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CO2 pilot study part 2
1. CO2 in Primary School
Classrooms
Or
The effect of shutting windows in naturally ventilated
classrooms
2. Hypothesis
• Higher CO2 levels, indicating lower than acceptable
ventilation, may be found in naturally ventilated classrooms
when:
• windows and blinds are drawn to reduce glare, noise or wind
or distractions; or retrofitted split-system air conditioners are
used for heating or cooling and no make-up air is provided
3. CO2 as an Indicator of IAQ
Ventilation is the only process that can remove harmful substances
from the air.
Measuring expired air CO2 levels in a room has been demonstrated to
be a clear and accurate indicator of ventilation effectiveness.
4. Standards for Ventilation in
Classrooms
• BCA (Building Code of Australia)
– Operable openings to equal 5% of floor area
• ASHRAE(American Society of Heating, Refrigerating and Air-Conditioning Engineers)
– CO2 concentration < 1000ppm (parts per million)
– Maximum occupancy of 50 people per 100sqm
– Fresh outdoor air rate 8/l/s/person
– (typical USA practice includes mechanical ventilation)
– Advisory levels in Tasmania are give by Dept Health as 1000 ppm
maximum
5. Direct Reasons for CO2 Increase
• Time
• Occupant
numbers
• Room volume
• Room design
C02 levels vs time
(Grimsrud 2006)
School daySchool day CO2 decayCO2 decaySteadySteady
6. Indirect Reasons for CO2 Increase
• Summer
– Glare
– Heat gain
– Noise/distractions
– Wind
– A/C units
• Winter
– Glare
– Heat loss
– Noise/distractions
– Cold air
– A/C units
Common teacher comments:
“We need to keep the windows/blinds closed,
it’s too hot/cold/glary/noisy/drafty”
“The students look out the windows and
don’t concentrate”
“The principle says we need to close the
windows and save energy”
“The wind is too cold if the windows are
open”
“The cars make a lot of noise”
7. Previous Research
• Seppanen (1999)
– Relates IAQ with detrimental effects on the school children's
concentration and fatigue levels.
• Daisey (2003)
– ‘Ventilation and CO2 data strongly indicate that ventilation is
inadequate in many classrooms, possibly leading to deleterious
outcomes in health and performance.’
• Brennan (1991)
– Reports on nine non-compliant US schools, mid-afternoon CO2
measurements ranged from approx. 400 to 5000 ppm with an
average of 1480 ppm.
8. Methodology research
Continuous assessment – accepted method
• Grimsrud et al (2006)
– 85 classrooms in 8 Minesota schools
– Continuous method - 20 sec intervals on day or more
– Monitors placed 1.5m above the ground
Spot assessment – unreliable varies as a function of time
• Shendell et al (2004)
– Short term measurements
– 2 measurements for no longer than 5mins
– Sensors placed 1.5m above the ground (child's breathing zone)
Spot measurement are not reliable but as Shendell shows they are enough to warrant a further,
larger study in CO2 concentrations.
9. Other CO2 factors
• CO2 levels are not related to temperature
• C02 is evenly dispersed within a room (Grimsrud 2006) however:
– Breathing zone of child is 1.2 - 1.7m off the ground
– Children's exposure to air pollutants is greater that that of adults Bearer,
– Environmental pollutants are often more present at a child’s breathing zone.
(Bearer, 1995)
10. Pilot Study Method
Spot testing using GLX CO2 sensors
- Data used from t=15 to t=40 seconds
- Consistent testing process and calibration before each school
Other room data collected
- Open to outside (y/n)
- Open to inside hall (y/n)
- Open cross ventilated doors or windows (y/n)
- Window covering state (% closed)
- Orientation (N S E W)
- Room size (estimate)
- Room activity (Low Med High)
- Number of students
11. Method validation test
Instrument was calibrated to
middle of fresh air range
(450-500 ppm)
Consecutive tests showed
sensor takes 15 to
stabilize
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
6 0 0
7 0 0
8 0 0
9 0 0
1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0
T i m e ( S e c o n d s )
CO2Concentration(ppm)
S e r i e s 1
S e r i e s 2
S e r i e s 3
S e r i e s 4
S e r i e s 5
S e r i e s 6
S e r i e s 7
S e r i e s 8
S e r i e s 9
S e r i e s 1 0
C O 2 s e n s o r n e e d s 1 5 s e c o n d s t o c a l i b r a t e ,
t h i s d a t a w i l l b e e x c l u d e d f r o m r e s u l t s .
Method repeatability tests (above) showed a standard deviation of 13 ppm in a room
with a steady 600ppm CO2.
12. Tests conducted
Approx 20 rooms in two
schools (DPS and EUPS)
measured between 30 and
50 min after lunch or
morning break.
Data taken from a part of room
away from openings and
children
Sensor held at 1.5 m above
floor and at arms length.
Mean and SD taken from t-15
to t=40 seconds Typical data set for one room showing
selected data area.
13. Average 1400 ppm, 3 rooms under limit
Most blinds open and some windows
Results 1
14. Average 1715 ppm, 1 room under limit
Most blinds closed, 1 room with windows open
Results 2
16. Analysis
IN a typical room of 80 m2 with 20 children and 1 adult:
• Cross ventilation effective at keeping Co2 levels below 1000ppm
(n=3, P=0.003)
• An open outside window lowers CO2, but not enough to reduce
levels to below 1000ppm, no statistical significance (n=5, p=0.7)
• Openings to hallways appear to have no correlation to co2 levels
(n=5, p=0.6)
• Having all windows closed is related to higher CO2 levels (n=7,
p=0.15)
17. Discussion
• 85% of classrooms exceed 1000ppm. Warrants enough concern for
further testing.
• Further observations
– 80% of rooms with outside distractions had blinds and windows
closed - this was is strongly related to high CO2 levels validating
part of the hypothesis
NEXT Questions
1. Plan for a more prolonged and detailed study?
2. Can we related unintended design outcomes to higher CO2 levels?
3. Can we produce additional design guidelines suitable for naturally
ventilated GLA’s in primary schools?
Editor's Notes
First praise the summer scholarship program and Greg A g reat for the student but also provides a real prompt for staff to engage in a project they would otherwise not begin. IT also provides me ( a relatively unexperienced academic with the opportunity to assist someone through the ir research which in turn is a great way to learn more about research practice. The research that I have been doing over the summer investigated carbon dioxide (CO2) levels in the general learning areas (GLA ’ s) of primary schools in the Devonport district to determine whether poor indoor air quality (IAQ) is common. The focus is on naturally ventilated spaces that may have the windows closed for reasons such as heat loss, glare or noise, wind or other operational reasons, rather than those with poor design.
We used CO2 as a surrogate to determine the ventilation rates within the classrooms. We did this by using CO2 testers, that we placed approx an arms length away from our body. It is important to measure the level of ventilation through classrooms, as ventilation is the only process that can remove harmful substances from the air, that can lead to adverse health affects.
The Building Code of Australia (BCA 2008-? F4), states that natural ventilation must consist of permanent or operable openings in the building, which are a least 5 percent of the classrooms floor area. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard for CO2 concentration is 1000 ppm (parts per million) and the outdoor air requirements for a classroom with a maximum occupancy of 50 people per 100m2 of floor area is 8 l/s/person. Levels of CO2 above 1000ppm are regarded as indicative of ventilation rates that are unacceptable. (Daisey, 2003).
Low levels of ventilation, poor cross ventilation, window location, occupant numbers, space and design are all contributing factors to the increase in CO2 in a classroom. The combination of occupant numbers and ventilation rates are the main cause of CO2 build up. CO2 concentrates inside a classroom significantly when there is a lack of natural ventilation from outside air. Humans produce CO2 during respiration; therefore the CO2 concentration in enclosed spaces increases with time and occupancy. Grimsrud mapped CO2 levels versus time in a typical classroom and found that CO2 levels peak when student occupancy has reached its maximum, relative to time spent in the room. CO2 concentrations are at a steady level in the morning before students start class at 8am. CO2 increases dramatically as students enter the room, and continues to build with time. CO2 levels peak and drop, around times that students leave the building for lunch and other out of class activities. CO2 levels then reduce after the end of the school day, when student occupancy is 0.
Heat loss, glare, noise, wind, distractions that cause the windows or openings to be closed, indirectly affect the classrooms ventilation. In summer for example a classroom may be north facing, and have problems with the glare from the harsh sun. This results in teachers shutting the windows and blinds to block out the sun, and in turn block out the classrooms natural ventilation source. Outdoor noise is another distraction that will lead to teacher shutting the windows to avoid distraction. In winter its the reverse. Teachers shut windows to avoid heat loss, and in turn loose their only source of ventilation. Maintaining a thermal comfort by using a retrofitted A/C unit, will also lead to a lack of fresh air supply. Air conditioning retrofits, in older buildings where there is no mechanical ventilation, need the windows to be closed in order to cool or heat the room, resulting in a lack of fresh air and increase in CO2.
Previous research into primary schools indoor air quality has been made throughout Europe and the United States, and suggests that a large amount of classrooms do not meet the ASHRAE standard for minimum ventilation rate. In 1999 Seppanen did a comparative study of previous research done on ventailtion and relates indoor air pollutants with detrimental effects on the occupant ’ s concentration and fatigue levels In 2003 Dasiey also did a report that summarised previous studies and reported that ventilation and CO2 data strongly indicate that ventilation is inadequate in many classrooms, possibly leading to deleterious outcomes in health and performance. The focus of previous studies has generally been on noncompliant schools – those that don ’t meet the local ventilation requirements. Brennan (1991) conducted a study of nine US noncompliant schools, reporting mid-afternoon CO2 measurements. Concentrations ranged from approx. 400 to 5000 ppm with a mean average of 1480 ppm. The CO2 concentrations exceeded the 1000 ppm ASHRAE ventilation standard in 74 percent of the rooms.
There are two main ways to measure CO2 in the classroom. The first is the continuous method, and is the most accurate for long term results. This method was used in 2006 by, Grimsrud et. al. Here they collected data using continuous monitoring in 85 classrooms and other spaces located in eight schools in Minnesota, US, during the 2003–04 school year. Measurements were made using unobtrusive sensor packages mounted on classroom walls that transmitted data to a remote site using the Internet. The method of testing was a continuous method (20 sec intervals) using PureTrac continuous IAQ monitoring systems. Rooms were representative of typical classrooms state wide in terms of size, type and use. Monitors were placed 1.5 above the ground and out of direct path of any airflows from ventilation systems. The second method is spot testing. An example of this can be seen in the testing done by Shendell et al. (2004), here they uses a similar methodology to that of what we used, testing classrooms by recording short-term measurements of CO2 during school hours. Inside each classroom, two short term measurements, each no more than a 5min average, were conducted sequentially and the measurement times were recorded. First, indoor CO2 was assessed near the centre of the classroom at the breathing zone height of seated students and not directly underneath the supply air diffuses. Secondly, the CO2 concentration in the HVAC supply air was measured. Indoor CO2 concentrations are difficult to adequately characterise, as they are a function of occupancy and ventilation rate, both of which vary as a function of time. (Daisey et al. 2003). Grab samples or other short-term measurements, such as the point testing, which we are using may be inadequate to provide information on the long-term ventilation conditions in primary schools. But as Shendell et al (2004), report in their findings, it is enough to warrant whether there is concern for a further, larger study in CO2 concentrations.
Poor ventilation in schools maybe more important than other buildings. Children are more susceptible to some environmental pollutants than adults, as they breath higher volumes of air relative to their body size. Because children are physically smaller than adults, their metabolic rate is higher and they consume more oxygen relative to their size. Therefore, a child ’s exposure to air pollutant is greater than that of an adults. (C. F. Bearer, 1995, Landigram, 1998) Furthermore it is not just the quantity of pollutants but also the type. Even though CO2 is evenly dispersed within a room, breathing zones, are closely related to the quality of air intake. The breathing zone for an adult is usually 1.2 to 1.8 meters off the ground. A primary school students’ breathing zone is considerably lower. Grimsrud (2006), shows that environmental pollutants are often more present at a child’s breathing zone than that of an adults. Bearer (1995) also shows that it is within these lower breathing zones that heavier chemicals such as mercury and large breathable particles settle
Testing recorded short-term measurements, approximately 30 seconds of CO2 in 20 classrooms from 2 primary schools in the Devonport area. Room size and student occupation numbers were recorded and reflected the typical Devonport classroom. The method of CO2 measuring was consistent with Shendell (et. al. 2004), and Grimsrud (2006) where measurements were taken 1.5m above the ground. Approx height of child ’ s breathing zone. The technique used to measure CO2 concentration was kept constant. Environmental conditions, such as temperature, glare, noise, and wind were recorded, along with the percent of windows closed to see if these conditions were resulting in the windows being closed. These were measured by observation and recorded in the proforma. CO2 measurements were compared with these results to determine if CO2 increases when windows in the classroom are closed for a variety of reasons.
NOTE LOW SD and how it became larger later To validate our method of testing, we trialed the technique beforehand in a controlled environment. Consistent results were found after a series of test. The CO2 measuring technique was tested through taking ten separate CO2 measurements in a controlled CO2 environment. Spot measurements were taken for approximately 30 seconds each, with the measuring device being held at arms length from the person recording. Results from the ten separate tests concluded that this way of measuring could be repeated, with a standard deviation of the results averages being 13ppm. Results aslo concluded that the sensor needs 15 seconds to calibrate, and therefore this time period was taken out of the final results.
In order to relate a cause and effect of windows being closed due to a variety of reasons and a build up of CO2, we measured through observation in each classroom, the total area of windows, their orientation, the percent that where operable, and then how many were open. We also recorded floor area, height and whether the room had connections to hallways or open out spaces, as larger volume spaces and student occupancy have a direct correlation with CO2 build up over time. We then recorded the conditions that we thought may have impacted on the windows being closed. Glare, wind, outside noise levels and distractions
Our results show that lower CO2 levels are clearly linked to the ventilation type and cross ventilation has >99% chance of being effective. Ventilating to an outside window is also effective but not enough to reduce levels to under 1000 PPM. Openings to shared hallways where seen to be not effective in reducing any CO2 level and little better than no openings at all.
The other more complex hypothesis was that design outcome may have a intended outcome in terms of IAQ. We have two outcomes that lead use to believe this hypothesis may be true. Firstly, of the two school tested DPS was in an active area with some traffic noise, 80% of the rooms had the blinds completely drawn and only one room was open to the outside - this was a room facing a private internal court. The EUPS School, in a quite ocean side position was the opposite with most windows free of blinds (90%) and 80% open to the outside. The second school had an average of a statistically significant 300 PPM Co2 less (P=0.15). The final observation is the not statistically significant but encapsulates the issue. Two rooms at EUPS with the same orientation and the same number of students (15) had CO2 levels of 900 and 1500 respectively. In the second room the teacher (who was the principal) had the windows closed to save heat energy costs, the first room had the windows ajar. If a similar response is forced on teachers because of glare, noise, cold winds, distracting outlooks or simply trying to make AC systems work effectively, then the outcome is likely to be the same More testing needs to be done in order to gain more reliable results.
