1、2009 ASHRAE 769ABSTRACT Ventilation in schools has a direct relation to health and performance of pupils and thus is very important. The present situation of school ventilation in the Netherlands is presented which is rather poor: there were a lot of insufficient situations found. Different aspects
2、of the problems were studied to find new solutions. The design of a new and better functioning ventilation system for schools is a complex process. Design methodology helps the designer to give structure to the design tasks and solutions. The design process should not only lead to a solution, but al
3、so give insight in the reasoning about the design problems and the solutions itself. The decisions made during the design process should become clear and reproduc-ible for other designers and disciplines. This simulates the multidisciplinary exchange of ideas and concepts. A new Integral Design appr
4、oach was developed to design adequate solutions for ventilation of school buildings. The design procedure and a first design result are described.INTRODUCTIONIndoor Air Quality (IAQ) at schools is of special concern since children are extremely sensitive to results of poor air quality. IAQ in school
5、s must reach the basic requirements and should be considered as a high priority because 1: (1) Chil-dren more sensitive as they still developing physically and more likely to suffer from indoor pollutants, these growth processes are delicate and vulnerable to disruption, (2) Chil-dren are less well
6、able than adults to metabolise and excrete most environmental toxins, (3) Children are relatively more heavily exposed to environmental toxins as they breathe higher volumes of air relative to their body weights. Good air quality in classrooms supports childrens learning ability. Poor IAQ in schools
7、 influences the performance and attendance of students, primarily through health effects from indoor pollut-ants 2. There is a direct relationships between indoor air and environmental quality (IEQ) in class rooms and students health and academic performance 345. In a study by Myhrvold et al., in 19
8、96 6 correlations between pupils health and performance and CO2-concentrations were deter-mined. These researchers conducted physical measurements of CO2and other indoor air parameters, distributed question-naires, and administered a Swedish Performance Evaluation (SPES) test to students in eight sc
9、hools in Sweden. Correla-tions were found between measured CO2-concentrations and performance of students: higher CO2-concentration resulted in less performance. CO2-concentration is an indicator for the amount of ventilation and thus indirectly for the quality of the indoor air. It can be concluded
10、 that: less adequate the ventila-tion leads to higher CO2-concentrations and less student performance. Many factors affect indoor air quality. Outdoor pollut-ants (e.g. pollen, traffic and factory emissions) enter buildings through open windows, ventilation system air intakes, and building leaks and
11、 cracks. These contaminants, along with those that arise inside the building (mould spores and chem-ical emissions from carpeting, wallpaper, furnishings, and cleaning products) concentrate in tightly sealed buildings with inadequate ventilation 7. The required ventilation in buildings depends on po
12、llutants created by metabolic func-tions (bio-effluents) of occupants or pollutants emitted by other sources in the building. CO2 has been used as an indi-cator of human bio-effluents for more than a century. Humans produce carbon dioxide (CO2) proportional to their meta-bolic rate. In terms of quan
13、tity it is the most important human Integral Design of School VentilationW. Zeiler G. Boxem D. SchuilingAssociate Member ASHRAEW. Zeiler is a professor and G. Boxem is an associate professor of building services and D. Schuiling is a masters student in the Department of Architecture, Building and Pl
14、anning, Building Physics and Systems Unit, Technische Universiteit Eindhoven, Eindhoven, The Netherlands.LO-09-073 2009, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2009, vol. 115, part 2. For personal use only. A
15、dditional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.770 ASHRAE Transactionsbio-effluent. Although at the low concentrations typically occurring indoors, CO2 is harmless and not perceived by humans. Still it i
16、s a good indicator for the concentration of other human bio-effluents being perceived as a nuisance. In schools with a high occupancy, CO2 monitoring is a well-established practice for controlling supply of outdoor air. Comparing schools with offices, office spaces will contain relatively more texti
17、les of furnishings and carpets per floor-area, which will be responsible for emissions of VOCs. Here the CO2-concentration is an incomplete indicator. It does not acknowledge the many perceivable pollution sources not being producing CO2and certainly not the non-perceivable hazardous air pollutants
18、such as carbon monoxide and radon. Still it is the easiest to determined important parameter of the indoor air quality. That is the reason why the focus in this arti-cle in on CO2 concentrations in classrooms as an indicator.The indoor air humidity plays an important role in the quality of the indoo
19、r environment. On the one hand there are direct effects of air humidity on the comfort and perceiving of human beings and on the other hand there are indirect effects of air humidity on the indoor environment, where effects will be felt at later stages. High air humidity may stimulate the growth of
20、mites, moulds and other fungi, which can cause allergy and foul odors. Increased humidity may also enhance the emissions of chemicals like formaldehyde from materials. A low humidity may cause a sensation of dryness and irritation of skin and mucous membranes of some occupants. Normally few problems
21、 occur when the relative humidity (RH) is between 30 and 70%, assuming that no condensation takes place. It may be necessary to protect the building construction by means of vapor barriers and proper insulation. The number of mites per area or per amount of dust is directly related to the relative h
22、umidity and the air temperature. Suitable opportuni-ties for mite growth are RH between 75% and 95% and temperatures between 15C and 33C, with its optimum at 80% RH and 25C 8.To show what is possible in practice with school building design, the Dutch government subsidized five pilot school projects,
23、: Van Hall Institute, Hogeschool Limburg, Educato-rium, Peuterpalet and Scholencomplex Rijkerswoerd. The performance of these schools were monitored during a couple of years and presented in a overall study 9. The results showed that there were almost no problems (on average less than 5%) related to
24、 the moisture levels within the schools. For the present Dutch situation a research was done 10 to look for the occurrence of problematic situations concern-ing the indoor air quality and the thermal comfort of schools. As can be seen from Figure 1 the most problems were related to the high CO2 conc
25、entrations and less to particle concentra-tion and moisture concentration. So it is important to look at ventilation and its regulation.Ventilation StandardThere are numerous standards and guidelines covering indoor air quality (IAQ), recommended by international health associations, industry organi
26、zations and governments. Dutch schools have to meet the Dutch Building Code (Bouwbesluit), which requires a classroom ventilation rate of 2.8 l/sm2(5,9 cfm/m2) at an occupancy rate with 1.3 to 3.3 m2floor area per person. For a standard classroom of 50 m2and a maximum occupation of 32 students, this
27、 results in a ventilation rate of 4.2 l/s (8,9cfm)per person. Dutch Building Code refers also to guideline NEN 1089, which requires a ventilation rate of 5.5 l/s (11,7cfm)per person based on a level of 1000 ppm (part per million) CO2-concentration with a maximum of 1200 ppm. Depending on the situati
28、on the highest ventilation rate should be used.The guidelines for ventilation in North America ASHRAE Standard 62.1-2007, recommends a minimum ventilation rate of:15 cfm/person (7 l/s.person) for students age 5-813 cfm/person (6,1 l/s.person) for students age 9+This results in an acceptable indoor a
29、ir quality when the fresh outside air is free of pollution in damaging concentra-tions and leeds to a majority of satisfaction (80% or more). Carbon dioxide concentrations are often used to indicate the indoor quality 11. As mentioned before the IAQ in schools is depending on many factors still it i
30、s primarily eval-uated by CO2-concentrations. ASHRAE Standard 62.1-2007 recommends an indoor CO2-concentration of less than 700 ppm above the outdoor concentration which leads to indoor Figure 1 Occurrence of problems related to indoor air quality and comfort of Dutch schools 10.ASHRAE Transactions
31、771concentrations of around 1200 ppm to satisfy comfort crite-ria with respect to human bio effluents. So what is the situation in reality?Several field studies were conducted on the performance of ventilation systems in schools. For European schools some results are shown in Table 1 4. In the Nethe
32、rlands different investigations on indoor air quality were conducted and CO2 levels measured. In 1987 the Agriculture University of Wageningen conducted research to indoor air quality. Measurements of CO2concentrations were done and in 8 out of 12 schools, CO2levels rose above the marginal value of
33、1200 ppm in more than 50% during school hours 12. In 1992 the local health department (GGD) in West-Brabant researched indoor air quality in secondary education buildings. Measurements of CO2levels were done and levels up to 4800 ppm were detected 13. In 1993 in Groningen different primary schools w
34、ere inspected. In 3 out of 4 class-rooms, CO2levels reached the marginal value of 1200 ppm. Maximums of 2400 ppm were detected 14. In 1997 IAQ measurements were done at 4 primary schools in the region of East Noord-Brabant. Peak levels of 3500 ppm were detected 50. Municipality Groningen did measure
35、ments in 16 class-rooms and they found median levels of 919 to 1940 ppm 16.Indoor Quality Level in Dutch SchoolsPresent Situation. The goal of a first study was to evaluate the performance of exhaust-only ventilation systems. In 5 Dutch schools (Loes A/E) measurements were conducted in the heating s
36、eason for a period of around 7 days 17. In a next study in 9 schools measurements were done during one day as part of a OGO (Ontwerp Gericht Onderwijs= Design Oriented Education)-project 18, see Table 1 OGOschools.In a following study, 6 schools (Manual A/F) with different ventilation systems were s
37、tudied 19, to search for concepts which had fewer problems. These measurements included: IAQ (CO2), thermal comfort, airflow and outdoor condi-tions. A logbook and questionnaires obtained information about use of ventilation facilities and satisfaction of users. In this article the focus is on the C
38、O2-concentration which is directly related to the occupancy and the ventilation rate. The CO2-concentrations can be calculated with the following equation 20wherect= concentration CO2indoors at time t, ppmco= concentration CO2outdoors, ppmP = production of CO2(l/h) = 2.1 cfmN = air change rate, h1V
39、= volume of room, m3= 35.3 ft3t = time, hWith the formula for calculating the CO2-concentration in a space, the air change rate can be calculated. This formula is used to calculate the CO2-concentration for a situation with 32 students in a classroom and 1 teacher. Results of different class-rooms a
40、nd schools can now be compared. Input data for the calculation are: ctis measured P95 value where t is set at 1.5h. The results are given Figure 2 presents the diagram of the PM 95 value, representing the CO2 concentration calculated for the situation of 32 pupils in the classroom (the Dutch norm) a
41、nd which is not succeeded during 95% of the occupation time. The results of the measurements indicated that, based on the current ventilation standards, many classrooms are not adequately ventilated. As an object for further research is an improvement of the design process 2. A first line of defense
42、 against poor IAQ in classrooms is adequate ventilation and this should be a major focus of design efforts 4. Daisy et al. 4 also communicates the complexity and uncertainty in the problem for instance, “. exposures to VOCs, molds and microbial VOCs, and allergens generally measured in class-room fl
43、oor dust, are related to asthma, SBS and other respira-tory symptoms. There is some indication in the literature that carpets in the classroom are a causal factor for health symp-toms. Mendell et al.s 2 more recent study says, “Immediate actions are warranted in schools to prevent dampness prob-lems
44、, inadequate ventilation, and excess indoor exposures to substances such as NO2 and formaldehyde. Also, siting of new schools in areas with lower outdoor pollutant levels is preferable.”So the “first line of defense” is not so universally accepted as the most important. It may be equally or more imp
45、ortant to avoid moisture problems, to control contaminants, to achieve basic thermal comfort, etc. The rest of the paper on the design method does not address these very significant issues, because in the present Dutch situation as stated before the main prob-lem is inadequate ventilation. Still thi
46、s could be very different in other countries.METHODOLOGYThe current design process for schools normally begins with selection of an architect and proceeds with programming and schematic design. Next the structural engineer comes in and finally the BS (Building Services)-engineer completes the design
47、 team. But already many decisions were made in the ctcoPNV- 11eNt-+=Table 1. Average and Range of CO2Concentrations Reported in the Scientific Literature ofEuropean Schools 4StudyNumber of SchoolsCO2,ppmAverage RangeNielsen (1984) 11 1000 5001500Norback et al. (1990) 6 1290 9501950Norback (1995) 6 1
48、320 7002700Smedje (1997) 96 990 4252800772 ASHRAE Transactionsearly conceptual design that influences the development, contract documents, construction, commissioning and occu-pancy. Clear goals were not part of the often general program-ming and design brief. The sooner goals, to ensure IAQ are bro
49、ught into the design process, the easier and less costly they will be incorporated.Integrated design promises major advantages. It draws from all disciplines involved in designing a building and reviews their recommendations as a whole from the early start of a project. Project team collaboration and integration of design choices should begin at the programming phase. Indoor air quality encompasses such factors as maintenance of acceptable temperature and relative humidity, control of airborne
