1,721,193 research outputs found
A tool for HVAC systems operational strategy assessment for reducing infection risk in existing and newly designed buildings
Full text linkThe tool is based on the standard airborne disease transmission Wells-Riley model, i.e. quanta based and full mix hypothesis behind, described in [2] and [3]. It extends the single room model to a Multi-rooms Model with possible air recirculation among rooms, through centralised HVAC system and via air transfer to common service area (corridor, toilettes and staircases) where air extraction to outside is performed via dedicated exhaust air ductwork. The model is a dynamic model, i.e. the time dependent problem is solved
Experimental validation of a steady periodic analytical model for Breathing Walls
Full text linkThe Breathing Wall behaviour under variable boundary conditions is described by an analytical model based on a one-dimensional porous domain crossed by air and subject to third type steady periodic boundary conditions. To the best of the authors’ knowledge, its experimental validation is not provided in literature. In this work, a new model is derived considering Dirichlet steady periodic boundary conditions. The model is experimentally validated testing a 1 m2 no-fines concrete sample in the Dual Air Vented Thermal Box apparatus, specially improved to replicate dynamic thermal conditions. The experiments show that increasing the air flow velocity across the Breathing Wall from 0 to 12 mm/s enhances thermal coupling between the two environments, namely reduces the wall thermal capacity, with a decrease in the penetration time from 4.3 h to 3 h. The model shows a very good agreement with experimental data when predicting temperature distribution across the domain, with error averages and standard deviations within the thermocouple accuracy after calibration, assumed to be 0.15 ∘C. The lesser yet good agreement concerning conduction heat flux density is explained in terms of accuracy in the measurement of the boundary conditions and critical issues in the heat flow measure itself (i.e. probe thermal resistance, thermal contact, emissivity mismatch)
A numerical model to simulate the dynamic performance of Breathing Walls
Full text linkA one-dimensional Finite Difference Model for Breathing Wall components under time dependent Dirichlet boundary conditions is presented. The algorithm undergoes a comprehensive validation against a dynamic analytical model, under either sinusoidal and generically periodic boundary conditions, adopting different airflow velocities and in relation to capacitive and resistive materials alternatively. It is found that the accurate prediction of the temperature profile inside the wall is influenced primarily by the timestep, whose optimal value can be identified through a preliminary frequency analysis of the boundary conditions. Moreover, for a better prediction of the surface heat flow density, and especially in insulating materials, refining the space grid below 1 mm is recommended, as well as the adoption of a 3-point numerical scheme. The numerical model is finally tested against experimental data on a porous concrete wall, showing that numerical errors may compare to other sources of uncertainties, regarding materials properties and boundary conditions
Optimization of the acoustic response both for orchestra and for a solo instrument, the exquisitely romantic piano of Chopin, in the case study 'Chopin concert hall'
Full text linkThe Chopin concert hall’s shape takes account of classical forms: starting the design from a shoebox volume it tends to approach a vineyard, as a reinterpretation and synthesis of both ones. The proposed method involves a predictive analysis. Acoustics performance evaluation have been carried out using the room acoustic modeling program, Catt Acoustic. This has been used with two source types with the same sound power: an omni-directional source and a source with realistically-directional characteristics based on measurements from a real grand piano instrument. Objective analyses have been carried out on three acoustic parameters: the Sound Pressure Level (SPL), the Reverberation Time (T30) and the Clarity Index (C80). The proposed designed room shape, materials and the selected stratigraphy of the coatings are the ones for which the differences in SPL, T30 and C80 are negligible when comparing the two source types simulations, moreover the parameters values are optimized
Mechanism of 2,5-Dioxopiperazine Formation
No full textThe cyclization of H-Ala-Pro-NH2 to the 2,5-dioxopiperazine (DKP) has been Studied as a model for the spontaneous cleavage of the peptide bond with concomitant formation of 2,5-dioxopiperazine that can occur at the N-terminus of a polypeptide chain. The reaction involves pre-equilibrium attack of the N-terminal amino group on the carbonyl carbon of the second residue giving a zwitterionic intermediate, T(±) which is in acid-base equilibrium with various forms characterized by the different grades of protonation, T0, T+ and T-. The Bronsted plot for the base-catalysis and the pH-rate profile give pK(a) ~ 7 and ~ 13 for the equilibria T- + H+ ⇆ T(±) + T(-) + H(+) ⇆ T0 respectively. The reaction is subjects to general base and general acid cataysis on different steps. Departure of the amino group from T0 and T- by two parallel routes gives the product. The bifunctional acid catalyst HCO3- strongly increase the reaction rate and at high concentrations cause a of the rate-limiting step. At high pH, the overall reaction rate is limited by the trans - cis isomerization of the Ala-Pro peptide bond
Numerical validation of a simplified design procedure for calculating the heating load in buildings with Breathing Wall components
Full text linkBreathing Walls (BWs) can provide significant building energy saving in winter conditions, but the present standard methodology for heating load calculation fails to consider this technology, thus limiting its application. In this paper, a procedure to include BWs in the EN 12831-1:2017 is then proposed. The methodology is tested against a numerical calculation of the heating load based on the coupling between the Building Energy Simulation (BES) engine TRNSYS and a Matlab Finite Difference Model (FDM) addressing heat and mass transfer across the BW. The very good agreement demonstrates that the BW can be syntethized by two key parameters, namely the effective thermal transmittance at the interior surface and the thermal recovery efficiency
Measuring a Breathing Wall's effectiveness and dynamic behaviour
Full text linkBreathing Walls are building structures based on porous materials crossed by an airflow, which act both as building envelopes and ventilation system components. In climates where both heating and cooling are needed, a pro-flux configuration (heat and air mass both flowing in the same direction) might be alternated with a contra-flux configuration (heat and air mass flowing in opposite directions) during the year or even on a day. Understanding and modelling the Breathing Walls' stationary and dynamic behaviour is thus fundamental, in order to optimize their design and to fully exploit their energy-saving potential. In this experimental study, a small-scale no-fines concrete Breathing Wall was investigated. The steady-state contra-flux tests performed in a Dual Air-Vented Thermal Box laboratory apparatus were used to derive the heat recovery efficiency of the sample as a function of the cross airflow velocity. The effectiveness of this technology was then evaluated in a virtual case study. An optimal airflow velocity across the Breathing Wall was found, leading to energy savings between 9% and 14%. Dynamic tests were performed assuming a sinusoidal variation of the operative temperature on one side of the sample. They showed how airflow velocity affected the Breathing Wall inertia and dynamic behaviour
What is a Nearly zero energy building? Overview, implementation and comparison of definitions
Full text linkThe reduction of energy consumption in buildings is an important pillar of the European strategy to ensure that future climate and energy targets are reached. This paper focuses on the definition of Nearly zero energy buildings (NZEBs) that represent one of the greatest opportunities to increase energy savings in Europe. As this term appears to be subject to different interpretations, the paper explores the NZEB literature to provide an overview of definitions. The analysis underlines inconsistencies and critical issues among them. The paper also assesses the progress of the NZEB implementation in Europe, and compares the EU-NZEBs and the US-NZEBs definitions. The main debates arisen around NZEBs are evaluated. Among these topics, there are: the distinction between energy and primary energy, and between energy sources and energy carriers. A focus is also due to metrics and primary energy conversion factors. Special attention is provided in defining primary energy factors for energy carriers produced from renewable energy sources on site, nearby or far. After specifying the role of “plus” buildings, a complementary energy index, useful for defining incentives for buildings is formulated to overcome the questioning on the “negative” primary energy index that can be achieved using some of current net ZEB definitions. A proposal for clarifying the meaning of near zero, zero and plus energy buildings is also given. The analysis highlights that, although the attention given to NZEBs increased over the last years, the NZEB topic is still under discussion and not uniformly implemented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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