Modelling and optimization of direct expansion air conditioning system for commercial building energy saving

This paper presents a comprehensive refinement of system modeling and optimization study of air-cooled direct expansion (DX) refrigeration systems for commercial buildings to address the energy saving problem. An actual DX rooftop package of a commercial building in the hot and dry climate condition is used for experimentation and data collection. Both inputs and outputs are known and measured from the field monitoring. The optimal supply air temperature and refrigerant flow rate are calculated based on the cooling load and ambient dry-bulb temperature profiles in one typical week in the summer. Optimization is performed by using empirically-based models of the refrigeration system components for energy savings. The results are promising as approximately 9% saving of the average power consumption can be achieved subject to a predetermined comfort constraint on the ambient temperature. The proposed approach will make an attractive contribution to residential and commercial building HVAC applications in moving towards green automation

A Gray-Box Dynamic Modeling Method for Variable Speed Direct Expansion Systems

In this paper, a gray-box dynamic modeling approach for variable-speed direct-expansion systems is presented. The overall approach incorporates a multi-stage training procedure that consists of 1) identification of component sub-models from quasi-steady-state performance data, 2) system model integration with estimation of refrigerant charge and 3) fine tuning of thermal capacitances of the evaporator and condenser to capture the system dynamic responses. Compared to traditional physics-based models, the proposed modeling approach has advantages including reduced engineering efforts in the model development phase, improved computational efficiency and reduced uncertainties. The modeling method was applied to a 3-ton variable-speed heat pump and proved to be capable of accurately capturing the system transient behaviors over a wide range of operating conditions

Experimental and numerical study of a water-to-water heat pump working with CO2

[SPA] En esta tesis, se analiza numérica y experimentalmente una bomba de calor agua-agua en un ciclo de transcrítico de CO2 de una etapa en la producción de agua caliente para calefacción y ACS. Se estudian y comparan diferentes configuraciones comúnmente utilizadas en el mercado para las mismas temperaturas del agua evaporador y condensador. A partir de ahora, dado que en los ciclos transcríticos del CO2 no existe cambio de fase, el condensador se denomina Gas Cooler. Inicialmente, se presentan cuatro configuraciones (C#), tres de ellas son con evaporador seco, C1 y C2, incluyen receptor de líquido, control de alta presión y control de sobrecalentamiento, y la restante, C4, no usa receptor de líquido, ni tiene control de alta presión, solo control de sobrecalentamiento. La diferencia entre C1 y C2 es un bypass que se usa en C1, pero cuando el bypass está cerrado, el ciclo está funcionando en C2. La otra configuración, C3, es un sistema de evaporador inundado, con control de alta presión, pero sin sobrecalentamiento ya que es un ciclo de evaporador inundado. Uno de los estudios más importantes de esta tesis fue la presión óptima del Gas Cooler. Se ha desarrollado y validado experimentalmente un modelo numérico para describir el comportamiento de una bomba de calor transcrítica de CO2 para la producción de agua caliente. Este modelo ha permitido obtener expresiones relativamente simples que se pueden programar en un PLC para regular la presión en el Gas Cooler midiendo la temperatura del refrigerante en tres puntos del ciclo. El modelo propuesto es capaz de limitar la temperatura de descarga del compresor a 140 °C manteniendo el COP con desviaciones teóricas inferiores al 2% respecto a las condiciones óptimas de presión. La presión del depósito de líquido, la temperatura de evaporación, la eficiencia del Intercambiador de calor interno (IHX) y el grado de recalentamiento tienen una influencia relativamente baja en el comportamiento del sistema. Además, dado que la influencia de la eficiencia del compresor también es relativamente baja, el modelo es aplicable para una amplia gama de modelos de compresores semi-herméticos alternativos, que son los más comunes en el campo de las bombas de calor estacionarias. Considerando la comparación de las diferentes configuraciones, una de las primeras decisiones luego de realizar las pruebas experimentales, fue eliminar el C4 ya que esta configuración no podía competir con las otras tres por falta de control de alta presión. La segunda decisión tras analizar que la influencia del depósito de líquido era insignificante mostrando rendimientos ligeramente mejores cuando el bypass estaba totalmente cerrado y seguido de totalmente abierto, las dos primeras configuraciones se trataron como una única configuración, denominada “C1&C2”. Así, las comparaciones solo se realizaron entre “C1&C2” y C3, con todas las configuraciones utilizando Intercambiador de Calor Interno (IHX) totalmente abierto ya que se ha concluido previamente en la literatura y probado experimentalmente durante esta tesis, para ciclo transcrítico, el rendimiento del sistema aumenta cuando aumenta la eficiencia de IHX. La superficie de los intercambiadores de calor (HX) también se estudió en calefacción. Para aplicaciones de calefacción y ACS, las diferencias entre “C1&C2” y C3 son despreciables. Sin embargo, en los ciclos de evaporador seco, si el depósito de líquido suele estar regulado por un bypass de gas con el objetivo de reducir la presión de las líneas que distribuyen el líquido a los evaporadores, para permitir un rango de regulación de presión adecuado, el depósito de líquido debe dimensionarse según resto de componentes y a las condiciones habituales de funcionamiento. El aumento de la superficie de los diferentes intercambiadores de calor (HX), mostró una mejora en la mayoría de los casos estudiados numéricamente para la aplicación de calefacción, pero existe una superficie óptima para los diferentes rangos de temperatura y esto debe tenerse en cuenta al diseñar los intercambiadores de calor, al menos para temperaturas baja/media y altas/muy altas. In this thesis, a one-stage transcritical CO2 water-to-water heat pump is numerically and experimentally analyzed in the production of hot water for the applications of space heating and domestic hot water generation. Different configurations commonly used in the market are studied and compared for the same wáter temperatures at the heat sink (evaporator) and heat source (condenser). From now on, since in CO2 transcritical cycles does not exist phase change, the condenser is called Gas Cooler. Initially, four configurations (C#) are presented, three of them belong to the dry evaporator group, C1 and C2 include liquid receiver, high pressure control and superheating control, and the remaining one, C4, doesn’t use liquid receiver, neither has high pressure control, only superheating control. The difference between C1 and C2 is a bypass that is used in C1, but, when the bypass is closed, the cycle is working in C2. The other configuration, C3, is a flooded evaporator system, with high pressure control, but without superheating since it is a flooded evaporator cycle. One of the most important studies in this thesis was the Gas Cooler optimal pressure. A numerical model to describe the behavior of a CO2 transcritical heat pump for hot water production has been developed and experimentally validated. This model has allowed obtaining relatively simple expressions that can be programmed in a PLC to regulate the pressure in the gas cooler by measuring the temperature of the refrigerant in three points of the cycle. The proposed model is capable of limiting the compressor discharge temperature to 140 °C while maintaining the COP with theoretical deviations of less than 2 % respect to optimal pressure conditions. The liquid receiver pressure, the evaporation temperature, the Internal Heat Exchanger (IHX) efficiency and the Superheating degree, have relatively low influences on the system behavior. Furthermore, since the influence of the compressor efficiency is relatively low as well, the model is applicable for a wide range of reciprocating semihermetic compressor models, which are the most common in the field of stationary heat pumps. Considering the comparison of the different configurations, one of the first decisions after performing the experimental tests, was eliminating the C4 since this configuration was not able to compete with the other three due to the lack of high pressure control. The second decision after analyzing that the influence of the liquid receiver was negligible showing slightly better performances when the bypass was totally closed and followed by totally opened, the first two configurations were treated as a single configuration, called “C1&C2”. Thus, the comparisons were only performed between “C1&C2” and C3, with all configurations using Internal Heat Exchanger (IHX) totally opened since it has been previously concluded in the literature and experimentally tested during this thesis, for transcritical cycle, the system performance increases when IHX efficiency increases. The Heat Exchangers (HX) surface was also studied for space heating applications. For the space heating and domestic hot water applications, the differences between “C1&C2” and C3, are negligible. However, in the dry evaporator cycles, if the liquid receiver is usually regulated by a gas bypass with the aim of reducing the pressure of the lines that distribute liquid to the evaporators, to allow an adequate pressure regulation range, the liquid receiver should be sized according to the rest of the components and to the usual operating conditions. Increasing the Heat Exchangers (HX) surfaces, showed improvement in most cases numerically studied for space heating application, but there exists an optimal surface for the different temperatura range and this should be considering when designing the heat exchangers, at least for low/medium and high/very high temperatures.Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Tecnologías Industriale

Gray box dynamic modeling of vapor compression systems for control optimization

Buildings account for 75% of electricity use in the U.S. and more than 24% of building electrical energy is consumed by vapor compression equipment, including air-conditioners, refrigerators/freezers and heat pumps. Dynamic modeling of vapor compression systems (VCS) is particularly important for developing and validating optimal control strategies to maximize the system efficiency and reliability. However, existing modeling techniques are rarely used in control practices because of the significant model development effort and requirement of high computational resources. This dissertation presents an efficient and robust gray-box dynamic modeling approach for VCS to support control optimization. The presented methodology allows automated construction of data-driven VCS models with minimum training data and human inputs. The overall approach incorporates a multi-stage training procedure with separate estimation of the steady-state and dynamic model parameters along with a finite control volume scheme to achieve good model identifiability while ensuring adequate prediction accuracy. To improve model reliability, the modeling approach incorporates sensitivity analysis and de-correlating steps in a pre-conditioning procedure to avoid over-parameterization. The system-level training identifies the refrigerant charge that minimizes the steady-state simulation errors while the dynamic modeling stage transforms the established steady-state system model into a dynamic counterpart, in which the optimal thermal capacitances of the heat exchanger walls are identified to best reproduce system transient responses

NASA Tech Briefs, November 1990

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences

Dynamic energy demand prediction and related control system for UK households

PhD ThesisDomestic energy consumption is not only based on the type of appliances, weather conditions, and house type; it is also highly depended on related occupancy profiles. In order to manage and optimise energy generation and the effective use of energy storage, it is important to be able to accurately predict energy demand in advance. However, high-resolution (like below 1-min) occupancy profiles for domestic UK households are not ideally possible to be recorded or measured in nature. Therefore, an alternative approach to transfer particular electricity load to the number of active occupancy during selected time interval is identified by analysing the average electricity consumption of occupancy in this study. Real load data analysis for three type of participated UK households is presented throughout the year. Then the seasonal synthetic high-resolution (30s) occupancy patterns for each household are generated independently. Weekday occupancy profiles are collected seasonally and used in a Markov-Chain model to produce particular occupancy daily activity sequence for each household. A stochastic model by using Markov-Chain Monte Carlo is presented to randomly generate high-resolution occupancy profiles in dynamic. Then the predicted electricity loads are produced by mapping occupancy profiles to average electricity consumption. By validating the predicted results, it is found that maximum of sub-hourly aggregate result can mostly cover the measured demand in advance. Therefore, it is set the sub-hourly electricity demand boundary independently for each household during weekday throughout the year. Heat demand for each household is simulated in sub-hourly resolution by using DesignBuilder with EnergyPlus throughout the year. Thus, sub-hourly energy demand of each household is applied in the control system of Bio-fuel Micro Trigeneration with Hybrid Electrical Energy Storage. The control system is designed and implemented by using Siemens software STEP-7 S-300 and WinCC. In addition, the predicted energy demands are utilized into the optimization of the control system. The comparison of optimized and general control strategies shows that optimized strategies by applying prescient sub-hourly energy demand can improve system efficiency significantly

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

Industrial-Scale Manufacture of Oleosin 30G for Use as Contrast Agent in Echocardiography

In ultrasound sonography, microbubbles are used as contrasting agents to improve the effectiveness of ultrasound imaging. Monodisperse microbubbles are required to achieve the optimal image quality. In order to achieve a uniform size distribution, microbubbles are stabilized with surfactant molecules. One such molecule is Oleosin, an amphiphilic structural protein found in vascular plant oil bodies that contains one hydrophobic and two hydrophilic sections. Controlling the functionalization of microbubbles is a comprehensive and versatile process using recombinant technology to produce a genetically engineered form of Oleosin called Oleosin 30G. With the control of a microfluidic device, uniformly-sized and resonant microbubbles can be readily produced and stored in stable conditions up to one month. Currently, Oleosin microbubbles are limited to the lab-scale; however, through development of an integrated batch bioprocessing model, the overall product yield of Oleosin 30G can be increased to 7.39 kg/year to meet needs on the industrial-scale. An Oleosin-stabilized microbubble suspension as a contrast agent is in a strong position to take a competitive share of the current market, capitalizing on needs unmet by current market leader, Definity®. Based on market dynamics and process logistics, scaled-up production of Oleosin 30G for use as a contrast agent is expected to be both a useful and profitable venture

A simulation environment for dry-expansion evaporators with application to the design of autotuning control algorithms for electronic expansion valves

In this paper we report some results of a research project aimed at deriving high-performance, adaptive control algorithms for electronic expansion valves (EEVs) to be used in finned-coiled, dry-expansion evaporators for refrigeration systems. The approach we use in the design is that of virtual prototyping, with the aim of developing a software environment that can be used for controller design, rapid prototyping, optimization of data collection, and test design. We describe the development of a simulation model of the evaporator, and its use for deriving autotuning PID control algorithms. Experimental results confirm the effectiveness of the approach