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Comparison of Analog vs. Advance Comparison of Analog vs. Advance Technology Air Sampling System Designs Technology Air Sampling System Designs

To Facilitate Correction of Measured or To Facilitate Correction of Measured or Calculated Volumes to a Set of Reference Calculated Volumes to a Set of Reference

Temperature and Pressure ConditionsTemperature and Pressure Conditions

By By

Frank M. GavilaFrank M. Gavila

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The basis for correcting air sampling The basis for correcting air sampling volumes to a reference temperature volumes to a reference temperature

and pressureand pressure

Typical volume measurement systems Typical volume measurement systems and/or calculational methods of and/or calculational methods of determining volumesdetermining volumes

Validity of sample volumes determined Validity of sample volumes determined

by the different types of flow/volume by the different types of flow/volume measurement systemsmeasurement systems

The bottom lineThe bottom line

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I.I. Why is there a need to correct Why is there a need to correct volumes to a reference temperature volumes to a reference temperature and pressure?and pressure?

The basis for correcting measured or The basis for correcting measured or calculated volumes to a mutually calculated volumes to a mutually agreed upon reference temperature and agreed upon reference temperature and pressure rests upon the premise that pressure rests upon the premise that the volume that a gas occupies is a the volume that a gas occupies is a function of its temperature and function of its temperature and pressure based on the laws of physics pressure based on the laws of physics applicable to ideal gases.applicable to ideal gases.

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Comparison of two gas volumes collected at different times and/or different locations can only be made if the volumes are compared at the same reference temperature and pressure conditions.

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It is irrelevant what the temperature and It is irrelevant what the temperature and pressure conditions are as a practical pressure conditions are as a practical matter. Where regulatory or scientific matter. Where regulatory or scientific reasoning dictates a need for consistent reasoning dictates a need for consistent behavior among many individuals behavior among many individuals performing similar volume performing similar volume determinations ,a mutually agreed upon determinations ,a mutually agreed upon set of values is chosen. set of values is chosen.

This agreed upon set of values becomes a This agreed upon set of values becomes a reference standard. reference standard.

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Examples of reference standards are as follows:Examples of reference standards are as follows:

Classical STP:Classical STP: Standard Temperature and Standard Temperature and Pressure (0Pressure (0ooC, 1 ATM)C, 1 ATM)

SATP:SATP: Standard Ambient Temperature Standard Ambient Temperature and Pressure (25and Pressure (25ooC, 1 ATM)C, 1 ATM)

NTP:NTP: Normal Temperature and Normal Temperature and Pressure (20Pressure (20ooC, 1 ATM)C, 1 ATM)

MNTP:MNTP: Modified Normal Temperature Modified Normal Temperature and Pressure (70and Pressure (70ooF, 1 ATM)F, 1 ATM)

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Typical Volume Measurement Systems Typical Volume Measurement Systems and/or Calculational Methods of and/or Calculational Methods of

Determining VolumesDetermining Volumes

Volume measurements are of two forms:Volume measurements are of two forms:

Measurement of average flowrate Measurement of average flowrate

multiplied by elapsed timemultiplied by elapsed time Direct display of the measured Direct display of the measured

volumevolume

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Measurement of average flow rate multiplied Measurement of average flow rate multiplied by elapsed sample timeby elapsed sample time

ExamplesExamples RotametersRotameters Analog differential pressure metersAnalog differential pressure meters Digital differential pressure metersDigital differential pressure meters Mass flow metersMass flow meters

In the above the average flow is determined by In the above the average flow is determined by a simple method such asa simple method such as

Average Flow = Average Flow = Beginning Flow + Ending FlowBeginning Flow + Ending Flow 22

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The more flow measurements that are madeduring the sampling activity the more accurate the average flow value becomes.

The most accurate value for average flow is expressed by the equation where n equals infinity.

Average Flow = i=1

n

n

Fi

Where i= n different observations of flow measurement.

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Sufficiently accurate values for average flowrate can also be obtained when i is a large number such as 168 or greater in a 7 day (168 hour) sampling duration.

Volume DeterminationVolume Determination

Volume = Avg. Flow x Sample DurationVolume = Avg. Flow x Sample Duration

Where sample duration is determined by Where sample duration is determined by measuring the difference between the measuring the difference between the time the sample was started and the time time the sample was started and the time the sample was terminated (the pollutant the sample was terminated (the pollutant collection period).collection period).

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Measuring instruments utilized for this Measuring instruments utilized for this determination of elapsed time can vary determination of elapsed time can vary from a wristwatch observation to an from a wristwatch observation to an accurate elapsed time meter accurate to accurate elapsed time meter accurate to the nearest 0.01 seconds.the nearest 0.01 seconds.

The accuracy of the volume determination The accuracy of the volume determination is a function of the accuracy of the flow is a function of the accuracy of the flow measurement and the sample duration measurement and the sample duration measurement.measurement.

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b.b. Direct display of the measured volumeDirect display of the measured volumeExamples:Examples:i.i. Dry gas test metersDry gas test metersii.ii. Advance technology instruments that Advance technology instruments that

internally compute total sample volume internally compute total sample volume including mass flow meters and including mass flow meters and microprocessor controlled electronic microprocessor controlled electronic instruments.instruments.

The user observes a dial or digital display indicating The user observes a dial or digital display indicating the accumulated sample volume. the accumulated sample volume.

Some devices permit zeroing the accumulated volume Some devices permit zeroing the accumulated volume to zero prior to beginning a new sample. Other to zero prior to beginning a new sample. Other instruments, such as dry gas test meters, require the instruments, such as dry gas test meters, require the technician to read the dial or digital meter’s numeric technician to read the dial or digital meter’s numeric values prior to beginning the sample and immediately values prior to beginning the sample and immediately after the sample is terminated. The difference after the sample is terminated. The difference between beginning and ending values is the sample between beginning and ending values is the sample volume.volume.

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III.III. Validity of sample volumes determined Validity of sample volumes determined by the different types of flow/volume by the different types of flow/volume measurement systemsmeasurement systems

The traditional air sampling systems The traditional air sampling systems utilizing variable area rotameters, utilizing variable area rotameters, analog differential pressure meters and analog differential pressure meters and even dry gas totalizers display flows or even dry gas totalizers display flows or volumes that reflect the conditions of volumes that reflect the conditions of the absolute pressure and temperature the absolute pressure and temperature existing at the flow measurement existing at the flow measurement device or the volume measurement device or the volume measurement device at the time the observation is device at the time the observation is made.made.

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What factors influence the absolute What factors influence the absolute pressure and temperature conditions at pressure and temperature conditions at the flow or volume measurement device?the flow or volume measurement device?

Absolute PressureAbsolute Pressurea)a) Elevation of sampling siteElevation of sampling siteb)b) Variations in local barometric pressure Variations in local barometric pressure

conditions during the sample periodconditions during the sample periodc)c) Pressure drop across the filter(s) utilized Pressure drop across the filter(s) utilized

in the sampling systemin the sampling systemd)d) Pressure drop caused by the air sampling Pressure drop caused by the air sampling

system flow path circuitrysystem flow path circuitrye)e) The pressure drop due to the presence of The pressure drop due to the presence of

dust loadingdust loading

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TemperatureTemperaturea)a) Seasonal temperature variation of Seasonal temperature variation of

sampling sitesampling siteb)b) Daily variations in temperatureDaily variations in temperaturec)c) Recirculation of pump exhaustRecirculation of pump exhaustd)d) Local artificial temperature influences of Local artificial temperature influences of

sample site locationsample site location

Flow measured by rotameters and analog Flow measured by rotameters and analog differential pressure sensors is called differential pressure sensors is called actual flow The flow at the actual actual flow The flow at the actual condition of T and P existing at the flow condition of T and P existing at the flow measurement device.measurement device.

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What are the characteristics of actual flow?What are the characteristics of actual flow?

The flow value at any point in time, is influenced The flow value at any point in time, is influenced by a combination of all the values listed above as by a combination of all the values listed above as influences to T and P.influences to T and P.

The longer the duration of the sample period, the The longer the duration of the sample period, the greater the variability of differences in actual flow greater the variability of differences in actual flow conditions.conditions.

Sample volumes determined at the same sample Sample volumes determined at the same sample location at different time periods are not readily location at different time periods are not readily comparable due to differences in actual flow comparable due to differences in actual flow conditions that exist during the different sample conditions that exist during the different sample events.events.

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Sample volumes at different locations can Sample volumes at different locations can not be accurately compared due to the not be accurately compared due to the high probability of differences in actual high probability of differences in actual flow conditions.flow conditions.

Downstream calculations involving sample Downstream calculations involving sample volumes determined from actual flow volumes determined from actual flow (such as uCi/cc or Bq/m(such as uCi/cc or Bq/m33) are ) are contaminated with the accuracy contaminated with the accuracy uncertainties involved in the sample uncertainties involved in the sample volumes due to constantly varying actual volumes due to constantly varying actual flow conditions. Furthermore, these flow conditions. Furthermore, these downstream calculated values for different downstream calculated values for different sample events can’t really be compared sample events can’t really be compared accurately to each other either.accurately to each other either.

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What is the solution?What is the solution?

Correct actual conditions of flow or volume Correct actual conditions of flow or volume measurement devices in air sampling measurement devices in air sampling systems to a mutually agreed upon set of systems to a mutually agreed upon set of temperature and pressure conditions. This temperature and pressure conditions. This will permit accurate comparisons of flows, will permit accurate comparisons of flows, volumes or downstream calculated values volumes or downstream calculated values involving volumes on a common basis.involving volumes on a common basis.

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How do we implement the solution?How do we implement the solution?

Option 1Option 1

Install advanced technology instrumenta-tion Install advanced technology instrumenta-tion that frequently measures flow/volume and that frequently measures flow/volume and corrects both values to the industry mutually corrects both values to the industry mutually agreed upon T and P conditions at the instant agreed upon T and P conditions at the instant the flow is measured.the flow is measured.

Instruments exist that incrementally totalize Instruments exist that incrementally totalize corrected volumes as frequently as once per corrected volumes as frequently as once per second which gives a very accurate volume second which gives a very accurate volume totalization for each sample event.totalization for each sample event.

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These smart instruments are generally These smart instruments are generally equipped with RS232 communication equipped with RS232 communication ports that open the pathway for future ports that open the pathway for future real-time remote monitoring applications. real-time remote monitoring applications. Other functionality features usually Other functionality features usually include the following:include the following:

a)a) Automatic shut-off on time or volumeAutomatic shut-off on time or volumeb)b) Multiple display of on-board calculated Multiple display of on-board calculated

valuesvaluesc)c) Bright digital displayBright digital displayd)d) Data storage for future detailed Data storage for future detailed

analysis of periods during a discharge analysis of periods during a discharge eventevent

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Option 2Option 2

Upgrade traditional technology systems with Upgrade traditional technology systems with temperature and absolute pressure sensors temperature and absolute pressure sensors installed at the flow measuring device location installed at the flow measuring device location coupled with data logging devices to record data coupled with data logging devices to record data at a scientifically adequate frequency.at a scientifically adequate frequency.

Additionally, more frequent flow measurement Additionally, more frequent flow measurement observations must be made of the analog flow observations must be made of the analog flow device in order to improve the legal and scientific device in order to improve the legal and scientific credibility of the volume determinations. This can credibility of the volume determinations. This can be performed by more frequent human be performed by more frequent human observations, or by installing a photographic observations, or by installing a photographic system with a date and time stamp for purposes system with a date and time stamp for purposes of combining the observed flow with the of combining the observed flow with the corresponding absolute pressure and corresponding absolute pressure and temperature measurements occurring at the temperature measurements occurring at the same date and time.same date and time.

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NOTE:NOTE:

Manpower is required to review, interpret Manpower is required to review, interpret and input the collected data in a computer and input the collected data in a computer database to enable higher technology to database to enable higher technology to crunch the numbers and determine the crunch the numbers and determine the corrected volume values for each station.corrected volume values for each station.

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The Bottom LineThe Bottom Line

Comparison of the capital costs to upgrade Comparison of the capital costs to upgrade existing traditional air sampling systems existing traditional air sampling systems utilizing rotameters or analog volume utilizing rotameters or analog volume totalizers vs. installing currently available totalizers vs. installing currently available advance technology air sampling systems advance technology air sampling systems indicates that the advanced technology air indicates that the advanced technology air sampling systems are less expensive, or at sampling systems are less expensive, or at most, comparable in price to the hardware most, comparable in price to the hardware upgrades required for traditional analog upgrades required for traditional analog systems.systems.

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The Bottom Line (cont.)The Bottom Line (cont.)

Comparison of the operating and Comparison of the operating and maintenance costs required by upgraded maintenance costs required by upgraded traditional systems vs. advance traditional systems vs. advance technology systems indicates that the technology systems indicates that the upgrades of traditional technology upgrades of traditional technology systems will result in continued intensive systems will result in continued intensive manpower for data evaluation and data manpower for data evaluation and data input for multiple REMP stations and may input for multiple REMP stations and may require the following additional manpower require the following additional manpower support:support:

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The Bottom Line (cont.)The Bottom Line (cont.)

IT department assistance may be needed IT department assistance may be needed for set up of partial system automation.for set up of partial system automation.

Maintenance and periodic calibration of Maintenance and periodic calibration of the additional pressure and temperature the additional pressure and temperature sensors added to the analog system.sensors added to the analog system.

Maintenance and inspection of data Maintenance and inspection of data logging instrument added to the analog logging instrument added to the analog system.system.

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ConclusionConclusion

A detailed cost analysis of the two A detailed cost analysis of the two available options, i.e. upgrading available options, i.e. upgrading existing systems or installing new existing systems or installing new advanced technology which credibly advanced technology which credibly meets the scientific requirements meets the scientific requirements should to be made by each should to be made by each organization to ensure consistency in organization to ensure consistency in the reporting of data to regulatory the reporting of data to regulatory agencies.agencies.