dynamic simulation of an air handling unit and validation through monitoring data

Abstract This paper presents the model for the simulation of the behavior of an air handling unit (AHU), consisting of two heating coils, a cooling and dehumidifying coil, and a vaporizer. The proposed model reproduces the behavior of its single components, using the suitable e-NTU relations for the heat exchangers on the basis of actual geometries (e.g., type of heat exchanger, number of tube rows, number of passes), and mass and heat balance equations for the vaporizer and dehumidifying coils. The routine is developed as a MATLAB script and it is linked to a TRNSYS model, which simulates the building. The model is applied to a real AHU, which provides fresh air for an exhibition room of a museum, varying the supply relative humidity based on the indoor set point. During a one-month monitoring campaign in the building, several data about the external and internal climate were acquired, together with specific parameters of the AHU system (e.g., temperature and water flow rate at the heat exchangers, supply temperature and relative humidity of the air flow). These monitored data were compared with the outputs of the MATLAB script, validating the AHU model in the error band of the monitoring system

Modellazione dinamica di un sistema pompa di calore - edificio

Lo scopo della tesi è creare un modello che simuli il funzionamento di una pompa di calore durante il periodo invernale. Dopo la parte iniziale, dedicata all’analisi delle pompe di calore, viene descritta la modellizzazione, creata in ambiente MATLAB, composta da più sotto-modelli (nell’ordine: circuito idronico con pannelli radianti, condensatore, evaporatore e compressore). In base ai dati inseriti (riguardanti potenza termica oraria da soddisfare, condizioni climatiche esterne, presenza o meno dell’accumulo), il modello è in grado di determinare le prestazioni della macchina. Queste vengono poi confrontate con dati sperimentali forniti da costruttori. In seguito viene analizzato un edificio preso come benchmark destinato ad uffici (implementato tramite il software TRNSYS), supponendo che venga riscaldato con utilizzo diretto della pompa di calore o passando attraverso un sistema di accumulo. I dati ottenuti sulle prestazioni dinamiche della pompa di calore vengono infine confrontati con quelli risultanti dall’applicazione delle normative tecniche in vigore

3D Measurement of Large Deformations on a Tensile Structure during Wind Tunnel Tests Using Microsoft Kinect V2

Wind tunnel tests often require deformation and displacement measures to determine the behavior of structures to evaluate their response to wind excitation. However, common measurement techniques make it possible to measure these quantities only at a few specific points. Moreover, these kinds of measurements, such as Linear Variable Differential Transformer LVDTs or fiber optics, usually influence the downstream and upstream air fluxes and the structure under test. In order to characterize the displacement of the structure not just at a few points, but for the entire structure, in this article, the application of 3D cameras during a wind tunnel test is presented. In order to validate this measurement technique in this application field, a wind tunnel test was executed. Three Kinect V2 depth sensors were used for a 3D displacement measurement of a test structure that did not present any optical marker or feature. The results highlighted that by using a low-cost and user-friendly measurement system, it is possible to obtain 3D measurements in a volume of several cubic meters (4 m x 4 m x 4 m wind tunnel chamber), without significant disturbance of wind flux and by means of a simple calibration of sensors, executed directly inside the wind tunnel. The obtained results highlighted a displacement directed to the internal part of the structure for the side most exposed to wind, while the sides, parallel to the wind flux, were more subjected to vibrations and with an outwards average displacement. These results are compliant with the expected behavior of the structure

Cost-optimal sizing of solar thermal and photovoltaic systems for the heating and cooling needs of a nearly Zero-Energy Building: design methodology and model description

This paper deals with the cost-optimal sizing of solar technologies for thermal and electrical needs of residential or tertiary buildings. We consider a typical nearly Zero-Energy Building, whose requirements of thermal and electrical energy are evaluated on the basis of internal loads and external climate. The building is heated and cooled with radiant panels; a heat pump and a system consisting in solar thermal collectors and a thermal storage provide thermal energy, while PV modules supply electricity. The proposed design procedure finds the best number (i.e. the size) of solar thermal and PV modules to be installed, through a lifetime simulation of building loads and energy system according to proper cost-optimality considerations. The paper is divided in two parts. In this first part, we describe general features and principles of the methodology, together with the physical models of each component of the building-plant system. Then, in the second part, we present a case study implementing the illustrated procedure. Results show the notable benefits of the proposed design approach with respect to traditional ones, in terms of both energy and economic savings. We consider simulation-based technique a promising tool for engineering activity as its results can be used to compare different design alternatives and choose a proper cost-optimal solution according to the specific project, context and goals priority. Besides, the proposed methodology can be successfully applied in the more general framework of Net Zero Energy Buildings (NZEBs) in order to fulfill recent regulatory restrictions and objectives in building energy performances

A Proposal for New Microclimate Indexes for the Evaluation of Indoor Air Quality in Museums

A correct artwork preservation requires strict values of several microclimate parameters, in particular temperature, humidity, and light. In existing museums, the evaluation of the effectiveness of current building plant systems and management is essential to avoid artwork deterioration. In this work, we propose the use of five simple performance indexes that use monitored data to estimate the suitability of the whole museum system in the maintenance of benchmark values of temperature, humidity, and light. The new indexes also take into account microclimate daily span and spatial homogeneity, which can represent a criticality in the preservative process. We apply these new indexes to the results of a monitoring campaign in Palazzo Blu, a museum in Pisa, which lasted for almost four months during a temporary exhibition on Toulouse-Lautrec works. The indexes show a mainly acceptable instantaneous microclimate, but HVAC (Heating, Ventilating and Air Conditioning) system improvement is necessary to avoid high thermo-hygrometric daily span. This methodology is useful for the identification of microclimate criticalities and can help the cooperation between conservation experts and professionals giving hints to improve museum internal microclimate. In case ofalready optimal microclimate, these indexes can be useful in more complex analyses, including simulations of possible retrofit actions, keeping microclimate suitability as a constraint

Towards a kerogen-to-graphite kinetic model by means of Raman spectroscopy

Acknowledgements This work was funded by the School of Geosciences, University of Aberdeen. Stimulating discussion with Sveva Corrado and Thomas Theurer greatly enriched this work. The Editor Shuhab Khan, the reviewer Aaron Jubb and two anonymous reviewers are kindly acknowledged for their comments that significantly improve the original version of the manuscript.Peer reviewedPublisher PD

Cost-optimal sizing of solar thermal and photovoltaic systems for the heating and cooling needs of a nearly Zero-Energy Building: the case study of a farm hostel in Italy

In this paper, the second of two parts, we apply the cost-optimal design method illustrated in Part 1 to a case study. We select a farm hostel located in Enna, Italy, as the local climate and the required energy services are suitable for the development of a solar-assisted nearly zero-energy building. The system is connected to the electric grid and does not use any other thermal energy vector. Energy demand includes heating, cooling, domestic hot water production, lighting and other electric uses, viz. inductance cooking, food refrigeration, local dehumidification, household appliances, and office devices. The building-plant system is described in terms of both technical characteristics of each component and internal loads. According to the proposed simulation-based methodology, we investigate the best design configuration by minimizing the lifecycle cost after 20 years of operation. The results of the procedure identify the optimal solution, in terms of number of solar thermal and photovoltaic panels, volume and control strategy of the thermal storage. Other outputs are the dynamic and seasonal energy balance of each system component and of the whole system, and additional economic parameters. The results show that the proposed method leads to a very favorable design with relevant notable economic and energy benefits with respect to a no-solar design solution (ΔCTOT=11%, ΔEINTOT=67%). However, several nearly optimal configurations provide very similar outcomes in terms of lifecycle costs, with different initial investment and energy performances. Consequentially, we introduce a multi-objective optimization approach aimed at identifying the best solution in terms of investment availability and energy objectives

Feasibility of using bio-mimicking fish scale textures in LPBF for water drag-reducing surfaces

In this work, bio-mimicking fish scale textures are produced by LPBF and AlSi7Mg0.6 powder to reduce drag forces on nautical components. For this purpose, a surface texture inspired by the European bass skin was modelled and parametrized. Textures were applied over the external surface of purpose-designed specimens. Additive manufacturing quality of textures was assessed using focus variation microscopy to examine surface roughness as well as geometrical errors. Once the feasibility of producing the desired bio-mimicking surfaces was confirmed, the designed surface patterns were analysed in the computation fluid dynamics modelling environment. The behaviour of the surfaces was characterized in terms of drag force generated over a fixed dimension plate model. The most promising configuration was further investigated in a sensitivity analysis where variations in main stream velocity and in surface roughness are applied. Drag reduction was related to the lowering of the viscous component and was found to be in the order of 1–2%, with respect to a smooth surface, for free stream velocity of 2.5–5 m s−1 and average roughness smaller than the as-built condition. The results confirm that the modelled surfaces can be reproduced with sufficient geometrical fidelity, showing great promise for drag-reducing metallic components produced by additive manufacturing

Windbreaks for railway lines: Wind tunnel experimental tests

A number of tests were carried out in the Politecnico di Milano wind tunnel to study the properties of different windbreak barriers for high-speed railway lines. A possible problem with the wind tunnel testing of these devices is the need to create wide scenarios (long barriers) and achieve high Reynolds number values in order to avoid scaling problems. In this study, two experimental campaigns were performed. In the first stage, the Reynolds number sensitivity was checked through specific tests in a high-speed test section (Remax= 7 × 105): it was found that, in the presence of barriers, the rolling moment coefficient is independent of the Reynolds number. A second experimental campaign was then carried out in a low-speed test section (Remax= 1.3 × 105) where a very long scenario was reproduced (150 m at real scale): barriers of different types, heights and porosities were tested. To compare them, forces and pressures on the vehicle model as well as forces on the barrier were measured