Mean Age of Air in Natural Ventilated Buildings: Experimental Evaluation and CO2 Prediction by Artificial Neural Networks

The mean age of air (MAA) is one of the most useful parameters in evaluating indoor air quality in natural ventilated buildings. Its evaluation is generally based on the CO2 monitoring within the environment; however, other methods can be found in the literature, but they have not always led to satisfactory results. In this context, the present paper is focused on two main topics: the effect of the windows airtightness and of the environmental conditions on MAA and the application of artificial neural network (ANN) for the CO2 prediction within the room. Two case studies (case study 1 located in Terni and case study 2 located in Perugia) were investigated, which differ in geometric dimensions (useful area, volume, window area) and in airtightness of windows. The indoor and outdoor environmental conditions (air temperature, pressure, relative humidity, air velocity, and indoor CO2 concentration) were monitored in 33 experimental campaigns, in four room configurations: open door-open window (OD-OW); closed door-open window (CD-OW); open door-closed window (OD-CW); closed door-closed window (CD-CW). Tracer decay methodology, according to ISO 16000-8:2007 standard, was compiled during all the experimental campaigns. A feedforward ANN, able to simulate the indoor CO2 concentration within the rooms, was then implemented; the monitored environmental conditions (air temperature, pressure, relative humidity, and air velocity), the geometric dimensions (useful area, volume, window area), and the airtightness of windows were provided as input data, while the CO2 concentration was used as target. In particular, data of 19 experimental campaigns were provided for the training process of the network, while 14 were only used for testing the reliability of ANN. The CO2 concentration predicted by ANN was then used for the MAA calculation in the four room configurations. Experimental results show that MAA of case study 2 is always higher, in all the examined configurations, due to the higher airtightness characteristics of the window and to the higher volume of the room. When the difference between indoor and outdoor temperature increases, the MAA increases too, in almost all the investigated configurations. Finally, the CO2 concentration predicted by ANN was compared with experimental data; results show a good accuracy of the network both in CO2 prediction and in the MAA calculation. The predicted CO2 concentration at the beginning of experimental campaigns (time step 0) always differs less than 2% from experimental data, while a mean percentage difference of −18.8% was found considering the maximum CO2 concentration. The MAA calculated using the predicted CO2 of ANN was greater than the one obtained from experimental data, with a difference in the 0.5–1.3 min range, depending on the configuration. According to the results, the developed ANN can be considered an alternative and valuable tool for a preliminary evaluation of MAA

Prediction Of Indoor Conditions And Thermal Comfort Using CFD Simulations: A Case Study Based On Experimental Data

Abstract In the present paper CFD tool was used for thermal comfort evaluation in natural convection and in transient conditions in a room by setting only the external weather conditions as input parameters. A survey in a classroom at the Department of Engineering, University of Perugia, was carried out and data required for the thermal comfort evaluation and CFD simulation model set up was acquired. The simulation model was validated with experimental data and it was used for the thermal and velocity profiles simulation and for the thermal comfort indexes calculation, according to UNI 7730

Masonry wall panels retrofitted with thermal-insulating GFRP-reinforced jacketing

Today there is a need to provide thermally efficient walls, while at the same time to increase the mechanical properties of old unreinforced masonry walls that will not require large amounts of energy in the retrofitting or deconstruction processes. To address this problem, this paper gives the results of shear tests carried out on masonry panels made of solid bricks retrofitted with a new technique based on the use of glass fiber-reinforced polymers (GFRP) grids inserted into a thermal insulating jacketing. This was made of different low-strength lime-based mortars. Tests were carried out in laboratory and results were used for the determination of the shear modulus and strength of the wall panels before and after the application of the GFRP reinforcement. Retrofitted panels exhibited a significant enhancement in the lateral capacity when compared to the control panels. The thermal performance of the proposed mortars was also investigated both with and without GFRP. Low values of thermal conductivity were found, especially for the samples with GFRP; a reduction of the thermal transmittance value in the 34–45 % range was also obtained by applying 45 mm layer of coating in conventional masonry walls

comparison of the energy performance of existing buildings by means of dynamic simulations and artificial neural networks

Abstract The energy efficiency of buildings can be evaluated by using the methodology provided by European regulations; however, this method required a lot of information which is generally not available for the existing buildings. In this paper an alternative method for the energy efficiency investigation of buildings is proposed and tested by means of Artificial Neural Networks (ANNs); an existing building built in 1990 and located in Perugia was chosen as case study and it was investigated by adopting both the mentioned approaches. An experimental campaign was also carried out in order to implement and validate the 3D model developed in TRNSYS. Results showed that the indoor air temperature trend simulated with ANN is closer to the measured data than the one simulated with TRNSYS, with lower mean error and MSE values. The energy consumption simulated with ANN is slightly higher than the one returned by using TRNSYS code of about 20 kWh/m 2 year (difference lower than 7%). In agreement with the results, the proposed method can be considered as an alternative tool that can be used for the thermal-energy investigation of existing buildings, with important money and time saving

Development of Innovative Aerogel Based Plasters: Preliminary Thermal and Acoustic Performance Evaluation

The thermal and acoustic properties of innovative insulating systems used as building coatings were investigated: Granular silica aerogel was mixed with natural plaster in different percentages. This coating solution is transpiring and insulating, thanks to the use of a natural lime coat and aerogel, a highly porous light material with very low thermal conductivity. The thermal conductivity of the proposed solution was evaluated by means of a Heat Flow meter apparatus (EN ISO 12667), considering different percentages of aerogel. The natural plaster without aerogel has a thermal conductivity of about 0.50 W/m

Thermal and Acoustic Properties of Aerogels: Preliminary Investigation of the Influence of Granule Size

8th International Conference on Sustainability in Energy and Buildings, SEB 2016 The influence of granules size in silica aerogels is experimentally investigated in terms of thermal and acoustic performance characteristics. The transmission loss (TL) is measured at normal incidence in a traditional impedance tube, whereas the thermal conductivity (?) is evaluated using a Hot Plate apparatus, setting up an appropriate methodology, due to the nature of the sample. The results reveal that the small granules (granules size in the 0.01-1.2 mm range), which have the highest density, have the best performance both in terms of thermal and acoustic properties. Depending on the granules size, ? varies in 19-22 mW/mK range at 10°C, whereas a TL equal to 13 dB at about 6400 Hz for 20 mm thickness is obtained for small granules. © 2017 The Authors

Energy Performance Database of Building Heritage in the Region of Umbria, Central Italy

Household energy consumption has been increasing in the last decade

Experimental and Numerical Energy Assessment of a Monolithic Aerogel Glazing Unit for Building Applications

In the last few decades, the attention of researchers has been focused on the characterization of aerogels in order to improve the thermal performance of transparent building envelopes. Granular aerogel is already spread in the market thanks to the easy manufacturing system, whereas the difficulty in producing monoliths without defects, cracks, and inhomogeneity limited the diffusion of monolithic aerogel systems. A new production process for the monolithic panels was developed at Union College (Schenectady, NY, USA); it is a rapid supercritical extraction technique which allows a reduction in production time (only a few hours) and results in less solvent waste. Panes with maximum dimensions of about 100 × 100 mm were fabricated and composed in a unique glazing system, with external dimensions 300 × 300 mm. The thermal characterization of the innovative monolithic aerogel glazing system (simple float glazing 4.7-mm-thick monolithic aerogel pane 15-mm-thick simple float glazing 4.7 mm thick), which was carried out by means of a Small Hot Box apparatus, showed a thermal transmittance value of about 1.1 W/(m2K). Data was used in dynamic simulations of a typical non-residential building. They showed that the new investigated solution allows a valuable reduction with respect to a low-e double glazing system in terms of heating energy demand (about 5–7% for Helsinki, 8–12% for Paris, and 10–15% for Turin), for different window-to-wall ratios

Thermal and Acoustic Performance Evaluation of New Basalt Fiber Insulation Panels for Buildings

Abstract Thermal insulation of building envelope is very important in energy saving: a growing interest is focused on using insulating recycled and sustainable materials. The thermal and acoustic properties of innovative basalt natural fiber insulating panels were investigated. The thermal conductivity was evaluated by means of a Heat Flow meter apparatus: it is included in 0.030-0.034 W/mK range. The acoustic absorption coefficient was measured by means of Kundt's Tube. The results were compared to traditional solutions with similar chemical composition, but worse mechanical resistance. The easy application of this solution could be useful especially for refurbishments

Towards a holistic approach to indoor environmental quality assessment: Weighting schemes to combine effects of multiple environmental factors

Abstract In the recent past, great attention has been posed on the assessment of the energy performance and of the operating and maintenance costs of the building stock. Currently, new approaches of analysis are considered by the scientific community, which put the occupant's well–being at the centre of the evaluation process. In this context, the IEQ assessment acquires an ever increasing importance, especially if the combined effects of multiple environmental factors are considered. With this purpose, to date, different weighting schemes can be found in the literature, obtained through subjective investigations and mathematical methods. In this paper, the weighting schemes proposed in the literature in the period 2002–2018 were examined, considering the survey methodologies used. The more relevant studies found in the literature were compared and the related weighting schemes were discussed, based on the intended use of the buildings. In particular, 122,000 questionnaires in 18 different countries all over the world were examined and the most relevant environmental factors were selected: Thermal Environment (TH), Air Quality (AQ), Acoustics (AC), and Lighting (LT). Three different average weighting schemes were obtained for each of the following uses: offices, schools, dwellings; a final additional weighting scheme was obtained considering the average values of the normalized weights for all the building uses, a possible solution for buildings with an unspecified or not unique intended use. Moreover, an original weighting scheme was obtained and proposed on the basis of the results of three different subjective surveys, involving about 1400 participants, carried out in some university classrooms at the School of Engineering of the University of Pisa: it was compared with the one obtained by the literature for school buildings. It was observed an overestimation of the importance of TH (0.42 instead of 0.33) and an underestimation of AC (0.19 instead of 0.26), whereas AQ and LT are in accordance (0.17 instead of 0.19 and 0.22, respectively). The results of the present study can be useful to those who intend to deal with holistic approaches to building design, for which accurate assessments of occupants' well-being are taken into consideration as well as aspects related to energy performance and building management costs