Academic literature on the topic 'Vapour compression system'

The purpose of a heat pump is to control the temperature of an enclosed space. This is done by using heat exchange with a heat source, for example water, air, or ground. In the air source heat pump that has been studied during this master thesis, a refrigerant exchanges heat with the outdoor air and with a water distribution system. The heat pump is controlled through the circuit containing the refrigerant and it is therefore crucial that this circuit is functional. To ensure this, a diagnosis system has been created, to be able to detect and isolate sensor errors. The diagnosis system is based on mathematical models of the refrigerant circuit with its main components: a compressor, an expansion valve, a plate heat exchanger, an air heat exchanger, and a four-way valve. Data has been collected from temperature- and pressure sensors on an air source heat pump. The data has then been divided into data for model estimation and data for model validation. The models are used to create test quantities, which in turn are used by a diagnosis algorithm to determine whether an error has occurred or not. There are nine temperature sensors and two pressure sensors on the studied air source heat pump. Four fault modes have been investigated for each sensor: Stuck, Offset, Short circuit and Open circuit. The designed diagnosis system is able to detect all of the investigated error modes and isolate 40 out of 44 single errors. However, there is room for improvement by constructing more test quantities to detect errors and decouple more fault modes. To further develop the diagnosis system, the existing models can be improved and new models can be created.

In this work a steady-state model of a simple vapor compression refrigeration cycle is presented. All the fundamental components of this system are modeled separately in order to consider them as black boxes that take inputs and convert them into output variables. The heat exchangers are treated as a set of multiple zones, identified by the refrigerant's state, connected in series, in which the heat transfer coefficient (HTC) is constant. A non-linear system of equations is obtained applying the energy balances and the ε-NTU method for each zone in the heat exchangers. A study on the HTC correlations used to connect the length of the zones with the value of the respective HTC is developed. The compressor is modeled using a polynomial function. Some iterative methods for the resolution in Matlab of the models of the components and the machine are presented, focusing on the strategy to decrease the execution time and to increase the accuracy of the results. Finally, all the models are validated through a set of experimental data and the global model is used to make some considerations about the efficiency and the exergy destruction in the plant.

La refrigeració manté la qualitat sensorial del productes i minimitza la pèrdua en les cadenes de valor del fred. Les àrees remotes dels països en desenvolupament es caracteritzen principalment pels baixos nivells de tecnologia, accés limitat a la xarxa elèctrica i el predomini de les petites explotacions agrícoles com un desafiament. El principal objectiu d'aquesta tesi és desenvolupar i caracteritzar un sistema de refrigeració modular multipropòsit basat en l'emmagatzematge de gel per a aplicacions de petita escala. El sistema d'emmagatzematge de gel va utilitzar un equip de refrigeració amb un compressor de corrent continu i velocitat variable. La càrrega de refrigerant i les dimensions de l'tub capil·lar es van optimitzar experimentalment per maximitzar el rendiment i evitar la caiguda de temperatura de la línia de succió. A més, es va avaluar experimentalment el rendiment de sistema sota diversos paràmetres. Els usos de l'emmagatzematge de gel per a refrigeració de llet i aplicacions de càmeres frigorífiques també es van investigar experimentalment. Es van utilitzar deposits de llet convencionals en un bany de refredament aïllat, i en una cambra frigorífica dotada d'una unitat de fancoil amb els seus respectius sistemes experimentals. En general, el treball de recerca realitzat en aquesta tesi aporta més coneixements sobre el desenvolupament de tecnologies de refrigeració baixes en carboni adequades per a països en desenvolupament.<br>La refrigeración mantiene la calidad sensorial del producto y minimiza la pérdida en las cadenas de valor del frío. Las áreas remotas de los países en desarrollo se caracterizaron principalmente por bajos niveles de tecnología, acceso limitado a la red eléctrica y el predominio de las pequeñas explotaciones agrícolas como un desafío. El principal objetivo de esta tesis es desarrollar y caracterizar un sistema de refrigeración modular multipropósito basado en el almacenamiento de hielo para aplicaciones de pequeña escala. El sistema de almacenamiento de hielo utilizó un equipo de refrigeración con un compresor de corriente continua y velocidad variable. La carga de refrigerante y las dimensiones del tubo capilar se optimizaron experimentalmente para maximizar el rendimiento y evitar la caída de temperatura de la línea de succión. Además, se evaluó experimentalmente el rendimiento del sistema bajo diversos parámetros. Los usos del almacenamiento de hielo para refrigeración de leche y aplicaciones de cámaras frigoríficas también se investigaron experimentalmente. Se utilizaron cantaras de leche convencionales en un baño de enfriamiento aislado, y en una cámara frigorífica dotada de una unidad de fancoil con sus respectivos sistemas experimentales. En general, el trabajo de investigación realizado en esta tesis aporta más conocimientos sobre el desarrollo de tecnologías de refrigeración bajas en carbono adecuadas para países en desarrollo.<br>Refrigeration and cooling maintains the sensory quality of the product and minimizes the loss in cold value chains. Remote areas of the developing countries were mainly characterized by low levels of technology, limited access to modern energy and dominance of small-holder farms as a challenge. Hence, the main objective of this thesis is to develop and characterize a modular-multipurpose cooling system based on an ice-storage for small-scale applications. As part of the experimental system, the ice storage with a variable speed DC-compressor was developed and fabricated. The refrigerant charge and the capillary tube dimensions were experimentally optimized to maximize performance and avoid suction line temperature drop. Moreover, performance of the system under varying parameters was evaluated. Uses of the ice storage for milk cooling and cold room applications were also experimentally investigated. Conventional milk-cans with insulated box and a heat simulated room with a FCU were utilized as respective experimental systems. Chilled water recirculation rates, ice-storage energy density, and air flow rate across FCU were varied as main experimental parameters. Improvement of the ice production technique and corresponding performance data obtained were among main contributions of this research. In general, the research work performed in this thesis contributes more knowledge on development of low-carbon cooling technologies suitable for developing countries. Therefore, piloting and field testing of the technology are among major recommendations for future work.

Currently, the two dominant desalination methods are reverse osmosis (RO) and multi-stage flash (MSF). RO requires large capital investment and maintenance, whereas MSF is too energy intensive. An innovative vapor-compression desalination system is developed in this study. A comprehensive mathematical model for the heat exchanger/evaporator is described. The literature indicates that extraordinarily high overall heat transfer coefficients for the evaporator are possible at selected operating conditions that employ dropwise condensation in the steam side and pool boiling in the liquid side. A smooth titanium surface is chosen to promote dropwise condensation and to resist corrosion. To maximize energy efficiency, a combined-cycle cogeneration scheme is employed composed of a gas turbine, a heat recovery boiler, and a steam turbine that drive a compressor. The combined-cycle power source is oversized relative to the needs of the compressor. The excess power is converted to electricity and sold to the open market. A three-effect evaporator is employed. It is fed with seawater, assumed to be 3.5% salt. Boiling brine (7% salt) is in the low pressure side of the heat exchanger and condensing steam is in the high-pressure side of the heat exchanger. The condensing steam flows at 1.52 m/s (5 ft/s), which maximizes the heat transfer coefficient. The plant is sized to produce 37,854 m3/d (10 mill gal/day) and is assumed to be financed with a 5%, 30-yr municipal bond. Two economic cases were emphasized: the United States and the Middle East. For the United States, the fuel costs $5/GJ ($5.27/mill Btu) with the latent heat exchanger at ( ) 1.11 K 2.00 F T Ä = ° . The required compressor energy is 14 MJ/m3 (14.7 kW h/thous gal). The capital cost for the U.S. is $884 d/m3 ($3,342/thous gal) and the delivered water selling price is $0.47/m3 ($1.79/thous/gal). For the Middle East, the fuel costs $0.5/GJ ($0.53/mill Btu) with the latent heat exchanger at K T 33 . 3 = Ä ( ) F 00 . 6 ° . The required compressor energy is 26 MJ/m3 (27.3 kW h/thous gal). ). The capital cost for the Middle East is $620 d/m3 ($2,344/thous gal), and the delivered water selling price is $0.25/m3 ($0.95/thous/gal). In all cases, the water selling price is attractive relative to competing technologies.