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Guidance for standard evaluation procedures of indoor environmental parameters in schools
Prof. Dr.-Ing. Thomas
Hartmann,
Dipl.-Ing. Christine Knaus
(ITG Dresden Institute for Building Systems Engineering – Research and
Application)
Prof. Dr.Ing Martin H.
Spitzner (engineering office for energy, building physics and projects)
A meta study “Fundamentals
and concept development for the analysis of practice-oriented ventilation
concepts for mechanical or window ventilation” shows with the focus on Germany
an evaluative overview of the current state of research regarding to
CO2-concentration during lessons in schools. For a systematised comparison of
measurement results a number of options to the graphical presentation like
Carpet-Plots, Box-Plots and scatter diagrams were examined. The analysis shows
that caused by the different aims of the individual studies a direct comparison
between different studies is hardly possible and many questions are still open.
Future studies regarding this subject should be oriented towards the defined
“ideal study” taking into consideration minimum requirements for the documented
information and factors.
Within the
framework of the further development of the "Assessment System for
Sustainable Building" (Bewertungssystem Nachhaltiges Bauen - short BNB)
and the evaluation criteria profile for "indoor air hygiene"
respectively, a number of parameters (CO2 measurements, indoor
climate, indoor thermal comfort, surveys on individual comfort experience) are
evaluated for a number of field-tested ventilation solutions. With the focus on
classrooms, recommendations for action for practice-oriented ventilation
concepts as well as proposals for a well-argued evaluation approach in relation
to the CO2 requirements are established.[1]
Keywords:
ventilation, sustainable building, school, CO2
Background
The Federal
Government of Germany has defined mandatory specifications for holistically
improved buildings in the "Guideline for Sustainable Building" and
the "Assessment System for Sustainable Building" (short BNB). Since
October 2013, the BNB system is compulsory for the design and realisation of
Federal Government buildings and was partially revised and updated in 2015.
With regard to indoor air hygiene, particularly indoor air pollution by
pollutants from building products and by carbon dioxide emissions from users
are in focus.
Both the
current normative requirement for outdoor air volume flow per person and the
recommendations within the relevant workplace directive do not take into
account all necessary parameters which govern the effectiveness of a suitable
air exchange rate. From technical discussions and practical experience, it is
known that poor ventilation leads to problems with respect to indoor air CO2
concentration and, where appropriate, with respect to thermal comfort. This is
especially true for rooms with high occupancy. It is also especially true for
rooms with window ventilation but it affects also rooms with mechanical
ventilation or a combination of both.
Concept
For the
further development of BNB (evaluation system for sustainable buildings) the
meta study “Grundlagen- und
Konzeptentwicklung für die Analyse von praxisgerechten Lüftungskonzepten bei
mechanischer oder Fensterlüftung” (fundamentals and concept development for the
analysis of practice-oriented ventilation concepts for mechanical or window
ventilation) shows with the focus on Germany an evaluative overview of the
current (published) state of research regarding to CO2-concentration
during lessons in schools. 6 studies of the requested 15 studies could not be
analysed, because no measurement values were available or no feedback was
received. The raw data of the other 9 studies (see Table 1)
could be prepared according to a standard procedure.
Table 1. Summary of the considered studies.
Considered studies | Brief description |
Müller | 9 schools in Berlin were
examined. They were different
regarding to type of building, implemented restructuring measures and
ventilation concepts. For a period of one day of class respectively one week
of class random measurements in selected classrooms were done with regard to
indoor air temperature, relative humidity, C02-concentration,
sound pressure level and air velocity. Window ventilation as well as
mechanical ventilation were considered. |
Bischof | 10 schools in Erfurt were
selected for this study. During the study the classrooms where not ventilated
during the lessons, but only in the breaks in all classrooms for two days CO2-concentrations,
relative humidity and operative temperature and additionally in some
classrooms the airborne germ rate was measured. The classrooms were ventilated by window
ventilation, shaft ventilation and mechanical ventilation systems. |
Fromme | Schools located in Munich
and in the District of Dachau were chosen for this study. During the measurement
in the winter 46 schools (in total 62 days) and during the measurement in the
summer 38 schools have been more closely analysed. CO2-concentration,
relative humidity, temperature and sometimes further air chemistry parameters
were measured. So far as this is known, the classrooms were ventilated by
window ventilation. |
Lambertz | This study took a closer
look at a vocational college in Aachen after renovation. Different mechanical
ventilation systems were compared among each other by measuring the CO2-concentration,
temperature, relative humidity, VOC emissions and energy consumption. For
comparative purposes measurements with window ventilation were done bevor the
renovation started. |
Dietz/Sick | The primary school Hohen
Neuendorf has been equipped with a hybrid ventilation (mechanical ventilation
for the basic ventilation in combination with automatically opening windows
and normal windows with a “ventilation signal light”). In two selected
classrooms detailed parameters with regard to indoor air quality (CO2-concentration,
relative humidity, air temperature, radiation temperature and climate data)
were recorded. |
Bolsius | The individual elements of
the rehabilitation were assessed after the energy rehabilitation of the
school complex in Olbersdorf. The energy-efficient school ventilation
consists of supply box-type windows (windows with framed grounds) in
combination with a CO2 controlled exhaust ventilation system. For selected
classrooms the CO2-concentration, temperature, illuminance and
outside climate were recorded. |
Wargocki | A Danish study took a closer
look at two mechanically ventilated classrooms of a comprehensive school (age
of pupils: 6 to 16 years). In a blind crossover design with new and soiled
filters, high and low ventilation rates performance test, indoor air
parameters (CO2-concentration, temperature, relative humidity,
etc.) and as well questionnaires were documented. The boundary conditions
were defined for one week. The experiment was performed both in winter and in
summer. |
Lahrz | A closer look at
energetically rehabilitated schools in Berlin regarding the air quality
during the heating period was taken in this study. Classrooms with window
ventilation were considered as well as classrooms with mechanical
ventilation. Parameters like carbon dioxide, temperature, relative humidity
and diverse dust fractions were documented for a school week. |
Birmili | Study to determine the
„Leitfaden für die Innenraumhygiene in Schulgebäuden“ (Guideline for Indoor
Air Hygiene in schools) of the Federal Environmental Agency (UBA) as well as
the EU joint project “Sinphonie” (further information are not available,
because no publications are available) |
To evaluate
CO2-concentrations measured over a longer period usefully, it is
necessary to know the school hours. Studies where the school hours remained
unknown are analysed by a VBA-based evaluation.
For a
systematised comparison of measurement results a number of options to the
graphical presentation like Carpet-Plots, Box-Plots and scatter diagrams were
examined (see Figure 1). In this study the evaluation was
carried out mainly with scatter diagrams for individual lessons or individual
classrooms to avoid possible increased weighting caused of individual studies.
|
|
|
Figure 1. Exemplary
presentation as Carpet-Plot (left) – Box-Plot (top right) – scatter diagram (on
the bottom right).
In the
framework of this study the following measurements of CO2-concentration
exist:
·
Window
ventilation (5 studies): 652 lessons in 121 classrooms in at least 16 schools
·
Hybrid
ventilation (1 study): 375 lessons in 2 classrooms in 1 school
·
Mechanical
ventilation (5 studies): 513 lessons in 38 classrooms in 12 schools.
Results
The
following recommendations can be concluded for the individual ventilation
concept due to the findings of the meta study as well as of the publications on
individual studies and the participation in the AIVC-Workshop:
Window ventilation
Figure 2. Scatter
diagram of the arithmetic mean for window ventilation of the considered studies
(lessons).
Figure 2shows that:
·
16%
of the lessons have an arithmetic mean of the CO2-concentration that
meets the quality level 1 or 2 of BNB and comply with a positive BNB evaluation
of the building and with the workplace regulation ASR A3.6. 35% of the lessons
meet the quality level QN 0 (1000 ppm to 1400 ppm = 0 points
according to BNB / non-compliance with ASR (workplace regulations)), 10%
quality level QN 1 (800 to 1000 ppm) and 6% quality level QN 2 (< 800 ppm).
·
The
arithmetic mean of the CO2-concentration depends clearly on time. In
later hours of the day the probability that the arithmetic mean is under 1000 ppm
decreases. (1. and 2. lesson with 23% and. 21% < 1000 ppm vs. 6.
and 7. lesson with 7% respectively 3% < 1000 ppm).
·
A
clear dependence of the CO2-concentration on the ventilation habits
could not be shown. Lessons with tilted windows and closed windows lead to
similar frequency of mean CO2-concentrations under 1000 ppm (35%
respectively 40%), whereas full opened windows lead to a decreased room air
quality (only 15% of lessons with arithmetic mean < 1000 ppm).
Causal should be that in the questionnaires the duration of ventilation
processes was not documented.
Hybrid ventilation
In the
framework of this study hybrid ventilation is the combination of mechanical
ventilation which is designed for the basic ventilation and a user-independent
automatically window ventilation for example with servomotors at the windows.
Figure 3. Scatter
diagram of the arithmetic mean for hybrid ventilation of the considered studies
(lessons)
Figure 3shows that:
·
7%
of the lessons have an arithmetic mean of the CO2-concentration that
meets the quality level 1 or 2 of BNB and comply with a positive BNB evaluation
of the building and with the workplace regulation ASR A3.6. 42% of the lessons
meet the quality level QN 0 (1000 ppm to 1400 ppm = 0 points
according to BNB / non-compliance with ASR (workplace regulations)), 5% quality
level QN 1 (800 to 1000 ppm) and 2% quality level QN 2 (< 800 ppm).
·
The
arithmetic mean of the CO2-concentration depends clearly on time. In
later hours of the day the probability that the arithmetic mean is under 1000 ppm
decreases. (1. lesson with 52% < 1000 ppm vs. 5. lesson with 4% < 1000 ppm).
The observed increase in the room air quality after the 5. lesson can be
probably traced back to a change in use in the afternoon. Characteristic of
elementary schools are also whole-day classes in smaller groups for example
joint ventures or homework done under supervision.
Mechanical ventilation
Figure 4. Scatter
diagram of the arithmetic mean for mechanical ventilation of the considered
studies (lessons).
Figure 4shows that:
·
39%
of the lessons have an arithmetic mean of the CO2-concentration that
meets the quality level 1 or 2 of BNB and earns a certification of the building
according to BNB. 53% of the lessons meet the quality level QN 0 (1000 ppm
to 1400 ppm = exclusion from building certification according to BNB /
non-compliance with ASR (workplace regulations)), 27% quality level QN 1 (800
to 1000 ppm) and 12% quality level QN 2 (< 800 ppm).
·
Based
on arithmetic mean values and maximum values of the measured CO2-concentration
statistical parameters (median as well as 10. and 90. percentile) were
determined for classrooms if there are measurement values for more than one
lesson per classroom.
A
comparative overview of the CO2-concentrations shows that with
mechanical ventilation 38% in the total of 513 considered lessons meet an
average value under 1000 ppm, respectively under 1500 ppm are 94% of
the lessons. The arithmetic mean of the CO2-concentration of a
lesson with window ventilation is under 1000 ppm in 16% of cases in the
total of 652 considered lessons, 58% meet under 1500 ppm.
Regardless
of the ventilation concept a reduction of number of students respectively an
increase of classrooms, finally a larger area per person, results in lower CO2-concentrations
in classrooms.
Arithmetic
mean values of the CO2-concentration under 1000 ppm can be met
for window ventilation and hybrid ventilation easiest in the early lessons. In
the later lessons of the day a lower CO2-concentration can only be
reached taking into account certain boundary conditions like for example long
break with intensive cross ventilation, a longer duration without teaching or
smaller students per class.
Hybrid
ventilation concepts combine mechanical ventilation with user-independent
automatically window ventilation (for example motorised casements). The
mechanical ventilation system provides a cost- and sound-optimised basic
ventilation. This basic ventilation is supported by the automatically window
ventilation in case of peak loads.
Ventilation
systems should be designed for example according to DIN EN 13779 IDA 2, so no additional
ventilation during the lesson is necessary. Organisational restrictions,
discomfort of the persons in the room (temperature, draft risk) and disturbance
through sound by window ventilation could be avoided with such a design. By
optimising the control and operation mode of mechanical ventilation an
improvement of the indoor air quality and an increase of acceptance can be
reached.
In the
current evaluation system BNB for school buildings the evaluation of the CO2-concentration
is made on the basis of requirements regarding to the (arithmetic) mean value
and the maximum value of a lesson of 45 minutes. In future, the following
extension options could be considered:
·
Determination
of maximum values based on the moving average over 5 minutes
·
Determination
of mean values based on the acceptable frequency of CO2-values per
lessons over a limit value (mathematical: percentile)
·
Determination
of a cumulative CO2-exposure in ppmh (per lesson, school day,
school week)
·
Creation
and if necessary BNB certification of a tool to classify according to BNB
evaluation system
The
analysis shows that caused by the different aims of the individual studies a
direct comparison between different studies is hardly possible. For future
studies, especially in the context of the evaluation and optimization of the
BNB, the requirements for the parameters of an “ideal study” can be derived
(see Table 2).
The
research project shows that although so many different studies were implemented
many questions are still open respectively have not been finally clarified yet.
Answering these open questions should be tried in future studies. Such future
studies regarding this subject should be oriented towards the defined “ideal
study” taking into consideration minimum requirements for the documented
information/factors.
Table 2. Parameter of the „ideal study“.
General
parameters | |
-
Ventilation system (window
ventilation, mechanical ventilation, hybrid ventilation) -
Number of schools -
Type of school (primary
school, secondary school) -
Number of classrooms (same
number of ventilation system) -
Number of lessons (same
number of lessons per classroom) -
Room occupancy (protocol) -
Age of pupils (class level) -
Area and volume of the classroom -
Lesson and break time -
Measurement period (for
example one week in summer, winter, transition period) define minimum
standards -
Measurement of outdoor air
conditions where the school is located (wind, temperature, CO2,
etc.) -
Measurement of carbon dioxide
in classrooms (one-minute interval) -
Logging of the situation in
the breaks -
Uncertainty of the
measurement technique, automation → Analysis not immediately after the
commissioning, after all errors have been eliminated, stable running system -
Calibration of the measurement technique -
Measurement technique
(arrangement, type, precision) -
Comfort (thermal comfort,
sound…) as measurement or/and questionnaire | |
Additionally,
with window ventilation | Additionally, with mechanical ventilation system |
-
Window profile (dimensions, number
of casement, opening options [buttom hung, side-hung]) -
documentation of ventilation
with information about window position and duration of the ventilation for the
lessons and the breaks including information which window is opened -
Kind of ventilation
(one-sided or cross ventilation) -
Ventilation concept | -
Information of the
ventilation system (operating period, operating mode, contact switches at the
windows, CO2-control, combination of automatically casements etc.)
-
Volume flow rate
(development, actual state) -
Planned size (CO2,
temperature, volume flow etc.) |
Additionally, with hybrid ventilation | |
Combination of the listed
parameters of window ventilation and mechanical ventilation system - planned volume flow rates
(shares mechanical ventilation and window ventilation) | |
Supplementary (optional) recommendations | |
-
Measurement of pollutants in classrooms (formaldehyde,
radon, particulate matter etc.) (particulate matter PM based on the
aerodynamic diameter 10 µm, 2,5 µm respectively 1 µm with
PM10, PM2,5 and PM1classified) -
Performance tests | |
Literature/References
[Bebersdorf] | Bebersdorf J. (2010): Untersuchungen zur Raumluftqualität an Erfurter
Schulen. (Dissertation) Jena: Universität Jena. |
[Bischof1] | Lahrz T.; Bischof W.; Sagunski H. et al. (2008): Gesundheitliche
Bewertung von Kohlendioxid in der Innenraumluft. (Mitteilungen der
Ad-hoc-Arbeitsgruppe Innenraumrichtwerte der Innenraumlufthygiene-Kommission
des Umweltbundesamtes und der Obersten Landesgesundheitsbehörden, Artikel aus
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz, Heft 11). |
[Bischof2] | Bischof W. (2010): Kurzbericht über die 2. Messwoche in 2 Klassenräumen
der Jenaplanschule. (unveröffentlicht) Jena. |
[Bolsius] | Bolsius J.; Grötzschel J.; Hennig A. et al. (2014): Vorbildhafte
Energetische Sanierung des Schulkomplexes Olbersdorf. (Schlussbericht)
Zittau. |
[Dietz] | Sick F. und Dietz S. (2015): Monitoring Plusenergie-Grundschule Hohen
Neuendorf und IEA Task 41 (Solar Energy and Architecture). (Schlussbericht)
Berlin. |
[Fromme1] | Fromme H.; Dietrich S.; Kiranoglu M. et al. (2006): Frische Luft an
bayrischen Schulen - Untersuchungen zur Verbesserung der Luftqualität.
(Vorläufige Zusammenfassung). |
[Fromme2] | Fromme H.; Heitmann D.; Dietrich S. et al. (2008): Raumluftqualität in
Schulen - Belastung von Klassenräumen mit Kohlendioxid (CO2), flüchtigen
organischen Verbindungen (VOC), Aldehyden, Endotoxinen und Katzenallergenen.
(Artikel aus Gesunheitswesen, Heft 70). |
[Lahrz] | Lahrz T.; Burghardt R.; Pfeiler P. et al. (2016): Luftqualität in
Schulklassenräumen im Anschluss an energetischen Sanierungen. (Kurzfassung). |
[Lambertz] | Lambertz M.; Klima M.; Bähr R. et al. (2006): Energetische
Sanierung der Käthe Kollwitz Schule in Aachen - Förderung Energetische
Verbesserung der Bausubstanz. (Schlussbericht) Aachen. |
[Müller] | Müller B.; Geier M. und Krimmel P. (2014): Raumluftkonditionierung in
Schulen bei Neubau und Sanierung unter Beachtung ökonomischer, ökologischer
und soziokultureller Aspekte. (Projektbericht) Berlin. |
[Sinphonie] | Stylianos Kephalopoulos (Europäische Kommission
G.F.É.C.(.U..Y.B.d.B.(.N.E.d.O.F.(.-F.P. (2014): Leitlinien für eine gesunde
Umbegung in europäischen Schulen. (Abschlussbericht) Luxemburg: Europäische
Komimission. |
[Wargocki] | Wargocki P. und Wyon D.P. (2007): Indoor Enviromental Effects On The
Performance Of School Work By Children (1257-TRP). (Final Report). |
[1]Acknowledgements: The research project (10.08.17.7-16.33) has
been financed by the research initiative “Future Building” of the German
Federal Ministry of Environment, Nature Conservation, Building and Nuclear
Safety. The project has been supervised by Heidemarie Schütz and Dr. Olaf
Böttcher from the German Federal Institute for Research on Building, Urban
Affairs and Spatial Development (BBSR). https://bit.ly/2GqNOlK
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