ME425/525: Advanced Topics

in Building Science

CO2 and personal exposure: Lecture 12

Dr. Elliott T. Gall, Ph.D.

2

Lecture 12

• Today’s objectives– CO2 sensor applications

• CO2 exposure study

– Arduino, part IV• Start CO2 sensor build

– Work on responsive CO2 sensor – add in LED to your circuit

(+10 points on HW3)

• HW overview– HW2: Sorption review

– HW1 redo: Due Monday, May 15th

– HW3: Assigned Monday, May 15th

• Start working with sensor today to familiarize

3

Sensor calibration

• Sensors were calibrated yesterday

• Should see a log from about 12:30 PM to 4

PM

All sensors were in same chamber

Compressed CO2 cylinder

Compressed zero-air cylinder

Mass flow controller: Devices that regulate flow to desired flowrate

4

Sensor calibration

• Sensors were calibrated yesterday

• Should see a log from about 12:30 PM to 4 PM

– All sensors in a 11.4 L chamberTime CO2 cylinder

flowrate, 100%CO2 (cc/min)

Zero-air cylinder flowrate, 0% CO2level (LPM)

12:49 PM 0 1

2:01 PM 1.01 2.5

2:40 PM 1.01 1

3:31 PM 1.01 0.5

4:20 PM stop stopOn last calibration curve, you may notice data is not quite at steady-state… make an assumption and move forward with calibration

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Sensor calibration

• Calibration curve determination

• Use reverse calibration subsequently to “correct” your sensors readings to the calibration standard

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Sensor co-location

• Compare K-30 to onset

– Place sensors in same location

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• Should we be concerned?

– ASHRAE 62.1-2010: 700 ppm above outdoor

• substantial acceptance of bioeffluents (body odor)

CO2 in indoor spaces

Q QindoorCO ][ 2

outdoorCO ][ 2E

Q

Eppmppm 400100,1

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CO2 exposure and health

• At high levels (2%, 1 h) acute effects:

– Headache, dyspnea, dizziness, higher breathing

• Occupational standards:

– US: OSHA sets “transitional limit” of 5,000 ppm

– US: NASA lowers limit in spacecraft to 5,000 ppm

lethargy, headache at lower than expected CO2

• Variability in response

– In a study of 35 divers, 17% had high sensitivity

based on ventilatory response to high CO2

References:

• Environmental Protection Agency. EPA430-R-00-002, 2000

• Law et al., NASA Technical Report 2010-216126

• Pendergast et al., 2006, Undersea Hyperb Med, 33:447-53

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• Occupational settings higher than for public

– In Germany, based on health, hygiene:

• A possible role at lower [CO2]

– Review of 20 studies: “SBS symptoms decrease ↓ 800 ppm”

– Impacts on decision-making:

High performance buildings

< 1000 ppm acceptable; 1000-2000 ppm elevated; >2000 ppm unacceptable

Nine metrics of decision-making performance

Re

lative

pe

rce

ntile

sco

re

References:

• Seppӓnen et al. 1999,

Indoor Air, 9: 226-252

• Figure adapted from

Satish et al. 2012, EHP, 120(12): 1671-77

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CO2 and cognitionImplications for cognitive function: Further evidence emerging for a direct role for CO2:

• Satish et al. (2012): Observations of decrements in metrics of decision making at elevated CO2 (2.5-h exposures to 1000 ppm or 2500 ppm)

• Strøm-Tejsen et al. (2015): Objectively measured sleep quality and subsequent test of logical thinking improved when CO2 reduced from avg. of 2400 ppm to 830 ppm.

• Allen et al. (2015) (figure below): Significantly reduced cognitive metrics when space operated with ↑CO2.

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CO2 and cognitionOther studies indicate that CO2 levels do not adversely affect metrics of cognition.

These metrics are different from the previous two slides – could this be a possible reason for the differing conclusion?

Zhang et al. 2017, Indoor Air (27) 1:47-64

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Monitoring CO2 exposure

There is a lack of data quantifying personal exposure to CO2

• CO2 measurements often spatially fixed; i.e. installed in building

• Cognitive, health implications compel characterization of personal CO2 exposures

Participants carry sensor continuously for seven days, record [CO2], T, RH w/ Δ=1min

How do exposures to CO2 vary as a function of time, space?

Complete recall-based time-activity budget

Home Work

‘Other’ indoor Transit

Outdoor

Record perception of air quality, thermal comfort

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Data collection

16 participants, 7 days of continuous monitoring/person• Over 2,600 hours of monitoring• Example data from one participant below:

Sleeping microenvironment makes important contribution:• Fans on, windows open = 6,800 ppm-h; CO2= 800 ppm • Air-con, windows closed = 25,000 ppm-h; CO2= 2370 ppm

≈4× higher ≈3× higher

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6/10 12:00 PM 6/11 12:00 PM 6/12 12:00 PM 6/13 12:00 PM 6/14 12:00 PM 6/15 12:00 PM

Pers

on

al c

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xixd

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ntr

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n (

pp

m)

Date and time

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8/21 12:00 PM 8/22 12:00 PM 8/23 12:00 PM 8/24 12:00 PM 8/25 12:00 PM 8/26 12:00 PM

Pers

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arb

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pm

)

[CO2]avg= 5740 ppmover 14 min

[CO2]avg= 4675 ppmover 6 min

[CO2]avg= 6500 ppmover 16 min

AC-F-01

AV-M-02

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Quantifying exposure

• Total exposure: AC > MX > AV; exposures in home dominate: 66-68% for all groups • Activity patterns (not shown) are statistically similar across all groupings• Differences driven by [CO2]: CO2,AC home = 1100 ppm vs. CO2,AV home = 650 ppm (U < 0.005)

0

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Allparticipants

AC AV MX

Dai

ly in

tegr

ated

CO

2ex

po

sure

(1

00

0 p

pm

×h

/d) Outdoor

Other indoor

Transit

Work

Home

0%

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100%

Allparticipants

AC AV MX

Tim

e-ac

tivi

ty b

ud

get

Outdoor

Other indoor

Transit

Work

Home

p < 0.005

0%

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AC

-M-0

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AC

-M-0

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AC

-F-0

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AC

-F-0

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MX

-F-0

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MX

-M-0

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NV

-M-0

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NV

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Tim

e-a

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dge

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Participant ID

Home Work Transit Other indoor Outdoor

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5

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Allparticipants

AC AV MX

Dai

ly in

tegr

ate

d C

O2

exp

osu

re

(10

00

pp

m ×

h/d

) Outdoor

Other indoor

Transit

Work

Home

0%

10%

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100%

Allparticipants

AC AV MX

Tim

e-a

ctiv

ity

bu

dge

t

Outdoor

Other indoor

Transit

Work

Home

p < 0.005U

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Exposure: how high?

Singapore/ASHRAE standard

Figure: Max daily 2.5-h CO2

exposure concentrations, rolling avg.; time of exposure based on Satish et al. (2012)

Satish et al. – significant, moderate decrements in 7 of 9 metrics of decision making

Satish et al. – significant, substantial decrements in 8 of 9 metrics of decision making

75%

50%

25%

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Exposure: how frequent?

30-150 min, >1000 ppm>150 min, 1000-2500 ppm>150 min, 2500+ ppm

In aggregate, indicated exposures occur once every:

1.6 days 2.2 days 8.3 days

AC group AV group

1.4 days 5.7 days n/a

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0 3 6 9 12 15 18 21 240

1000

2000

3000

4000 AC participants

0 3 6 9 12 15 18 21 240

1000

2000

3000

4000

Hour of day daily max occurring (mid-point of 2.5 h)

Daily

maxim

um

2.5

-h C

O2 m

ixin

g r

atio (

ppm

)

AV participants

Home

Other indoor

Transit

Work

Exposure: when and where?Daily max 2.5-h exposure concentration (rolling average), by microenvironment

Likelihood of daily max 2.5-h >1000 ppm: AV: 50%

Likelihood of daily max 2.5-h >1000 ppm: AC: 75%

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Summary

• Bedroom ventilation is a determinant of CO2 exposure

• Exposure concentrations frequently exceed building standards

- 1100 ppm standard: 77th percentile for AC group

• Exposure with cognitive implications occur frequently

- 86% of such exceedances occur in home (8% in office, 5% transit)