How to Select a Gas Meter for Your Application

Metering devices are crucial for controlling gas flow in residential, industrial, and commercial settings. With the many gas meter models currently on the market, choosing a meter that suits your application can be exhausting and confusing. Nonetheless, there are common aspects that should be considered when shopping for a gas meter to get the right one.

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The main factors that should guide your gas meter selection include:

• Application
• Required Load/Capacity
• Pipe Size
• Gas Line Pressure
• Installation Constraints
• Long-term maintenance

Below, we examine each of these factors in more detail.

Application

When choosing a gas meter, you should consider why you need it. Do you want to measure fuel gas volume? Is it for industrial, commercial, or residential use, or do you need a solution to measure custody transfer? You also need to consider the accuracy level, repeatability, flow rate, fluid temperature, pressure, gas type, and location of your meter. There are several types of gas meters, including differential pressure, motion mechanics, positive displacement, thermal dispersion, variable area, and velocity-based meters, each suited for different applications.

Positive displacement-based meters like diaphragm meters and rotary meters work best for low-pressure systems with PSI rates of 0-100 and not more than 175, respectively. They are thus often used in domestic settings. Though they have high turndown and adequate accuracy, you will have issues with them when using wet or dirty gas because they have no moving parts. Velocity-based meters like turbine flow meters are suited for high-pressure systems with PSI ratings as high as 220.

Differential pressure-based meters like orifice meters are primarily used in industrial settings because they have no moving components, and their field servicing is easy. Rotameters, a type of variable area-based meters, are used in hazardous places with flammable gases since they need no external power and are highly resistant to damage from chemicals. They, however, have fair accuracy levels. Coriolis gas meters, a type of motion mechanic-based meters, are suited for applications requiring the highest accuracy and those with wide flow rate ranges.

Mass flow meters excel at combustion control. They are also the best for biogas, natural gas, flare gas, and energy management applications. Ultrasonic and vortex gas meters are velocity-based meters. Ultrasonic meters are primarily used in natural gas custody transfer since they excel at measuring the flow of gases and steam with high accuracy. They also measure slurry and liquids. On the other hand, vortex meters work best for accurately measuring steam or compressed air.

Required Load/Capacity

When selecting a gas meter, you should know your gas consumption rate in the area where the meter will be used. This will determine the maximum flow rate for your meter. It is crucial to match the gas meter to the capacity it is required to handle. Under-sizing the meter means that your equipment will be starved for gas and will thus not function at its maximum capacity. Moreover, the equipment will be at risk of soot buildup.

You can get the load/capacity of your gas meter on its small print, often somewhere near its readout. The number is stated in cubic meters of cubic feet per hour. You should compare this with your building&#;s total gas demand. This demand for each gas appliance in your property is stated in Btu/h ratings on the nameplates. Experts recommend that your maximum gas flow rate be less than 80% of your meter&#;s maximum capacity.

Pipe Size

The right pipe size affects the efficiency and safety of your application, so it is a crucial element to focus on in gas meter selection. A pipe&#;s size affects how much gas will pass through to your appliance and how much will reach the device. For instance, long pipes might initially seem ideal, but the excess length can cause lower volumetric gas flow.

When determining the perfect pipe size for your gas meter, pay attention to its nominal size, length, application, and material. Moreover, the pipe you pick should match your gas meter type. For example, small pipes are used with diaphragm meters, while large ones work with turbine meters.

Gas Line Pressure

The gas line pressure depends on your gas meter type and its usage. Diaphragm meters, for instance, are often used in low-pressure applications and can endure maximum pressures of 1.5 bar. On the other hand, turbine meters are the leading options in the industrial sector and heavy commercial applications. These can withstand line pressures of up to 6 bar.

Installation Constraints

Like in real estate, the location of your meter is a significant consideration when choosing it. Will your meter be installed outdoors where it is exposed to different elements or installed in a controlled location? Are there space constraints you should take into account? Some gas meters need a lot of straight pipe stretches for accurate flow readings. For instance, if your pipe is 2&#;&#; in diameter, you need about 20&#;&#; after and before your meter for accurate readings. Moreover, you should keep in mind whether you are vertically or horizontally mounting the meter. Variable flow meters, for instance, are primarily reliant on gravity, so they should be installed vertically.

When considering location, pay attention to the environmental conditions and available infrastructure in your installation space as well. Typically, sites with no or minimal electrical interference, vibrations, and magnetic fields are ideal for maximizing the performance of a gas meter. The ideal site should also have no electric or pneumatic power nearby because this might cause explosions. Moreover, installing your gas meter in places with a lot of condensation, such as in direct rain, may cause inaccurate readings and eventually corrode the meter.

Long-Term Maintenance

One of the elements that will impact your ownership of a gas meter is its long-term maintenance needs and expenses. You need a regular inspection of the meter by a qualified inspector to ensure it is in optimal condition and reduce repair costs. You should also factor in the costs of periodic repairs, which are often higher for meters with many moving parts and those in hard-to-access areas.

Conclusion

With the information provided in this article, you now have a better understanding of the importance of knowing all the factors that will affect the selection of the proper gas meter for your application. Remember that even when you factor in the long-term maintenance needs, pipe size, required load/capacity, installation constraints, gas line pressure, and application of your meter, there are still pros and cons of specific meters to consider. The selection of a gas meter that perfectly fits your needs might thus not be so straightforward, even when you know the elements that should guide you.

If you need help selecting the right gas meter for your application, do not hesitate to contact the experts at Norgas. We offer a variety of gas meters for all types of applications, so you are sure to find one that meets your needs.

This article classifies nine types of natural gas meters in six styles. The infographic below groups meters into custody transfer and industrial classes, mass flow versus volumetric flow, and new versus traditional technology.

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Each natural gas meter has its own benefits and excels in different applications, from gas distribution (residential gas meters to high-pressure applications) to industrial uses.

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1. Differential Pressure

Differential pressure meters are approved for custody transfer applications. They measure volumetric flow rates and are a traditional technology. Different differential pressure meters are orifice plates, pitot, and Venturi tubes.

Orifice Meter

An orifice meter is a differential pressure meter that infers the flow by measuring the pressure drop over an obstruction inserted in the flow. As the turbine meter, the orifice plate is an inferential meter, as it infers the volumetric flow rate by measuring a property of the flow stream. Along with custody transfer, orifice meters are a commonly accepted method of flow measurement for industrial applications; they have no moving parts and are easy to service. Unfortunately, they have limited turndown and do not handle a wide range of flow rates. They also have reduced low-flow sensitivity and require gas static pressure, differential pressure, viscosity, density, and temperature to measure gas flow accurately.

2. Motion Mechanics

Coriolis Meter

Coriolis meters&#; principle of operation is based on motion mechanics. The meter provides a direct mass flow measurement based on the fluid&#;s deflection force moving through a vibrating tube. They are a custody transfer meter, considered new technology, very accurate with high turndown capabilities, and independent of fluid properties. They are also costly to install and unsuitable for larger pipe sizes.

3. Positive Displacement Meters (PD Meters)

Positive displacement meters are direct measurement meters and are considered a traditional technology. They operate on the volumetric flow principle by sectioning the gas flow into specific segments that fill and empty (displace) as the meter revolves. Each revolution is associated with a particular volume, and the meter reads in cubic feet (or cubic meters). Positive displacement meters have sufficient accuracy and high turndown. However, they have moving parts, so wet and dirty gas are problematic when using them.

Diaphragm Meters (Residential Gas Meter)

Diaphragm meters are residential gas meters for commercial and light industrial applications. They are approved as a custody transfer meter. The gas or fluid flows into the meter inlet with an oscillating diaphragm. The compartment fills and displaces to the outlet; each diaphragm revolution determines the flow rate.

Rotary Gas Meter

The rotary meter is for higher volume or pressure use for commercial or industrial applications. They are also custody transfer meters. For this meter type, the gas or fluid flow divides by a rotating impeller or rotor, which has vanes, and each rotation determines the flow rate.

4. Thermal Dispersion

Thermal dispersion is a new technology.

Thermal Mass Flowmeter

A thermal mass flow meter is an instrument that directly measures gas mass flow in many industrial applications to improve process efficiency and conserve energy. They also are used for methane emissions monitoring and greenhouse gas reporting. The meters have a wide turndown, excellent repeatability, and no moving parts. They have a low-pressure loss and can withstand high temperatures but require a long straight run. There is no need for ancillary pressure and temperature equipment.

5. Variable Area Meter

A variable area flow meter is a traditional gas technology meter consisting of a tube and float. The float response to flow rate changes is linear with a 10-to-1 flow range or turndown.

Rotameter Meter

The rotameter is an industrial flow meter that measures the volumetric flow rate of gases and liquids in a closed tube. It is a variable area meter and provides a simple and inexpensive indication of flow rates. It has fair accuracy.

6. Velocity-Type Meters

Turbine

The turbine gas meter is considered a traditional technology and measures the volumetric flow rate calculated based on a rotor&#;s angular velocity in the meter. It is a custody transfer meter with high accuracy but requires pressure and temperature compensation. It also has moving parts, so the user must consider gas cleanliness. This meter type is limited to measuring low flow rates and has a high-pressure loss.

Ultrasonic flowmeters

The ultrasonic meter indirectly measures mass flow. Ultrasonic flowmeters measure the difference in pulse transit time that travels from a downstream transducer to the upstream transducer compared to the upstream sensor back to the downstream transducer. The meters are usually used at pipeline meter stations in high-flow and high-pressure applications where the slightest inaccuracy can negatively impact the bottom line. This meter style is exceptionally accurate, has a high turndown ratio, and has excellent rangeability, but it is costly.

Vortex

Vortex meters are a latecomer to API approval for custody transfer of natural gas. This late approval has made it difficult for the meter to catch up to other custody transfer meters (Coriolis, Diaphragm, rotary, turbine, ultrasonic). Consequently, vortex meters are primarily used in industrial markets with very little custody transfer of natural gas usage. The meters measure volumetric gas flow; they have good rangeability but are costly.

What are the 6 custody transfer meter types for natural gas?

4 Traditional Gas Technology Meters

1. Positive displacement (diaphragm meter, rotary meter)
2. Turbine meter
3. Differential pressure (&#;P) (orifice plates, venturi tubes)
4. Rotameter (variable area (VA))

4 New Gas Technology Meters

1. Coriolis
2. Thermal mass flow meter
3. Ultrasonic flowmeters
4. Vortex

Helpful Tips on the Natural Gas Meters

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