# 1 Comparison of Analog vs. Advance Technology Air Sampling System Designs To Facilitate Correction of Measured or Calculated Volumes to a Set of Reference.

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1 Comparison of Analog vs. Advance Technology Air Sampling System Designs To Facilitate Correction of Measured or Calculated Volumes to a Set of Reference Temperature and Pressure Conditions By Frank M. Gavila

2 The basis for correcting air sampling volumes to a reference temperature The basis for correcting air sampling volumes to a reference temperature and pressure Typical volume measurement systems and/or calculational methods of determining volumes Typical volume measurement systems and/or calculational methods of determining volumes Validity of sample volumes determined Validity of sample volumes determined by the different types of flow/volume measurement systems The bottom line The bottom line

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

4 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.

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

6 Examples of reference standards are as follows: Classical STP:Standard Temperature and Pressure (0 o C, 1 ATM) SATP:Standard Ambient Temperature and Pressure (25 o C, 1 ATM) NTP:Normal Temperature and Pressure (20 o C, 1 ATM) MNTP:Modified Normal Temperature and Pressure (70 o F, 1 ATM)

7 Typical Volume Measurement Systems and/or Calculational Methods of Determining Volumes Volume measurements are of two forms: Measurement of average flowrate Measurement of average flowrate multiplied by elapsed time multiplied by elapsed time Direct display of the measured Direct display of the measured volume volume

8 Measurement of average flow rate multiplied by elapsed sample time Examples Rotameters Rotameters Analog differential pressure meters Analog differential pressure meters Digital differential pressure meters Digital differential pressure meters Mass flow meters Mass flow meters In the above the average flow is determined by a simple method such as Average Flow = Beginning Flow + Ending Flow 2

9 The more flow measurements that are made during 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.

10 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 Determination Volume = Avg. Flow x Sample Duration Volume = Avg. Flow x Sample Duration Where sample duration is determined by measuring the difference between the time the sample was started and the time the sample was terminated (the pollutant collection period).

11 Measuring instruments utilized for this determination of elapsed time can vary from a wristwatch observation to an accurate elapsed time meter accurate to the nearest 0.01 seconds. The accuracy of the volume determination is a function of the accuracy of the flow measurement and the sample duration measurement.

12 b.Direct display of the measured volume Examples: i. Dry gas test meters ii. Advance technology instruments that internally compute total sample volume including mass flow meters and microprocessor controlled electronic instruments. The user observes a dial or digital display indicating the accumulated sample volume. Some devices permit zeroing the accumulated volume to zero prior to beginning a new sample. Other instruments, such as dry gas test meters, require the technician to read the dial or digital meter’s numeric values prior to beginning the sample and immediately after the sample is terminated. The difference between beginning and ending values is the sample volume.

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

14 What factors influence the absolute pressure and temperature conditions at the flow or volume measurement device? Absolute Pressure a) Elevation of sampling site b) Variations in local barometric pressure conditions during the sample period c) Pressure drop across the filter(s) utilized in the sampling system d) Pressure drop caused by the air sampling system flow path circuitry e) The pressure drop due to the presence of dust loading

15 Temperature a) Seasonal temperature variation of sampling site b) Daily variations in temperature c) Recirculation of pump exhaust d) Local artificial temperature influences of sample site location Flow measured by rotameters and analog differential pressure sensors is called actual flow The flow at the actual condition of T and P existing at the flow measurement device.

16 What are the characteristics of actual flow? The flow value at any point in time, is influenced by a combination of all the values listed above as influences to T and P. The longer the duration of the sample period, the greater the variability of differences in actual flow conditions. Sample volumes determined at the same sample location at different time periods are not readily comparable due to differences in actual flow conditions that exist during the different sample events.

17 Sample volumes at different locations can not be accurately compared due to the high probability of differences in actual flow conditions. Downstream calculations involving sample volumes determined from actual flow (such as uCi/cc or Bq/m 3 ) are contaminated with the accuracy uncertainties involved in the sample volumes due to constantly varying actual flow conditions. Furthermore, these downstream calculated values for different sample events can’t really be compared accurately to each other either.

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

19 How do we implement the solution? Option 1 Install advanced technology instrumenta- tion that frequently measures flow/volume and corrects both values to the industry mutually agreed upon T and P conditions at the instant the flow is measured. Instruments exist that incrementally totalize corrected volumes as frequently as once per second which gives a very accurate volume totalization for each sample event.

20 These smart instruments are generally equipped with RS232 communication ports that open the pathway for future real-time remote monitoring applications. Other functionality features usually include the following: a)Automatic shut-off on time or volume b)Multiple display of on-board calculated values c)Bright digital display d)Data storage for future detailed analysis of periods during a discharge event

21 Option 2 Upgrade traditional technology systems with temperature and absolute pressure sensors installed at the flow measuring device location coupled with data logging devices to record data at a scientifically adequate frequency. Additionally, more frequent flow measurement observations must be made of the analog flow device in order to improve the legal and scientific credibility of the volume determinations. This can be performed by more frequent human observations, or by installing a photographic system with a date and time stamp for purposes of combining the observed flow with the corresponding absolute pressure and temperature measurements occurring at the same date and time.

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

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

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

25 The Bottom Line (cont.) IT department assistance may be needed for set up of partial system automation. IT department assistance may be needed for set up of partial system automation. Maintenance and periodic calibration of the additional pressure and temperature sensors added to the analog system. Maintenance and periodic calibration of the additional pressure and temperature sensors added to the analog system. Maintenance and inspection of data logging instrument added to the analog system. Maintenance and inspection of data logging instrument added to the analog system.

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

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