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Part 2: Challenges with Submetering Natural Gas

Nov 11, 2013

I previously shared a post on how mid-to-large size facilities can save money by taking the initiative to submeter natural gas usage, titled Part 1: Challenges with Submetering Natural Gas. The traditional diaphragm meters used by utility companies rely on fixed compensation variables that can lead to inaccuracies and overcharging. While this can affect residential customers, it comes as no surprise that it can have a major impact on businesses with a large amount of square footage, such as a multi-building campus.

As a result, these facilities often employ flow meters to better measure total natural gas usage to reflect more accurate billing and total energy costs. But, traditional flow meters cannot automatically adjust for changing gas composition and pressure changes, effectively limiting their usefulness when they need to be continuously recalibrated at the factory. Our solution? Four sensors instead of two, an innovative take on solving an age-old problem of flow meter flexibility.

Flow Meter Natural Gas SubmeteringFour-sensor Thermal technology by Sierra Instru­ments provides a method for dealing with changing natural gas compositions and density changes caused by pressure variations. This flow meter corrects for den­sity variations using the AGA Report No. 8-approved density equations for natural gas. Instead of having two sensors, one a temperature sensor in the temperature probe and the other, a self-heated sensor in the velocity probe, there is an additional sensor strategically located in each, giving a total of four sensors. The extra temperature sensors in the stem of each probe measures the stem conduction, which is a function of the total heat transfer budget and must be accounted for. Stem conduction depends on the ambient tem­perature outside of the pipe (See Figure ).

Improved Flow Meter Measuring Accuracy

In this four-sensor Thermal technology, branded QuadraTherm by Sierra, a traditional analog measurement circuit is now a hyper-fast microprocessor that runs a comprehensive flow-measurement algorithm set. This algorithm solves the first law of thermodynamics and calculates the various heat transfer properties of the gas.  Accuracy for this new breed of mass flow meter is +/- 0. 5% of reading for in-line meters, better than the typical 1.0% reading of a utility grade diaphragm meter.

Four-sensor technology has the capability to address changes in natural gas compositions with “Dial-A-Gas”. The meter can hold four gas mixtures onboard, allowing facilities managers to select the appropriate heating value through software Sierra calls qMix. The QuadraTherm essentially eliminates the need to send a thermal flow meter back to the factory for recalibration each time the gas composition changes or the application changes. QuadraTherm also has the capacity to totalize four different billing tiers, allowing consumers to enter different dollar rates for baseline usage and every tier exceeded.

In the next decade, efficient energy management will be a cornerstone to the profitability of mid- to large-size facilities. Through managing energy costs, including natural gas, facilities can save thousands of dollars a year in reduced utility bills. Facilities managers will continue to need innovative new gas meters like QuadraTherm for accurate and flexible sub-metering to drive down energy costs and keep utility companies in check. Find out more about this emerging trend by downloading the full article, and be sure to check out our sub-metering infographic to find out the secret to slashing your facility’s natural gas bills.

Scott Rouse, Product Line Director
Written By:
Scott Rouse, Product Line Director
Sierra Instruments

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