Modelling of small capacity absorption chillers driven by solar thermal energy or waste heat

Aquesta recerca es centra en el desenvolupament de models en règim estacionari de màquines d’absorció de petita potència, els quals estan basats en dades altament fiables obtingudes en un banc d’assajos d’última tecnologia. Aquests models podran ser utilitzats en aplicacions de simulació, o bé per a desenvolupar estratègies de control de supervisió dels sistemes d’aire condicionat amb màquines d’absorció. Per tant, l’objectiu principal d’aquesta investigació és desenvolupar i descriure una metodologia comprensible i que englobi el procés sencer: tant els assajos, com la modelització, com també el desenvolupament d’una estratègia de control per a les màquines d’absorció de petita potència. Basant-se en la informació obtinguda de forma experimental en el banc d’assajos, s’han desenvolupat cinc models, cadascun amb una base teòrica diferent. Els resultats mostren que és possible obtenir models empírics summament precisos utilitzant únicament com a paràmetres d’entrada les variables dels circuits externs d’aigua. Aquest treball finalitza amb la proposta de dues estratègies òptimes de control i el seu ús per al control on-line de sistemes basats en refredadores tèrmiques d’absorció.This research deals with the development of the simple, yet accurate steady-state models of small capacity absorption machines which are based on highly reliable data obtained in the state-of-the-art test bench. These models can further be used in simulation tools or to develop supervisory control strategies for air-conditioning systems with absorption machines. Therefore, the main aim of this research is to develop and to describe a comprehensive methodology which encloses entire process which consists of testing, modelling and control strategy development of small capacity absorption machines. Five different models are developed based on the experimental data obtained in the test bench. The results show that it is possible to develop highly accurate empirical models by using only the variables of external water circuits as input parameters. Finally, two optimal control strategies are developed to demonstrate how these models can be used for on-line control of absorption systems

Homogeneidad y variabilidad espacial de series meteorológicas del área del proyecto “Ciudad del Conocimiento - Yachay ”

Using Einstein’s field equations, the energy-momentum tensor components are deduced for a Morris-Thorne wormhole in a cosmological background. The embedding surfaces for these wormholes are studied and also the red shift parameter is calculated in terms of the conformal factor Q. The exoticity condition is analyzed and an analytic solution for the form factor of such wormholes is introduced. Finally, we study the weak energy conditions (WEC) and deduce an equation for the acceleration parameter of the universe in terms of the conformal factor.Usando las ecuaciones de campo de Einstein se deducen las expresiones de las componentes del tensor energía-momentum para un agujero de gusano del tipo Morris-Thorne inmerso en un background cosmológico. Las superficies de inserción (embedding surfaces) para dichos agujeros son analizadas y se calcula la expresión del parámetro de corrimiento hacia el rojo en términos del factor conforme Q. Se analiza la condición de exoticidad y se introduce una solución analítica para la función de forma de un agujero de gusano de las características señaladas inmerso en un background cosmológico. Finalmente se analizan las condiciones de energía débil y se deduce una expresión para el parámetro de aceleración del universo en términos de dicho factor conforme

Biomass gasification with chp production a review of the state-of-the-art technology and near future perspectives

This paper is a review of the state-of-the-art of biomass gasification and the future of using biomass in Serbia and it presents researches within the project "The Development of a CHP Plant with Biomass Gasification". The concept of downdrafi demonstration unit coupled with gas engine is adopted. Downdrafi fixed-bed gasification is generally favored for CHP, owing to the simple and reliable gasifiers and low content of tar and dust in produced gas. The composition and quantity of gas and the amount of air are defined by modeling biomass residues gasification process. The gas (290-400 m(3)/h for 0.5-0.7 MW biomass input) obtained by gasification at 800 degrees C with air at atmospheric pressure contains 14% H-2, 27% CO, 9% CO2, 2% CH4, and 48% N-2, and its net heating value is 4.8-6 MJ/Nm(3). The expected gasifier efficiency is up to 80%. The review of the work on biomass gasification has shown that the development of technology has reached the mature stage. There are CHP plants with biomass gasification operating as demonstration plants and several gasification demonstration units are successfully oriented to biofuel production. No attempt has been made here to address the economic feasibility of the system. Economics will be the part of a later work as firmer data are acquired

Review on absorption technology with emphasis on small capacity absorption machines

The aim of this paper is to review the past achievements in the field of absorption systems, their potential and possible directions for future development. Various types of absorption systems and research on working fluids are discussed in detail. Among various applications, solar cooling and combined cooling, heating and power (CCHP) are identified as two most promising applications for further development of absorption machines. Under the same framework, special attention is given to the small capacity absorption machines and their current status at the market. Although this technology looks promising, it is still in development and many issues are open. With respect to that fact, this paper covers all the relevant aspects for further development of small capacity absorption machines

The Influence of Weather Conditions on Energy Performance of HVAC System and Absorption Cooling System Coupling

In this study, the attention is focused on the influence of climate conditions and absorption chiller configurations on the energy performance of heating, ventilating and air conditioning (HVAC) systems. We will analyze the correlation between HVAC system dynamic load profile and the performance of various absorption cooling system configurations for two typical European climates: Mediterranean (more specific Spain) and Mild Atlantic Climate (UK). Dynamic simulation software EnergyPlus is used to calculate HVAC system cooling demand of typical narrow plan office building, equipped with variable air volume (VAV) system and placed in chosen climate regions. This cooling demand has been coupled with different absorption cooling system configurations developed in MatLab in order to analyze absorption chiller heat energy consumption. Preliminary results of this study shows that energy savings in terms of heat supply can be achieved when multiple absorption chillers are used. Spanish case study shows that up to 4.9% can be saved while in the UK savings go up to 6.17% when compared with basic scenario which is a single absorption chiller plant. The results also indicate that for the same building type, the combined influence of climate and national standards can produce up to four times higher cooling demand for building in Spain when compared with buildings in the UK. This directly affects the size of the absorption chiller plant which is 50% bigger and the number of hours when chillers are operating which is twice higher

ANN application to modelling and control of small absorption chillers

The main aim of this paper is to demonstrate the application of Artificial Neural Networks (ANN) in small absorption chillers modelling and their control optimisation. The Genetic Algorithms (GA) optimisation method was coupled to the ANN model in order to solve the optimal operation problem where the objective function was the minimal primary energy consumption. This paper analyses the impact of control strategy on energy performance of small capacity absorption chillers, while emphasizing the usability of ANN model, and comparing this strategy to conventional operation strategies