1,720,972 research outputs found
On the use of geometrical acoustic models of a reverberant chamber to improve the reliability of sound absorption measurements
No full textFurther investigations on the definition of a new parameter to assess noise annoyance in air conditioned offices
No full textAt the conclusion of a noise annoyance survey in air-conditioned offices a new parameter was proposed. The aim was to define a noise index well correlated with subjective ratings of noise annoyance and able to account for the imbalance of the noise spectrum. As the RC Mark 11 procedure for rating the noise of HVAC systems in buildings introduced the "quality assessment index" (QAI), which provides a measure of the spectral imbalance of a noise, the combination of this parameter with the RC criterion number (which only measures noise level) was proposed. In a previous paper, the combination factor that maximised the correlation was determined and a validation procedure was used to test the repeatability of the results. In this paper, a new procedure to calculate the mean subjective. ratings has been introduced and more demanding procedures to test the repeatability of the results have been used. Finally, it was found that a combination factor varying in a range from 0.24 to 0.31 provided the highest correlation between the new parameter and the subjective sensation of annoyance
Acoustic characterization of different road materials
No full textPavements that produce less noise at the tire/pavement interface represent an important
strategic solution necessary to minimize the traffic acoustic impact. Several studies have
shown how the most important parameters affecting tire noise are associated with the road
surface that influences both the generation and propagation of sound waves. On this
subject, the Italian National Road Agency (ANAS) sponsored a research project related to
quiet pavements. The project was developed by Università Politecnica delle Marche based
on a trial section where different kinds of wearing courses were laid down. The selected
materials were a Splittmastix Asphalt (SMA), an Open Graded Friction Course (OGFC) and
a dense graded asphalt containing Expanded Clay (EC). Furthermore, two sub-sections of
SMA and of OGFC were covered respectively with a Slurry Seal with dry addition of Crumb
Rubber (SSCR) and a Photocatalytic cement Mortar (PM), obtaining five different materials
to be tested. In this paper the Authors present preliminary results, analyzing the acoustic
characterization of the selected materials in terms of absorption coefficient. Moreover, in situ
noise measurements have also been repeated at different stages in order to find possible
correlations with acoustic properties of the mixes and to investigate the time dependency of
the performance
Sperimentazione e sviluppo di impianti di refrigerazione ecosostenibili
No full textIn questo lavoro è stato studiato un ciclo Joule-Brayton inverso ad aria, con una variante al fine di realizzare un impianto di refrigerazione mediante l’utilizzo di un turbogruppo di derivazione automobilistica. Inizialmente, è stato realizzato e testato presso il Laboratorio di Macchine del Politecnico di Bari un impianto sperimentale al fine di analizzare le problematiche principali che limitano le prestazioni del ciclo ad aria. Si tratta di un impianto a circuito aperto con una compressione bistadio interrefrigerata, senza scambiatore di recupero. Le misure effettuate hanno rivelato performance inadeguate, sia in termini di efficienza sia di temperatura minima raggiungibile, causate principalmente dal basso rendimento della turbina nelle condizioni di utilizzo rispetto a quelle per cui sono progettati i turbogruppi automobilistici. E’ stato quindi proposto un nuovo layout dell’impianto, basato su due criteri progettuali. Il primo prevede una condizione di accoppiamento ottimale tra il turbogruppo e l’impianto di refrigerazione; il secondo, invece, l’utilizzo di gruppi di sovralimentazione più grandi, in grado di raggiungere efficienze maggiori. In accordo con questi due criteri progettuali è stato simulato al calcolatore un ciclo recuperativo, che lavora in gran parte in depressione, rispetto alla pressione atmosferica, in modo da avere portate volumetriche circolanti più grandi e poter utilizzare macchine di più elevata efficienza. I risultati ottenuti mostrano che il nuovo impianto è in grado di fornire aria a temperatura relativamente bassa (-60°C ed oltre), rendendolo adatto anche per applicazioni di congelamento. Inoltre, la presenza del recuperatore rende la temperatura dell’aria in uscita dalla turbina praticamente indipendente dalla temperatura ambiente, per cui il ciclo proposto potrebbe operare adeguatamente anche in ambienti molto caldi
Using neural networks to predict hourly energy consumptions in office and industrial buildings as a function of weather data
No full textOffice and industrial premises are among the most energy consuming type of buildings. Compared to residential buildings, they are characterized by more regular occupation patterns and stricter control of building systems. Under these conditions, it is expected that energy consumptions may be more easily predictable and may be significantly influenced by outdoor conditions more than by individual preferences. This may result in availability of straightforward predictions of energy use (at daily or hourly basis) which may contribute to trade energy at lower costs, make a better use of renewable energies, while balancing energy saving and occupants’ comfort. An essential contribution to the ability to
easily and accurately predict energy consumptions, is given by the ever-increasing number of smart and IoT-based devices that collect data inside and outside buildings and consequently make them available for processing. Taking advantage of such data, it is worth investigating if advanced artificial intelligence methods (like neural networks and machine learning) are capable of yielding predictions of energy consumptions and, ideally, indoor conditions. For the
purpose of the present paper, the dataset (including both input and output parameters) was obtained through simulation (using the popular EnergyPlus tool), including one office and one industrial reference building, and using three different climatic datasets. Finally, artificial neural networks were trained assuming daily and hourly energy consumptions (subdivided by category) as the target variable, showing that in most of the cases very accurate predictions
could be obtained
A new approach to assessing the performance of noise indices in buildings
No full textThe results of a wide acoustic environment survey are presented. Sound pressure measurements were carried out in a group of offices. These measurements lasted for five minutes and the resulting noise spectra were used to calculate the most significant acoustic parameters. During each measurement a questionnaire was administered to workers near each measuring position. The questionnaire asked them to indicate their subjective judgement about noise annoyance, noise loudness and dissatisfaction induced by noise present in the environment. The aim of the research was to investigate the performance of the measured noise indices in describing subjective responses to noise. A new method to calculate the average subjective responses is proposed. The performance of the noise indices was studied by means of linear regression analysis. Finally-the A-weighted equivalent sound pressure level proved to be the best index among those analysed in describing subjective auditory sensations
On the use of artificial neural networks to model household energy consumptions
Full text linkModern houses are more and more frequently characterized by the presence of "smart" metering devices, capable of measuring air temperature, relative humidity, air quality, and in the more sophisticated cases, even electric equipment consumptions. In addition, other relevant parameters such as illuminance may often be determined and they can be used as proxy variables to account for other important aspects (such as solar irradiance) influencing the energy balance of a building. Such information, in combination with weather data which can be retrieved by other sources (or by additional sensors), may conveniently contribute to the creation of a "black box" model in which, given a few input variables it is possible to output a variable which would result from otherwise complex calculations (e.g. an energy balance) requiring many data. The availability of such a "black box" could be helpful under many points of view, such as benchmarking energy consumptions and stimulating virtuous behavior from the occupants. To test whether such approach can be feasible, an EnergyPlus model of a real house was made, trying to accurately reproduce building features, systems set-points, and occupant behaviors. The overall simulated energy consumptions were compared with the real ones resulting from energy bills, thus ensuring a good agreement with reality. The dataset resulting from EnergyPlus was then used to train an artificial neural network (ANN) capable of yielding hourly energy consumptions based on limited input data. Finally, the relative importance of the different input variables was analyzed to understand which might influence prediction accuracy most
Ambient and Personal Noise Exposure Assessment in a Pasta Factory
Full text linkNoise pollution is one of the most important risk factors in industrial settings. This study is assessing ambient and personal noise exposure among workers of a pasta factory. Two kinds of measurements were taken; at a fixed work point in three areas and personal ones for different employees; for 8h at different times. Results for the measurements carried out at fixed sample points show that exposure times of = 8h are the same. The highest noise levels are in the press and packaging areas. Worker’s activity is well planned as their movements avoid staying for a long time in areas where their continuous noise exposure can exceed the most critical values. Dosimeter data can be a source of concern for the workers’ health and therefore for their employers. Operators are engaged to work very close to machines; so they are subjected to levels of noise exposure different from that measured in fixed sample points. This study has further confirmed that the risk evaluation is not an exact science; as it doesn’t consist only of technical and mechanical factors, but needs also to consider the factors connected to workers’ interaction with the workplace.
Keywords: Phonometer, dosimeter measures, noise risk assessment, safety procedures
Malte di calce idrata contenenti aggregati non tradizionali
No full textLe malte di calce sono tra i materiali più rispettosi dei principi che regolano la bioedilizia. Pertanto,
in questo lavoro, sono state studiate le proprietà di malte di calce addizionate di aggregati non
tradizionali in sostituzione parziale della sabbia calcarea. I risultati ottenuti da prove reologiche,
meccaniche e fisiche sono estremamente interessanti per alcune tipologie di conglomerato
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