Summary

Once you have optimized energy use through common methods, consider where energy waste arises.

In 1954, U.S. Atomic Energy Commission chairman Lewis Strauss predicted that one day electrical energy would become “too cheap to meter.” People jumped on the idea with relish. What most did not realize, however, was that Strauss was making the prediction based on advances in fusion power, not on the nuclear fission power we still use today. For fusion to occur, you need to harness the mechanisms of the sun on earth and generate a temperature of at least 100,000,000 degrees Celsius. Nuclear fission energy creates its own types of problems—the biggest being nuclear waste and safety. Consequently, saving energy and minimizing energy waste became the most important aspects of energy usage.

Through the 1950s and 1960s, energy reduction programs flourished and, in the 1970s, became even more important as oil prices rose. It is ironic that, worldwide, politicians argue that users should not have to worry about such matters, but every year energy costs increase. New sources are identified to reduce costs for a while, but energy use expands. The market does its job of increasing the price in line with scarcity. 

Sometime in the 1980s, as a young hospital engineer, I was tasked with implementing an energy savings program in a 1,000-bed general hospital. There were a wide range of properties in the complex, from those that were not more than one year old to those over 100 years old. As you can imagine, the challenge was interesting.

The site was going to be completely rebuilt over the next two to five years, so a priority system was developed to work on buildings that were not going away soon. Fortunately, it seemed that most of the oldest properties would be decommissioned in two to three years, and many temporary buildings would also disappear. I built my plan accordingly. (Although I left the hospital and the area many years ago, Google Maps shows that many of the buildings expected to be decommissioned are still in use—even the temporary ones!)

Benchmarking electrical energy consumption

The first step in developing the energy program was benchmarking electrical energy consumption across the property. The first targets were areas where energy could be controlled relatively easily, such as buildings with departments that would typically close on the weekend and not allow public access.

Through an initial survey, we soon discovered that these departments used a significant amount of energy during times when they were closed. Contributing to the energy usage was supplementary electrical heating, lighting, and computers not switched off. The supplementary electrical heating had been installed when the normal building heating had been faulty or was being refurbished—no one could quite remember why. It was no longer needed, so it was disconnected. Policies were implemented to ensure all lighting and computers were switched off in the evenings and on weekends. The survey was extended for some weeks to make sure this was happening; the policy was quickly accepted without complaint.

After identifying areas that could provide quick wins, more detailed studies were performed in more contentious areas. The first was in operating rooms (ORs).The hospital at that time primarily carried out nonemergency surgery; a second hospital in the group contained the emergency OR. However, the general hospital did have an intensive care unit, and the surgical staff insisted that it had to be ready and working 24 hours a day, seven days a week.

Of the five ORs, two were specifically designed for orthopedic surgery and had laminar flow air systems, which are designed to minimize the possibility of cross-infection. Surgeries were always planned many weeks in advance, and these ORs were always scheduled to operate during weekdays, from early morning into the evening and sometimes on Saturday mornings.

Operating the laminar flow ventilation was very expensive due to the electrical loads needed to move huge volumes of air through resistant HEPA filters. Measurements showed significant energy-saving opportunities from switching off these systems during the night and during nonoperating times. But surgeons were very resistant to switching these off. To convince them, we worked on a plan that included junior surgical staff who were responsible for setup prior to surgery. They were able to show that setup could be done in less than one hour, during the time the surgeon would be driving to the hospital. The cross-contamination expert in the hospital shared studies showing only having one hour of startup time for the air system would not create any issues.

Once the method was proven, automatic controls were installed to ensure savings repeatability. In each of the areas where savings were possible, the hospital followed a similar pattern where it made economic sense.

Another key area for energy waste reduction is improving the power factor for the larger loads. Much has been covered on power factor correction elsewhere, but here is the key takeaway:

• When you monitor larger loads and check the power factor, if it is less than 0.9, then it is a strong candidate for correction. A power factor equipment supplier will help you chose the best solution based on the power rating of the system and the optimal power factor, considering the cost of the equipment.

These examples reveal that energy savings are not as simple as turning off the lights. Saving energy requires cooperation with the tenants and operators of the properties affected. It requires the person performing the studies to be a cross between an energy engineer and a politician.

Advanced power quality considerations

Once you have reduced energy consumption through the common method of turning off stuff that is not in use, turn to a more advanced approach: Consider where energy waste arises. One area is through losses in conductors. As current flows through conductors, some energy will inevitably be generated that becomes wasted as heat (Figure 1).

Remember the fundamental I²R equation, which indicates the power delivered, described as Joule losses? What can you do about those? Reduce the current flow (I) so the power is less, or reduce the resistance (R). Both present a problem. If you deliver lower current, the load will not operate correctly. The cost of reducing the resistance is high, as it requires the installation of more copper or aluminum conductors. So what do you do?

First, consider the optimal conductor sizing. The National Electric Code (NFPA 70 or NEC 100) provides a lot of help to correctly size a conductor. This document is one of a group of documents that describes the ideal conductor sizes for almost every circumstance. For example, the situation in a residential property in the southern U.S. is very different from operating inside a substation in a remote pumping station in the Canadian Northern Territories in the middle of winter, where thousands of amperes may be flowing. The NFPA 70 provides guidance for both situations. 

The main consideration for conductor sizing is to ensure safe operation of the conductors by having the correctly sized conductor with the most appropriate insulation. The correct size will be dependent on the length, the cross-sectional area, and the anticipated current rating required, which provides minimized Joule losses and acceptable voltage drop in the conductor. Typically, the Joule losses will be 2 percent or less.

You may now be thinking, if I design to code then my energy waste will be minimized. In an ideal world that would be correct. But once the installation of the cabling is completed and the loads are installed, the situation can change. It may be that when the first equipment is installed, everything works just fine, but over time things change as additions, moves, and changes take place. It may be that new equipment is required for processes that were not considered during the original installation. Perhaps the location of equipment does not make sense once it is being integrated into a larger process, or upgrading to new equipment is required that on paper can save energy or result in higher efficiency. These additions, moves, and especially changes can have a significant effect on the installation in terms of waste energy. Key areas in which energy waste may occur are related to voltage regulation, harmonics, heating, and unbalanced loads. 

Voltage regulation. As more efficient loads are installed, the voltage in the system may rise or not be correctly controlled at the transformer. Voltage regulation or optimization works like a control valve to reduce energy consumption in voltage-dependent loads by reducing or controlling voltage levels to within the equipment manufacturer’s specified voltage limits to return an energy saving.

As for voltage optimization, it is not widely accepted as practical in the U.S., as it requires very specific use cases to be successful. The upfront cost of the equipment is a significant barrier to adoption too. Most of the material explaining voltage optimization appears to be marketing material, although the American National Standards Institute does have some recommendations for very specific use cases.

Harmonics. Harmonics distort the voltage and current so that the ideal sine wave for voltage is not maintained. This results in overheating in phase and neutral conductors. These are known as “triplen harmonics” as they typically affect third, ninth, 15th, 21st, etc., sine waves. These are additive and will flow in the neutral, causing additional Joule losses (wasted energy) and risk of failure due to overheating. This heating can take place in cable runs, or in motor windings and transformers. The latter two are very prone to overheating, as the lengths of the conductors in the windings are of significant length. Ultimately, overheating can cause significant damage or complete failure (which could be massively expensive and disruptive for larger motors and transformers).

Unbalance. As loads are added, the unbalanced voltage between phases can change. This may be from installing multiple single-phase loads on the same phase or may be from three-phase loads that are not balanced. For example:

• Motors with unbalanced mechanical loading can affect the voltage and current.
• Transformers receiving unbalanced voltage can overheat and potentially fail.
• Electric vehicle charging points can be unbalanced.

Benefits of power quality studies

Many users are dismissive of power quality studies because they think there is nothing that can be done to reduce Joule losses. The fact is that much can be done to save energy through power quality monitoring. Also, many happy users have discovered other important findings by performing power quality surveys:

• They discovered potential failure points in key equipment, such as large motors and power transformers. These would be very expensive if they failed and caused major disruption.
• They found equipment malfunctions in systems.
• They came across breakers prone to accidental tripping due to improper setup.

Once power quality studies reveal areas where energy is being wasted due the effects of harmonics and unbalance (Figure 2), steps can be taken to fix the problems: 

1. Install a range of harmonic filters on loads that are contributing to harmonic distortion. Some of these might be at the main service entrance. Some might be at specific pieces of equipment such as drives.

2. Consider the sources of unbalance. Often these are large motors that also have mechanical unbalance issues that have not been addressed.

3. Some unbalance mitigation is simple: Single-phase loads can be more equally distributed across the phases. Some installers have considered the problem and avoided adding all the loads to phase A/1, but then added them all to phase B/2 instead.

4. Redistributing and reconnecting single-phase loads can reduce voltage unbalance caused by unequal load distribution across the phases. The most prevalent culprits among heavy, single-phase loads are lighting equipment and occasionally welders. A blown fuse on a bank of three-phase power factor improvement capacitors could also cause the problem; simply replacing the fuse can resolve a major unbalance.

Best way to reduce energy costs

There are many technical ways to reduce energy costs: benchmarking through energy surveys, installation of mitigation equipment for harmonic voltage distortion, reduction of unbalance, etc. But the best place to start is with your electricity bill from your utility. This is often the single most effective way to reduce energy cost.

First, discover who is responsible for the bill if it is not you. It may be that your organization has an individual who is solely responsible for the bill. If it is an energy manager, that is a good thing, as he or she will be aware of at least some of the issues. Or it may be a financial administration manager, which might not be so good. We have discovered during many exercises we have done that many financial administration managers adopt a standard procedure of paying suppliers based on the company’s terms, not the supplier’s terms. Consequently, the supplier has been applying a late payment penalty over every billing period that has not been questioned by any administrator. In some cases, we found that an excess of 10-15% was being paid on bills totaling hundreds of thousands of dollars per billing period. The result was a huge waste that could be fixed in seconds.

Consider also the tariff being applied. Industrial electricity bills often include a demand charge, which is an agreed cost of energy for peak times and off-peak times. The tariff often includes a maximum available demand, which is the maximum amount of power that may be drawn during a defined period, typically 15 or 20 minutes. If the user exceeds the specified amount, the user will pay a penalty, and this penalty might not just be for that period. It can be across the whole billing period, which can get very expensive. 

Ensure that the maximum demand you use is close to the demand you are paying for, otherwise you may be paying too much. Also, ensure that you are not too close to the peak demand, otherwise you may find you exceed the demand frequently. This adds to your bills, and may make your supplier very unhappy as it tries to optimize its network energy for all users to provide a reliable service at the best cost. 

Finally, have a discussion with your supplier about your bill to find out if they can offer you better products that will save you money and enable them to improve the network stability. Electricity suppliers are generally very helpful in reducing your bill, as it also helps them.

This article was originally published in InTech's July/August issue.