Application Guide: Harness The Power Of Portable CO

AirTest PT9250 & CO2 Application Guide 1 of 12

Application Guide:Harness The Power Of Portable CO2 Measurement

With The PT9250 Hand Held Monitor

Measure Ventilation – Estimate Energy Savings – Building Troubleshooting

Overview

This application guide is much more than a product manual. It is also targeted at making youknowledgeable as to how the measurement of carbon dioxide (CO2) can help you understandbuildings better in order to save energy and solve problems. Its one thing to measure CO2,however this book provides a study guide that will quickly give you the critical knowledge and acompetitive advantage in using CO2 as a powerful, and profitable measurement parameter ofventilation and building performance.

Table Of Contents

1. Introduction ................................................................................................................... 2

2. Quick Start Basics ........................................................................................................ 2

3. Spot Check Ventilation Rates ...................................................................................... 3

4. Using The UIP Software Interface With The PT9250 ................................................. 5

5. Data Logging With The PT9250 .................................................................................. 7

6. Calibration ..................................................................................................................... 7

7. Making Most Of The TR9250 – Some Application Examples .................................... 8


1. Introduction To The PT9250Hand Held CO2 Sensor

Overview

The PT9250 is a versatile tool that can be usedby building owners and contractors to betterunderstand the operation of buildings and assesstheir potential for energy savings using a CO2

based ventilation control strategy. It can also bea useful tool for checking the operation of existingventilation systems and the degree to whichventilation is being delivered to individual zonesto meet occupant needs.

What’s Inside

Inside the TR9250 is a temperature sensor and aunique infrared sensor that optically detects andmeasures the concentration of carbon dioxide inthe air. Its operation is based on the sameprincipal used by infrared spectrometers typicallyused in medical and scientific applications. TheLCD display on this versatile tool will provide adirect indication of both CO2 and temperatureconcentrations. The hand held unit alsoincorporates a powerful “smart” microprocessorused to perform the complex task of analyzingthe CO2 sample.

The microprocessor allows the sensor to data logconcentrations over time, to perform a self-calibration, and to calculate and displaycfm/person ventilation rates (which are directlyrelated to CO2 concentrations). Themicroprocessor also allows the TR9250 to beconnected to a PC where you can customizeinformation provided on the display, set datalogging preferences (like sampling time interval)and view the results of a current or pastmeasurement that has been data logged. Youcan also download the recorded CO2 and

temperature data to a program like Windows®Excel® for more detailed graphing and chartingoptions.

2. Quick Start Basics

Turning On The Hand Held Sensor

Plug the charger provided with the sensor intothe bottom of the TR9250 and allow it to chargefor at least 1.5 hours.

To power up the TR9250 you will have to holdthe power button down for approximately 10seconds while the sensor performs a self-diagnostic check.

Once you press the power button you will see88.88 displayed on the upper display and –88.88on the lower display for approximately 4 secondsand then the screen will go blank forapproximately 2 seconds. Continue holding thebutton until you see the word “test” on the lowerdisplay. At this point, the TR9250 will continueit’s self-diagnosis until readings on the upperdisplay reach 5000 ppm and all the LED’s havebeen illuminated. Once this sequence iscompleted the display will immediately begin todisplay current readings. If the display goes blankwhen you release the button, the internal batterywill need to be charged before you can use thehand held sensor.

Turning Off The Hand Held Sensor

Press and hold the power button for 10 seconds.During that time you will see the display cyclethrough two modes. One mode is “read” and theother mode is “cal b”. These functions will bedescribed later in this manual and are brieflydescribed below. When the display goes blankyou can remove your finger from the powerbutton.

“read” This mode is used to change the outsideconcentration used for the calculation ofventilation rate to an actual outside measurementrather than the assumed 400 ppm. Read modewill be activated whenever the power button ispressed during operation. The use of this buttonis explained further in the next section.

“cal b” This mode Is used for automaticbackground calibration. When left in this modeovernight in an unoccupied area, the unit willcalibrate itself so that the lowest level observedduring the period will be 400 ppm (typical outsidelevels).


The Display

When the sensor is powered up for the first timeCO2 concentrations will appear on the upperscreen. The lower screen will alternate betweena display of the temperature in ºF or ºC, and thecubic feet per minute (cfm) per person of outsideair delivered to the space. CO2 levels can beused to determine fresh air ventilation rates in thespace.

Battery power level is also displayed in themiddle left portion of the display. Three smallbars indicate a full charge.

The LED’s underneath the display provide aquick check of the concentration.

By using the provided PC interface software andcable you have the ability to customize howinformation is to be displayed by the digitaldisplay and LED’s.

Upper Display: CO2 Reading

Carbon dioxide concentrations are displayed inparts per million (ppm). The PT 9250 will displayconcentrations up to 9,999 ppm . Typical outsidelevels are 380 to 450 ppm. Typical inside levelscan vary from 400 ppm to as high as 3,000 ppm.

Lower Display: Temperature & VentilationRate

The lower display alternates between displayingtemperature and providing a calculated value ofthe cfm/person ventilation rate in the space. Byusing the pC program provided with the sensoryou can change both the location and the waythis information is displayed on the screen.

3. Spot Check Ventilation Rates

Background

The PT9250 not only measures CO2 andTemperature but it also calculates the outside airventilation rate in cfm per person based on thedifference between inside and outside CO2

levels.

So how can we determine the cfm per personventilation rate from CO2 levels? This calculationis based on a widely recognized engineeringprincipal. People will produce almost identicalamounts of CO2 when at the same level ofexertion or activity (e.g. office work). So anindoor CO2 measurement indicates how muchoutside air (at low CO2 concentrations) is beingintroduced to dilute or remove the CO2 beingproduced by people in the space. Regardless ofwhether there is one or a hundred people in thespace, the CO2 level will reflect how muchoutside air is being delivered for each person.This is because the calculation of ventilation rateis based on theknown amount ofCO2 produced byeach person and theknown quantity ofoutside air that isrequired to diluteconcentrations to aparticular level ofCO2. The adjacentchart shows thisrelationship betweenCO2 and ventilationrate. This wouldapply for a typicaloffice space andoutside air CO2

concentrations of400 ppm. In effect,this chart is built intothe PT9250.


When a space is under-ventilated, CO2 levels willbe very high (e.g. over 1500 ppm). Conversely,concentration of CO2 close to outside levels(typically around 400 to 450 ppm) indicates veryhigh ventilation, or perhaps over-ventilation.Levels of approximately 1100 ppm will indicate aventilation rate of 15 cfm per person, which istypically required by most ventilation codes.

Spot Measurement Application Tips

Note CO2 Is Not Harmful In BuildingEnvironments: It is important to note that at thelevels we normally measure in buildings CO2

itself is not harmful. In an occupational healthenvironment, exposure to CO2 levels up to 5,000ppm over 8 hours, is considered acceptable byOSHA. In buildings the CO2 concentration ismore an indication of ventilation. If a space feelsuncomfortable, stuffy, or stale and the CO2 levelsare high, it is not really the CO2 having the effect.The high CO2 levels are telling you thatventilation is insufficient, and you are likelyreacting to all the things that build up when thereis insufficient fresh air ventilation.

CO2 Levels Must Be Stable For An AccurateSpot Ventilation Measurement: A truecorrelation between CO2 levels and ventilationrate can only be made by a spot measurementwhen concentrations appear to have stabilized ina space. If levels are continuing to change it maybe an inappropriate time to measure ventilation.For low-density office spaces and retailapplications it is best to take measurements 2-3hours after occupancy in the space has begun(late morning or afternoon). In higher densityapplications like school classrooms, theaters andmeeting rooms measurements can be made 15to 20 minutes after the start of occupancy.

Avoid Measurements When BuildingEconomizer Is On: Be aware that ventilationrates will appear very high if the building isoperating in economizer mode (using outside airfor free cooling). It is best to ensure theeconomizer is temporarily disabled or notoperating when performing spot CO2

measurements.

Measurement Location Tips: Carbon dioxidewill readily disperse and equalize within a space.Therefore measurements can be taken just aboutanywhere or at any height. However one shouldkeep away from open doors or windows as wellas the area directly surrounding a discharge grill.

Blowing Into The Sensor: Pure exhaled breathcontains 40,000 ppm of CO2 that will readilydisperse in air. Try to avoid breathing directly onthe sensor when taking a measurement. If youdo breath into the sensor, it will not hurt the

sensor but it may take a few minutes for thesensor to readjust to normal background levels.Since the PT9250 measures up to 10,000 ppmyou may also temporarily send the display offscale.

Estimating The Total Ventilation Rate To ASpace: If you actually count the number ofpeople in the space when you take themeasurement, you can multiply this numbertimes the cfm-per-person ventilation rate todetermine the total amount of outside air beingdelivered to the space.

Using Actual Outside CO2 Levels To CalculateVentilation Rate: In some cases you may findthat the outside levels are slightly higher or lowerthan the 400 ppm level assumed by the PT9250.(A difference of about 50 ppm will result in anerror of about 0.5 cfm/person in the calculation.)For a more accurate calculation of ventilationrates you can reset the outside level used in thePT9250 calculation based on actual conditions byexposing the sensor to outside air. Once levelshave stabilized, press the power button for abouta second. The word “read” should flash on thescreen. Now the outside concentration you justmeasured will be used for the calculation ofventilation rate until you power off the sensor.Once powered up again the sensor will assumean outside level of 400 ppm until you power theunit off.

Battery Life: Battery life of the sensor is 8 to 14hours. It is a good idea to charge the sensor upevery night. Regular charging will not hurt thebattery inside the PT9250.

Car Charging: If desired you can also purchasean automotive phone charger to keep the sensorpowered up between calls. Select a charger witha 3.5 mm (od) connector that provides an outputvoltage of 6 VDC with a current of 500 mA. Theplug-in is configured for positive in the center andnegative on the outer portion of the plug. CallAirTest for further information.

Battery Charge Indicator: The current batterycharge level is indicated by the small graphicsymbol on the left side of the line dividing theupper and lower display. Three bars indicate afull charge.

Calibration: There are a number of easy waysto calibrate the sensor. These are discussed insection 6 of this document.


4. Using The UIP SoftwareInterface To The PT9250

Overview

The PC software provided with the PT9250allows you to customize the appearance andoperation of the hand held monitor. It also allowsyou to view graphed CO2 concentrations thathave been recorded using the on-board datalogger, and lets you export this information toanother program such as Excel® where you cancustomize the appearance of the report. You canalso calibrate the sensor using this program anda known source of CO2.

Using The UIP Program

To get started, install the UIP (User InterfaceProgram) program into your PC. Once theprogram is installed it is a good idea to restartyour machine before using the program.

Prior to starting the program on your PC, turn thePT9250 on and plug it into your PC using thecable provided. (Note: If your computer does nothave a RS232 Serial Port, most computerperipheral suppliers should be able to provide aconverter attachment that will allow the cableprovided to interface with a USB port.)

When you start the program it will immediatelysearch for the sensor plugged into your computerand start to download information in the sensor.This may take a few minutes. If you are havingproblems with connecting to the sensor visit thetroubleshooting section of this document.

General Tab

Once the program has loaded data from thesensor, the first screen you will see providessome general information about the sensor.Other functions of the software can be accessedvia the tabs on the program interface, and via themenu options at the top of the program window.The sections below will provide more informationon each of the tab selections available in the UIP.

LED Tab

This part of the program allows you to adjust theCO2 concentrations that will illuminate thedifferent LED’s (light emitting diode) below thesensor display. Once you make a change pressthe “send to sensor” button at the bottom of thescreen to transfer the new setting to the PT9250.The new setting will be applied the next time thesensor is powered on. The new settings will beapplied within a few seconds.


Display Tab

Here you can change a number of characteristicsof the LCD display on the PT9250. By clicking inthe box you will see a menu of the displaychoices that are available. You can also chooseto have the hand held display English/US units ormetric units (SI). Ventilation rate is displayedeither in cubic feet per minute (cfm) or liters persecond( l/s). Once you make a change press the“send to sensor” button at the bottom of thescreen to transfer the new setting to the PT9250.The new setting will be applied the next time thesensor is powered on. The new settings will beapplied within a few seconds.

Logger Tab

This section discusses the data loggingadjustments and options available using the PCinterface. Further guidance on data logging andits use is also provided in the next chapter. Thispart of the program allows you to view loggeddata, set the logger interval, and create a timestamped text file that can easily be read byprograms like Excel®. The sensor can log up to895 points for both temperature and CO2. Theselections available on this tab are describedfurther below.

Sample Interval: The sampling rate of thesensor can be adjusted from every 6 seconds toevery 4 hours using the selection menu. Once anew setting is selected it must be sent to thesensor and the sensor will have to be turned offthen back on for the new setting to take effectNote: the battery charger should also bedisconnected from the PT9250.

Graphed Results: Each time the sensor isturned on a new logger file is created and can beidentified at the top of the graphical display. Byclicking on the file you can view the set of datafor that file. The oldest files will have the lowestnumber. Once the data logger has reached itsmaximum capacity it will begin logging over theoldest data. The graph function is very basic andautomatically adjusts the scale of the graphbased on the range of measurements observed.For more options in graphing, the logged datacan be exported to a text file and graphed in aprogram like Excel®.

Update Button: When this button pressed it willupload the latest data from the sensor anddisplay it on the graph. This is useful if youwould like to show readings on a real time basiswith an operating sensor connected to the PC.This can be useful for customer presentations ortraining.

Save As Text Button: This option will export thedata shown on the graphical display as a text filethat can easily be read by programs like Excel®.When you export the file you will be asked to timestamp the data (see below).

Time Stamping Exported Data: While thePT9250 can record readings at a selectedinterval it does not have a real time clock.However it is possible to have the recorded datadate and time stamped when it is exported.When you export the data you will be asked forthe date when the sensor was last turned off aswell as the time the sensor was turned off.Based on this information all the data will beassigned a date and time value. This has theeffect of adding two columns of information to thedata, one for the date and one for the time.


5. Data Logging With The PT9250

Overview

The ability to record CO2 and temperature dataover time and graph it is a powerful analytical toolthat can help you better understand how abuilding is operated.

When assessing a building’s ventilation ratesoften the first step is to do a spot measurementas described in chapter 3. If unusually high orlow levels are detected, the next logical step is toverify the reading by measuring concentrationsover time and graphing the results.

When assessing ventilation rates, the graphedpeak CO2 concentration becomes readilyapparent for estimating ventilation rates. And ifconcentrations are measured over a number ofdays, consistency patterns of occupancy andventilation can be verified.

Application Tips For Data Logging

Note End Of Logging Period: In order toproperly time stamp data, make note of the timeyou turn off the sensor after the logging session.You will be asked for this data when exportingthe data to a text file.

Managing Data: If possible, it is recommendedthat you download logged data to a text file soonafter completing a measurement. Once the datahas been exported, reset the data logger to erasethe memory. This will make it much easier tomanage files on the data logger and will ensurethat old data will not be erased if all 895 datapoints are used.

Setting Logging Interval To DesiredMeasurement Time Period: To ensure you donot exceed the database memory (895 points)

and write over previously recorded data, asampling interval should be selected that allowsfor adequate space in the data logger. Someguidelines on maximum sampling periods areprovided below.

• 1 Day – 2 minute sampling• 2 Day – 4 minute sampling• 5 Day – 10 minute sampling• 7 Day – 15 minute sampling

Battery Life & Logging: The battery life of thePT9250 is 10 to 16 hours. As a rule you shouldhave the PT9250 plugged into it’s chargerwhenever you are logging concentrations forextended periods of time.

Graphing Text Data In Excel: It is very easy tograph the exported text files in Excel.

1. Open the Excel® program.2. Under ‘file’, select open and locate the

exported text file.3. Highlight the cells containing the time

and reading data.4. Select the chart wizard and it will guide

you through the creation of a graph thatcan easily be changed, labeled andinserted into other documents,

6. Calibration

Overview

There are two methods that can be used tocalibrate the sensor.

Background Calibration

Background calibration is an easy way tocalibrate the PT9250 overnight without the needfor special calibration gases. Using this process,the sensor is left overnight in an area that will beunoccupied for a number of hours, and as aresult the space will likely drop to backgroundoutside levels (always around 400 ppm).

When in background calibration mode the sensorwill record the lowest CO2 level measuredovernight and calibrate this point to 400 ppm.

To activate background calibration:

1. Turn the sensor on and plug it into itscharger.

2. Hold the power button down until yousee “cal b” on the display of the PT9250and then release the button.


3. Leave the sensor in place for at least 5hours.

4. When the background calibration periodis complete hold the power button downto power off the hand held unit.

5. Once powered on (restarted), thesensor is ready to use.

The maximum correction the sensor will make ina 5 hour period is 130 ppm, If you suspect thesensor is significantly out of calibration you mayhave to perform a number of backgroundcalibrations.

UIP Based Calibration

By using the capabilities of the UIP softwareprogram you can quickly (approximately 5minutes) calibrate the sensor to a known sourceof CO2. Using the UIP program you can performa quick background calibration, a zero calibrationand a span calibration. You can also calibratethe temperature sensor if desired. The processfor each type of CO2 calibration is very similar.

1. Expose the sensor to a knownconcentration of gas either usingambient concentrations or by flowingcalibration gas through the calibrationport on the bottom of the sensor.

2. Go to the “Sensor” heading on theprogram menu bar and select‘calibration’.

3. Choose the type of calibration youwould like to perform: Background,Zero Cal, Span Cal or Temperature Cal.

4. A series of menus will lead you throughthe calibration process for the type ofcalibration you wish to perform.

Application Tips

Calibration Gas: Calibration gases, tubing andregulators are available from AirTest.

Zero & Span Calibration: Typically, drift of thePT9250 is on the zero adjustment of the sensor.The sensor generally should not require spanadjustment. If performing both types ofcalibration the zero calibration should beperformed first.

7. Making Most Of The TR9250 –Some Application Examples

Overview:

This section provides a brief description of anumber of real world applications for the PT9250hand held.

Estimating Ventilation Rate From A DataLogged Sample:

Data logged over time samples have a greatadvantage over a spot measurement.

• You can get a clear profile of ventilationin the space over the course of a day,week or more.

• It is possible to determine the peakvalue that will determine what thecfm/person ventilation rate is.

• You can determine if occupancy anduse patterns are consistent over anextended period of time.

• The data logged sample provides anexcellent tool for comparing before andafter ventilation performance, forexample, after retrofit work has beenundertaken.

The chart below shows data logged temperatureand CO2 concentrations in an office space thatwere recorded on the PT9250, downloaded to atext file, and then graphed using the chartingcapabilities in Excel®. The charting capabilities ofthis and other spreadsheet programs offertremendous versatility in customizing theappearance of your reports.

To use data logged information to estimateventilation rate, find the areas on the graphwhere CO2 levels appear to level off late in theday or afternoon. Note how concentrationsconsistently level off at 650 ppm to 675 ppm forhours at a time. This indicates that the CO2

production by occupants has reached equilibriumwith the outside ventilation air delivered to the


space. Also note that the lowest level measuredis 400 ppm (measured over the weekend). Giventhe stability of measurements at this level we canassume that the space is unoccupied and thelevels measured are typical of outside levels.

There are two ways to measure ventilation rate.If outside levels are at or near 400 ppm and theactivity level is close to office type activity thenthe CO2/cfm-per-person conversion chart inSection 3 of this guide can be used.

You can also calculate the cfm-per-person in thespace using the following formula:

Vop = NCs – Co

Where:

Vop = outdoor ventilation rate in cfm-per-person

Cs = CO2 concentration in the spaceCo = outside CO2 concentrationN = CO2 production of individuals based

on age and activity level.

For most calculations the value for N is based onadults undertaking office type activity (highlightedin yellow in the chart below). Production Of CO2at the same activity level varies less than 10%over ages ranging from 6 to 65+ years old butguideline values are provided in the table forspecific age groups and different activity levels.

As an example of how to use the formula above,we will calculate the ventilation rate resulting froma peak level of 675 ppm CO2 when outsideconcentrations are 400 ppm. The assumption isthat the space has adults engaged in office-typeactivity. It is important to note that in theequation, the CO2 concentrations are expressedin the decimal equivalent of parts per million.

Vop = 0.01060.000675 – 0.000400

= 3 8.5 cfm/person

If the number of people in the space is knownwhen the measurement is taken the total outsideair ventilation rate to the space can be calculatedby multiplying the occupancy times the number ofpeople in the space. This value in most buildingswill represent the fixed ventilation rate provided to

the space and can be used as part of an energyanalysis comparing the existing fixed ventilationrate to a control strategy based on CO2

ventilation control.

Accessing Buildings For Energy SavingsPotential Based On CO2 Control:

AirTest has just release an easy to use softwaretool that allows you to compare the cost ofventilation at a fixed ventilation rate (asmeasured with CO2), with a CO2 basedventilation control strategy that modulatesventilation rates based on occupancy in thespace. The program utilizes local climatic andenergy data to estimate the cost to preconditionoutside air.

Contact AirTest at 888-855-8880 or [email protected] to find out how toget a coy of this software.

By using this predictive tool you can get anestimate of energy savings and as a resultcalculate payback and return-on-investmentresulting from a CO2 upgrade on a particularbuilding. It is ideal to use as part of a proposal toa building owner.

AgeSleeping / Resting

Sitting / Standing (Office)

Light Work (Walking)

Heavy Work

(Exercise)1 - 5 years 0.0050 0.0060 0.0127 0.02016 - 11 years 0.0094 0.0112 0.0236 0.037512 - 65 years 0.0088 0.0106 0.0223 0.035365 + years 0.0079 0.0094 0.0198 0.0314

CO2 Production For Various Ages & Activity Levels (cfm)


Calibrate You And Your Customers:

The AirTest PT 9250 is an ideal tool that can beused to calibrate you and your customers to CO2

and ventilation. Recently a contractor wasloaned a PT9250 with the cfm/person displayfunction. Within two weeks the building ownerwalked many of his buildings, resolved threeindoor air quality complaints and decided toretrofit two buildings that were undergoingrenovation, with CO2 based ventilation control.

A written application guide like this one can bevery useful in understanding how to use andinterpret ventilation measurements with CO2.However, hands on experience, and seeing andsensing what various ventilation rates andcorresponding CO2 concentrations are, can takethe place of a multi-hour training course.

Here are a few suggestions on how you cancalibrate yourself to CO2 and ventilation.

• Experiment with how blowing in the vicinityof the sensor will affect its reading. Howlong does it take to recover?

• Find out what outside concentrations aretypically in your area. Check it out on a fewdifferent days and locations. Does it matter ifyou are close to a highway or majorintersection, near a lake, in the suburbs, or inthe middle of the city? Are outsideconcentrations different above street level?

• Carry the PT9250 around with you for a day.Measure at home, at the office, in meetings,in your car or in an airplane. Note the CO2

and ventilation rate and see if you can senseareas that have more fresh air than others. Ifyou note the time you are in various areas,you can download the data loggedinformation for the day and see what the CO2

levels where throughout the day.

• When entering a space note how CO2 levelsrise and eventually stabilize in a space.

• Attach the PT9250 to your desk PC usingthe software provided, and periodically pressupdate to view the history of CO2 in thespace. You can also use this as a tool fortraining others.

• Hold the PT9250 near the exhaust of a caror truck. How much CO2 is produced?

• Open a couple of carbonated drinks in aclosed room and see what happens.

• If CO2 levels are high in the space, see howquickly levels change when you open awindow or a door.

Dealing With IAQ Complaints:

Many symptoms related to indoor air quality(IAQ) complaints can also be associated withother physical ailments, stress, or emotionalissues related to the individual. If you areinvolved in investigating a suspect IAQ problemyou can use the PT9250 to determine ifventilation is a factor in the complaint or concern.Most buildings by code must be provided with 15to 20 cfm/person of outside air to ensureadequate air quality. You can use the PT9250 tobenchmark your building to ensure you meetthese or other code required levels.

One school maintenance person keeps a numberof PT9250 sensors on hand to loan to teachers ifthey have a concern with the ventilation rate intheir classroom. If by measuring over a few daysthe teacher finds reduced ventilation rates, themaintenance people can adjust air delivery to thespace. More often than not, the maintenanceperson has found the ventilation is sufficient andthat use of the PT9250 convinces the teacherthat lack of fresh air is not the problem.

Baseline Monitoring As A Business:

Many building owners are now looking to thirdparties to inspect and monitor their buildings toensure they are providing a good environment fortheir tenants.

A number of contracting and consulting firms areusing the PT9250 to benchmark various areas ofa building several times per year. The data-logging feature is ideal for providing a clearlydocumented report on building operating statusas it relates to ventilation.

This process can provide peace of mind tobuilding owners and occupants and can also beused to quickly identify potential problems with airintakes or the mechanical systems within abuilding.

I Smell Combustion Fumes:

While people produce CO2, it also is one of themajor components of combustion fumes (8 to11% by volume). As a point of comparison, amedium sized, residential high-efficiency furnaceproduces as much CO2 as about 160 people. IfCO2 levels in a space seem excessively high(e.g. over 4,000 ppm) unwanted combustionfumes may be present. Here are some examplesof how elevated CO2 concentrations can be usedas a diagnostic for combustion fumes:

• Check areas around building air intakes tosee if idling vehicles are venting into thebuilding (especially an issue with schools).


• Check air intakes on rooftops to ensure flueexhausts from kitchen or furnace vents arenot being drawn into air intakes.

• Use CO2 to check for spillage of combustionflues at water heaters or furnaces.

• Check the effectiveness of commercialventilation systems in removing combustion-related CO2.

Odor Control In Garages:

In parking garages, bus garage and fire hallscarbon monoxide (CO) or nitrogen dioxide (NO2)is often used to control ventilation. However dueto the effectiveness of catalytic converters muchless CO is now produced by cars and trucks. Insome cases combustion fumes may build up tothe point where there is no CO or NO2 danger,however odors associated with combustion arenoticeable and unpleasant. This is also acommon problem with diesel vehicles thatproduce little CO but numerous other particulatesand smelly contaminants.

In many cases, odor perception of combustionfumes will correspond to a CO2 level. You canuse the PT9250 to determine the level of odorperception in a facility. A permanently installedCO2 monitor in the space can then use thisthreshold CO2 level to activate fans to controlodors related to vehicle combustion.

Building Commissioning:

Building Commissioning is becoming commonpractice in many areas of the country. ThePT9250 has a number of applications to buildingcommissioning:

• By calibrating the PT9250 to outside air or aknown source, calibration of CO2 sensorsfor ventilation control can be quicklychecked.

• If the space is occupied during thecommissioning period, ventilation levels ineach zone can be checked and comparedwith design requirements.

Building Trouble Shooting:

Unusually high or low CO2 levels in an occupiedspace may indicate the malfunctioning ofmechanical equipment serving the space. Forexample:• A difference in measurements of CO2

between a space and a ceiling return plenummay reflect excessive supply air ductleakage into the plenum.

• Calculation of percentage of outside air in anair handler can be performed using aprocess identical to the differentialtemperature method, except substituting CO2

levels measured.

• Determine if ventilation systems aredelivering adequate fresh air to a particularzone based on its current occupancy.

• Improperly adjusted, or broken fresh airdampers can often be identified if unusuallyhigh or low levels occur within a spaceduring occupied periods.

• Periodic day-long data-logging of a majoroccupied space or floor can give a goodindication of occupancy hours. Thisinformation can be used to reset timerschedules on equipment.

Planning For A CO2 Retrofit:

Ok, so you have measured CO2 in the space andused the AirTest Energy Analysis Program toidentify a significant potential for energy savings.This section briefly describes what typically isinvolved in a CO2 retrofit.

Location Of Sensors: Sensors should belocated in each major occupied space. Ductmounting of sensors is not recommended for thesame reasons that temperature control does notuse in-duct sensing.

C o n t r o l A l g o r i t h m : Typically CO2

concentrations are used to proportionatelymodulate fresh air to the space. There are threecomponents to a control strategy:

1) Minimum Ventilation Rate: This is a lowlevel of ventilation provided to the spaceduring all occupied hours. Since CO2 isprimarily related to people, this minimum rateprovides ventilation for non-occupant relatedcontaminants such as off gassing fromfurniture and carpets. As a rule of thumb thisrate should be 30% of the Design ventilationrate (Design rate = Design Occupancy XTarget cfm/person rate).

2) Start Of Control: Modulation of the airdelivery to the space should begin 100 ppmto 150 ppm above outside concentrations(e.g. 500-550 ppm).

3) Upper Control Point: The algorithm shouldbe designed so that the Design VentilationRate (defined in 1) above), is provided whenthe CO2 concentration equal to the targetcfm/person ventilation rate is reached. For


15 cfm/person this is approximately 1100ppm and for 20 cfm/person the level is 930ppm.

Multiple Zones Served By One Air Handler:This could occur when a number of spaces areserved by a single rooftop or where fresh air to afloor is controlled separately for each floor. Inthis case control modulation of fresh air shouldbe based on the highest level measured in all ofthe spaces served by the air handler.

AirTest also has products that will allow you tocontrol a VAV box based on CO2 andtemperature.

Other Equipment: In a typical CO2 retrofit youmay also want to include use of Variable SpeedDrives to modulate air delivery. Ideally thesystem should be integrated with the existingbuilding control system. Most major controlmanufacturers have CO2 control routinesavailable thatwill run with their systems.

Further Application Reference: AirTest hasnumerous articles and application notes availableon CO2 control systems and their installation. Todownload a one-page resource guide to articleson CO2 type this link into your browser or click onthe link if this is viewed on your computer.

http://www.airtest.ca/docs/article/co2reference.pdf

© 2003 AirTest Technologies Inc.

For more information On AirTest Products:

Call: 888-855-8880Visit: http://www.AirTestTechnologies.comEmail: [email protected]

Application Guide: Harness The Power Of Portable CO

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