Dissertations / Theses on the topic 'Air conditioning – Noise'

This thesis aims at preparing a user-friendly software tool for the prediction and analysis of the noise generated in Heating, Ventilating and Air Conditioning (HVAC) Systems elaborating the standardized prediction formulae and data coming from the research studies. For the analysis portion of the software, different types of indoor noise criteria are introduced and implemented in the software to ease the investigation of the level and the quality of the sound perceived by the occupant in a room through such criteria. General software structure and implementation of HVAC elements are explained by different userinterface samples in the thesis. Several case studies are presented to demonstrate the capabilities of the tool prepared in VISUAL BASIC programming language within the scope of the study.

This thesis details a study of strategies used to limit the flow generated noise encountered in the outlet diffusers of high velocity heating, ventilation and air conditioning (HVAC) duct systems. The underlying noise rating criterion is drawn from the specifications covering ocean going aluminium fast ferries. Although directed primarily towards the fast ferry industry the results presented herein are applicable to other niche high velocity HVAC applications. Experimental tests have been conducted to prove the viability of a high velocity HVAC duct system in meeting airflow requirements whilst maintaining acceptable passenger cabin noise levels. A 50 mm diameter circular jet of air was expanded using a primary conical diffuser with a variety of secondary outlet configurations. Noise measurements were taken across a velocity range of 15 to 60 m/s. An optimum outlet design has been experimentally identified by varying the diffuser angle, outlet duct length and the termination grill. A 4 to 5 fold reduction in required duct area was achieved with the use of a distribution velocity of 20 to 30 ms-1, without exceeding the prescribed passenger cabin noise criteria. The geometric configuration of the diffuser outlet assembly was found to have a pronounced effect on the noise spectrum radiating from the duct outlet. The development of a numerical model capable of predicting the flow induced noise generated by airflow exiting a ventilation duct is also documented. The model employs a Large Eddy Simulation (LES) CFD model to calculate the turbulent flow field through the duct diffuser section and outlet. The flow-generated noise is then calculated using a far field acoustic postprocessor based on the Ffowcs-Williams and Hawkings integral based formulation of Lighthill???s acoustic analogy. Time varying flow field variables are used to calculate the fluctuating noise sources located at the duct outlet and the resulting far field sound pressure levels. This result is then used to calculate the corresponding far field sound intensity and sound power levels. The numerical acoustic model has been verified and validated against the measured experimental results for multiple outlet diffuser configurations.

Noise between 25-500 Hz is a common problem in Heating, Ventilating, and Air Conditioning (HVAC) systems. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Handbook lists values of end reflection loss (ERL), a frequency dependent parameter describing energy reflected back up a duct at a termination impedance, to help engineers design and account for noise. The ASHRAE Handbook does not account for common termination variations and only lists ERL values using octave bands down to 63 Hz. This thesis experimentally determined the ERL of a variety of rectangular duct configurations and termination conditions between 25-500 Hz. This research also compared experimental ERL results with analytic predictions and ASHRAE Handbook values. Seven duct sizes were tested, from 6X6 to 18X54 inches. Duct termination baffle hardness was varied between acoustically hard (plywood) and soft (ceiling tiles) for the 6X6, 6X10, and 6X18 ducts. Five duct termination distances above the termination baffle were tested, between flush and 1D for the 6X10 and 6X18 ducts and between flush and 5D for the 6X6 duct, where D equals the duct s effective diameter. Diffusers and flex duct configurations were installed at the end of the rigid duct to test their effect on ERL on the 6X6, 6X10, and 6X18 ducts. ERL was determined using an adaptation of the ASTM E1050 Standard, an application of the two-microphone impedance tube method. Experimental results closely conformed to analytic predictions and are an improvement over ASHRAE Handbook ERL values. The results indicate that baffle hardness has a negligible impact on ERL, which contradicts the ASHRAE assumption that diffusers that terminate in a suspended lay-in acoustic ceiling can be treated as terminating in free space. Termination distance above the baffle has a negligible impact on ERL at distances less than six inches for the 6X6 duct. Termination distances above the baffle greater than six inches exhibit limited free space ERL behavior for the 6X6 duct. The use of flex duct greatly reduces low frequency ERL and this is not accounted for by the ASHRAE Handbook. The impact from flex duct usage also negates any influence from downstream termination variations.

Researchers and practitioners have found that the type of mechanical system utilized to thermally condition a space impacts the noise level for occupants. Indeed, in schools, air conditioning systems are by far the largest contributors to room noise (Bradley, 2002; Nelson et al., 2005; Siebein et al., 2000). Studies have also demonstrated the impact of noise on youth\'s cognitive performance. The problem is worsened in non-native speakers and children with hearing loss (which can be temporary due to colds and allergies or permanent). No studies yet have bridged those two widely-supported findings: if the type of mechanical system impacts (and often dictates) the noise level in the room, and if the noise level in the room impacts the performance of the student, might there be a correlation between mechanical system type and student achievement? An examination of 73 elementary schools in a single Orlando, Florida school district suggests that, for schools populated with students of similar socio-economic background, schools cooling with the noisiest types of mechanical system, with both a compressor and fan exposed to the room, underperformed on standardized student achievement tests relative to those with quieter types of systems. Also, schools with the highest percentages of low socio-economic level children are more likely to get the noisiest type of cooling system. Mechanical system data was gathered through an online survey answered by facility maintenance managers and school percentage student achievement scores on the Florida Comprehensive Assessment Test (FCAT) were obtained from public online data for years 2003 to 2010 for third grade only. This is the earliest students are tested by the FCATs and studies show a larger impact of noise at an early age. This study examined as well the extent to which teachers believe noise from mechanical systems has an effect on student learning and under what conditions. Results from an online survey sent to third grade teachers in the same schools show that teachers generally judge noise levels in their classroom to be sufficiently quiet and do not consider noise to be a problem that needs addressing. However, in open-ended questions teachers demonstrated an understanding of the effects of noise in children\'s concentration and classroom speech communication.
Ph. D.

The thesis deals with issues of noise ventilation outlets in a passenger car. There is a description of the noise reduction in the acoustic background, optimizing experimental measurement methodology and familiarization with measuring equipment. The next step includes measuring of individual outlet options, results post-processing and comparison of tested alternatives. Based on these results the best variants are chosen and measures for decreasing noise in the ventilation outlets are proposed.

Dissertation thesis falls within area of indoor climate and deals with investigation of acoustic microclimate in sanitary rooms of residential buildings during a mechanical ventilation. Sources of a noise in these areas are small fans. The thesis contains the evaluation of the existing situation concerning the referred issue, physical laws of acoustics and theoretical basics of acoustics of air conditioning. The part of the thesis is experimental measurement which aims to evaluate the situation in real applications and the possibility of influencing the acoustic microclimate by affixing of small fans on the building structure. The work contains a model for the verification of certain anticipated dependencies and theoretical investigation of the distribution of sound pressure levels in the sanitary room, depending on the location of the noise source. The last part of the work offers possible measures to improve the acoustic microclimate and elimination of the noise in sanitary rooms and in protected areas of residential buildings.

The aim of the thesis "Design and optimization of the heat pump" is the project documentation for building permits, finding a suitable source of heat and cold. The problem is solved for a Tesco hypermarket. The device is designed to meet the health, performance and functional requirements for indoor climate. The task of this device is to transport fresh air into the interior cover heat losses in winter and coverage heat gains during the summer. The theoretical part deals with the problem of heat pumps. Special mention is about heat pump air x air. Calculation and design part is a specific proposal, two air conditioners and optimizing for winter. The experimental part deals with the processing of data on existing rooftop units.

This master´s thesis focuses on effect of acoustic microclimate in non-production buildings to human. Within elaboration this topic was made measurment acoustic power level and created protocols by valid technical standards and law. I dedicate to damping noise and aerodynamic noise in airconditioning in part topic analysis. The part aplication on real object deal with assessment current status and draft measure for improve acoustic ratio in laboratories in center of research located in Brno. That includes describe of air-cndition unit and development two variants and their rating.

碩士
國立臺北科技大學
車輛工程系
107
Vibration and noise are often accompanied along the operation of the air-conditioning (AC). Evaluating their effects on the performance of the AC system is necessary. However, measurements require time, and resources. This study utilized computer-aided engineering to analyze the design according to the requirements, and compared the analysis results with the actual testing data. Establishing proper procedure for analysis would help to improve the accuracy of prediction and to reduce the time and cost required for the design development. In this paper, an existing air-conditioning outdoor unit was used for the study. Modal analyses were performed to ensure the accuracy of the analysis model. Vibration analysis was carried out to simulate the compressor running under steady operation speed. Acoustic analysis was then performed to predict the noise level of the air-conditioning outdoor unit. Results obtained from analyses and measurement are compared and correlated. The study shows that the natural frequencies of normal modal has less than 12% differences between the results of analyses and experiments. The acceleration values on the compressor has maximum discrepancy about 46% between analysis result and measurement in harmonic analysis. The tubes around the compressor appear larger vibration. For acoustic analysis, there is a higher sound pressure distribution around the compressor, and that is consistent with the experimental one, even the values still exist differences. The process developed from this research can be applied to for the assessment of vibration and noise performance, which will be helpful for product design and evaluation.

This diploma thesis deals with the basic theoretical overview of air-conditioning noise, the description of individual devices used in ventilation and active ventilation during storage of cereals. It also describes the possibilities of application of silencers for these devices. In the practical part, it focuses on the noise measurement in the post-harvest line and the design of appropriate noise measures to meet the under-noise levels.

Noise control in the heating, ventilation and air-conditioning (HVAC) systems is one of the critical design parameters in measuring the occupant comfort. The noise generated by air-handling units propagates through the ducts in the axial as well as transverse direction. Noise radiated in the transverse direction from the duct walls excited by the internal sound field is called the breakout noise. An analytical formulation has been developed in this thesis in order to predict the breakout noise by incorporating three-dimensional effects along with the acoustical and structural wave coupling phenomena. The first step in the breakout noise prediction is to calculate the interior acoustic response and flexural vibration displacement of the compliant walls. Dynamic interaction between the internal acoustic subsystem and flexible structural subsystem has been expressed in terms of the modal characteristics of the uncoupled response of the acoustic and structural sub-systems. Solutions of the inhomogeneous wave equation are rearranged in terms of impedance and mobility, and the equations describing the complete system are expressed in terms of matrices, which result in a compact matrix formulation. Examples of the formulation are a rectangular cavity with one flexible wall and a rectangular cavity with four-flexible walls. The formulation is modified to incorporate complex boundary conditions by means of appropriate Green’s functions. It is implemented for flexible wall duct using the modified cavity Green’s function. Another objective of the present investigation is to understand the coupling phenomenon and its effect on the compliant wall vibration displacement. The developed three-dimensional analytical analysis of the breakout noise is convenient to implement on the computer, and also to extend the sub-system level model to the system level model in order to analyze a complex acoustic-structural system for the breakout noise problem. The extent of coupling is calculated using a transfer factor based on the uncoupled natural frequencies of the acoustic and structural subsystems. It is observed from the free vibration analysis that a coupling between the cavity and the flexible panel exists in the vicinity of an uncoupled acoustic natural frequency. If a strong coupling occurs between an acoustic mode and a panel mode, then damping of structural subsystem would control it. The cavity volume changes stiffness of the panel, which in turn affects noise radiation in the stiffness-controlled region. The second step is to calculate the sound power radiated from complaint wall. The wall vibration velocity is a linear combination of the uncoupled flexural modes of the structural subsystem. It is substituted into the Rayleigh integral and Kirchhoff– Helmholtz (KH) integral formulation to predict the sound pressure radiated by the vibrating duct wall. The radiated sound power can be obtained by integrating the acoustic intensity over the surface of the flexible duct wall making use of appropriate expressions for radiation impedance. The radiation impedance terms involve a quadruple integral. Evaluation of this integral is quite complex and poses formidable computational challenges. These have been overcome by means of a co-ordinate transformation. Sound power radiation from flexible walls of the plenum and duct walls has been calculated using an equivalent plate model. Analytical results are corroborated with numerical models. The second part of thesis deals with a one-dimensional model to predict the breakout noise from a thin rectangular duct with different end conditions like anechoic termination, rigid-end termination, and the open-end termination. This model incorporates acoustic reflection effects in the duct internal sound field by using standing wave pattern by means of the transfer matrix approach. A one-dimensional prediction method based on the four-pole parameters has been developed to evaluate the lagged duct performance in terms of the breakout noise reduction. Radiation impedance of a duct is calculated by three different methods: (i) finite line source model (ii) finite cylinder model, and (iii) equivalent plate model based on fundamental bending mode of the duct. It is observed that the proposed model that uses the equivalent plate model for the lagged duct and the line source model for the bare duct is appropriate to predict the transverse insertion loss of the lagging, particularly at the lower frequencies that are of primary interest for reducing the breakout noise of rectangular ducts. The bare duct breakout noise results are compared with those of the corresponding 3-D analytical models. It shows that the one-dimensional model captures the overall mean pattern of breakout noise very well. The third part of the thesis examines the internal acoustic field and thence the transmission loss (TL) of a rectangular expansion chamber, the inlet and outlet of which are situated at arbitrary locations of the chamber; i.e., the sidewall or the face of the chamber. The four-pole parameters have been expressed in terms of an appropriate Green’s function of a rectangular cavity with homogeneous boundary conditions. A transfer matrix formulation has been developed for the yielding-wall rectangular chambers by considering structural-acoustic coupling. It may be combined readily with the transfer matrices of the other constituent elements upstream and downstream in order to compute the overall transmission loss or insertion loss. Wherever applicable, parametric studies have been conducted to evolve the design guidelines for minimizing the breakout noise from the HVAC ducts, plenums and cavities.