1,721,022 research outputs found
Le caldaie a condensazione - Confronto tra metodi di calcolo delle perdite di generazione
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Numerical Evaluation Of Local Radiant Asymmetry
No full textPeople may feel uncomfortable inside environments with optimal values of global comfort indices. This is due to nonuniformities of environmental variables’ values as a cold window, a hot surface, a draft and produces the so called “local discomfort”. The aim of this work is to value the local discomfort caused by asymmetric thermal radiation by means of numerical simulations with a software which has been modified to calculate the plane radiant temperature of every point inside occupied spaces. We will consider moderate environments, conditioned by ceiling and wall radiant panels. Finally we will determine the percentage of dissatisfied
Stima del risparmio energetico ottenibile in impianti a radiatori abbinati a caldaie a condenzazione
No full textNumerical simulations of coupled conduction-free convection in low conductive vertical finned surfaces
No full textOut-of-plane structural identification of a masonry infill wall inside beam-column RC frames
No full textField observations after seismic events have shown that out-of-plane collapses are one of the predominant modes of infill masonry wall failure leading to life-safety hazards. This type of mechanism depends on the geometrical and mechanical features of the structure, but it is substantially affected by the constraints along the structural frame. However, the actual boundary conditions are very difficult to define, especially in the case of an existing building, for which information is lacking, a visual screening can be inefficient, and deterioration may have occurred due to the design conditions. In this paper, a procedure for the structural identification of the out-of-plane behaviour of infill masonry walls using a simple and cost effective innovative procedure based on an in situ experimental dynamic test and a consequent process of updating is proposed. The procedure, composed of the in situ test and the updating of the numerical model, was implemented for a case study to confirm that it is effective in defining the mechanical characteristics of the masonry, the absence of collaboration between the two brick leaves of the infill wall, and the out-of-plane constraints along the perimeter
Efficiency and Energy Savings Evaluation for Dry-Cooler Equipped Plants
No full textThe problem of the high energy requirements for the building climatization is well known. Some significant energy savings may be achieved by means of indirect free cooling. The aim of this work is to analyze the possibility to exploit this systems to cool down water of fan coil plants, in some kind of buildings taking into account different climate conditions and internal gains. The water supplying the plant terminals is cooled in the Dry-Cooler or in the chiller: an external air-water heat exchanger. The external climate conditions can guarantee a free cooling effect in order to reduce the load absorbed by the chiller. First of all, the thermal loads of two kind of buildings (a shopping centre and an office block) have been evaluated through the simulation of their behaviour during a whole year, with a hourly time-step, for different climate conditions, using the software Energy Plus. Realistic working conditions, suggested by Dry Coolers manufacturers, have been imposed. For each hour during the simulation period, it has been determined the external maximum temperature that lets the Dry Cooler balance the cooling load while the chiller is off. Then it has been possible to verify the sharing out of the thermal load between Dry Cooler and Chiller
Influence of Supply Air Ceiling Diffusers on Surface Temperature of Display Cabinet Doors and on Customers Comfort in Food Stores
No full textVertical display cabinets are widespread in food stores, because they have a large
display area and an ease access for customers. Recently, open cabinets has been
replaced with closed ones in order to reduce energy consumptions for refrigeration.
However, the presence of the glass doors can have an effect on product visibility
because of mist formation on the glass, particularly for low temperature display
cabinets. This effect appears when the temperature at the external surface of the
glass falls below the ambient dew temperature, which is a quite common situation in
humid climate in the mid-season, when neither indoor air heating nor cooling is
performed. Today the mist formation is prevented increasing the surface
temperature at external side of the glass doors by means of electrical resistances
embedded in the doors frame. The glass door surface temperature can be raised
enhancing the heat transfer coefficient driving the supply air towards the display
cabinet doors. This paper investigates the behaviour of different air ceiling diffusers
(vortex diffusers and linear diffusers) in order to reduce the risk of mist formation
and the energy consumption of electrical resistances. Initially, 3D numerical
simulations of isothermal airflow field has been performed and, later, summer and
winter conditions were considered.
The air flow field in the display zone, the temperature distribution on the glass
surfaces and the influence of different diffusers on customers comfort condition are
investigated
Evaporative cooling systems to improve internal comfort in industrial buildings
Get PDFSeveral studies were carried out to determine how hot or cold environments can affect task performance and can influence productivity. Usually, HVAC plants are exactly designed in order to guarantee comfortable internal conditions inside built environments, but not all kind of buildings are equipped with a heating or cooling plant, like for example, some industrial buildings. These buildings are often characterized by high internal thermal loads. For those buildings the ability of different plant configurations to improve indoor thermal conditions was considered taking into account the influence of several parameters, like weather conditions, internal gains, thermal transmittance, ventilation air flow rate, etc. Simulation results are compared in terms of energy savings and thermal comfort. © 2017 The Author(s)
Discussing optimal sensor placement for ambient vibration test of an existing bridge
No full textThe operational modal analysis (OMA) allows the identification of the dynamic (i.e., modal) characteristics of an existing structure, analyzing the data recorded by sensors, usually ad-hoc positioned on it. The number of sensors and their locations affect the accuracy of the dynamic identification results: as the number of sensors increases, the quality of the results improves, but the installation and operational costs of the monitoring system also increase. The methods of optimal sensor placement (OSP) were developed in literature to identify a set of sensor locations, from a larger candidate set, to perform OMA without losing information. These methods are based on numerical analysis of a finite element model that surrogates the structure to be monitored before installing any instrument. Among the OSP techniques, the effective independence (EFI) method is one of the best performing according to literature; it associates a ranking coefficient to each possible sensor location as a function of its usefulness in detecting the dynamic properties of the structure. The aim of this work is to highlight pros and cons of the OSP technique analyzing the results of an actual ambient vibration test for dynamic identification of an existing prestressed concrete viaduct. The adopted sensor network was designed starting from an optimization algorithm based on the EFI method, and the recorded signals, freely available, were used for both the dynamic identification of the structure and the experimental validation of the optimized sensor network. Results show that, for the analyzed structure, the optimized sensor network, constituted by four accelerometers, allows the identification of the same natural frequencies of the structure identified by a larger network of thirty accelerometers adopted as benchmark. Moreover, the optimized network shows the best performance in terms of frequency identification with respect to several alternative layouts characterized by the same number of instruments in different positions
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