Ventilating of old apartment buildings

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1 Ventilating of old apartment buildings Teet-Andrus Koiv 1, Alo Mikola 1 Department of Environmental Engineering 1 Tallinn University of Technology Ehitajate tee 5 Estonia teet.koiv@ttu.ee Abstract: - In old apartment buildings there is generally natural ventilation. It works particularly badly with renovated windows, in which case the air change rate is typically up to For renovating the ventilation in old apartment buildings, exhaust air heat pump systems or room-based equipment are used. This study is devoted to the latter. The performance of spatial equipment in real operating conditions in 2-room apartments have been studied. Meltem and Inventer equipment were under investigation. Real supply and exhaust air temperatures and temperature ratios have been studied. The efficiency of the investigated air handling units (AHU) has been characterized. Key-Words: Old apartment building, Ventilating, Room based AHU, Temperature ratio of AHU 1 Introduction Ventilation has an important place in ensuring good air quality in apartment buildings. Besides the carbon dioxide level, indoor air temperature has a significant impact on the air quality. At the same time the ventilation solution is important. Frontczak and Wargocki have pointed out that in naturally ventilated buildings, the acceptable temperature range is wider than in buildings with mechanical ventilation [1]. In the review about ventilation in European dwellings, it was pointed out that the ventilation of residential spaces in Nordic countries is often poor [2]. As a result of refurbishing, the air tightness of the building envelope increases and as many buildings have natural ventilation, the air change rate is reduced. The performances of the ventilation systems in low-energy residential houses have been presented by Maier et al [3]. The energy performance of heat recovery units has been investigated by Jaber et al [4] and Laverge et al [5]. Ventilation heat recovery in residential buildings has been investigated by Dodoo et al [6]. A number of studies about the ventilation and indoor air quality in apartment buildings have been carried out at Tallinn University of Technology by Mikola, Koiv and Kalamees [7, 8, 9, 10]. The present study focuses on the ventilation of apartment buildings, more precisely on the investigation of the room based AHU. 2 Method and investigated apartments The determination of the air flow rate in the room by CO 2 concentration is based on the balance equation m dτ + L C v dτ - L C dτ - V dc = 0 (1) Air change in a bedroom can be determined by equation (2), obtained from equation (1) [11] ISBN:

2 m + Cv C L τ = ln L (2) V m + Cv Co L where m - carbon dioxide generation in the room, L - air change in the room, V - volume of the room or design volume, C v - carbon dioxide concentration in external air (in supply air), C - carbon dioxide concentration in the room air (in exhaust air), C o - carbon dioxide concentration in the air of the room at the beginning of human activity, τ - time. Air flow rates determined by formula (2) give satisfactory results. Studies were carried out in 2-room apartments of apartment buildings, Fig.1 and 2. Fig.2 2-room apartment with the room AHU Inventer R14 in the bedroom and living room 3 Indoor air quality The European indoor climate Standard EN15251:2007 [10] takes into account different allowed CO 2 levels depending on the CO 2 concentration of the external air. Table 1 presents the CO 2 values according to EN Table 1. CO 2 levels according to EN15251 Category Respective CO 2 level exceeding external air concentration in ppm for energy calculations I (A) 350 II (B) 500 Fig.1 2-room apartment building with the room AHU Meltem III (C) 800 IV (D) > 800 The CO 2 concentrations measured in the bedrooms of apartments with natural ventilation in the winter period varied from 370 to 4000 ppm. In some apartments the CO 2 level for a short time exceeded 4000 ppm the maximum limit of the measuring unit. In the investigated apartments the indoor air quality corresponded to class B 59% of the time of measuring and to class C 87% of the time, Fig. 3. As on average people spend only about 14 hours a day at home, the CO 2 concentration corresponded to level B 38% of the time the ISBN:

3 apartments were used and to level C 81% of the time. 2/3 of the windows in the studied apartments had been renovated. kitchen, Fig.1 and 2 - one of the most efficient solutions. This research studies the latter approach. The study is based on two devices: Meltem AHU and Inverter AHU mounted in 2-room apartments, Fig.1 and 2. Meltem AHU, Fig. 4 based on the recuperative heat exchanger, Fig. 5. Heat recovery takes place through an aluminum plate heat exchanger. Fig. 3 Cumulative graph of CO2 2 concentration in apartments during the winter period The CO 2 concentrations measured in the bedrooms of apartments in the summer period (thanks to partial opening of windows) were lower up to 3200 ppm. We can see that in apartments with natural ventilation and renovated windows it is necessary to renovate the ventilation in order to ensure the required indoor air quality. Fig.4 Meltem AHU 4 Results Possible solutions for renovating the ventilation in old apartment buildings: -Installation of fresh air valves in buildings with natural ventilation - high heating costs. -Balancing ventilation - almost impossible to use in old apartment buildings. -Exhaust mechanical ventilation - could be used in new apartment buildings, high heating costs. -Apartment based balancing ventilation - difficult to use in old apartment buildings as people do not like duct installation in the flat. Fig.5 Meltem device in the open position Inventer AHU based on the regenerative ceramic heat exchanger, Fig.6. This is a paired device, each of which is typically located in a separate room. -Exhaust mechanical ventilation with the heat pump and fresh air valves in living rooms - increasingly more widely used recently. -Installation of the room based AHU and exhaust ventilators in the WC, bathroom and ISBN:

4 Fig.6. Inventer AHU with the ceramic heat exchanger They operate intermittently, the air flows out for 70 s and in for 70 s. One of devices provides the room with fresh air, the other removes the exhaust air, the latter also heats up the ceramic heat exchanger. The studies were carried out in winter conditions. To examine the basic measure of effectiveness the supply air and exhaust air temperature and external temperature were measured. Characteristic temperatures of Meltem and Intellivent AHU are shown in Fig.7. We can see that in winter conditions (external temperature from 0 C to -5 C) the supply temperature of Meltem AHU is significantly higher than with Inventer AHU. Fig.8 shows supply/exhaust temperatures in the conditions of different air flow rates (external temperature from -5 C to -10 C). The graph shows that with the higher air flow rate the efficiency of Inventer AHU is higher, but the temperature ratio is still nearly 20%. Due to natural extract ventilation from WC/bathroom and kitchen the temperature ratio is very low. Fig.8 Supply/exhaust temperatures of Meltem and Inventer AHU for different flow rates The temperature ratios for Meltem AHU with external air temperatures from 4 C to -4 C are shown in Fig.9. We can see that the temperature ratio remains mostly between 0.6 and 0.5. Fig.9 Temperature ratios for Meltem AHU The temperature ratios for Meltem AHU with a wide range of external temperature are shown on Fig.10. Fig.7 Supply/exhaust temperatures of Meltem and Inventer AHU Fig.10 Temperature ratios for Meltem AHU with different external temperatures In Fig.10 the temperature ratios are calculated for various parameters of the external. ISBN:

5 temperature. It turns out that the dependence of temperature ratios calculated on the basis of measurement results on the external temperature is best characterised by the quadratic equation y = x x The correlation is relatively weak, R2 = Fig.10 shows that the average temperature ratio is lowest at temperature 0 C and increases in the case of higher and lower temperatures. Investigations showed that temperature ratios for Meltem AHU are close to 60%. Tenants have a positive attitude towards the use of the equipment. The working graph of Inventer AHU is well described in Figure 11 where the supply and exhaust temperatures are given. Fig. 11 Operating cycle of Inventer AHU, mode 70 s supply air and 70 s exhaust (air flow rate of 100%) The graph shows that the temperature ratio of Inventer AHU is relatively low. The low temperature ratio results in the low temperature of the supply air, which causes inconvenience to residents. This in turn causes the configuration of the device to low flows (2-4 L/s), not providing the necessary CO 2 levels in bedrooms. It should be noted that additional studies of Inventer AHU are necessary. 5 Conclusion The air quality in the bedrooms of old apartment buildings with natural ventilation and renovated windows is unsatisfactory. When renovating old apartment buildings it is necessary to pay serious attention to the renovation of the ventilation. The investigation has shown that the room-based device Meltem AHU can ensure the required indoor climate and the required level of noise within. Inventer devices are more problematic. Initial testing in winter conditions showed that the temperature ratio as well as the supply air temperature are low. As a result, the device is set for a small air flow rate, which cannot ensure the necessary quality of indoor air, especially in bedrooms. Acknowledgements The publication of this article was supported by the ESF measure Development of cooperation and innovation of universities, the sub-measure "Doctoral Schools" that finances the project "Construction and Environmental Engineering PhD School" project code References: [1] C. Dimitroulopoulou, Ventilation in European dwelling: A review, Building and Environment, 47, 2012, pp [2] M. Frontczak, P. Wargocki, Literature survey on how different factors influence human comfort in indoor environments, Building and Environment, 46, 2011, pp [3] T. Maier, M.Krzaczek, J. Tejchman, Comparison of physical performances of the ventilation systems in low-energy residential houses. Energy and Buildings,Vol 41, 2009, pp [4] Samar Jaber, Salman Ajib, Energy Recovery System in Mediterranean region. Sustainable Cities and Society, Vol 3, pp. 1-66, [5] J. Laverge, A. Janssens, Heat recovery ventilation operation traded off against natural and simple exhaust ventilation in Europe by primary energy factor, carbon dioxide emission, household consumer price and exergy. Energy and Buildings, Vol 50, 2012, pp [6] A. Dodoo, L. Gustavsson, R. Sathre, Primary energy implications of ventilation heat recovery in residential buildings. Energy and Buildings, Vol 31, 2000, pp [7] Koiv, T.-A.; Mikola, A.; Kuusk, K., Energy Efficiency and Indoor Climate of Apartment Buildings in Estonia. International Journal of Energy Science, 2, 3, 2012, pp ISBN:

6 [8] Koiv, T.-A.; Voll, H.; Mikola, A.; Kuusk, K.; Maivel, M., Indoor Climate and Energy Consumption in Residential Buildings in Estonian Climatic Condition, WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT, 6, 4, 2010, pp [9] Mikola, A., Koiv, T.-A., Indoor Air Quality in Apartment Buildings of Estonia. Computers and simulation in modern science : selected papers from WSEAS conferences, 2011, pp [10] Koiv, T.-A., Kalamees, T., Indoor Climate and Energy Efficiency in Typical Residential Buildings. INTECH, 2011, pp [11] Koiv, T-A., Indoor climate and ventilation in Tallinn school buildings. Proceedings of the Estonian Academy of Sciences. Engineering, 13(1), 2007, pp [12] EVS-EN 15251:2007. Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics. Estonian Centre of Standardisation, ISBN: