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EXPERIMENTAL AND THEORETICAL STUDY OF ADIABATIC HUMIDIFICATION IN HVAC&R APPLICATIONS

Este articulo presenta los resultados del estudio realizado para obtener un tratamiento teorico unificado de la humidificacion adiabatica, aplicable a sistemas de refrigeracion y acondicionamiento de aire con la cual generar una herramienta de calculo que pueda ser utilizada en terreno como parte de su diagnostico en auditorias energeticas de este tipo de sistemas. Para lograr esto se realizan una serie de ensayos y analisis de tipo experimental en dos diferentes clases de equipo. El modelo computacional permite predecir la efectividad del sistema y principales variables de salida como la temperatura y contenido de humedad mediante la medicion de las condiciones de entrada de temperatura y flujos masicos de los fluidos que intervienen en la transferencia de masa y energia. La clave en el analisis es la definicion del coeficiente global de transferencia de calor AU, considerando la influencia de los flujos de agua y aire en el sistema. Se describe un ejemplo de validacion del modelo por cada tipo de sistema seleccionado en este estudio. This article presents the results of the study performed to obtain a theoretical unified treatment of adiabatic humidification to be applied in refrigeration and air conditioning systems that can be used as a calculate tool in field as a part of diagnosis in audit processes of this kind of systems. To achieve this, a series of tests and experimental analysis are performed on two types of systems. The computational model is able to predict the effectiveness of the system and the main variables at the system exhaust as temperature and humidity by using the measurement of temperature and mass flow rates that participle in the energy and mass and transfer. The key in the analysis is the global heat transfer coefficient AU, considering the influence of the water an air mass flow rates in the system. An example of each system considered in this study is shown, illustrating the validation of the model.

Experimental study of the energy and thermal comfort performance of chilled ceiling panels

This article presents the results of a study performed to obtain the main operating characteristics of a chilled heating ceiling system in cooling mode. An experimental analysis of the cooling ceiling system in a climatic chamber is presented in order to evaluate the behavior of its cooling capacity, pressure drop, and thermal comfort. The purpose of the present study is to evaluate the influence of certain factors, such as the ventilation strategy, water mass flow rate, water temperature, and load distribution, on the global behavior and performance of the system. The results show that a high cooling load can be removed, and also a high degree of thermal comfort can be achieved, with this kind of system. However, strong influences of the heat sources distribution and surface temperatures inside the room on its performance are observed, especially for thermal comfort conditions (asymmetric thermal radiation).

Modelado de un sistema de refrigeración caracterizado en un rango amplio de condiciones de operación

espanolEn este estudio se presenta la metodologia para desarrollar un modelo semiempirico de un sistema de refrigeracion clasico, compuesto de un compresor, un condensador, una valvula de expansion y un evaporador, el que es ensayado en un rango muy amplio de condiciones de operacion. Los modelos se presentan en forma modular, lo que permite que puedan adaptarse a cualquier tipo de aplicacion que utilice un sistema de refrigeracion por compresion de vapor: refrigeracion, aire acondicionado o bombas de calor, con componentes similares a los utilizados en este estudio. Los resultados de los modelos son confrontados con datos experimentales, los cuales son obtenidos de un sistema de enfriamiento que trabaja con un compresor a espiral, un evaporador a placas y un condensador de tubos planos y de aletas con persianas. Esta confrontacion es en este caso utilizada para determinar algunos parametros empiricos de los modelos. Una vez validados los modelos individuales se procede a conectar cada uno de ellos para definir el modelo global, se asume que el condensador impone la presion de condensacion, el evaporador la presion de evaporacion y el compresor el flujo de refrigerante, entre otras variables intermedias. Las principales salidas del modelo global son la potencia de refrigeracion, la potencia del compresor y el COP (coeficiente de desempeno) del sistema. El modelo de simulacion predice el COP del sistema con una diferencia inferior a un 8% con respecto a los valores experimentales, los que consisten en un total de 76 ensayos realizados en regimen estacionario y los que son utilizados para validar los modelos individuales y globales. Una vez realizado lo anterior, se determina, por simulacion, el dominio de trabajo del sistema. EnglishIn this study a methodology to develop a semi-empirical modelling of a classic refrigeration system is presented, which is composed by a compressor, a condenser, an expansion valve and an evaporator, and is characterized under extended operating conditions. The models are developed in a modular way, thus these can be adapted to a similar configuration related with refrigeration, air conditioning and heat pumps. The results of the modelling are compared with experimental results obtained in a refrigeration system composed by a scroll compressor, a plate heat exchanger as evaporator a louvered fin and flat tube condenser. This comparison is also used to determine some empirical parameters of the models. First the models are validated individually and then these are interconnected to develop the global model. In this approximation, the condenser imposes the condensing pressure, the evaporator the evaporating pressure and the compressor the refrigerant flow rate, among other intermediate variables. The main outputs of the model are the evaporator cooling power, the compressor power and the system COP (Coefficient of Performance). The model is validated with 76 tests developed in a steady-state, by obtaining a COP with a difference lower than 8% between the measurements and the results of the model, which is here considered as acceptable. Finally, by simulation, the model is used to determine the refrigeration system working domain.

Caracterización experimental y modelación de una bomba de calor reversible para un vehículo eléctrico

espanolEl sistema de aire acondicionado y de calefaccion en los automoviles se utiliza principalmente por motivos de seguridad para garantizar que el conductor este concentrado y con buena visibilidad durante la conduccion. Para la calefaccion, en los vehiculos convencionales, se cuenta con una energia termica considerable y a una excelente temperatura, esto debido al calor disipado por el motor a combustion. Los vehiculos electricos no cuentan con esta fuente de calor, por lo que se debe suplir por algun sistema auxiliar como resistencias electricas o una bomba de calor. En el estudio que se desarrolla en esta investigacion se propone utilizar una bomba de calor para la calefaccion del automovil. El objetivo que se plantea en este estudio es validar experimentalmente un principio de calefaccion para automoviles electricos basado en una de bomba de calor reversible y desarrollar un modelo de simulacion para explorar su desempeno a diferentes condiciones de operacion. La bomba de calor se logro ensayar a temperaturas de hasta -10 °C, obteniendose COP superiores a 2,0 en todo el rango experimental. La modelacion de la bomba de calor permite establecer que esta es capaz de funcionar en condiciones aceptables de hasta -10 °C, con un COP del orden de 1,48 y un calor transferido por el radiador de 4,1 kW, con un flujo de aire impulsado a la cabina a 45 °C, lo que permite mantenerla a temperaturas por sobre los 20 °C. EnglishAutomotive air conditioning and heating are mainly used for security, to facilitate driving and to guarantee a good visibility. In conventional vehicles, heating is provided by the cooling system of the internal combustion engine. Electric vehicles do not have this kind of heating source, thus heating must be provided by electric resistances or heat pumps. In this article this last technology is considered in this article as a heating system for vehicles. The aim of this study is to validate experimentally a proposed heating principle for vehicles based on a reversible heat pump and to develop and validate a semiempirical model used to explore the heat pump performance under different working conditions. The heat pump is characterized at temperatures as low as –10 oC, by obtaining COPs higher than 2,0. The heat pump simulation shows that the heat pump gives a COP of 1,48 at an ambient temperature of –10 oC, by supplying 4,1 kW to the vehicle cabin at 45 oC and keeping a temperature over 20 oC at the vehicle cabin

ANÁLISIS EXPERIMENTAL Y MODELADO DE COMPRESORES A ESPIRAL EN APLICACIONES HVAC/R

This article presents the results of the experiment al study of scroll compressors . The orders of magnitude of the isentropic and volum etric efficiencies of these compressors are studied. For the modeling a semi-em pirical approach is used, where some model parameters are defined from labora tory measurements or catalogues data. Some examples of identification of parameters and simulation are presented. The modeled shows the importance of considers the physical phenomena that happen inside of the machine to repr esent in a better form their behavior. The modeling showed is modular; therefore it can be used in a more complex system: as it is the case of a heat pump, a n air conditioning or cooling system.

UTILIZACIÓN DE DATOS DE CATÁLOGO PARA EL MODELADO DE EQUIPOS HVAC/R

This article presents the results of a study perfor med to develop a computational model of HVAC/R equipment that can be used from man ufacturer catalog data. As example of the model in this article the model o f a fan, cooling coil and a condensation boiler are presented. It is observed t hat in most of the case the data information is not sufficient to develop a goo d representation of its behavior using of the model.