my first paper

AARJMD VOLUME 1 ISSUE 32 (APRIL 2015) ISSN : 2319 - 2801

Asian Academic Research Journal of Multidisciplinary

www.asianacademicresearch.org

108

A Peer Reviewed International Journal of Asian

Academic Research Associates

AARJMD

ASIAN ACADEMIC RESEARCH

JOURNAL OF MULTIDISCIPLINARY

EVALUATION OF CO2 LEVEL AS A FUNCTION OF WINDOW AREA AND TOTAL

ROOM VOLUME RATIO FOR OFFICE BUILDINGS IN JOS, NIGERIA.

JIMOH, A.O 1; OGUNRAYEWA, B.O.

2

1Dept. of Architecture University of Jos,Jos, Nigeria

2Dept. of Architecture University of Jos,Jos, Nigeria

Abstract

The subjective data for this study was obtained from questionnaires while the objective data was

obtained from measurement instruments. The subjective measurements shows a 45% votes of

respondents that found the indoor air flow just right as outdoor air flow requirements are met.

This was in consonance with objective measurements, which show interior Co2 level above

outdoor level but way below recommended maximum for indoors of offices. The Co2

levels

decreases as the day proceeds. This seems to be connected with increases in outdoor air velocity

as the day proceeds. Also, a linear relationship between the ratio of Operable Window Area to

Total Office Volume and Co2 levels was established. The lower the Operable Window Area to

total Office Volume Ratio, the higher the Co2 levels. Hence, by simple linear regression analysis,

it concluded that the ratio of operable window area to total room volume of 0.0229 would be

required for an acceptable indoor CO2 level of 509 ppm in East-Facing, naturally ventilated

Office Buildings in Jos, Nigeria. The offices under study show an average ratio of 0.0023.

Keywords: Co2 Level, Indoor Airflow, Natural Ventilation, Office Buildings.




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1.0 INTRODUCTION

Carbon dioxide is a natural component of air and it is a colorless, odorless gas. It is

produced naturally and through human activities such as people exhaling Co2, burning gasoline,

coal, oil, and wood. The amount of Co2 in a given air sample is given in parts per million (ppm).

The outdoor concentration of carbon dioxide varies between 350-400 parts per million (ppm).

This can be higher in areas with high traffic or industrial activity. The level of Co2

indoors

depends upon the number of people present, how long an area has been occupied, the amount of

outdoor fresh air entering the area, the size of the room or area, and outdoor concentration.

Co2

measurements are a parameter for establishing the integrity of indoor air quality in

terms of amount of ventilation and general comfort. Indoor concentration level of Carbon

dioxide varies from outdoor norm of 400ppm to over 1000ppm. This depends on outdoor

concentration, indoor efficiency of ventilation system and number of occupants present in a

space and for how long.

Outdoor “fresh” air ventilation has the capacity to dilute indoor concentration of carbon

dioxide. In office spaces, ASHRAE recommends 17 (cfm) cubic feet per minute person (for a

1000 square foot occupied by 5 people). These are standards developed for healthy working

adults. This standard further recommends a maximum of 600ppm concentration above that

obtained outdoor. This gives a maximum recommended indoor Co2 level at 1,000ppm for

outdoor air ventilation rate of 17 cfm/person given an outdoor baseline Co2

concentration of 400

ppm for office spaces (ANSI/ASHRAE 62-1999).

Productivity and efficiency are important attributes of an office environment. It is of

interest to note that at carbon dioxide concentration level of between 300–700 ppm above




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ambient carbon dioxide levels (i.e 400ppm), occupants of office building will begin to feel the

classic symptoms of carbon dioxide poisoning which are difficulty in breathing, rapid pulse rate,

headache, hearing loss, hyperventilation, sweating and fatigue and general loss of concentration

(See Robertson, 2006, Charles et al, 2009 and Vimalanathan et al, 2014).

Previous studies evaluating Co2 intensity as a function of office indoor comfort were

evaluated on the bases of percentage window area to floor area or the degree which the windows

are physically opened or closed (See James et al 2008, IMC 2009 and Sribanurekha et al 2010).

To the best knowledge of these authors, none have utilized total interior volume as a variable.

2.0 AIM OF THE STUDY

The aim of this study is to evaluate the relationship between total office volume and

operable window area and its effect of Co2 level in the office space. This is to establish comfort

conditions, in the context of ventilation required in office spaces in Jos, Nigeria.

3.0 METHODOLOGY OF STUDY

The study was carried out in the month of April 2014 in Jos, Nigeria. The location had an

altitude above sea –level of 1286 meters. The GPS location is given as Lat. (N) 90

58’ 01.83 and

Long. (E) 80

52’ 21.63. All offices under study were selected randomly, east-facing and naturally

ventilated (NV). The period of study was between 8.00hrs and 15.00hrs week days.

Measurements were taken at intervals of 8.00hrs, 12.00hrs and 15.00hrs. These conveniently

represent opening hours, mid-day break and closing hours of the offices under study (See Fig 1

and 2). Measurements obtained were indoor and outdoor Co2 levels, outdoor and indoor wind

velocity, operative temperature and Humidity (See Table 3).




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Subjective data collected from questionnaires were presented using simple bar graphs and

percentages. While objective data obtained from Measurement Instruments were put through

bivariate correlation analysis and scatter graph. To obtain a predictive value for any value of

predictor and dependent variable combination, a regression formula was obtained from the above

mentioned bivariate correlation (See Fig 4 and Table 5 to 7). The instruments enumerated below

were used to obtain objective data as tabulated in Table 2 to Table 4.

Indoor/Outdoor Air velocity

A Pyle PMA90 Digital Thermo-Anemometer was used to measure air movement indoor

and outdoor. This meter was place to take readings at body level at the different room locations

indoors. The windows in all the rooms were left in their usual open positions during the survey

as is the case during working hours. For outdoor readings, the device was located away from any

large object that could cause local interference in wind speed dynamics. This device has a range

of 0.40 - 30m/s and an accuracy level of ±3% for readings greater than 0.20m/s. The average of

these readings for each office was used as the air velocity of the room.

Global Positioning System

A Cobra GPS 100 global Positioning System receiver was used to obtained global location

of building of interest. This device provided accurate positioning to within 3 meters, if held in

any position open to the sky. It offers information as to current positioning, altitude above sea

level, bearing and time of the day.




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Co2 Meter

An Amprobe Co2-100 meter was used to measure Co

2 level within the working space. The

meter was carefully placed to take readings at body level at the different room locations. It has a

range of between 0-9999ppm and a resolution of 1ppm. It has an accuracy level of ±30ppm.

3.1 Methods of Subjective Data Analysis.

For subjective data from questionnaires, data presented were analyzed using simple bar

graphs and percentages. This is to grant visual correlation to relationships between the variables

under study. This enhances understanding of subsequent objectives inputs and inferences.

3.2 Methods of Objective Data Analysis.

For objective data obtained from measurement instruments, a bivariate correlation

analysis of scatter graph was first produced to obtain a perfect +1 for Pearson correlation with a

P-Factor (level of significance) of less than 005 (See Fig 4 and Table 5 to 7). This indicates that

the two variables are perfectly related in a positive linear sense. To obtain a predictive value for

any value of predictor and dependent variable combination, a regression formula is obtained

from the above mentioned bivariate correlation.

4.0 FIELDWORK

The field work consists of obtaining subjective and objective data for the purpose of

analysis. Subjective data for this study was obtained from questionnaires while the objective data

was obtained from measurement instruments. The purpose of the questionnaire was to obtain

inputs as to indoor comfort levels of occupants of these offices while objective data obtained

included Co2

level, temperature and humidity readings under varying ventilation rates.




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4.1 Sample Area Characteristics

The survey for this Co2 level data acquisition was carried out in Jos, Nigeria. The studies

were executed in the Administrative Building of University of Jos in four (4) different offices

within the building Complex. In all, two (2) survey sessions were conducted in this Naturally

Ventilated (NV) building in the month of April 2014. The first session was to obtain objective

data using instruments earlier enumerated. There was the need to conduct the instrument data

session for all offices simultaneously on same day to ensure integrity and interoperability of data

collected. The second session was for the subjective data using the questionnaires.

4.2 Recorded Environmental Variables

These values are obtained in Table 2 to Table 4 and shows details of the survey location.

These include GPS determined latitude, longitude and altitude readings of the site as well as the

survey dates, prevailing outdoor and environmental variables etc. Table 3 shows indoor

environmental variables that also have bearing on office comfort in terms of Co2 intensity.




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Table 1. Summary of Occupants’ Characteristics in Sampled Buildings.

Office 1 Office 2 Office 3 TOTAL

Sample size

Gender Total 7 2 9 18

Male 5 2 6 13 (72%)

Female 2 0 3 05 (28%)

Age (Years)

Maximum 38 36 38

Minimum 36 32 32

Mean 37 34 35

Height (M)

Maximum 1.8 1.7 1.8

Minimum 1.6 1.6 1.5

Mean 1.7 1.7 1.7

Weight (Kg)

Maximum 70 68 93

Minimum 62 64 68

Mean 66 66 81




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Table 2. Summary of Survey Locations’ Environmental Variables.

Space ID Lat. (N) Long. (E) Alt. (M) Date To (Oc) Vo (cfm) Rho (%)

Outdoor

Conditions

90 58’ 01.83 80 52’ 21.63 1286 9th April 2014 32 672 31.8

Office 1 90 57’ 01.83 80 53’ 18.63 1286 9th April 2014 32 0 49.5

Office 2 90 57’ 01.83 80 52’ 18.64 1286 9th April 2014 32 0 41.8

Office 3 90 57’ 01.55 80 52’ 22.63 1286 9th April 2014 32 0 41.8

Office 4 90 57’ 01.55 80 52’ 22.63 1286 9th April 2014 32 0 45.7

Where:

Lat: Latitude (°N)

Long.: Longitude (°E)

Alt.: Altitude (m)

To (oC) Average outdoor temperature recorded at the time of survey

Vo (cfm) Average outdoor wind velocity recorded at the time of survey

RHo (%) Average outdoor Relative Humidity recorded at the time of survey




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Table 3. Summary of Indoor Climatic, Metabolic and Clothing Variables.

Space

ID

Sample

Size

Vol. (M3) Ta (OC) Vel.

(M/S)

RH (%) Co2

(ppm)

Ar (met) Cl (clo)

Office 1 12 40.32 28.30 0 38.2 524 1.2 0.57

Office 2 4 50.24 26.60 0 43.9 533 1.2 0.57

Office 3 15 324 27.76 0 61.2 478 1.2 0.57

Office 4 8 75.61 29.45 0 42.3 502 1.2 0.57

Average 9.75 122.54 28.02 0 46.4 509 1.2 0.57

Where:

Vol: Volume of air/space (Length x Breadth x height)

Ta: Air temperature (°C) (average at 2 heights and multiple locations in the room)

Vel: Air velocity (m/s) (average at multiple locations in the room)

Tr: Meant Radiant temperature (°C)(average of room surfaces)

RH: Relative Humidity (%) (Average across multiple locations in the room)

Co2: Carbon dioxide levels (ppm) (average of several readings taken at centre of the room)

Ar: Activity Rate (met) (ISO 8996-See Appendix G)

Cl: Clothing Level (clo): (See Appendix H)




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Table 4. Percentage Area of Windows and Indoor Environmental Variables.

Space

ID

Sample Size Vol. (M3) Wa (M2) Ra Ta

(OC)

Vel.

(M/S)

Tr (OC) RH (%) Co2

(ppm)

Office 1 12 40.32 1.44 0.036 26.2

0 27.87 38.2 524

Office 2 4 50.24 1.44 0.029 31.9

0 29.37 43.9 533

Office 3 15 324 2.88 0.008 36.2

0 27.52 61.2 478

Office 4 8 75.61 1.44 0.019 31.3

0 28.76 42.3 502

Average 9.75 122.54 1.8 0.023 31.4 0 28.38 46.4 509

Where:

Vol: Volume of air/space (Length x Breadth x height)

Wa: Window Area (Length x Breadth)

Ra: Ratio of Percentage Area of Window to Room Volume

Ta: Air temperature (°C) (average at 2 heights and multiple locations in the room)

Vel: Air velocity (m/s) (average at multiple locations in the room)

Tr: Meant Radiant temperature (°C)(average of room surfaces)

RH: Relative Humidity (%) (Average across multiple locations in the room)

Co2: Carbon dioxide levels (ppm) (average of several readings taken at centre of the room)




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4.3 Outdoor Air Ventilation Rate

This is the distance moved by air per unit of time. A digital anemometer, earlier described,

was used for these measurements. Outdoor air velocity ranges from 250cfm at 8am, 350cfm at

noon and 300cfm at close of day (See Fig. 1).

The ASHRAE Standard 62.1-2013 recommends a minimum steady state of outdoor air

ventilation rate of about 7.5 L/s/person or 15 cfm/person in other to achieve a comfortable indoor

level of humidity and Co2 concentration. For an average rate of office occupation stated as ten

(10) persons for this research (See Table 3), the minimum steady state of outdoor air ventilation

rate required would therefore be 150 cfm/person.




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Fig. 1 Showing Outdoor Air Ventilation Rate.

4.4 Carbon Dioxide Concentration

As earlier stated, indoor Co2 concentration levels have been known to aggravate certain

respiratory ailments and general reduction in productivity level and efficiency (Robertson, 2006).

Co2 build up is often used as a proxy for other occupant-generated pollutants that are associated

with sick building syndrome (Charles et al 2009). The ASHRAE Standard 62.1-2013

recommends a maximum steady state indoor Co2 concentration of 870ppm (part-per-million)

based on the assumption of an outdoor concentration of 350ppm.

Fig. 2 shows a tolerable increased in Co2 concentration indoor in relationship to maximum

indoor conditions. This Co2

levels decreases as the day proceeds. This seems to be connected

with increase in outdoor air velocity as the day proceeds (See Fig. 1).




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Fig. 2 Showing Carbon Dioxide Concentration

5.0 ANALYSIS OF FINDINGS

5.1 Air Movement and Air Quality in Offices

Fig. 1 showed minimum standard outdoor air ventilation rate of 150cfm/person. This is

according to ASHRAE Standard 62.1-2013 (See 4.3). However, measured outdoor rates

increased from 250cfm/person to a mid day maximum of 350cfm/person. At the close of work,

300cfm/person air ventilation rates was measured. This showed that measured outdoor

ventilation rates were higher than minimum acceptable outdoor rate all through the working

hours of the day.

Fig. 2 show interior Co2 level above outdoor levels but way below recommended maximum

for indoors of offices. This Co2

level decreases as the day proceeds. This seems to be connected

with increases in outdoor air velocity seen in fig.1 as the day proceeds. The subjective

measurements however shows a 45% votes of respondents that found the indoor air flow just

right, while 55% found the air flow slightly still or too still. This inadequacy is partly explained




121

by the low window area to volume of office as enumerated in Table 4. Fig. 4 shows a linear

relation between Percentage Window Area to total office volume and Co2 levels. From this

graph, the higher the ratio of window area to total office volume, the higher the Co2 intensity

level.

Fig. 3 How do you feel about the airflow in your office at the moment?

5.2 CO2 Level (ppm) and Window Area to Total Office Volume Analysis.

A relationship between percentage operable window area and Co2 levels was also

established. A scatter plot was executed showing a visual correlation (See Fig. 3). A bivariate

correlation confirmed correlation with a Pearsons Correlation index of 1 and a 2 tailed p factor of

7.4% (See Table 5). This value is cogent considering the fact that the minimum outdoor airflow

conditions were met. Table 6 shows an R2

value of 86% indicating considerable fit of data’s

statistical model of predictor (Window Area Ratio) and dependent variable (Co2 Level). The

Coefficient Summary Analysis of Window Area Ratio and Co2 with a p factor = 0.075 or 7.5%




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and the dependent variable is Co2 level is seen in Table 7. This gives a regression formula for

any value of CO2 level (ppm) from 470-550 ppm

as:

y=bx +a

Where;

y= 1.865 (x) + 466.344

The given recommended maximum Co2 level permissible in an office building is 900

ppm. Optimum outdoor conditions are 350ppm (See Fig 2). These figures do not fall within the

range of our regressive analysis (See Fig. 4). A mean of the objective data obtained in fieldwork

was adopted (i.e 509ppm) since this figure falls well below acceptable maximum indoor limits

(See Table 3 and Fig 2). From the regression formula stated above, it would require an operable

window area to room volume ratio of 0.0229 to achieve 509ppm Co2 concentration.




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Fig 4. Showing Bivariate Correlation Relationship between CO2 Level and Percentage Window

Area to Total Office Volume.

TABLE 5. Showing Bivariate Correlation relationship between Indoor CO2 Level and Percentage

Window Area to Total Office Volume.

Correlations

CO2 RATIO

CO2 Pearson Correlation 1 .926

Sig. (2-tailed) .074

N 4 4

RATIO Pearson Correlation .926 1

Sig. (2-tailed) .074

N 4 4




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TABLE 6. Showing R2 is 86% indicating considerable fit of data’s statistical model of predictor and

dependent variable for CO2 Level and Window Area.

Model Summary

Model R R Square

Adjusted R

Square

Std. Error of the

Estimate

1 .926a .857 .786 11.3727

a. Predictors: (Constant), RATIO

Table 7. Showing Coefficient Summary Analysis of CO2 Level and Window Area.

Coefficientsa

Model

Unstandardized Coefficients

Standardized

Coefficients

t Sig. B Std. Error Beta

1 (Constant) 466.344 13.629 34.218 .001

RATIO 1865.471 538.515 .926 3.464 .074

a. Dependent Variable: CO2

Where p factor = 0.074 or 7.4%

6.0 CONCLUSION

The research established a linear relationship between the ratio of Window Area to total

office volume and Co2 levels. The lower the ratio of window area to total office volume, the

lower the Co2 intensity. Offices used in this research showed window area ratio of between 0.008

to 0.036 as opposed to the 0.229 required by calculation. In as much as the measured indoor Co

2

levels met required standards, this recommended increase of 0.0229 would ensure that these

conditions are optimized.

7.0 RECOMMENDATION

1) Climate and weather conditions differ from place to place even within the sub-saharan region.

Weather components are also a large determining factor in Co2 level analysis. There will




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therefore be need for similar research to be carried out in under region with differing weather

characteristics.

2) Humans are the main indoor source of carbon dioxide. Indoor occupant density and metabolic

activity are therefore related to Co2 intensity. Further research would need to be carried out in

spaces other than offices so as to grant greater insight into the relationship between Co2 intensity

in spaces with differing human activity.

3) The research recommends increase in indoor air movement as a mitigating factor to high

indoor Co2 level. This can be achieved with a larger window area to total indoor volume. This

lower indoor Co2 level can also be achieved by means of non passive mean such as mechanical

ventilators.




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8.0 REFRENCES

ANSI/ASHRAE Standard 62.1-2013, Thermal Environment Conditions for Human

Occupancy. American Society of Heating, Refrigeration and Air-conditioning

Engineers (ASHRAE), Atlanta.

ASHRAE (1999) ASHRAE Standard 62: Ventilation for Acceptable Indoor Air Quality.

Atlanta, GA.

Charles, R. Reardon, J.T. Magee, R.J. (2009) Indoor air quality and thermal comfort in open-

Plan offices. In Construction Technology Updates, Volume 64.

Institute for Research in Construction (IRC): National Research Council of

Canada. ISSN; 1206–1220.

James, P., Kirchgaessner, B., Jentsch, M and Bahaj, A. (2008) Impact of user behaviour on the

heating season carbon footprint of naturally ventilated UK offices. World Renewable

Energy Congress (WRECX) Editor A. Sayigh © 2008 WREC.

Robertson, D.S. (2006) Health Effects of Increase in Concentration of Carbon Dioxide in the

Atmosphere. Current Science, VOL. 90, NO. 12, Pp 1607-1609.

Sribanurekha, V. Wijerathne, S.N., Wijepala, L.H.S and Jayasinghe, C. (2010) Effect of

Different Ventilation Conditions on Indoor CO2 Levels.

www.iiirr.ucalgary.ca/files/iiirr/114.pdf.

The International Mechanical Code, Fifth Edition, (2009).

http://publicecodes.cyberregs.com/icod/imc/2009/

Vimalanathan, K.and Babu, T.R. (2014) The Effect Of Indoor Office Environment on the Work

Performance, Health and Well-Being of Office Workers. Journal of

Environmental Health Science & Engineering2014,12:113.

http://www.ijehse.com/content/12/1/113.

http://www.iiirr.ucalgary.ca/files/iiirr/114.pdf

../../AppData/Local/Microsoft/Windows/Temporary%20Internet%20Files/Content.Outlook/6MR67QDJ/PHD%20Publish/(2009

http://publicecodes.cyberregs.com/icod/imc/2009/

http://www.ijehse.com/content/12/1/113

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