Air Conditioning Systems from a 2nd Law Perspective

In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather lo

Analysis and design of an air handling unit using thermopsychro software

This work presents a software for the study of air conditioning processes, from the basic processes, sensible heating and cooling, humidification, dehumidification, evaporative cooling, mixing of humid air currents, cooling towers, etc.; as well as air handling units for summer and winter. The software allows an exhaustive study of all thermodynamic variables involved in the design, including enthalpy, entropy and exergy in each state, and losses due to irreversibilities in each process. It is supported by the psychrometric diagram, allowing its visualization for all the cases to be analyzed. Finally, it is worth highlighting the pedagogical use of these tools that improve the learning experience by providing students with a greater mastery of the aspects of psychrometry, facilitating calculations that would otherwise be tedious and repetitive, motivating them to focus more on the design aspects and the analysis of the meaning of the different parameters for technological application purposes

Herramienta computacional de evaluación termoeconómica para la selección de plantas de agua fría con caudal variable en circuito primario.

Este trabajo consiste en el desarrollo de una herramienta computacional de evaluación termoeconómica para la selección de plantas productoras de agua fría en sistemas de aire acondicionado que son actualmente utilizados en los edificios del sector terciario (hoteles, oficinas, centros comerciales, hospitales) denominados sistemas de aire acondicionado por agua fría en primario variable, con subsistema de refrigeración por compresión mecánica. Con esta herramienta computacional se podrá conocer el costo de generación total del agua fría de dos alternativas de diseño, y seleccionar así aquella cuyo costo sea el menor

Caratterizzazione e Ottimizzazione Energetica di un Condizionatore Portatile per uso Domestico

La crescente preoccupazione circa l’impatto antropico sull’ambiente e sul clima mondiale ha determinato, negli ultimi decenni, una spinta verso la ricerca di Efficienza, intesa come minor consumo energetico e contemporaneo mantenimento di prestazioni elevate, in modo da determinare un minor impatto ambientale del prodotto/servizio/impianto in questione. Nel seguente lavoro di tesi, verranno riassunte le analisi svolte su di un condizionatore portatile De’Longhi con l’obiettivo di individuare i punti critici e con maggior margine di miglioramento dal punto di vista energetico ed exergetico. Nel primo capitolo verrà descritta la situazione a livello globale relativa al settore del condizionamento, con un successivo approfondimento circa la nicchia dei condizionatori portatili. Il secondo capitolo riassume le tre tipologie di analisi che sono state eseguite: termodinamica, exergetica e termoeconomica, basate su un modello di calcolo implementato tramite Excel utilizzando le Addin di Refprop. Nel terzo capitolo verranno riassunti tutti i tentativi di ottimizzazione del condizionatore portatile, effettuati attraverso il software di simulazione “Shark”; in questo capitolo sarà anche descritta un’attività sperimentale svolta in camera biclimatica per testare tre tipologie alternative di tubi di scarico lato aria al condensatore. Nel capitolo finale sarà descritta brevemente una possibile idea di valorizzazione delle prestazioni del condizionatore portatile tramite la cooperazione con un fornitore energetico in modo da favorire la diffusione del Demand Response.The growing concern about the anthropic effects on environment and the world climate has determined, in recent decades, a push towards the search for Efficiency, intended as lower energy consumption maintaining high performance, in order to determine a lower environmental impact of the considered product / service / facility. In the following thesis, the analyses carried out on a De'Longhi portable air conditioner will be summarized with the aim of identifying the critical points and the rooms of improvement from an energy and exergetic point of view. The first chapter will describe the global situation regarding the air conditioning sector, with a specific focus on the portable air conditioners. The second chapter summarizes three analyses that have been performed: thermodynamics, exergetics and thermoeconomics, based on a calculation model implemented on an excel sheet linked to Refprop Addins. In the third chapter all the opportunities to optimize the portable air conditioner will be summarized; simulations have been carried out through the specific software “Shark”. This chapter will also describe the experimental activity carried out in a bi-climatic chamber to test three types of alternative air-side exhaust hoses. In the final chapter, a possible idea of enhancing the portable air conditioner will be briefly described through cooperation with an energy supplier in order to favor the diffusion of the Demand Response model

Análise de um modelo de recuperação de calor com trocador de calor de placas fixas

The objective of this work is to analyse the application of a sensible heat recovery system in the context of ventilation and air conditioning, meeting as priority demands the thermal comfort, energy efficiency, and indoor air quality of an occupied space. Among the several possible techniques, it was chosen a recovery device formed by a plate heat exchanger with circulating minichannels of the air flows. Its geometric data and operational parameters were compiled in a computer program developed in the MATLAB platform for simulation of the system considering both design conditions and effects of climatic variations related to Rio de Janeiro. Other types of the air conditioning systems were also simulated in the computer code and compared to the recovery system through the exergetic analysis of moist air using both the usual psychrometric approach of perfect gas and a model that applies the virial equation of state. The results showed that the sensible recovery system obtained higher level of efficiency than the other system in applications with room sensible heat factor above 0.7.Este trabalho tem como objetivo analisar a aplicação de um sistema de recuperação de calor sensível no contexto de ventilação e ar condicionado, atendendo como demandas prioritárias o conforto térmico, a eficiência energética e a qualidade do ar interno de um recinto ocupado. Dentre as diversas técnicas possíveis, optou-se por um dispositivo de recuperação formado por um trocador de calor de placas fixas com minicanais de circulação dos fluxos de ar. Seus dados geométricos e parâmetros operacionais foram compilados em um programa computacional desenvolvido em MATLAB para simulação do sistema considerando tanto condições de projeto como efeitos de variações climáticas relacionadas ao Rio de Janeiro. Outros tipos de sistema de ar condicionado também foram simulados no programa e comparados ao sistema de recuperação através da análise exergética do ar úmido, utilizando tanto a abordagem psicrométrica usual de gás ideal, como um modelo que aplica a equação virial de estado. Os resultados demonstraram que o sistema de recuperação sensível obteve níveis de eficiência superiores aos demais sistemas nas aplicações com fator de calor sensível da zona térmica acima de 0,7

Thermodynamic Modeling of a Membrane Dehumidification System

In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The proposed system utilizes a selective membrane to remove water vapor from ambient air as opposed to a vapor compression cycle or a desiccant. This work provides an analysis of the membrane dehumidification system with a focus on the energy performance of the system. A system performance goal was set at the beginning for a given inlet and outlet ambient air condition and a total cooling load of one ton. The target COP of the combined sensible and latent cooling is 3.58 with a target value for only the latent system of 3.34. Two different simulations were developed including an initial simulation which uses a basic mass transfer model and a simpler condenser model. The initial model was used to develop the system, analyze operating parameters and provide initial performance results. The initial simulations indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. The latent only COP including the optimizations was a maximum of 4.23. A second model was then developed which uses a more detailed mass transfer model and a more detailed condenser model based on the operating conditions. This simulation yielded a maximum latent only COP of 4.37 including the optimizations. The work also analyzes two different combined systems capable of providing both sensible and latent cooling. The first utilizes a conventional vapor compression cycle for sensible cooling and has a maximum COP of 3.93. The second uses multiple evaporative coolers in between multiple membrane dehumidification steps and was found to have a maximum COP of 3.73. Second law analysis of the systems was also conducted and found that the greatest reduction in latent system exergy loss can be obtained by improving the selectivity of the membrane. Apart from improving the membrane selectivity, the results show the greatest improvement can be found in improving the operation of the gas compression devices

Avances en Ciencias y Técnicas del Frío - 11

Este año 2022 se han cumplido 20 años desde la fundación de la Sociedad Española de Ciencias y Técnicas del Frío (SECYTEF; http://secytef.upct.es/), que tuvo lugar precisamente en la Universidad Politécnica de Cartagena, durante la celebración en esta Universidad del primer congreso CYTEF en 2002. Fue el Primer Congreso Español de Ciencias y Técnicas del Frío de esta serie de congresos CYTEF. Posteriormente, los congresos CYTEF han tenido lugar cada 2 años, y de su organización se ha encargado especialmente la SECYTEF, ya que es su principal cometido Los trabajos de investigación presentados en los Congresos CYTEF han sido publicados en los libros de actas correspondientes que constituyen una serie denominada Avances en Ciencias y Técnicas del Frío. Contando con este libro de Actas del CYTEF 2022, ya son 11 números de esta serie de libros los publicados. Representan una valiosa fuente de información científico-técnica para los investigadores, técnicos y profesionales interesados en las Ciencias y Técnicas del Frío, tanto en lo que se refiere a tecnologías de producción de frío, como a las tecnologías de su aplicación en los distintos sectores

Air Conditioning Systems from a 2nd Law Perspective

In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather low; thus the quest for more appropriate technologies. Solar-assisted air-conditioning is also discussed, outlining the possibilities and the constraints