1. INTRODUCTION
⌅Indoor
Environment Quality (IEQ) attracts scientific interest especially when
it concerns the health of vulnerable populations such as children. IEQ
refers to the state of health and comfort conditions of the different
elements that condition our life. The main aspects to be considered to
ensure the IEQ must satisfy the conditions of thermal comfort, acoustic
comfort, visual comfort, physical-chemical and microbiological
contaminants in the air, and the electromagnetic environment (1(1) Bluyssen, P.M. (2009). The Indoor Environment Handbook. How to make buildings healthy and comfortable. London: Routledge.
).
The indoor environment should not hinder the learning of the children,
e.g. with high noise level, overheated rooms or inadequate lighting
conditions or stuffy and unhealthy air. Unfortunately, many schools do
not provide an adequate indoor environment. Air supply rate is
insufficient and temperatures are too war during summer months (2(2)
Grün, G., & Urlaub, S. (2015). Impact of the indoor environment on
learning in schools in Europe. Fraunhofer-Institut für Bauphysik IBP
2(5), 5.
).
In relation to thermal comfort,
particularly in Spain and Portugal, but also in southern Europe, there
is an alarming situation. The impacts of climate change are affecting
and will affect all European cities but with regional and local
differences. The regions of Southern Europe are already experiencing a
marked increase in maximum temperatures and a consequent and marked
decrease in rainfall. More frequent heat waves and changes in the
distribution of infectious diseases sensitive to climate change are
expected to increase, which will result in risks to human health and
wellbeing (3(3) European Commission. (n.d.). Climate change consequences. Retrieved from https://ec.europa.eu/clima/change/consequences_en
). The month of June 2017 was marked by high
temperatures across Western Europe with heat waves triggering national
heat-health plans and wildfires requiring evacuations in Portugal and
Spain, sending monthly mean temperatures about 3 degrees Celsius (4.8
degrees Fahrenheit) above normal levels (1981-2010) (4(4) Thompson, A. (June 29, 2017) Climate central. Global Warming Tipped Scales in Europe’s Heat Wave. Retrieved from https://www.climatecentral.org/news/warming-tipped-june-heat-wave-21585
). The heat wave in 2017 highlighted the lack of
adaptation strategies to climate change of educational buildings since
it took place during the school period. Other heat waves have taken
place on dates (5(5) World weather attribution (n.d.). Retrieved from https://www.worldweatherattribution.org/
) when most of the educational centers are not occupied and data of indoor temperatures was not recorded.
During
these heat waves, temperatures above 32ºC inside public education
centers were reached. This problem has generated an important social
alarm in the warmer regions of Spain; children went to school with water
sprayers, extreme circumstances occurred in the warmest regions, and in
large cities where the problem is accentuated by the thermal island
effect (6(6)
Agencias. (June 15, 2017). La solución del consejero de Sanidad de
Madrid para los colegios en plena ola de calor: “Dobla, dobla, dobla y
que hagan abanicos de papel”. El Mundo. Retrieved from https://www.elmundo.es/madrid/2017/06/15/594229a5468aebba588b460c.html
, 7(7)
Gómez, G., Frutos, B., Alonso, C., Martín-Consuegra, F., Oteiza, I., De
Frutos, F., Castellote, M.M., Muñoz, J., Torre, S., Fermoso, J.,
Torres, T., Antón, M.A., Batista, T., Morais, N., 2021. Selection of
nature-based solutions to improve comfort in schools during heat waves.
Int. J. Energy Prod. Manag. 6, 157-169. https://doi.org/10.2495/EQ-V6-N2-157-169
). Therefore the press in Spain echoes this
pressing situation in educational centers on their covers. For example,
the following press releases for this year 2017: The Andalucía
Government gives permission to students to miss classes due to the heat
wave with their parents’ authorization (8(8) 20 minutos. La Junta de Andalucía da permiso a los alumnos para que falten a clase por la ola de calor. https://www.20minutos.es/noticia/3068977/0/junta-andalucia-autoriza-faltar-a-clase-por-ola-calor/#xtor=AD-15&xts=467263
). The Community of Madrid has announced that schools may shorten the day due to high temperatures (9(9) 20 minutos. Los colegios de Madrid podrán reducir la jornada lectiva por la ola de calor. Retrieved from http://www.20minutos.es/noticia/3066061/0/colegios-madrid-ola-calor-reducir-jornada-lectiva/#xtor=AD-15&xts=467263
). In Valdemoro (Madrid) five students were
treated for symptoms of heat stroke, the rest of the students, as an
emergency measure, were transferred to the mortuary of the municipality,
being the nearest cool place, with vegetation and shade (10(10) 20 minutos. Atendidos cinco alumnos por síntomas de golpe de calor en un instituto madrileño. Retrieved from http://www.20minutos.es/noticia/3065817/0/atendidos-alumnos-golpe-calor-instituto-madrid/#xtor=AD-15&xts=467263
) The BBC’s “Maximum temperature call for heatwave classrooms” shows a similar situation in other European Union countries (11(11) BBC news. Maximum temperature call for heatwave-hit classrooms. Retrieved from http://www.bbc.com/news/education-23374561
).
Studies carried out conclude that there
is an effect on student’ performance as a result of anomalous
temperatures inside their classrooms (12(12) Nicol, F. (2013). The Limits of Thermal Comfort: Avoiding Overheating in European Buildings. London: CIBSE TM52.
).
Heat makes pupils lethargic, can affect concentration and lead to
fainting. Warmer and more humid conditions generally seem to have a
negative impact on learning; while in the early years specifically, poor
air quality and high noise levels have a negative impact (13(13) Keeble, D. R. (2016). Effective Primary Teaching Practice Teaching schools Council. London: Teaching Schools Council.
). A survey was performed (14(14)
De Dear, R., Kim, J., Candido, C., & Deuble, M. (2015). Adaptive
thermal comfort in Australian school classrooms. Building Research &
Information 43(3), 383-398.
) over 150 school
buildings finding neutral and preferred operative temperatures were
found to be about 22.5°C, which falls below predictions of both
Predicted Mean Vote index (PMV) and adaptive models of thermal comfort.
This finding reiterates the findings of other researchers (15(15)
Auliciems, A. (1972). Classroom performance as a function of thermal
comfort. International Journal of Biometeorology 16(3), 233-246.
, 16(16) Auliciems, A. (1973). Thermal sensations of secondary schoolchildren in summer. Journal of Hygiene 71(3), 453-458.
),
but a coherent explanation of why children’s thermal sensation and
temperature preference fall 1-2°C below those of adults is yet to be
developed. It is especially interesting that the student group exposed
to more diverse indoor and outdoor thermal environment showed greater
degrees of thermal adaptability.
Air quality is another factor
that influences learning, the available research indicates that
increased ventilation rates in classrooms are associated with reduced
student absence, but the available data is limited (17(17) Fisk, W. J. (2017). The ventilation problem in schools: literature review. Indoor air 27(6), 1039-1051.
).
In the early years specifically, poor air quality has a negative
impact. CO2 concentrations seem to affect attendance. Based on a review
of literature published in refereed archival journals a majority of the
averages and medians of time-average concentrations also exceeded 1,000
ppm with maximum values ranging from 1,400 ppm to 5,200 ppm (18(18)
Gaihre, S., Semple, S., Miller, J., Fielding, S. & Turner, S.
(2014). Classroom carbon dioxide concentration, school attendance and
educational attainment. Journal of School Health 84, 569-574.
).
Concentrations of CO2 do not appear to be systematically higher or
lower in naturally ventilated classrooms relative to mechanically
ventilated classrooms. This CO2 data indicates a widespread failure to
provide the minimum amount of ventilation specified in standards for
classrooms.
A 1,000 ppm-rise in CO2 concentration leads to
increased absenteeism of 10-20%and every increase of 100 ppm leads to a
decrease in annual attendance of about 0,2% (19(19)
Mendell, M.J., Eliseeva, E.A., Davies, M.M., Spears, M., Lobscheid, A.,
Fisk, W.J. & Apte, M.G. (2013). Association of classroom
ventilation with reduced illness absence: a prospective study in
California elementary schools. Indoor Air 23, 515-528.
).
If ventilation rates were increased over the recommended values (which
in fact is not the case in many schools, as outlined above), the illness
caused absence rate would seem to be reduced by about 11-17% (18(18)
Gaihre, S., Semple, S., Miller, J., Fielding, S. & Turner, S.
(2014). Classroom carbon dioxide concentration, school attendance and
educational attainment. Journal of School Health 84, 569-574.
).
An earlier study of one hundred elementary schools from two school
districts in the Southwest United States found that 87% of classrooms
studied (one classroom per school) had ventilation rates below 7.1 l/s
per person (20(20)
Haverinen-Shaughnessy U., Moschandreas D.J. & Shaughnessy R.J.
(2010). Association between substandard classroom ventilation rates and
students’ academic achievement. Indoor Air 21(2), 121-131.
).
The 7.1 l/s per person value was the minimum prescribed rate in the
2004 version of ASHRAE Standard 62, and is comparable to the 2013
version of the ASHRAE Standard. In addition, there was a linear
association between classroom ventilation rates and students’ academic
achievement within the range of 0.9-7.1 l/s per person.
The
evidence of an association of increased student performance with
increased ventilation rates is compelling. There is evidence of
associations of reduced respiratory health effects and reduced student
absence with increased ventilation rates (15(15)
Auliciems, A. (1972). Classroom performance as a function of thermal
comfort. International Journal of Biometeorology 16(3), 233-246.
).
Whatsoever, this trend supports the importance of a proper design and
operation of classrooms with respect to ventilation. In the AIRMEX study
(21(21)
Geiss, O., Giannopoulos, G., Tirendi, S., Barrero-Moreno, J., Larsen,
B. R., & Kotzias, D. (2011). The AIRMEX study-VOC measurements in
public buildings and schools/kindergartens in eleven European cities:
Statistical analysis of the data. Atmospheric Environment 45(22),
3676-3684.
) Indoor VOCs were measured in 11 European
cities, also in schools. All the measured substances were prevailing in
the indoor environment, and seasonal variations were analysed due to
changes in ventilation rates (20(20)
Haverinen-Shaughnessy U., Moschandreas D.J. & Shaughnessy R.J.
(2010). Association between substandard classroom ventilation rates and
students’ academic achievement. Indoor Air 21(2), 121-131.
).
According
to data provided by the Ministry of Education, Culture and Sport, in
Spain, there are a total of 27,790 schools, of which 18,855 are public (22(22) Ministerio de Educación y Formación Profesional. Datos y Cifras del curso escolar 2013-2014. Retrieved from http://www.educacionyfp.gob.es/prensa/actualidad/2013/09/20130916-datos-cifras.html
). Around 68% of Spanish students attend their
studies in a center of public ownership while the average in Europe is
81%. The annual expenditure per pupil in Spanish public centers was
€7,861 for the period 2013/2014, which exceeds the average of the
European Union (€6,829). According to official data, as a general rule
it can be said that the total energy consumption in schools is: heating
(30%), air conditioning (35%) and lighting (35%) (23(23)
Consejería de Economía y Hacienda, organización Dirección General de
Industria, Energía y Minas. (2011). Guía de ahorro y eficiencia
energética en centros docentes. Madrid: Fenercom.
).
This
work is based on the hypothesis that most educational centers in Spain
do not comply with the minimum requirements of Indoor Environmental
Quality. Temperature and CO2 concentration are measured. Temperature
related to thermal comfort analysis, which has generated social alarm in
Spain since the heat wave in 2017 and CO2 related to Air Quality
analysis is not an issue that has aroused social alarm. Therefore, in
Spain, despite the increasing number of energy studies on educational
centers, there is not yet a characterization of educational buildings
developed but studies of several buildings. One study approximates the
need to characterize school buildings by using previous classifications
made for residential buildings (24(24)
Liébana Durán, Esther; Serrano Lanzarote, Begoña; Ortega Madrigal,
Leticia. (2017). Análisis tipológico de centros escolares para
caracterizar los consumos energéticos. El caso de la ciudad de Valencia.
Proceedings 3er Congreso Internacional de Construcción Sostenible y
Soluciones Eco-Eficientes.
). Most of the existing
residential buildings in Spain have been built after the 2nd half of the
20th century (circa 90%). Parallel to housing construction, schools
where built, even though there is no characterization available, the
bigger amount of school buildings were built before the 2006, when
building regulations did not consider mechanical ventilation. Generally,
educational centers do not have mechanical ventilation and do not have
any ventilation protocols, in Mediterranean climate there is the
possibility to regularly ventilate but this act depends on the teachers’
habits and perception, so it is proposed to monitor this parameter to
determine what the situation is.
The objective of this work is, therefore, to analyze the situation, determine the causes that influence the aforementioned aspects and offer measures to correct the deviations recorded and improve the quality of the Indoor Environment of classrooms.
2. METHODOLOGY
⌅2.1. Case studies
⌅The study was carried out in three educational centers located in Madrid whose characteristics are shown in table 1.
The intention is to analyze buildings prior to 1979, as they are a
cluster of inefficiency in Spain, since they lack thermal insulation (25(25)
Oteiza, I., Alonso, C., Martín-Consuegra, F., González-Moya, M., Monjo,
J., 2015. Energy Retrofitting for Social Housing by Improving the
Building Envelope: Madrid, 1939-1979.
). However, a
recently constructed building was included in the sample, to analyze the
possible influence of the newest regulations. None of the educational
centers have mechanical ventilation. In all cases ventilation is done
manually by opening windows.
Three spaces were selected in each educational center. Different orientations were taken in order to include possible variations in wind and solar incidence.
| Educational Center A | Educational Center B | Educational Center C | |
|---|---|---|---|
| Eduacational Level | Infant and Primary | High School | High School |
| District | Hortaleza | Chamberí | Chamartín |
| Average income of the neighborhood (€) (26(26) Ayuntamiento de Madrid. Renta por barrios. Retrieved from https://www.madrid.es/UnidadesDescentralizadas/UDCEstadistica/Nuevaweb/Econom%C3%ADa/Renta/Urban%20Audit/urban%20audit/Renta%20media%20de%20los%20hogares%20(Atlas%20de%20distribuci%C3%B3n)/31097dbs_17.xlsx ) |
36,691 | 59,459 | 62,635 |
| Number of students | 200 | 800 | 700 |
| Class schedule | 9:00 - 13:30 15:30 - 17:00 | 9:00 - 15:00 | 9:00 - 15:00 |
| Construction year | 1967 | 1965 | 2010 |
| Area (m²) | 3,048 | 9,742 | 7,176 |
| Opaque facade | Single layer ceramic wall without thermal insulation | No opaque parts. Glazing facade (curtain wall) | Two layer ceramic wall with thermal insulation |
| Window frame | Aluminum without thermal break | Aluminum without thermal break | Aluminum with thermal break |
| Window glass | Single glass 3mm | Double glazing 3/6/3 | Double glazing 4/6/6 |
2.2. Data collection
⌅Data
of CO2 concentration and temperature are registered in the selected
buildings as case studies. Data is obtained with Wöhler CDL 210 data
recorders (27(27) Wöhler, 2020. Registrador de CO2 CDL 210 [WWW Document]. URL https://www.pce-iberica.es/medidor-detalles-tecnicos/instrumento-de-registrador/registrador-cdl210.htm
). They offer a CO2 measurement range between 0
and 2,000 parts per million (ppm), with an accuracy of 50 ppm ± 5% and a
resolution of 1 ppm. They use the NDIR procedure (non-dispersive
infrared absorption analyzer) as a measurement principle. They offer a
range of temperature measurement between -10ºC and + 60ºC with an
accuracy of ± 0.6% and a resolution of 0.1ºC.
Data has been taken every 15 minutes during one year, between the months of October 2017 and September 2018.
The recorders are installed in the classrooms on the outside wall, one meter from the ground, with the characteristics shown in table 2.
| Educational Center A | |||
|---|---|---|---|
| Designation | A1 | A2 | A3 |
| Device | CAI5 | CAI6 | CAI7 |
| Use | Classroom | Gym | Classroom |
| Student´s age | 11 years old | 6-11 years old | 5 years old |
| Mean occupation | 15 | 18 | 10 |
| Floor | Highest | Ground | Intermediate |
| Orientation | E | NW | E |
| Educational Center B | |||
| Designation | B1 | B2 | B3 |
| Device | CAI1 | CAI3 | CAI4 |
| Use | Classroom | Classroom | Classroom |
| Students age | 14-18 years old | 14-18 years old | 14-18 years old |
| Mean occupation | 22 | 22 | 22 |
| Floor | Intermediate | Intermediate | Intermediate |
| Orientation | E | S | N |
| Educational Center C | |||
| Designation | C1 | C2 | C3 |
| Device | CAI9 | CAI10 | CAI11 |
| Use | Classroom | Classroom | Classroom |
| Students age | 12-18 years old | 12-18 years old | 12-18 years old |
| Mean occupation | 16 | 34 | 29 |
| Floor | Intermediate | Over outer space | Intermediate |
| Orientation | N | W | S |
2.3. Indicators
⌅The
aim is to evaluate thermal comfort and air quality, comparing the data
obtained with the recommended values. To study the indoor air quality,
the CO2 concentration data is considered. This is one parameter used by
the Spanish Building 2017 (Code Document Base HS-3) (28(28)
Ministerio de Fomento. (2017). Orden FOM/588/2017, de 15 de junio, por
la que se modifican el Documento Básico DB-HE “Ahorro de energía” y el
Documento Básico DB-HS “Salubridad”, del Código Técnico de la
Edificación, aprobado por Real Decreto 314/2006, de 17 de marzo. Boletín
Oficial del Estado 149, 51621-51626.
), hereinafter DB HS-3 and by the Regulation of Thermal Installations in Buildings, (29(29)
Ministerio de Presidencia. (2007). Real Decreto 1027/2007, Reglamento
de Instalaciones Térmicas en los Edificios (RITE). Boletín Oficial del
Estado 207, 35931-35984.
) from now on RITE. This
parameter is chosen because the adequate instrumentation to obtain its
value is available and because it is a good indicator to observe the
amount of air renovation in spaces with human presence. Indirectly, the
higher or lower rate of ventilation influences to maintain better or
worse indoor air quality.
RITE sets a CO2 concentration for
classrooms of 500 ppm above the concentration in outside air. Regarding
the concentration of CO2 in outdoor air, the value of 400 ppm is adopted
(28(28)
Ministerio de Fomento. (2017). Orden FOM/588/2017, de 15 de junio, por
la que se modifican el Documento Básico DB-HE “Ahorro de energía” y el
Documento Básico DB-HS “Salubridad”, del Código Técnico de la
Edificación, aprobado por Real Decreto 314/2006, de 17 de marzo. Boletín
Oficial del Estado 149, 51621-51626.
, 30(30)
Berenger Subils, M. J., & Bernal Domínguez, F. (2000). NTP 549: El
dióxido de carbono en la evaluación de la calidad del aire interior.
Madrid: Centro nacional de condiciones de trabajo-Ministerio de trabajo y
asuntos sociales de España.
), so the value measured
inside the classroom should not exceed 900 ppm. This value is similar to
the expressed in DB HS-3 “Air Quality”, where it is stated that: “In
habitable rooms of the dwellings, a sufficient external air flow must be
provided to ensure that in each location the average annual
concentration of CO2 is less than 900 ppm and that the accumulated
annual CO2 that exceeds 1,600 ppm is less than 500,000 ppm · h” (30(30)
Berenger Subils, M. J., & Bernal Domínguez, F. (2000). NTP 549: El
dióxido de carbono en la evaluación de la calidad del aire interior.
Madrid: Centro nacional de condiciones de trabajo-Ministerio de trabajo y
asuntos sociales de España.
). Although this
limitation only applies to housing, it offers a second reference value
to guarantee the health of people. The standard UNE-EN 013779: 2008
“Ventilation for non-residential buildings - Performance requirements
for ventilation and room-conditioning systems” (31(31)
Aenor. (2008). Ventilation for non-residential buildings - Performance
requirements for ventilation and room-conditioning systems (UNE-EN No.
013779).
) also matches this value by marking in its
table A.10 the value of 900 ppm to activate ventilation systems that are
responsible for ensuring air quality.
To study thermal comfort, temperature data is taken, as contemplated in several studies (32(32) Givoni, B. (1992). Comfort, climate analysis and building design guidelines. Energy and buildings 18(1), 11-23.
, 33(33)
De Dear, R. J., & Brager, G. S. (2002). Thermal comfort in
naturally ventilated buildings: revisions to ASHRAE Standard 55. Energy
and buildings 34(6), 549-561.
, 34(34)
Pérez-Lombard, L., Ortiz, J., & Pout, C. (2008). A review on
buildings energy consumption information. Energy and buildings 40(3),
394-398.
, 35(35)
Gagnon, R., Gosselin, L., & Decker, S. (2018). Sensitivity analysis
of energy performance and thermal comfort throughout building design
process. Energy and Buildings 164, 278-294.
). Thermal
comfort depends on various factors such as the characteristics of the
users (age, sex, level of clothing...), the shape of the building, the
thermal facilities, as well as the ability to be controlled by the users
and the external climate, among others. So humans have an adaptive
capacity to feel comfort within varied thermal conditions (36(36)
Nicol, J. F., & Humphreys, M. A. (2002). Adaptive thermal comfort
and sustainable thermal standards for buildings. Energy and buildings
34(6), 563-572.
).
RITE establishes, as a requirement for thermal quality of the environment, a temperature range of 21ºC to 23ºC in winter and 23ºC to 25ºC in summer, when metabolic activity is maintained in a classroom (1.2 met) and clothing is usual for the season (0.5 clo in summer and 1.0 clo in winter).
For a
gym, the comfort temperature drops to 17-19ºC in winter and 19-21ºC in
summer, given that the metabolic activity is greater even though the
clothing is lighter (37(37) Sánchez, A. Bienestar térmico en un espacio climatizado. Retrieved from http://www.idae.es/uploads/documentos/documentos_BIENESTAR_TERMICO_EN_UN_ESPACIO_CLIMATIZADO_2_articulo_ASV_3725727c.pdf
). Nevertheless, Givoni (38(38) Givoni, B. (1969). Man, climate and architecture. Amsterdam: Elsevier.
) establishes as a comfort zone, the one comprised between values of 21ºC and 26ºC.
To study the quality of the interior environment and its effect on the wellbeing and comfort of the occupants, we proceed to compare the data obtained with the aforementioned reference values.
3. RESULTS
⌅The collected data on CO2 concentration and temperature is summarized.
3.1. CO2 concentration
⌅Mean monthly data is represented in figure 1.
The highest monthly average values are obtained in the month of January, while the lowest values are obtained in May. These values do not take into account the months of July and August that are not academic and the months of June and September in which the academic activity starts and ends.
In Figure 2, the evolution of CO2 concentrations during the worst and best week in each building is shown. The week from 22nd Jan. to 28th Jan. stands for the worst performance, while the week of May 20th to May 26th stands for the best performance.
Table 3 shows the annual indicators for CO2 concentration.
| Class-room | Mean CO2 concentration (ppm) | Percentage of hours with CO2 > 900 ppm (%) | Annual aggregate of CO2 > 1,600 ppm (ppm·h) |
|---|---|---|---|
| A1 | 640 | 13% | 411,059 |
| A2 | 468 | 2% | 1,561 |
| A3 | 524 | 5% | 1,778 |
| B1 | 509 | 5% | 35 |
| B2 | 514 | 5% | 2,294 |
| B3 | 549 | 8% | 32,697 |
| C1 | 553 | 8% | 93,492 |
| C2 | 624 | 8% | 431,819 |
| C3 | 552 | 8% | 114,770 |
The classrooms are occupied 6 hours a day, and the annual occupation period is 175 days according to the school calendar. This implies that the classrooms remain occupied 12% of the hours throughout the year. Therefore, Table 4 shows the CO2 concentration data obtained only during school hours.
| Classroom | Mean CO2 concentration (ppm) | Percentage of hours with CO2 > 900 ppm (%) | Annual aggregate of CO2 > 1,600 ppm (ppm·h) |
|---|---|---|---|
| A1 | 1,460 | 64% | 333,630 |
| A2 | 535 | 6% | 1,528 |
| A3 | 791 | 31% | 1,763 |
| B1 | 769 | 32% | 35 |
| B2 | 766 | 31% | 2,234 |
| B3 | 936 | 46% | 27,766 |
| C1 | 893 | 36% | 55,584 |
| C2 | 1,262 | 49% | 281,833 |
| C3 | 830 | 30% | 57,138 |
3.2. Temperature results
⌅The obtained average monthly values are shown in Figure 3. These values are compared to the average monthly outside temperature (39(39) Agencia Estatal de Meteorología. OPENDATA. Sistema para la difusión y reutilización de la información. Retrieved from https://opendata.aemet.es/centrodedescargas/inicio
).
The highest average monthly values are obtained in the month of October, while the lowest values are obtained in January, if we do not take into account the months of June, July, August and September. Figure 4 shows the temperature evolution in each teaching center during the week of January 22 to January 28, the coldest month.
Figure 5 shows the temperature evolution in each teaching center during the week October 23 to 29 are represented, the hottest month.
Figure 6 shows the percentage of hours in which each classroom is below/above or within the comfort temperature marked by RITE. Winter season and summer season are differentiated since the RITE identifies different comfort temperature values for each season. It is considered the winter season when the heating system is operating from November to April. The one in which the heating system is not working, from May to October, is considered the summer season. The comfort temperature in winter is 21-23ºC for the classrooms and 17-19ºC for the gym, and in summer is 23-25ºC for the classrooms and 19-21ºC for the gym.
As previously mentioned, the classrooms remain occupied for 12% of the hours throughout the year. Therefore, the temperature data is obtained only during the moments in which the classroom remained occupied and shown in figure 7.
4. DISCUSSION
⌅Discussion is set under the two main subjects addressed during the research: indoor concentration of CO2 and temperature results. At the end of this chapter, some considerations about the overall behaviour of each one of the monitored schools are included.
4.1. Indoor CO2 concentration
⌅The limit set by the current housing regulations in Spain for the annual cumulative CO2 that exceeds 1,600 ppm is 500,000 ppm h. To set this limit, a scenario of occupation of the dwelling in which users remain outside for 8 hours on weekdays and 2 hours on weekends is established. This scenario implies that users stay in the house 6,464 annual hours.
In the case of schools, the time spent in a classroom is 6 hours for 175 school days, which is 1,050 hours per year. The equivalent limit for the annual accumulated CO2 that exceeds 1,600 ppm in classrooms, to maintain the same level of health, would be set at 81,219 ppm · h. This value represents 16.2% of the limit marked on housing, since the annual time spent in the classroom is 16.2% of the time spent in the home.
Table 5 shows that classrooms A1 and C2 exceed the equivalent limit value for the annual cumulative CO2 that exceeds 1,600 ppm between 3.5 and 4 times, which means that students are exposed to high concentrations of CO2 accumulated during the period of occupation of classrooms. While the next two classrooms, C3 and C1 have values 0.7 times below the limit value, class B3 has a value 0.35 times below the limit value and the rest of the classrooms, values below 0.05.
| Class-room | Annual aggregate of CO2 > 1,600 ppm over the limit value of 81,219 ppm·h | Class-room | Percentage of hours with CO2 > 900 ppm (%) | Class-room | Average concentration of CO2 over the limit value of 900 ppm |
|---|---|---|---|---|---|
| A1 | 4.1 | A1 | 64% | A1 | 1.6 |
| C2 | 3.5 | C2 | 49% | C2 | 1.4 |
| C3 | 0.7 | B3 | 46% | B3 | 1.0 |
| C1 | 0.7 | C1 | 36% | C1 | 1.0 |
| B3 | 0.3 | B1 | 32% | C3 | 0.9 |
| B2 | 0.03 | A3 | 31% | A3 | 0.9 |
| A3 | 0.02 | B2 | 31% | B1 | 0.9 |
| A2 | 0.02 | C3 | 30% | B2 | 0.9 |
| B1 | 0.00 | A2 | 6% | A2 | 0.6 |
Regarding the percentage of hours in which the classrooms have a CO2 concentration above 900 ppm, Table 5 shows that classrooms A1, C2 and B3 exceed this concentration between 46% and 64% of the time in which they remain busy. The same classrooms have an average CO2 concentration value above 900 ppm, exceeding this value 1.6 times in the case of classroom A1. Table 5 shows the different classrooms ordered according to how they exceed the limit values of the different CO2 concentration indicators.
First of all, the good behavior that the gym offers in comparison of the classrooms should be highlighted. The value in which it shows the best performance is in Percentage of hours with CO2> 900 ppm (%), whose results are between 5 and 11 times lower than the classrooms. Despite the fact that in the gym, due to more intense metabolic activity than in the classroom, the emission of CO2 by the students increases, its greater volume makes the CO2 concentration lower than that achieved in the classrooms.
It can be observed that the same educational center has some classrooms with very unfavourable air quality conditions, and other classrooms with very favourable conditions regarding the concentration of CO2.
However, school C obtains the
worst results, while the other two schools obtain slightly better
results. This could be due to two reasons. School C was built in 2010
and has window framing which present more tightness than other schools,
this circumstance limits air infiltration. On the other hand, the
classrooms studied in case study C have an average occupation of 26.3
students compared to 22 and 14.3 students in cases B and A respectively.
Taking into account that the generation of CO2 is 19 l / h · occupant,
the generation of CO2 in school C is 20% higher than in school B and 80%
higher than in school A. So, since more CO2 is generated and less
dissipated, school C presents the worst results as a whole. The
SINPHONIE report: Schools Indoor Pollution & Health Observatory
Network in Europe (40(40)
Csobod, E., Annesi-Maesano, I., Carrer, P., Kephalopoulos, S.,
Madureira, J., Rudnai, P. & Moshammer, H. SINPHONIE: Schools Indoor
Pollution & Health Observatory Network in Europe. Final Report.
Luxembourg: Publications Office of the European Union. Retrieved from https://publications.jrc.ec.europa.eu/repository/bitstream/JRC91160/lbna26738enn.pdf
) studies air quality in 23 European countries
among which Spain is not included. The average value of CO2
concentration in the 114 schools studied in this report is 1,433 ppm,
while the average value obtained in the 3 Spanish schools studied in
this article is 916 ppm. In spite of being a value higher than 900 ppm,
only Norway with 686 ppm and Sweden with 657 ppm have lower average
concentrations.
Finally, it should be noted how the studied gym achieves very low results. This is due to the fact that, despite that the metabolic activity that takes place in it implies a greater emission of CO2 by the students, as it has a larger volume than a classroom, the CO2 concentration does not reach the values obtained in smaller spaces.
4.2. Indoor temperature aspects
⌅Table 6 shows different classroom analysis according to the comfort temperature for the winter season with space heating, and summer season, during the annual occupation period of the classrooms.
| November - April | May - October | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Classroom | Below C. T. | Classroom | Comfort temperature | Classroom | Above C. T. | Classroom | Below C. T. | Classroom | Comfort temperature | Classroom | Above C. T. |
| A1 | 58% | C1 | 43% | B2 | 83% | A3 | 76% | B1 | 49% | C2 | 61% |
| C2 | 37% | C2 | 41% | B3 | 66% | A1 | 47% | A2 | 46% | C3 | 61% |
| C3 | 36% | B1 | 39% | A2 | 51% | B2 | 20% | B3 | 45% | C1 | 54% |
| A3 | 23% | A3 | 34% | C3 | 48% | B1 | 18% | C1 | 40% | B2 | 48% |
| A2 | 20% | A1 | 31% | B1 | 46% | A2 | 17% | A1 | 38% | B3 | 40% |
| C1 | 19% | A2 | 29% | A3 | 43% | B3 | 15% | B2 | 32% | A2 | 37% |
| B1 | 15% | B3 | 28% | C1 | 37% | C2 | 12% | C2 | 27% | B1 | 32% |
| B3 | 7% | C3 | 15% | C2 | 22% | C3 | 12% | C3 | 27% | A1 | 15% |
| B2 | 6% | B2 | 11% | A1 | 11% | C1 | 6% | A3 | 19% | A3 | 4% |
It can be observed that the highest temperature during the heating period is school B (table 6), while school C has the highest percentage of hours inside the comfort temperature, and school A is the one that presents cooler temperatures.
However, in the periods when heating installations are not working, the warmest case is School C, which is the school with the longest period of comfort, and the coldest is case A. In this last period, thermal behaviour of the building is analysed in free oscillation (without an external incorporation of energy), since it is not affected by the operation of heating appliances.
None of the centers have shading devices such as blinds or horizontal overhangs that allow the entry of natural light while protecting windows from direct solar radiation. In all cases, the entry of direct solar radiation can be blocked deploying the blinds, but this forces the use of artificial lighting when protection from direct solar radiation is needed.
Summer season
⌅Table 7 shows the classrooms ordered according to the percentage of hours that they are above the comfort temperature, compared to the rest of the data that influences the heat gains during the summer period.
| Class-room | Above C. T. | Floor | Orientation | Students |
|---|---|---|---|---|
| C2 | 61% | Over outer space | W | 34 |
| C3 | 61% | Highest | S | 29 |
| C1 | 54% | Intermediate | N | 16 |
| B2 | 48% | Intermediate | S | 22 |
| B3 | 40% | Intermediate | N | 22 |
| A2 | 37% | Ground | NW | 18 |
| B1 | 32% | Intermediate | E | 22 |
| A1 | 15% | Highest | E | 15 |
| A3 | 4% | Intermediate | E | 10 |
In case C, a similar behaviour is observed in classrooms C2 and C3. The same number of hours is maintained above comfort temperature. Analysing the evolution of temperatures during a typical week shown in figure 6, we note that classroom C3 suffers the highest temperatures. This is because it receives heat gains through the roof and solar gains through the windows (in spite of its protection) facing south. One might think that the west orientation of the classroom C2 could be more unfavourable, but it receives the highest heat gains when the classroom is unoccupied. The greater number of students in classroom C2 compensates for its better location and orientation with respect to classroom C3. Class C1, due to its better orientation and location and its smaller number of students, behaves better than the rest of the classrooms. Although the temperature at which the three classrooms are located is excessive.
In School B, the number of students is similar in the classrooms, as well as its situation in the middle floor. The only difference is the orientation. A greater number of hours are observed above 25ºC in classroom B2 that has a south orientation. Next is classroom B3 with northern orientation and with more hours than classroom B1 with east orientation. However, if we observe the evolution of the temperatures over a typical week shown in figure 6, we can see how classroom B1 presents about one more degree of temperature than classroom B3. Even presenting better behaviour than school C, the temperature at which the three classrooms are located is excessive.
Classrooms and gym in school A profit from orientations with low thermal gains caused by solar radiation, low number of students. Only the gym A2 has 37% of hours above comfort temperature. The classrooms barely exceed these values.
Winter season
⌅Table 8 shows the classrooms ordered according to the percentage of hours below comfort temperature, together gains and losses of heat during the winter period-related data.
| Class-room | Below C. T. | Floor | Orientation | Students |
|---|---|---|---|---|
| A1 | 58% | Highest | E | 15 |
| C2 | 37% | Over outer space | W | 34 |
| C3 | 36% | Highest | S | 29 |
| A3 | 23% | Intermediate | E | 10 |
| A2 | 20% | Ground | NW | 18 |
| C1 | 19% | Intermediate | N | 16 |
| B1 | 15% | Intermediate | E | 22 |
| B3 | 7% | Intermediate | N | 22 |
| B2 | 6% | Intermediate | S | 22 |
School A has the best behaviour in summer. However, in winter it presents the worst conditions, which implies that the use made of the heating installations is insufficient to maintain an adequate indoor temperature. In spite of this, classroom A3 exhibits behaviour 2.5 times better than the other classroom in the same school. No factors that explain this difference are found, so it is considered that the heating installation could present imbalances in its regulation.
The worst behaviour in school C compared to school B is repeated both in winter and in summer. This circumstance may be due to the fact that its thermal envelope has worse performance. Given that building B was built before the first regulation, limiting energy demand in Spain (NBE-CT79) and building C is constructed according to this regulation; the worst behaviour of the envelope could be explained by the higher percentage of glazing surface in building C, which increases the global transmittance of its facade.
The only school that shows good behaviour in winter is B, although when analysing figure 6, it is observed that on Mondays the educational center has a hard time reaching 21ºC because during the weekend the heating installation is off.
Table 9 shows the classrooms in order according to the percentage of hours above comfort temperature, together with the rest of the data that influence the gains and losses of heat during the winter period in which the heating installation is operating.
| Class-room | Above C. T. | Floor | Orientation | Students |
|---|---|---|---|---|
| B2 | 83% | Intermediate | S | 22 |
| B3 | 66% | Intermediate | N | 22 |
| A2 | 51% | Ground | NW | 18 |
| C3 | 48% | Highest | S | 29 |
| B1 | 46% | Intermediate | E | 22 |
| A3 | 43% | Intermediate | E | 10 |
| C1 | 37% | Intermediate | N | 16 |
| C2 | 22% | Over outer space | W | 34 |
| A1 | 11% | Highest | E | 15 |
Registered data shows that 89% of the classrooms and the gym remain more than 20% of the time above the maximum comfort temperature. Such overheating may be due to the fact that the heating installations in the schools suffer from an adequate regulation system, which is capable of stopping the heat emissions when the set point temperature is reached.
It is noticed that school A, which has a more limited use of its heating installation and keeps its classrooms and gym below the comfort temperature for more hours during school hours, the A3 classroom is above the comfort temperature for 43% of the time.
Classrooms and gym that show better behaviour against energy waste exceed the comfort temperature, and are those that are on more exposed floors, have a smaller number of students and have orientations east and south with greater sunlight during the school day. It should be noted that the results reflect exceptions tothis criteria. Classroom A3 with the largest number of students, presents the third best behaviour. Classroom C3 has the third worst result. Classroom B3 faces north, so it does not receive solar radiation, presents the second worst result.
The large number of exceptions that are presented before the general criteria of expected behaviour, indicate, once again, that the regulation capacity of the heating systems are not able to adequately avoid the excess of energy consumption once the comfort temperature has been reached. The waste of energy that has been verified does not reflect the extra energy consumption that could actually have been produced, given that only temperatures have been measured and the time in which the classroom windows have been opened to relieve the excess heat that has been recorded is unknown. The thermal amplitude (difference between maximum and minimum daily temperature) of the different classrooms throughout the day, including school hours and closing hours, are shown in table 10 for the winter and summer seasons.
| Classroom | Orientation | Winter amplitude (ºC) | Summer amplitude (ºC) |
|---|---|---|---|
| A1 | E | 7.2 | 1.3 |
| A2 | NW | 4 | 1.4 |
| A3 | E | 7.7 | 1.4 |
| B1 | E | 9 | 1.7 |
| B2 | S | 11.8 | 5 |
| B3 | N | 11.3 | 2.2 |
| C1 | N | 4.1 | 1.9 |
| C2 | W | 10.5 | 4 |
| C3 | S | 12 | 6.5 |
During the periods in which the heating is off, the classrooms maintain a general thermal amplitude between 1.3 and 2.2ºC, except for the classrooms with west and south orientations, whose thermal amplitude increases to values between 4 and 6.5ºC.
In the periods in which the heating is on, the thermal amplitude stays around 4ºC in classrooms A1 and C1 with north-west and north orientations, given that they do not receive sunlight. In schools A and C, classrooms and gym that receive solar gains, present a thermal amplitude between 2 and 3 times higher, as this occurs during the summer. However, school B does not show a significant difference in thermal amplitude between classrooms that receive sunlight and the one that faces north. This may be due to the fact that the classrooms in school B reach higher temperatures in winter thanks to the contribution of energy by the heating system, which increases its thermal amplitude and reduces the influence of solar gains.
4.3. Global behaviour by schools
⌅Table 11 shows schools ordered from best to worst behaviour with respect to the different parameters studied.
| Order | CO2 | Winter T | Summer T |
|---|---|---|---|
| Best | A-B | B | A |
| Intermediate | C | B | |
| Worst | C | A | C |
It can be observed that case C, despite being in the neighbourhood with the highest average income and being of more recent construction, shows the worst behaviour.
As previously indicated, greater air tightness of windows in case C and the high occupancy of its classrooms are causing high concentrations of CO2. Also the fact of having opaque enclosures and glazing, both with lower thermal transmittances, together with their higher occupancy, are causing overheating in summer. Although, due to these circumstances, it would be foreseeable that school C presented the best temperature comfort in winter, this is not the case. This may be due to the fact that the heating installation in School B, which presents better comfort in winter, contributes with much more energy consumption, despite the fact that it has greater losses.
5. CONCLUSIONS
⌅5.1. Concentration of CO2
⌅The results of concentration of CO2 in the different classrooms lead us to the conclusion that the determining factor is not so much the constructive characteristics of the educational center or the number of students present in each classroom, which undoubtedly have an influence, but the use of natural ventilation by opening the windows which is done in each classroom. Since the CO2 concentration of the outdoor air is lower than the CO2 concentration of the indoor air, when the windows are opened, the CO2 concentration is reduced.
The worst values are obtained in a classroom from each school, while other classrooms in the same center obtain better results.However, school C built in 2010 whose window framing has greater tightness and whose occupancy by classroom is higher, gets worse results against CO2 concentrations, while the other two schools whose window framing is less tight and their classrooms are less busy, get better results.
It is concluded, therefore, that natural ventilation by opening the windows in the classrooms in the breaks between classes can be a sufficient measure to guarantee air quality in classrooms, but this is not carried out adequately in most cases. To avoid this situation and ensure adequate air quality, it is advisable to carry out a protocol in which someone is responsible for opening and closing the windows during the changing of class. The air quality delegate could be entrusted to supervise, for the good of all, that the classroom is adequately ventilated. Since opening windows in winter improves indoor air quality, but reduces thermal confort, it would be desirable for classrooms to have CO2 and temperature meters to manage window opening times so that neither of the two parameters were not compromised.
However, this form of ventilation is less energy efficient than double flow mechanical ventilation with heat recovery. Furthermore, with mechanical ventilation, adequate air renewal flow rates are guaranteed regardless of whether correct manual ventilation management is carried out.
Regarding the seasons, the highest concentrations of CO2 are reached in winter, which is when the windows are least opened due to the low outside temperatures.
5.2. Temperature
⌅The temperature results obtained show us that the classrooms meet comfort temperature only for 30% of teaching hours.
Summer season
⌅During the summer season in which the buildings operate in free regime, since the heating system remains off and there is no refrigeration installation, in each school the south-facing classrooms are the ones with the highest temperatures. This is because the east-facing classrooms receive solar radiation in the morning when the outside temperature is still low. While the classrooms facing west, which receive solar radiation in the afternoon when the outside temperature is higher, are unoccupied at that time of day.
It is concluded that it is more relevant to avoid the south orientation or to place external solar-luminance control devices, to reduce overheating during the summer in the classrooms, since they do not have a cooling installation.
Winter season
⌅During the winter season, it is observed that in school C, contrary to what would happen in the case that the building operated in free regime, the classroom facing north behaves better than the one oriented to the south. It is also observed that in school A, a classroom oriented to the east maintains cooler temperatures for 3 times longer than another classroom with the same orientation.
During the winter season, the installation of heating can limit the differences in behaviour due to orientation, as long as there is the possibility of selectively controlling the spaces according to the different orientations.
It is observed that 30% of the winter season time the classrooms are within the comfort temperature, while 30% of the time they are cold and for 40% they are hot. During this period, school A has low temperatures between 47% and 96% of teaching hours.
It is concluded that the regulation of the operation of the heating installation is inadequate to maintain comfort conditions. It should come into operation beforehand, so that the first hours of the day enjoy a higher temperature and should have regulation capacity that would enable centers to stop emitting heat in the classrooms before entering the overheating situation. To avoid overheating it would be desirable for the radiators to have thermostatic regulation valves that stop the emission of heat inside the classrooms once the comfort temperature has been reached. On the other hand, school A should extend the period of operation of the heating installation to overcome the low temperatures it presents once the heat supply stops working.
5.3. General conclusión
⌅The bad situation of air quality and thermal comfort in the public schools analysed in Madrid is noted. Adequate air quality is achieved for 64% of teaching time. Appropriate temperature conditions are achieved during 30% of teaching time. It is necessary to carry out an investigation of thermal comfort and air quality on a larger sample of schools in Madrid and other regions in Spain, in order to obtain a more accurate diagnosis, depending on the year of construction, the climatic zone in which it is located and other variables that can be identified, as building materials, location of the most polluted school zones, treatment of CO2 as a tracer gas, etc.