Written by Katie Flowers & Caleb Hulbert
Introduction
Natural gas plays a vital role in our country’s energy infrastructure. It is used in all parts of society, from power generation plants and your favorite local businesses to the homes in your neighborhood. When it comes to residential natural gas customers, they depend on their utility to reliably deliver gas to heat their homes and water, cook food, and dry clothing. Residential customers are also trusting that the utility is providing them with accurate billing each month for the natural gas they have consumed. Meters are often referred to as a utility’s cash register and if they are not measuring correctly, there will be a chain of problems that impact both the billing and operations departments, as well as the customer. Though uncommon, natural gas meters can over-measure and as a result, customers can be charged for gas consumption they did not use. This causes the customer to be over-billed and oftentimes the customer service department will receive an influx of phone calls from frustrated customers. More commonly, natural gas meters begin to fail in the customer’s favor by under-measuring consumption. This causes the utility to be shortchanged and can impact revenue, as well as accountability for the natural gas in the distribution system. Residential customers make up a considerable amount of a distribution utility’s business operations, so having a dependable and accurate residential meter fleet is essential.
While the measurement accuracy of natural gas meters is incredibly important, it’s just one piece of the meter selection puzzle. There are a variety of factors to consider when selecting which meter model is most suitable for the application. For gas utilities, one of the most crucial things to look for when selecting a meter is the integrated safety features it has to offer. These features can include shut-off valves, alarm functionality for temperature, flow rate, and pressure sensors, as well as mass disconnects performed over a network. And with rising costs on everything from parts to labor, it’s also a fiscally responsible idea to look for a model that has low maintenance requirements. Utilities prefer to not waste valuable labor hours by constantly sending technicians out to make meter repairs, especially when those repairs are performed during expensive after-hours calls. Another point to take into consideration is whether the utility plans on implementing more robust metering technology solutions, such as Advanced Metering Infrastructure (AMI). There are several residential metering options on the market today that are compatible with AMI, but there are differences that make some models more appealing than others.
Today, the two common options available for residential applications are diaphragm meters and ultrasonic meters. In this paper, we will examine how diaphragm meters define the current state of residential gas metering and explore some of the operational issues they create. Then we’ll turn to what the future could look like with the expanded use of ultrasonic meters, including the benefits they can bring to utilities’ residential meter fleets, and how they stack up in terms of accuracy, maintenance requirements, AMI compatibility, and safety features.
The Current State of Residential Metering
The natural gas industry has long been a fan of traditional routines, and for good reason. The processes and products chosen have real impacts on the safety of its customer base. For decades, the diaphragm meter has been the favorite measurement choice for a utility’s residential applications. Whenever there has been a need for a new residential meter installation, the first thought has traditionally been to deploy a diaphragm. Historically, the diaphragm meter has been the most cost-effective option, which is an appealing factor for large scale projects or when many meters need to be rotated out of service due to age. Diaphragm meters can measure small volumes of gas with consistent accuracy, so they make for a fitting choice in residential applications.
While diaphragm meters remain a trusted option for residential projects, they are not without issues. One problem utilities face with mechanically driven diaphragm models is lock-up. When the meter's drive train breaks due to mechanical wear and tear over time, the meter will provide a very limited flow of gas or won’t be able to pass any gas at all. This results in a loss of service to the customer and requires the deployment of a utility technician to replace the broken meter and relight pilot lights on customer appliances. Utility technicians, like most of us, operate during a standard 8-hour workday. For this reason, many of the emergency service calls happen during the remaining 16 hours of the day when customers are typically home. This results in after-hours service calls for most emergency meter replacements and almost all on-call technicians are paid overtime for after-hours deployments, so this issue usually results in a more expensive fix to resume the customer’s service. Another potential problem utilities experience with a diaphragm meter is a stopped index. This means the meter is functioning correctly and delivering gas to the customer, but it is not registering the volume of gas consumed. Oftentimes a utility will not notice this issue for multiple billing cycles which is typically 60-90 days of consumption. In the multiple billing cycles it takes a utility to identify and address the stopped measurement index, an estimated read is typically used for billing purposes and oftentimes the usage is underestimated in the customer’s favor. On a large enough scale, estimated reads can severely impact revenue and a utility’s profitability.
Diaphragm meters have been used in the natural gas industry for over 150 years, and as a result many of the available models have not changed much in design and operating principles. The lack of innovative updates puts diaphragm meters at the risk of being incompatible with the modern technology that is entering the industry and will cause utilities to miss out on valuable insights into their distribution system. Change can be intimidating, especially when a utility’s precedent has essentially been set in stone. And you may be wondering why you’d fix a process that isn’t broken. We are living in the age of technology and as a result there are more opportunities to upgrade residential metering assets for additional insights into how the distribution system is functioning in near-real time and these additional insights provide a host of benefits, from improved safety to reduced operational expenditures. A good place to start is with residential ultrasonic meters.
Ultrasonic Meters: Looking to the Future
Natural gas utilities are federally regulated entities. With an ever-present focus on how to remain compliant, now is the time to start investigating advanced metering technology. Part of this plan should include a focus on deploying the safest and most reliable equipment for natural gas distribution. The natural gas meters in a utility’s residential meter fleet should follow that same standard. Ultrasonic natural gas meters are not a new concept and have been a trusted choice for commercial and industrial applications for decades. The industry has made great strides to efficiently manufacture ultrasonic meters in recent years, and they will soon change the game for residential metering.
The Sensus Sonix IQ
Ultrasonic meter offerings help alleviate some of the aforementioned issues experienced with diaphragm models. Ultrasonic meters guarantee that interruption of natural gas service to the customer has no chance of being caused by meter lock-up. These meters function by measuring the speed of sound passing through the gas stream in a defined area, known as the flow tube, which is an open path from the meter inlet to outlet. An example of this using the Sonix IQ can be seen above. Even if the ultrasonic meter’s power source fails, there is no chance that a customer’s gas service will be interrupted. Stopped mechanical indexes can be a thing of the past because ultrasonic meters are digital platforms featuring an LCD index display. The meters are constantly sampling their own health for accurate measurement and the LCD index can display notifications of internal hardware or firmware issues that affect the accuracy of the measurement of natural gas. In some cases, the ultrasonic meter can send those alarms directly to utility personnel over an AMI, cellular, or IoT network, which allows for immediate resolution of the issue. This results in improved metrics for unaccounted gas, a reduced number of estimated utility bills, and a healthier meter fleet overall.
Residential ultrasonic meters are typically about half the size of traditional diaphragm models in the same measurement class, which provides versatility to fit in tight spaces such as high-rise utility closets or apartment meter banks. They are also less visually intrusive than diaphragms for the more traditional residential meter sets you’d see on the side of a single-family home. The smaller size also reduces the cost associated with storing and shipping meters, which is a major win in a world where prices for everything keep rising. And for some models, like the Sensus Sonix IQ, the footprint is the same from 250 to 425 CFH.
Perhaps the biggest hang-up that has prevented widespread implementation of ultrasonic meters in residential applications is their higher initial cost. However, with higher cost comes significant improvements and opportunities for cost reduction. Although we live in a world where the economics of an investment must make sense, there are some things that you can’t put a price tag on, and that includes an end-user’s safety. Deploying ultrasonic meters that include integrated safety features such as high-pressure or temperature-based automatic disconnects minimizes the risk of damage to property and the loss of life. Today, most ultrasonic meters incorporate a means of integrated communication, such as an AMR/AMI or cellular network radio. To integrate a means of communication to a traditional diaphragm meter, utilities must purchase a compatible meter radio separately and retrofit the existing index, requiring time and labor. When comparing the cost of a diaphragm meter and meter radio combination to the cost of an ultrasonic meter with an integrated radio, the price difference is negligible, and in some cases, the ultrasonic option is less expensive. Much like personal computers and flat-screen TVs, digital technology has continued to experience a downward trend in the cost of production. The natural gas sector is no different. Manufacturers have worked hard on making pricing more competitive and because of their solid state having no moving parts, ultrasonics have longer warranty periods than standard diaphragms. Making the investment now also gives utilities access to meter technology that goes beyond measurement and offers unique benefits that no other mechanical meter can.
Accuracy
When comparing diaphragm and ultrasonic meters, numbers don’t lie. While diaphragm meters do provide compliant accuracy, ultrasonic meters raise the standard. For example, let’s look at the Sonix line of meters from Sensus. Out of the box, Sonix meters are guaranteed to be within 0.5% of their initial calibration, compared to 1% for diaphragm meters in the same class. The long-term stability of that accuracy is within +/- 1% over the life of an ultrasonic meter versus 2% for diaphragms. At pilot flow rates, ultrasonic meters are +/- 5% accurate, while diaphragms are double that metric at +/-10% accurate. All those values may seem negligible, however, 1% of missed gas can add up very quickly across an entire natural gas distribution system of thousands or millions of residential meters. Temperature compensation is performed digitally with ultrasonic meters using live data from the integrated thermistor. Most ultrasonic meters have +/- 1% accuracy from -30 to 130 degrees Fahrenheit while diaphragm meters are +/- 2 % from -20 to 120 degrees. Pressure compensation can be performed either with live pressure data from an integrated transducer or through digital fixed factoring programmed directly into each meter.
Reduced Maintenance
Increasing productivity by reducing labor hours during daily operations is something every natural gas utility strives to achieve. One of the key benefits of ultrasonic meters is their solid-state design. The solid-state construction means there are no moving mechanical parts that will wear out or require replacement. This eliminates the need for many routine maintenance procedures that each utility is currently performing on diaphragm meters. It also means utilities no longer need to worry about having internal parts damaged from lock-up. Ultrasonic meters are built with integrated batteries that provide stable output for many years. The current industry standard for residential ultrasonic meters in North America provides a battery life of at least 20 years. This allows a near guarantee of uninterrupted service to an end-user for at least two decades, increasing the reliability of stable gas delivery for utilities across the country. With the deployment of residential ultrasonic meters utilities may experience a reduction in expenses associated with meter maintenance and proving operations.
Advanced Metering Infrastructure (AMI) Compatibility
Manual processes associated with operational tasks performed by utilities can be reduced or mitigated with the deployment of an AMI solution. Natural gas utilities that employ AMI networks have an increased level of insight into their distribution infrastructure when compared to traditional meter fleet management methods. Some AMI networks now go beyond the standard tasks of gathering consumption data. A robust AMI network allows operators to effectively communicate with their meters via true two-way communication, enabling a host of features from their ultrasonic meter fleet. Not only does AMI allow the utility to collect consumption data more accurately and efficiently but it also enables the functionality to assess near real time data of critical sensors typically used to monitor critical assets in the field. This is not limited to cathodic protection assets, pressures, temperatures, methane concentration, and fluid levels. When paired with an integrated valve available in some ultrasonic meters, AMI networks can enable remote service disconnects from a secure portal.
The remote disconnect capability allows utilities to act quickly in case of an emergency by shutting off the natural gas service before technicians can be sent out to investigate the issue. This helps ensure that the customer assets downstream of the meter are protected and that the site is safer upon arrival for the deployed technician.
The mandates of an ever-changing regulatory and environmental landscape have inspired utilities to investigate and even deploy AMI networks which help safeguard assets, customer satisfaction, and operational prowess. Having certain ultrasonic meters connected to an AMI network can provide an extra layer of protection to your residential meter fleet and an increased level of safety for your customer base.
Enhanced Safety Features
Utilities understand that safety is paramount when it relates to the distribution of natural gas to its customers. Having robust safety processes and dependable equipment is not only the right thing to do for the customer and operator, but it also helps utilities of all sizes stay compliant with industry regulations. Many residential ultrasonic meters on the market today have benefited from the innovative progress in computation power and advancement in manufacturing processes with the incorporation of enhanced safety features that bring an extra layer of protection when compared to legacy diaphragm meters.
Being able to react in a timely manner in the case of an emergency or other incident is vital for distribution operators. Arguably the most important safety feature seen in some ultrasonic gas meters is the integrated shut-off valve. Depending on the AMI network, a mass disconnect command can be issued to shut off all impacted services in the event of a catastrophic emergency, such as an earthquake, tornado, or fire. The disconnect command can be triggered remotely, which helps a utility secure the impacted area and protect its customers immediately, even before technicians arrive and assess the situation. The remote disconnect also ensures the site is safe upon technician arrival if the leak is downstream of the meter.
Another built-in safety feature seen on many ultrasonic models is alarm response functionality. Alarm category options include theft and tampering, low pressure, hardware failure, asset management, and safety and operational. When these alarms are activated on the meter, they can send a utility near-real-time data if they’re set up on an AMI network. If the meter senses something wrong at the service, for instance an unsuitable change in pressure, it will automatically trigger the shut-off valve to prevent the flow of gas to the residence. Some ultrasonic meter models can even perform this task without an AMI network. Alarm threshold parameters for temperature, pressure, and flow rate can be programmed into the meter. If those parameters are broken, alarms are initiated, and if they are unresolved, the meter will disconnect the gas service, potentially mitigating a hazardous scenario.
Conclusion
Many of the common operational processes and asset types used in today’s natural gas industry have been in use for decades. Routines and habits are instilled in people and utilities by countless years of doing things a certain way. As a result, routines can be hard to change, and new technology is often slow to be incorporated into a utility’s infrastructure. Modernizing utility infrastructure doesn’t need to be scary or difficult. Ultrasonic meters not only refresh infrastructure in the present time, but they also set utilities up for further success as technology in the industry continues to progress. Additional features can be added to an ultrasonic meter more readily thanks to its digital platform. Manufacturers of ultrasonic metering technology are constantly exploring and actively developing additional features such as methane detection at every meter set.
Diaphragm meters have played an important role in residential metering infrastructure throughout the last one hundred years. While diaphragms are still a tried-and-true option, now is the time to consider whether there is a better option for utilities and if they make the most sense for the business’s prospective plans. As we look to the future of the natural gas industry, there are countless examples that stimulate excitement about residential ultrasonic meters. The remote asset control and data acquisition seen in many ultrasonic meters allows the operator to be better connected to its system and to keep a pulse on meter fleet and distribution system health.
Ultrasonic meters have the potential to transform your residential metering infrastructure for the betterment of end user and operator. They are a worthwhile investment to keep your customers, employees, and system assets safer. Now’s the time to ask: What can be achieved if every utility had better insight into its distribution network and residential meter fleet?