TABS, THERMAL ACTIVATED BUILDING SYSTEM, TO IMPROVE COMFORT IN SCHOOLS

Transcription

1 TABS, THERMAL ACTIVATED BUILDING SYSTEM, TO IMPROVE COMFORT IN SCHOOLS Wim Zeiler, Robin Scholten, and Gert Boxem Technische Universiteit Eindhoven, TU/e, the Netherlands ABSTRACT Indoor air quality has caught attention of the Netherlands Ministry of Housing, Spatial Planning and the Environment and a large campaign was started in 5 to make the public aware of the dangers to health as result of poor ventilation in housing. Indoor Air Quality and thermal climate in schools is problematic in many countries. The status quo in the Netherlands is presented. The goal of a first study was to evaluate the performance of exhaust-only ventilation systems and in 5 schools were measurements undertaken. In a following study, 6 schools with different ventilation systems were studied. Main conclusions from these studies were: IAQ in the evaluated schools did not meet the requirements; more ventilation was essential for better IAQ and also the thermal comfort was not adequate. As many studies focus on the ventilation aspects we focus more on the thermal comfort of the schools. A new approach to design adequate solutions for school buildings was developed during the last years. Hydronic Radiant Heating Systems or also called Thermally Activated Building Systems, with thermo activated concrete is used. In three of these new schools the systems were examined and measurements were undertaken to determine the comfort generated by these new indoor climate concepts. The results are described in the paper. INTRODUCTION Normally heating in schools is done through convection by panel heating. An alternative is to provide heating through a combination of radiation and convection inside the building. This strategy uses warm surfaces in a conditioned space to heat the air and the space enclosed. Systems based on this strategy are often called Radiative Heating Systems. If heating of the surfaces is produced using water as transport medium, they are called Hydronic Radiant Heating Systems (HRH Systems). Different names are given to the system; Thermally activated building systems or parts or components (TABS), concrete core conditioning (Koschenz, 999), thermo active core systems (TACS). In Dutch, the name betonkernactivering or bouwdeelactivering is used primarily. By providing heating to the space surfaces rather than directly to the air, HRH Systems allow separation of ventilation and thermal space conditioning. While the primary air distribution is used to fulfill ventilation requirements for a high level of indoor air quality, the secondary water distribution system provides thermal conditioning to the building. The separation of tasks should not only improve comfort conditions, but should also improve indoor air quality. Basis of HRH systems is the idea of a floor heating system with tubes imbedded in the core of a concrete ceiling, see figure. Figure : Thermal Activated Building Systems: thermo active core system element While there are many examples of hydronic radiant heating and cooling installations in commercial office buildings available, very little has been reported about school applications. One of the most dominant features of a school is of course its classrooms with its high occupancy density. This high occupancy density results in a large internal heat sources (up to kw) and necessary extensive ventilation. Natural or controlled ventilation, needed for removing internally generated contaminants, without active heating, is not sufficient for the provision of required thermal comfort conditions. This paper will focus on the thermal comfort of HRH in classrooms. Studies of thermal comfort in school buildings are scare (Becker et.al. 7) and especially about the school with HRH. Corresponding Author: address: w.zeiler@bwk.tue.nl

2 METHODOLOGY In order to obtain information about the performance of comfort systems with respect to thermal comfort measurements were conducted. The measurements include long-term measurements, all conducted in the heating season. Long-term measurements were conducted during minimal week. One classroom in each school building was selected for measurements. A device was developed to measure indoor air quality and thermal comfort parameters on a continuous base for a one-week period. At the device, five sensors were placed at.m above floor level. Equipment for data logging and electrical supply are located below the cage. The measure device was positioned in the middle of the classroom if possible. The measurements in the classroom include measurements of air temperature, radiant temperature, relative humidity and air velocity and were logged every 6 minutes. Carbon dioxide concentration was measured by a silicon based non-dispersive infra-red sensor: Vaisala Corbon Dioxide Transmitter GMW.During the measurement period in a classroom, the teacher(s) kept a logbook. By this logbook information is obtained about: Time and motivation of opening and closing doors and windows The occupancy and activities. First series of measurements Between January 9 th till March st 4 long-term and short-term measurements were conducted in 5 selected schools. The measurements were conducted in alphabetical order from school A to E, see figure ( Joosten 4). School A B C D E Location Eindhoven Nuenen Voorschoten Geldrop Eindhoven Surface area class room [m²] Number pupils Figure. Information about schools of series (Joosten 4) Second series of measurements Between January th till February st 5 the second series of long-term measurements were conducted in 6 new selected schools. The measurements were conducted in the following order; school A -5 February, school B -8 February, school C -8 January, school D -5 January, school E 7 January February and school F 7- February. See figure. School School A School B School C School D School E School F Location Den Haag Den Haag Arnhem Leersum Tiel Castricum Surface space class 46,5 5, 5 6,4 57,7 6,5 room [m ] Number pupils [-] Figure. Information about the school of series (van Bruchem 5). FINAL MEASUREMENTS SCHOOLS WITH HRH In different school buildings with HRH measurements were done and questionnaires held. The characteristics of the different projects are given in figure 4. During one week all the relevant parameters to calculate the PMV values were determined. During the same period the questionares were held.

3 School A B C Location Assen Zutphen Haarlem Surface area class room [m²] Number pupils 5 5 Figure 4. Information about the schools of series (Scholten 6) RESULTS Ventilation and Indoor Air quality Indoor Air Quality (IAQ) at schools is of special concern since children are extremely sensitive to results of poor air quality. IAQ in schools must reach the basic requirements and should be considered as a high priority because (Landriga 997): () Children more sensitive as they still developing physically and more likely to suffer from indoor pollutants, these growth processes are delicate and vulnerable to disruption, () Children are less well able than adults to metabolise and excrete most environmental toxins, () 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 children s learning ability. Poor IAQ in schools influences the performance and attendance of students, primarily through health effects from indoor pollutants (Mendell and Heath 5). Literature on relationships (Shendell et al 4) between indoor air and environmental quality (IEQ) in class rooms and students health and academic performance has been reviewed (Daisey et al ). Carbon dioxide concentrations are often used as a substitute of the rate of outside supply air per occupant (Seppänen et al 999). IAQ in schools is primarily evaluated by CO-concentrations. ASHRAE Standard recommends an indoor CO-concentration of less than 7 ppm above the outdoor concentration (~ ppm) to satisfy comfort criteria with respect to human bio effluents. Dutch schools have to meet the Dutch Building Code (Bouwbesluit), which recommends a level of ppm CO-concentration with a maximum of ppm. In a first study in 5 Dutch schools measurements were conducted in the heating season for a period of around 7 days (Joosten 4). In another study another 6 schools were measured during a week (van Bruchem 5). All measurements were recalculated to a norm occupation for a classroom of pupils, see fig. 5. CO concentration pupils in class 4 5 CO 5 concentration in p.p.m 5 5 A B C D E A B C D E F school Series Figure 5. CO concentrations measured and recalculated to norm occupation for a classroom

4 4 4% % % % % 4 4% % % % % 4 4% % % % % 4 4% % % % % 4 4% % % % % 4 4% % % % % In school A, B and C the CO-concentrations were not measured as the specific focus was on the thermal comfort aspects of these schools compared to the earlier measured schools. The use of TABS has no direct relation to the ventilation of the class room. Thermal comfort: PMV The most important research on thermal comfort is done by P. Fanger (Fanger 97). Thermal comfort is expressed in The Predicted Mean Vote (PMV), which is calculated according to ISO-77. The Predicted Mean Vote model (PMV) is the basis of the most important indoor climate standards in Europe (NEN-EN-ISO 77) and America (ASHRAE Standard 55). This model assumes the thermo physiological properties of the human, such as sweat production and heat resistance of the skin. Measurements are done on order to determine what average people consider comfortable. This rate (PMV) is translated into a percentage of people dissatisfied (PPD). PMV(predicted mean value) is calculated during class hours, using metabolic rates of 65 W/m² and clothing value of. School A School B School C School D School E Figure 6. Results PMV schools of series (Joosten 4),8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 -,8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 -,8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - School A School B School C,8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 -,8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 -,8,6,4,,8,6,4,,8,6,4, -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - -, -,4 -,6 -,8 - School D School E School F Figure 7. Results PMV schools of series (van Bruchem 5).

5 The frequency of occurrence of PMV value s is given in the figures below for the projects with TABS, see figure 8 (Scholten 6). School A School B School C Figure 8. Results PMV schools of serie (Scholten 6) Figure 8 shows that 9% of the time, the PMV between -. and is achieved in a school A. It is shown in figure 8 that school B on the other hand predicts a lot more unsatisfied users, with 9% of the time, the PMV between -.5 and -.5. In school C 9% of the time the PMV is between -.5 and, figure 8. In school B more than % of time, the PMV is less than -.. To sum up all the results, we show an overview of all the calculated mean PMV based on the measurements during the winter period of all the projects. As can be seen the comfort of the schools with HRH is not any better than the other schools. That the schools with HRH have not a much better mean PMV was something not expected on forehand, we thought that it would have improved thermal comfort, see figure 9. Calculated mean PMV,8,6,4, PMV -, -,4 -,6 -,8 A B C D E A B C D E F A B C Figure 9. Overall results PMV of all the schools measured Questionnaire Users opinion is the central point of this research. First of all, perception of indoor climate is important for determining whether users are comfortable. Secondly it is important how the interaction with the system is experienced. Since measurements could only be done for a short period of time, the opinion of the user of summer conditions is also important. Users of both rooms are done have filled in a questionnaire. Unfortunately, it was not possible to survey all users. The questionnaire used is based on the validated list which has been developed in the Health Optimisation Protocol for Energy-efficient Buildings research (HOPE ). For clarity s sake, different scales are used in the questionnaire. These scales have been translated to one universal scale. The score of a bipolair scale are transformed to a score on a unipolair scale (Joosten 4). This seven point scale translates good results into point, and bad results in point 7. The users, the teachers and the pupils separately have been asked to rate different aspects of the comfort. In school A the pupils were not old enough to fill in questionnaires so for this school we have only the opinion of the teachers, see figure.

6 School A School B School C teachers pupils teachers pupils teachers pupils returned questionnaires Figure. Overview of the returned questionnaires from the three schools (Scholten 6) Distinction is made between summer and winter. In order to get a full view, some questions have been asked about the user s health. Results of the questionnaire are given in figures -. Respectively temperature, stability of temperature, air speed, humidity, freshness and smell of the air and sound is rated. Temperature Stability T Air velocity Moisture Fresness Smell Noise Temperature Stability T Air velocity Moisture Fresness Smell Noise Figure. School A winter (only teacher) and summer (only teachers) (Scholten 6) Temperature (LK) Temperature (LL) Stability temp (LK) Stability Temp (LL) Air velocity (LK) Air velocity (LL) Smell (LK) Smell (LL) Noise (LK) Noise (LL) Temperature (LK) Temperature (LL) Stability temp (LK) Stability Temp (LL) Air velocity (LK) Air velocity (LL) Smell (LK) Smell (LL) Noise (LK) Noise (LL) Figure. School B winter situation and summer situation (Scholten 6) Temperature (LK) Temperature (LL) Stability temp (LK) Stability Temp (LL) Air velocity (LK) Air velocity (LL) Smell (LK) Smell (LL) Noise (LK) Noise (LL) Temperature (LK) Temperature (LL) Stability temp (LK) Stability Temp (LL) Air velocity (LK) Air velocity (LL) Smell (LK) Smell (LL) Noise (LK) Noise (LL) Figure : School C winter situation and summer situation (Scholten 6)

7 Figure 4 shows that the Percperceived better than the comfort in summer, but is on average good to reasonable. Range is from averageived Temperature comfort in winter is mostly e,4 up to 6, A B k B l C k C l T Winter,5,,5 T Summer,5,8 4,,4, Figure 4: Perceived Temperature comfort Winter and Summer Figure 5 shoes that the Perceived temperature stability comfort is rated reasonable. There seems to be not much difference between the summer and winter situation A B k B l C k C l T stability Winter,8 4,8,7, T stability Summer,5 4,7,,,5 Figure 5: Perceived Temperature stability comfort Figure 6 shows that the perceived air speed comfort is slightly better in winter than in summer. With one exception, the teachers of school B, all other situations are perceived as good A B k B l C k C l air Speed Winter,8 5,,,5, air Speed Summer,8 6,,7,8 Figure 6: Perceived air speed comfort

8 CONCLUSIONS Some important conclusions can be drawn from the measurements and questionairs: -Measurements and calculations provide an insight in the effects of TABS on the climate itself and the individual perception. - TABS itself can assure an acceptable indoor temperature. The users are satisfied during winter. Questionnaire shows that the building users are slightly less satisfied in summer. - Bench marking of the specific parameters concerning thermal comfort gives a clear picture whether or not a project is within the normal range of performance - The comfort of schools with TABS is not necessary much better than schools with other heating systems ACKNOWLEDGEMENT The studies of Loes Joosten, Manuel van Bruchem and Robin Scholten, gathered the information in all buildings and happily lead to their graduation but also gave valuable insight in the comfort performance of TABS in buildings. Thanks also goes to PIT for their financial support. REFERENCES. M.Koschenz (999) Interaction of an air system with concrete core conditioning, Energy and Buildings, 999. R. Becker et al (7) Improving energy performance of school buildings while ensuring indoor air quality ventilation, Building and Environment 4(7) ISSO ( 4) Thermische Behaaglijkheid, eisen voor de binnentemperatuur in gebouwen, ISSO publication 74 (in Dutch) 4. R.Scholten (6) Prestatie- en optimalisatiestudie bouwdeelactivering in scholen, MSc-thesis draft 6 5. L.A.H. Joosten (4) Fieldstudy on the performance of exhaust-only ventilation in schools with regard to indoor air quanlity, MSc thesis Technische Universiteit Eindhoven 6. M.v.Bruchem (5) Verbeterd installatietechnisch ontwerp voor basisscholen om luchtkwaliteit en comfort te waarborgen, Master-thesis, Technische Universiteit Eindhoven 7. P.J. Landrigan (997) Children s Health and the Environment The first Herbert L. Needleman Award Lecture,Maternal and Child Health Journal, Vol., No., M.J. Mendell and G.A. Heath G.A. 5, Do indoor pollutants and thermal conditions in schools influence students performance? A critical review of the literature, Indoor Air, 5, D.G. Shendell et al (4) Associations between classroom CO-concentrationsand student attendance in Washington and Idaho, Indoor Air, 4, -4. J.M.Daisey et al () Indoor air quality, ventilation and health symptoms in schools: an analysis of existing information, Indoor Air,, O.A. Seppänen et al (999) Associations of ventilation rates and CO-concentrations with health and other responses in commercial and institutional buildings, Indoor Air, 9, 6-5. ASHRAE (999) Ventilation for Acceptable Indoor Air Quality, Standard 6-999, Atlanta, GA, American Society for Heating, Refrigerating and Air Conditioning Engineers.. P.O Fanger (97) Thermal comfort, PhD Thesis, McGraw-Hill Book Co 4. SO 77 (996) Moderate thermal environments Determination of the PMV and PPD indices and specification of the conditions for thermal comfort. 5. ASHRAE (99) ASHRAE 55, Thermal Environmental Conditions for Human Occupancy, American Society of Heating, Refrigerating and Air-conditioning Engineering, Atlanta, HOPE () Health Optimisation Protocol for Energy-efficient Buildings: Pre-normative and socio-economic research to create healthy and energy-efficient buildings. European Project No : NNE5--; Project Coordinator: TNO Building and Construction Research (NL).