How Much CO2 Do People EmitAndrew Persily

National Institute of Standards and Technology301 975-6418; andyp@nist.gov

Interagency Committee on Indoor Air Quality7 June 2017

Why are we interested in indoor CO2?

CO2 part of ventilation & IAQ discussions since 18th century

Discussions evolved over time Impacts on building occupants Relation to bioeffluent perception Estimation of ventilation rates Demand controlled ventilation

Antoine Lavoisier 1743-1794

IMPACTS OF CO2 ON OCCUPANTS

• 1800 mg/m3 (1000 ppm) a de facto standardNot based on CO2 health impactsLinked to 7 L/s per person outdoor air

• Higher CO2 correlates with increased SBS symptomsOther contaminants increased with lower ventilation

• Recent studies showing decreased decision-making performance as low as 1800 mg/m3

Other recent studies don’t

1800 mg/m3 and Perception of Body Odor

• Chamber studies since 1930s, later in buildings7 to 9 L/s per person, body odor acceptable to most individuals entering from clean air

• 80% acceptability for 1250 mg/m3 > outdoorsConsistent with 1800 mg/m3

• 1800 mg/m3 reflects acceptable body odorBut many other important indoor pollutants not associated with number of occupants

Peak CO2 to Estimate Outdoor Air per Person

Well-established tracer gas methodsASTM E741, ISO 12569, …

Single-zone, constant injection tracer methodAssumptions not generally acknowledged: constant air change,

single-zone, CO2 generation rate constant and known, …Estimating before steady-state overestimates air change rate

Demand Controlled Ventilation

• Required by some energy efficiency standards, e.g. ASHRAE/IES 90.1Primarily densely occupied spaces

• ASHRAE Standard 62.1 allowsBut no requirementsRelevant to per person ventilation

requirement, not floor area rateMore detail in California Title 24 and

ASHRAE/IES/USGBC 189.1, e.g. # of sensors, location, accuracy, …

Title 24 contains setpoint of 1080 mg/m3

above outdoors

Current Approach to Estimating CO2Generation Rates

VCO2 = CO2 generation rate, L/s•personVO2 = O2 consumption rate, L/s•personRQ = respiratory quotient = VCO2 / VO2

Function of diet, level of physical activity and physical condition of person, about 0.85 for lightly active adult

AD = DuBois surface area, m2

= 0.203𝐻𝐻0.725𝑊𝑊0.425, H is height in m, W is mass in kg

M = metabolic rate (met) ≠ 58 W/m2

𝑽𝑽𝑪𝑪𝑪𝑪𝟐𝟐 = 𝑽𝑽𝑪𝑪𝟐𝟐𝑹𝑹𝑹𝑹 =𝟎𝟎.𝟎𝟎𝟎𝟎𝟐𝟐𝟎𝟎𝟎𝟎𝑨𝑨𝑫𝑫𝑴𝑴 𝑹𝑹𝑹𝑹𝟎𝟎.𝟐𝟐𝟐𝟐 𝑹𝑹𝑹𝑹 + 𝟎𝟎.𝟎𝟎𝟎𝟎

𝑽𝑽𝑪𝑪𝑪𝑪𝟐𝟐 =𝟎𝟎.𝟎𝟎𝟎𝟎𝟐𝟐𝟎𝟎𝟎𝟎𝑨𝑨𝑫𝑫𝑴𝑴 𝑹𝑹𝑹𝑹𝟎𝟎.𝟐𝟐𝟐𝟐 𝑹𝑹𝑹𝑹 + 𝟎𝟎.𝟎𝟎𝟎𝟎

First appears in 1989 ASHRAE Fundamentals Handbook, which cited Nishi (1981), which doesn't cite anyone

Subsequently used in ISO Standard 8996 and ASTM D6245

Table of metabolic rates in ASHRAE Fundamentals Handbook and ASHRAE Standard 55 (Thermal Comfort)

Handbook values unchanged since 1977

Based on references from 1960s

WHERE DID IT COME FROM?

No explanation of technical basis of equation

Metabolic rates are old

AD = DuBois surface area only an estimate, metabolism experts prefer body mass

Doesn't account for sex or age of subjects

What's the Problem

Concepts from human metabolism and exercise physiologyBasal metabolic rate, BMR (sex, age, body mass)RQ based on composition of diet

Comprehensive databases of metabolic ratesFAO. 2001. Human energy requirements. Report of a joint FAO/WHO/UNU expert consultation, Food and Agriculture Organization of the United Nations.Ainsworth et al. 2011. The compendium of physical activities tracking guide, Healthy Lifestyles Research Center, Arizona State University, https://sites.google.com/site/compendiumofphysicalactivities/

Databases of body sizeEPA (2011) Exposure factors handbook, EPA/600/R-09/052F.

Persily and de Jonge. 2017, Indoor Air. doi: 10.1111/ina.12383

The "New" Approach

Step-by-step1. Estimate BMR for individual or group of individuals

based on sex, age and body mass2. Estimate level of physical activity M3. Multiply BMR (MJ/day) times M4. Convert to L/s of O2 consumption

0.206 L of oxygen per 0.42 MJ of energy (Lusk 1924)

5. Multiply O2 consumption by RQ to get CO2 generation6. Adjust for air temperature and pressure

𝑽𝑽𝑪𝑪𝑪𝑪𝟐𝟐 = 𝑹𝑹𝑹𝑹 𝑩𝑩𝑴𝑴𝑹𝑹𝑴𝑴 𝟎𝟎.𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎

𝑽𝑽𝑪𝑪𝑪𝑪𝟐𝟐 = 𝑩𝑩𝑴𝑴𝑹𝑹𝑴𝑴 𝟎𝟎.𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎Assuming RQ = 0.85

Step-by-step1. Estimate BMR for individual or group of individuals

based on sex, age and body mass

BMR: MJ/dayAge (y) Males Females

< 3 0.249 m – 0.127 0.244 m – 0.1303 to 10 0.095 m + 2.110 0.085 m + 2.03310 to 18 0.074 m + 2.754 0.056 m + 2.89818 to 30 0.063 m + 2.896 0.062 m + 2.03630 to 60 0.048 m + 3.653 0.034 m + 3.538

>= 60 0.049 m + 2.459 0.038 m + 2.755

(FAO, 2001; Schofield, 1985), m is body mass in kg.

Activity Males FemalesAverage

PARPAR

RangeAverage

PARPAR

RangeAerobic dancing – low intensity 3.51 4.24Aerobic dancing – high intensity 7.93 8.31Calisthenics 5.44Child care (unspecified) 2.5Climbing stairs 5.0Dancing 5.0 5.09Eating and drinking 1.4 1.6Housework (unspecified) 2.8 2.5 to 3.0Office worker – Filing 1.3 1.5Office worker – Reading 1.3 1.5Office worker – Sitting at desk 1.3Office worker – Standing/moving around 1.6Office worker – Typing 1.8 1.8Office worker – Writing 1.4 1.4Reading 1.22 1.25Sleeping 1.0 1.0Sitting quietly 1.2 1.2Sitting on a bus/train 1.2Standing 1.4 1.5Walking around/strolling 2.1 2.0 to 2.2 2.5 2.1 to 2.9Walking quickly 3.8Walking slowly 2.8 2.8 to 3.0 3.0

PAR values for various activities from FAO, 2001

2. Estimate Estimate level of physical activity M

Activity M (met) RangeCalisthenics – light effort 2.8Calisthenics – moderate effort 3.8Calisthenics – vigorous effort 8.0Child care 2.0 to 3.0Cleaning, sweeping – moderate effort 3.8Custodial work – light 2.3Dancing – aerobic, general 7.3Dancing – general 7.8Health club exercise classes – general 5.0Kitchen activity – moderate effort 3.3Lying or sitting quietly 1.0 to 1.3Sitting reading, writing, typing 1.3Sitting at sporting event as spectator 1.5Sitting tasks, light effort (e.g. office work) 1.5Sitting quietly in religious service 1.3Sleeping 0.95Standing quietly 1.3Standing tasks, light effort (e.g. store clerk, filing) 3.0Walking, less than 2 mph, level surface, very slow 2.0Walking, 2.8 mph to 3.2 mph, level surface, moderate pace

3.5

Physical activity levels (M) from compendium (Ainsworth et al., 2011)

CO2 generation rate (L/s)

Age (y) Mean mass (kg)

BMR (MJ/day)

Level of physical activity (met)

1.0 1.2 1.4 1.6 2.0 3.0 4.0Males

< 1 8.0 1.86 0.0009 0.0011 0.0013 0.0014 0.0018 0.0027 0.00361 to <3 12.8 3.05 0.0015 0.0018 0.0021 0.0024 0.0030 0.0044 0.00593 to < 6 18.8 3.90 0.0019 0.0023 0.0026 0.0030 0.0038 0.0057 0.0075

6 to < 11 31.9 5.14 0.0025 0.0030 0.0035 0.0040 0.0050 0.0075 0.010011 to < 16 57.6 7.02 0.0034 0.0041 0.0048 0.0054 0.0068 0.0102 0.013616 to < 21 77.3 7.77 0.0037 0.0045 0.0053 0.0060 0.0075 0.0113 0.015021 to < 30 84.9 8.24 0.0039 0.0048 0.0056 0.0064 0.0080 0.0120 0.016030 to < 40 87.0 7.83 0.0037 0.0046 0.0053 0.0061 0.0076 0.0114 0.015240 to < 50 90.5 8.00 0.0038 0.0046 0.0054 0.0062 0.0077 0.0116 0.015550 to < 60 89.5 7.95 0.0038 0.0046 0.0054 0.0062 0.0077 0.0116 0.015460 to < 70 89.5 6.84 0.0033 0.0040 0.0046 0.0053 0.0066 0.0099 0.013370 to < 80 83.9 6.57 0.0031 0.0038 0.0045 0.0051 0.0064 0.0095 0.0127

>= 80 76.1 6.19 0.0030 0.0036 0.0042 0.0048 0.0060 0.0090 0.0120

Females< 1 7.7 1.75 0.0008 0.0010 0.0012 0.0014 0.0017 0.0025 0.0034

1 to <3 12.3 2.88 0.0014 0.0017 0.0020 0.0022 0.0028 0.0042 0.00563 to < 6 18.3 3.59 0.0017 0.0021 0.0024 0.0028 0.0035 0.0052 0.0070

6 to < 11 31.7 4.73 0.0023 0.0027 0.0032 0.0037 0.0046 0.0069 0.009211 to < 16 55.9 6.03 0.0029 0.0035 0.0041 0.0047 0.0058 0.0088 0.011716 to < 21 65.9 6.12 0.0029 0.0036 0.0042 0.0047 0.0059 0.0089 0.011921 to < 30 71.9 6.49 0.0031 0.0038 0.0044 0.0050 0.0063 0.0094 0.012630 to < 40 74.8 6.08 0.0029 0.0035 0.0041 0.0047 0.0059 0.0088 0.011840 to < 50 77.1 6.16 0.0029 0.0036 0.0042 0.0048 0.0060 0.0090 0.011950 to < 60 77.5 6.17 0.0030 0.0036 0.0042 0.0048 0.0060 0.0090 0.012060 to < 70 76.8 5.67 0.0027 0.0033 0.0038 0.0044 0.0055 0.0082 0.011070 to < 80 70.8 5.45 0.0026 0.0032 0.0037 0.0042 0.0053 0.0079 0.0106

>= 80 64.1 5.19 0.0025 0.0030 0.0035 0.0040 0.0050 0.0085 0.0101

Steps 3, 4 and 5 Multiply BMR (MJ/day) times M; Convert to L/s of O2 consumption; and Multiply by RQ

𝑽𝑽𝑪𝑪𝑪𝑪𝟐𝟐 = 𝑩𝑩𝑴𝑴𝑹𝑹𝑴𝑴 𝟎𝟎.𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎

Variation in CO2 generation rate associated with variation in age, body mass and level of physical activity for females

Steady-state CO2 concentrations in selected spaces

Space typeOutdoor air ventilation

rate, Standard 62.1 (L/s•person)

Steady-state CO2 concentration above outdoors (mg/m3)

Divide by 2 for ppmv

Office 7.5 1116Conference room 3.1 3060Educational (5 y to 8 y) 7.4 801Lecture classroom 4.3 1907Lecture hall, fixed seats 4.0 2037Lobby 2.7 4015Auditorium seating area 2.7 3513

Outdoor air ventilation rate (h-1)

Residence 0.2 12970.35 7410.5 519

Adult bedroom 0.2 39070.35 22330.5 1563

Child’s bedroom 0.2 19940.35 11390.5 797

Very little CO2 generation rate data in the literature

Qi et al. 2014 Indoor Air44 young Chinese subjects in chamber"Old" equation overestimates 24 % (females) and 16 % (males)New equation reduces errors < 10 %

Fan et al. Indoor Air 2016 (Ghent)6 young Chinese subjects in ventilated room"Old" eqn overestimates by 25 % (females) and 17 % (males)New equation reduces errors to 8 % and 2 %

Is it Better?

New method and updated data for estimating CO2 generation rates of building occupants

Need to update standards and handbooks

Impact on indoor CO2 levels and ventilation rates being analyzed

Summary

Persily and de Jonge. 2017, Indoor Air. doi: 10.1111/ina.12383