Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 172 (217 ) 1154 116 Modern Building Materials, Structures and Techniques, MBMST 216 Attempt to improve indoor air quality in computer laboratories Marek Telejko a * a Kielce University of Technologi, al. Tysiąclecia Państwa Polskiego 7, 25-314 Kielce, Poland Abstract Low indoor air quality (IAQ) can impact occupants health and lead to poor productivity or low academic performance. Therefore the provision of good IAQ in classrooms and laboratories is very important. This paper presents the results of the investigation devoted to the quality of indoor air in computer laboratories of selected Polish high schools. Six schools in a town with a population of 2 inhabitants were involved in the investigations. The participating school buildings were built between 1975 and 1991 and had gravity ventilation systems. The variability of basic IAQ parameters, i.e., temperature, relative humidity and carbon dioxide level, was analysed and the assessment of the computer laboratories in terms of microbiological purity was performed. The outomes confirmed the low quality of the indoor air in these buildings. Certain modifications aimed at improving IAQ were proposed during the investigations. Two solutions were implemented. The first solution involved a twofold increase in the volume of supply air from 9 m 3 /h to 18 m 3 /h. The other modification consisted in installing indoor air cleaning devices based on the radiant catalytic ionization technology (RCI). The results of this study indicate that the proposed solution offers the potential to improve IAQ within computer labs. 217 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 216 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4./). Peer-review under responsibility of the organizing committee of MBMST 216. Peer-review under responsibility of the organizing committee of MBMST 216 Keywords: building physics, ventilation, air exchange, indoor air quality. * Corresponding author. Tel.: +48-41-34-24-48; fax: +48-41-34-42-997. E-mail address: mtelejko@tu.kielce.pl 1877-758 217 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4./). Peer-review under responsibility of the organizing committee of MBMST 216 doi:1.116/j.proeng.217.2.134
Marek Telejko / Procedia Engineering 172 (217 ) 1154 116 1155 1. Introduction Most high school buildings in Poland rely on natural ventilation. This fact is attributed to the age of these buildings constructed more than dozen or even several tens of years ago. Few of them were fitted with a mechanical ventilation system allowing for the adjustment of microclimate parameters. The national requirements for gravity ventilation included in the standards [1,2,3] provide general guidelines, specifying strict description only for the airtightness of windows and balcony doors and the minimum airflow to be supplied to the rooms. The minimum airflow supplied is independent of the number of occupants and purpose of the room. Despite the importance of the requirements for both new and existing structures that have underwent alterations, the provisions of the standard [1] are related only to the newly built buildings, as indicated by the application scope of the document. Reports [4,5,6] indicate, however, that in many cases alterations to buildings have a negative effect on the operation of natural ventilation systems and thereby on the quality of indoor air. In addition, owners of the buildings can make some alterations without obtaining any approvals or building permits, still in compliance with Polish laws [7]. Enforcement of these laws on the existing buildings is difficult for various reasons. Moreover, even the best ventilation system design is not able to predict extreme behaviours of occupants, who tend to take a number of actions that aim at, in their view, improving the comfort of use. But their actions usually impair the operation of gravity ventilation systems, thus worsening the indoor microclimate. 2. Carbon dioxide as an indicator of air quality The idea of conducting a questionnaire survey was abandoned owing to the character of the rooms and short stays of students in the computer laboratories. The author chose the CO 2 concentration for the indicator of the indoor air quality. The relationship between the amount of ventilation air and the concentration of carbon dioxide inside the rooms is a commonly used criterion for the air quality assessment [8,9]. In natural environment, carbon dioxide is a non-toxic gas. It may only give people a feeling of greater freshness or lesser freshness of the air. The present range of CO 2 in atmospheric air is 4 6 ppm. Its concentration usually increases in closed rooms with the supply of air from external and internal sources. Indoors, CO 2 comes primarily from living organisms and gas devices. Its emission depends on the activity level of a given organism (Table 1) and may vary from person to person depending on the diet, body weight, health condition, etc. It is obvious that the number of people present in the room, poor air exchange (drop in oxygen amount in air) or enhancement of combustion processes (e.g., smoking, cooking, etc.) have a direct effect on CO 2 levels. Table 1. Emission of CO 2 for various levels of activity [1]. Type of activity CO 2 generated per person [dm 3 /s person] [m 3 /s person] At rest.4 4 1-6 Doing light work.6.12 (6 12) 1-6 Doing moderate-hard work.12.2 (12 2) 1-6 Doing hard work.2.26 (2 26) 1-6 Doing very hard work.26.32 (26 32) 1-6 Table 1 shows the amount of carbon dioxide present in exhaled air depending on the level of activity. Data is presented here as a mean over the data measured. The present standards of the indoor air quality specify the allowable level of CO 2 concentration to be 1 ppm [11,12], taking it as a hygiene minimum requirement. Polish laws do not lay down the maximum CO 2 concentration level for housing units or public buildings. The standard in [13], applicable also in Poland, classifies the indoor air quality into categories by CO 2 concentration (Table 2) and provides the required minimum airflow per person for each category.
1156 Marek Telejko / Procedia Engineering 172 ( 217 ) 1154 116 Table 2. Classification of indoor air quality for rooms with low pollutant emission levels and a smoking ban [13]. Category Description of indoor air quality CO 2 level relative to outdoor air [ppm] IDA 1 High < 4 < 54 IDA 2 Medium 4 6 36 54 IDA 3 Moderate 6 1 22 36 IDA 4 Low > 1 > 22 Volume outside airflow [m 3 /h] It is worth noting that specified in [3] the minimum airflow of outside air to be supplied to a room is 3 m 3 /h per person, which corresponds to IDA 3 category according to [13], that is, to the moderate quality of indoor air. 3. Scope of study The investigations were conducted in six computer laboratories located in high schools built between 1975 and 1991. The external walls were insulated with 12 15 cm thick styrofoam blocks. The flat roofs were insulated with 15 2 cm thick rock wool panels. All buildings had natural ventilation systems with the ventilation air supplied through three window trickle vents with a capacity of 3 m 3 /h. The laboratories had 15 computer stations each and 15 to 18 users were assigned to each of them. The tests were carried out in the period between November 214 and February 215. The outside air temperatures ranged from 12 to +1 C, with relative humidity in the range 45% 99%, carbon dioxide concentration from 47 ppm to 73 ppm, and the wind speed of, 6,1 m/s. Average daily outside air parameters recorded during the investigations are summarized in Table 3. Table 3. Average daily outside air parameters in the period under investigation. Parameter October December February Temperature [ C] 8 15 9-2 7 Relative humidity [%] 58 92 7 96 73 86 Atmospheric pressure [hpa] 12 126 998 129 15 123 CO 2 concentration 43 416 429 441 46 483 The parameters measured included basic microclimate factors: carbon dioxide concentration in the rooms, temperature and relative humidity of the indoor air. The measurements were conducted for three months in twoweek periods at five minutes intervals. Three measurement series were conducted for each room. 4. Results Analysis of the measurement data collected shows that the plots of microclimate parameters are similar for all laboratories investigated. The values of CO 2 concentration and relative humidity recorded at the beginning of each class increase and reach the maximum very quickly to go down during a break. The breaks are too short to let the parameters come back to the initial values. With the start of a new class, CO 2 and RH values rise quickly again. After teaching hours, the values go down slowly, reaching minimum levels (Fig. 1). The lowest CO 2 concentrations, from 419 ppm to 517 ppm, were recorded at night or at early hours. During the day, the values rose quickly exceeding 32 ppm in some cases. Characteristic minor drops during the day (Fig. 1) result from short periods of ventilation by opening the windows and from breaks during which IAQ improves for a very short time.
Marek Telejko / Procedia Engineering 172 (217 ) 1154 116 1157 CO 2 [ppm] 35 3 25 2 15 1 5 CO2 Temperature RH 4 35 3 25 2 15 1 5 5 Temperature [ o C]; RH [%] 1 15 2 25 3 Test numer Fig. 1. Indoor air parameters, 24h pattern, for a selected laboratory (measured at 5 minutes intervals). A characteristic feature of the involved rooms was a number of additional heat sources, that is, computers. The temperatures recorded in all rooms exceeded the optimal values for thermal comfort. The maximum temperature, 29,6 C, was recorded on a sunny day in laboratory HS1 (Table 4) which has windows facing south. Maximum temperatures recorded in the other rooms ranged from 26,8 C to 29,5 C. During teaching hours, temperatures lower than 2 C were recorded only after intense and long (more than 3 minutes) period of window opening. The lowest indoor temperatures, from 19,8 C to 21,2 C, were recorded at night and early in the morning. Outside of teaching hours, relative humidity levels fell below 4% (Fig. 1). During the classes, a fast and considerable rise in relative humidity was recorded. These values, however, did not exceed the maximum allowable levels for thermal comfort, recommended in [14]. Table 4 summarizes the maximum and minimum values of indoor air parameters measured in laboratories HS1 HS6. Table 4. Maximum and minimum values of the indoor air parameters for labs HS1 HS6 in each measurement series. Maximum values Minimum values Laboratory HS1 HS2 HS3 HS4 HS5 HS6 HS1 HS2 HS3 HS4 HS5 HS6 CO 2 concentration [ppm] Series 1 2873 2927 2898 2854 2912 312 434 43 437 441 458 471 Series 2 31 379 324 3151 3138 326 419 435 43 438 442 463 Series 3 3198 3263 3212 3217 3189 3248 491 517 475 511 492 57 Temperature [ o C] Series 1 28,1 28,3 26,8 27,2 28, 27,5 2,6 2,5 2,9 21, 2,2 21,3 Series 2 29,5 28,2 27,4 27,9 27,6 26,9 21,2 19,8 2,7 2,6 19,9 2,7 Series 3 29,6 28,9 28,1 27,1 28,3 27,2 2,8 2,4 19,5 21,1 2,3 2,7 RH [%] Series 1 51,4 49,7 51,7 49,5 5,3 54, 33,4 33,1 32,5 33,2 31,8 31,2 Series 2 55,1 51,9 51,6 5,1 52,8 53,6 32,6 32,3 32,2 32,7 32,6 33,1 Series 3 49,2 5,6 5,9 5,6 51,5 54,8 31,7 31,6 31,4 33,6 31,4 32,9 To improve the quality of the indoor air in the participating laboratories, the authors proposed installation of three additional air vents, each of 3 m 3 /h capacity, which doubled the supply of outside air. As a result, CO 2
1158 Marek Telejko / Procedia Engineering 172 ( 217 ) 1154 116 concentration dropped from 8 ppm to about 1 ppm on average, with average indoor temperatures reduction of about 1, 1,5 C, whereas the mean values of relative humidity did not change substantially, nor did the plots of the measured parameters (Fig. 2) which remained the same as before the installation of the additional vents. The maximum and minimum values of the parameters measured in each computer laboratory are shown in Table 5. CO 2 [ppm] 35 3 25 2 15 1 5 CO2 Temperature RH 45 4 35 3 25 2 15 1 5 5 1 15 2 25 3 Test numer Temperature [ o C]; RH [%] Fig. 2. Indoor air parameters, 24h pattern, for selected laboratory (measurement step 5 minutes), after the installation of window vents. Table 5. Maximum and minimum values of the indoor air parameters for labs HS1 HS6 in each measurement series - after the installation of window vents. Maximum values Minimum values Laboratory HS1 HS2 HS3 HS4 HS5 HS6 HS1 HS2 HS3 HS4 HS5 HS6 CO 2 concentration [ppm] Series 1 1873 1952 1957 1864 1757 1921 428 43 417 421 419 438 Series 2 1792 1998 28 1971 1912 289 422 435 43 44 424 438 Series 3 1983 227 2184 1896 199 2111 491 517 475 443 464 51 Temperature [ o C] Series 1 26,9 27,1 26,1 26,1 26,8 27,1 2,2 19,8 21,3 2,5 2, 2,3 Series 2 28,3 27,5 26,7 25,9 27,2 26,4 2,8 2,1 2,4 2,8 19,8 19,9 Series 3 28,6 27,5 26,2 26,1 27,4 26,9 21, 19,6 19,8 2,7 19,9 19,9 RH [%] Series 1 52,1 51,2 49,9 49,2 5,6 53,3 32,9 34,1 35,2 33,3 3,6 3,9 Series 2 54,7 48,9 52,9 5,4 51,3 52,8 33,4 33,2 35,9 31,5 32,1 32,8 Series 3 5,1 53,1 52,6 49,5 51,7 53,8 32,1 36,4 34,7 32,7 31, 33,2 Further improvement of the indoor air quality (lowering CO 2 concentration) was possible through another increase in the airflow. But the owners of the buildings rejected this suggestion in fear of indoor temperature reduction or unexpected maintenance costs resulting from greater amounts of energy needed to heat the increased ventilation volume. 5. Microbiological testing Microbiological tests were carried out in parallel to the investigation of the indoor air quality and involved
Marek Telejko / Procedia Engineering 172 (217 ) 1154 116 1159 determining the presence of fungal species. The results were expected to answer the question whether and in what manner the solution implemented affects the microbiological purity of the participating laboratories. The tests were performed in accordance with Polish standards PN-89/Z-4111/1 [15], PN-89/Z-4111/2 [16] and PN-89/Z- 4111/3 [17]. After an incubation period, the mould strains were subjected to macroscopic and microscopic examinations to establish their taxonomy based on morphological and physiological characteristics. Typical asexual reproduction organs were taken into account, along with the structure and colour of the mycelium, the structure, colour and length of conidiophores (branches of the mycelium), the way the conidia are generated, their structure, shape and colour and the number of cells. The following macroscopic characteristics were evaluated: colony diameter, structure and character of growth, colour of the top and bottom sides, secretion droplets, colour of the pigment entering the substrate, middle and boundary layers of the colony and generation of concentric growth zones. The results of the observations indicate that the additional window air vents allow a reduction in the amount of mould spores present in the indoor air. However, it was impossible to eliminate all of the mould in the rooms (Table 6). Airborne fungal spores are naturally found in outdoor air, as confirmed by the appearance of Acremonium charticola spores in one of the series of tests after increasing the ventilation airflow. Another solution proposed to further improve the air quality included installing the RCI (radiant catalytic ionization) air cleaning devices in the laboratories [18]. These devices use active air purification technology, which consists in generating proper light wavelengths in the matrix. This allows recreating the photocatalytic process under artificial conditions. Oxidation and ionization processes are created using UVX radiation the same way they are produced in nature by sunlight. Air samples were taken at minimum 12 hours after activation of the device. The results indicated high efficiency of the devices at mould reduction. The efficiency of the portable devices used in the tests was more than 9%. The tests were conducted assuming that the outdoor air is supplied only via the vents. The analysis of the results shows that the presence of some of the moulds was dependent on the test period. Therefore, these results have to be considered as initial results that require a lot more repetitions with measurements of various outdoor air parameters taken into account, for example, time of year, etc. Table 6. Moulds in the rooms investigated (maximum values recorded). Fungal species identified Initial condition After the installation of window vents Aspergillus versicolor 15% 1% none Cladosporium herbarum 1% 5% none Aspergillus niger 2% 1% none Yeastoids 55% 3% 5% Penicillium meleagrinum 15% 5% none Penicillium expansum 1% 5% none Penicillium versicolor 5% - none Penicillium chrysogenum 7% 45% 5% Penicillium notatum 5% - none Acremonium charticola - 5% none Trichoderma viride 1% 5% none After the installation of RCI devices 6. Summary The outcome of the investigations indicates clearly that the low quality of indoor air in the computer laboratories involved results from improper management of air exchange. The proposed attempt to improve the indoor air quality (IAQ) by increasing the incoming airflow twofold (from 9 m 3 /h to 18 m 3 /h) brought evident effects. The initial CO 2 concentration level of up to 326 ppm was reduced substantially. With additional vents installed, the maximum CO 2 concentration over the analysis period dropped to 2184 ppm. The recorded maximum values were intermittent but the recommended levels were exceeded over the entire occupancy period. The measurement results from both
116 Marek Telejko / Procedia Engineering 172 ( 217 ) 1154 116 test series classify the participating classrooms as a category IDA 4, according to EN 13779:27. Further improvement of the indoor air quality by increasing the inflow of outside air would lead to the reduction in the indoor temperature or additional amount of energy would be needed to heat the increased volume of airflow. It should be noted, however, that computer laboratories provide additional heat gains from the computers. The results from the measurements show that the indoor air temperatures in the occupancy period exceeded those recommended for thermal comfort. This is a direct result of the fact that no consideration in terms of indoor air quality was given to proper location when selecting rooms for computer laboratories. At the designing phase, laboratories were not required to follow any microclimate-related guidelines as no such guidelines existed at that time. The increase in the outside airflow volume had a positive effect on microbiological purity of the indoor air. It was impossible to eliminate all the moulds by reason of the fact that they are naturally occurring and always present in the air. Excellent results in terms of mould spore reduction were achieved with the use of air cleaning devices based on the RCI technology. Nevertheless, the results are still to be considered as preliminary. To sum up, it can be stated that in many school computer laboratories fitted with natural ventilation systems, the improvement of indoor air quality is possible by introducing proper volume of outside air. The solutions are however limited and affect the energy performance of the building. References [1] Dz. U. Nr 75 z 22 r., poz. 69 z dn. 12 kwietnia 22 r. w sprawie warunków technicznych jakim powinny odpowiadać budynki i ich usytuowanie z późniejszymi zmianami, z późniejszymi zmianami (Dz.U. No. 75 of 22, item 69 as amended) Regulation of the Minister of Infrastructure of 12 April 22 on technical conditions of buildings and their location [2] PN-83/B-343 Wentylacja w budynkach mieszkalnych zamieszkania zbiorowego i użyteczności publicznej. Wymagania, PKN, 1983 [Ventilation in dwelling and public utility buildings. Specification] [3] PN-83/B-343:Az3 Wentylacja w budynkach mieszkalnych zamieszkania zbiorowego i użyteczności publicznej. Wymagania. Zmiana Az3, PKN, 2 [Ventilation in dwelling and public utility buildings. Specification. Amendment Az3] [4] J. Piotrowski, M. Telejko, E. Zender-Świercz, Wpływ szczelnej obudowy budynku na dystrybucję powietrza wentylacyjnego, Energia i budynek 7 (21) 23 25 [Effect of airtight building insulation on ventilation air distribution] [5] M. Telejko, J. Piotrowski, Dystrybucja powietrza wentylacyjnego w budynkach ze szczelną obudową, Fizyka Budowli w Teorii i Praktyce IV 183-186 [Distribution of ventilation air in buildings with airtight insulation] [6] Ewa Zender-Świercz, Jerzy Zbigniew Piotrowski, Thermomodernization a building and its impact on the indoor microclimate, Structure and Environment 5(3) (213) 37-4. [7] Dz. U. Nr 27 poz. 216 z roku 23, Ustawa z dn. 7 lipca 1994 Prawo Budowlane, z późniejszymi zmianami [Act of 7 July 1994 Building Law, as amended] [8] M.B. Nantka, Wentylacja w budownictwie ogólnym przegląd, działanie, problemy i mity, Materiały Forum Instalacyjnego, Poznań 24 [Ventilation in general construction overview, measures, problems and myths] [9] E. Nowakowski, Problemy z wentylacją grawitacyjną pomieszczeń, Rynek Instalacyjny 9(2) 58-62 [Indoor gravitation ventilation problems] [1] M.B. Nantka, Naturalna wymiana powietrza a szczelność mieszkań, Forum Wentylacja 25, Warszawa 25 [Natural air exchange versus airtightness of flats] [11] WHO Regional Office for Europe (2), Air Quality Guidelines for Europe, SE 2, Copenhagen, European Series, No. 91 [12] ASHRAE 62-1989 Ventilation for Acceptable Indoor Air Quality. [13] EN 13779:27 Ventilation for non-residential buildings Performance requirements for ventilation and room conditioning systems [14] EN ISO 773:26, Ergonomics of the thermal environment Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices [15] PN-89/Z-4111, arkusz 1, Ochrona czystości powietrza. Badania mikrobiologiczne. Postanowienia ogólne i zakres normy. [Air protection. Microbiological measurements. General provisions and scope of the standard] [16] PN-89/Z-4111 arkusz 2, Ochrona czystości powietrza. Badania mikrobiologiczne. Oznaczanie liczby bakterii w powietrzu atmosferycznym (imisja) przy pobieraniu próbek metodą aspiracyjną i sedymentacyjną. [Air protection. Microbiological measurements. Number of bacteria measurements by aspiration and sedimentation methods] [17] PN-89/Z-4111. arkusz 3, Ochrona czystości powietrza. Badania mikrobiologiczne. Oznaczanie liczby bakterii grzybów pleśniowych mikroskopowych w powietrzu atmosferycznym (imisja) przy pobieraniu próbek metodą aspiracyjną i sedymentacyjną [Air protection. Microbiological measurements. Number of fungi measurements by aspiration and sedimentation methods] [18] D. Malicka, Technologia oczyszczania powietrza Activtek, Polski Instalator 6 (21) 78-79 [Activtek air cleaning technology]