modelling and control of a free cooling system for data centers

Abstract Data centers are facilities hosting a large number of servers dedicated to data storage and management. In recent years, their power consumption has increased significantly due to the power density of the IT equipment. In particular, cooling represents approximately one third of the total electricity consumption, therefore efficiently cooling data centers has become a challenging problem and it represents an opportunity to reduce both IT energy costs and emissions environmental impact. The efficiency of computers room air conditioning (CRAC) systems can be increased using both advanced control techniques and new free cooling technologies, such as the indirect adiabatic cooling (IAC), that is the humidification of air under adiabatic conditions. Water sprinkled by spray nozzles humidifies and cools down the air taken from the outside, which then cools down the computers room air by means of a crossflow heat exchanger. In this way, the process air temperature is economically reduced and the cooling process is effective even when the outside temperature is warmer than that desired in the computers room. Beside the traditional approach, that improves energy efficiency of CRAC systems through advanced hardware design, nowadays advanced control systems offer the opportunity to improve both efficiency and performance by mostly acting on software components. In particular, a model-based paradigm can result very useful in the design of the controller. This approach involves three main steps: plant modelling, controller design, and simulations. In this paper, First-Principle Data-Driven (FPDD) techniques have been considered in the modelling phase, in order to obtain a model as simple as possible but accurate enough. All the main components of the plant, such as fans, spray nozzles, heat exchanger, and the computers room have been taken into account and they have been calibrated exploiting real data. The dynamics of the computers room variables (e.g. temperature) are slower than those of the components of the cooling system, due to higher thermal inertias of the computers room. Therefore, fans, heat exchanger, and spray nozzles are described by static models, whereas the computers room is described by a LTI dynamic model. Once obtained a model of the plant, a simulation environment based on Matlab/Simulink is designed accordingly. The developed control system is hierarchical: a supervisor determines the best combination of CRAC water and process air flows which minimizes the total power consumption, while satisfying the cooling demand. This system energy management problem is formulated as a non-linear optimization problem, subject to internal air condition requirements and system operating constraints. The optimization problem is repeatedly solved at each supervision period by using a population based stochastic optimization technique (Particle Swarm Optimization). Results of simulations show that the proposed control system is effective and minimizes the input electric power while satisfying both the data center thermal load and system operating constraints

A novel laboratory set-up for investigation of intelligent automatic control in complex HVAC systems

U radu je prikazano novo laboratorijsko postorojenje za analizu rada klimatizacionog sistema, koje je smešteno u Laboratoriji za automatsko upravljanje na Mašinskom fakultetu Univerziteta u Beogradu. Nova KGH laboratorija je projektovana u cilju ispitivanja različitih složenih režima rada, uz obezbeđenje željenih uslova komfora. Poseban akcenat je stavljen na uticaj režima rada na potrošnju energije. Laboratorijsko postrojenje je projektovano da radi u složenim dinamičkim uslovima, kada se unutrašnji i spoljni parametri sredine znatno menjaju tokom vremena. U cilju minimizovanja potrošnje energije razvijeni su novi upravljački softveri i različiti algoritmi upravljanja klima komore.This paper presents a new laboratory set-up for the air-conditioning operation analysis in the Laboratory for Automatic Control at the Faculty of Mechanical Engineering, University of Belgrade. The new HVAC laboratory is designed to investigate different complex HVAC system working regimes and to provide desired space comfort. The emphasis is specially given to an impact on energy consumption. The laboratory set-up is designed to operate in the complex, dynamic regimes, when indoor environment parameters are intensively changed, together with a change of outdoor conditions. In order to minimize energy consumption, a new software and various automatic control algorithms are designed for automatic control of the air handlig unit

A novel laboratory set-up for investigation of intelligent automatic control in complex HVAC systems

U radu je prikazano novo laboratorijsko postorojenje za analizu rada klimatizacionog sistema, koje je smešteno u Laboratoriji za automatsko upravljanje na Mašinskom fakultetu Univerziteta u Beogradu. Nova KGH laboratorija je projektovana u cilju ispitivanja različitih složenih režima rada, uz obezbeđenje željenih uslova komfora. Poseban akcenat je stavljen na uticaj režima rada na potrošnju energije. Laboratorijsko postrojenje je projektovano da radi u složenim dinamičkim uslovima, kada se unutrašnji i spoljni parametri sredine znatno menjaju tokom vremena. U cilju minimizovanja potrošnje energije razvijeni su novi upravljački softveri i različiti algoritmi upravljanja klima komore.This paper presents a new laboratory set-up for the air-conditioning operation analysis in the Laboratory for Automatic Control at the Faculty of Mechanical Engineering, University of Belgrade. The new HVAC laboratory is designed to investigate different complex HVAC system working regimes and to provide desired space comfort. The emphasis is specially given to an impact on energy consumption. The laboratory set-up is designed to operate in the complex, dynamic regimes, when indoor environment parameters are intensively changed, together with a change of outdoor conditions. In order to minimize energy consumption, a new software and various automatic control algorithms are designed for automatic control of the air handlig unit

Solar desiccant evaporative cooling with multivalent use of solar thermal heat

Solar DEC (Desiccant and Evaporative Cooling) air-conditioning is a renewable technological approach to the future air-conditioning of buildings driven with solar-thermal heat. The principal acceptance of solar airconditioning has led to system prototypes mainly across Europe, however the diffusion of this innovative technology is proceeding slowly due to little field testing experience. In climates with coexisting heating demand particularly, a multivalent system approach that utilizes solar-heat not only for air-conditioning but also for hot water preparation and heating has potential as a feasible concept. However, previous research focused on systems using solar heat exclusively for the DEC-process. This research contributes to the advancement of the solar DEC-technology with multivalent use of solar thermal heat. The investigation consists of an initial detailed in-situ monitoring analysis of a system prototype operated in an industrial environment, followed by the development of optimised system concepts and a climate-specific analysis of the solar DEC-technology. The monitoring provided in-depth knowledge about the system operation, revealing the reasons for the insufficient refrigeration capacity achieved in practice. A detailed simulation model for an entire multivalent solar DEC-system including the heat sinks, DEC-system, heating and hot-water preparation was developed and a DEC-control strategy has been formulated. A new optimised control strategy for multivalent systems with simultaneous sink supply concept was devised. A sensitivity analysis was carried out to investigate the key design parameters for the dimensioning of multivalent solar DEC-systems. The research concluded that the auxiliary primary energy consumption of the optimised system was lower by one third compared to the initial system. Finally, a methodological zoning approach was developed, to systematically produce design-specific outline data for the application of the solar DEC-technology at climatically different sites

Data-based fault detection in chemical processes: Managing records with operator intervention and uncertain labels

Developing data-driven fault detection systems for chemical plants requires managing uncertain data labels and dynamic attributes due to operator-process interactions. Mislabeled data is a known problem in computer science that has received scarce attention from the process systems community. This work introduces and examines the effects of operator actions in records and labels, and the consequences in the development of detection models. Using a state space model, this work proposes an iterative relabeling scheme for retraining classifiers that continuously refines dynamic attributes and labels. Three case studies are presented: a reactor as a motivating example, flooding in a simulated de-Butanizer column, as a complex case, and foaming in an absorber as an industrial challenge. For the first case, detection accuracy is shown to increase by 14% while operating costs are reduced by 20%. Moreover, regarding the de-Butanizer column, the performance of the proposed strategy is shown to be 10% higher than the filtering strategy. Promising results are finally reported in regard of efficient strategies to deal with the presented problemPeer ReviewedPostprint (author's final draft

Energy Intensity Reduction in Large-Scale Non-Residential Buildings by Dynamic Control of HVAC with Heat Pumps

One of the main elements for increasing energy efficiency in large-scale buildings is identified in the correct management and control of the Heating Ventilation and Air Conditioning (HVAC) systems, particularly those with Heat Pumps (HPs). The present study aimed to evaluate the perspective of energy savings achievable with the implementation of an optimal control of the HVAC with HPs. The proposed measures involve the use of a variable air volume system, demand-controlled ventilation, an energy-aware control of the heat recovery equipment, and an improved control of the heat pump and chiller supply water temperature. The analysis has been applied to an academic building located in Pisa and is carried out by means of dynamic simulation. The achieved energy saving can approach values of more than 80% if compared with actual plants based on fossil fuel technologies. A major part of this energy saving is linked to the use of heat pumps as thermal generators as well as to the implementation of an energy efficient ventilation, emphasizing the importance of such straightforward measures in reducing the energy intensity of large-scale buildings

Using Data Mining Techniques to Predict NOx Emissions Levels in Gas Fired Boilers

Natural gas industry becomes one of the largest sectors in the today’s world economy. With the growth of production, pollutants from gas processing plants continue to grow, forcing government and legislative authorities to compel stringent restrictions on the release of emissions. These restrictions become among top vital factors influencing plant operations nowadays in the state of Qatar. One of the most important tasks for gas processing plants is not only to ensure a continuous gas supply to customers, but also to monitor, control and address concerns about the environmental impact of the operations. The use of the gas fired steam boilers in the gas operations has led to a significant increase in the emissions of toxic substances such as NOx. Therefore, significant worries have been raised about the environmental effect on climate and air quality of noxious emissions associated with the steam generation process of the boilers. Data mining is a powerful tool that has been used for decades for advanced process analytics of large quantities of plant data in order to extract useful information and to reach a better understanding of the process. In this research, some of data mining techniques such as artificial neural networks and decision trees are applied on real plant data representing 27 industrial process parameters from a gas fired steam boiler of one gas processing plant at Ras-Laffan Industrial City in order to predict the most important factors impacting the NOx formation in the combustion process of the boiler. Closer attention to those factors can be given promptly in order to enhance the plant environmental performance. The results obtained by the artificial neural network and decision tree models showed that the NOx emissions are directly related to the air flow parameters such as O2 concentration, the excess air level in the boiler and the amount of the flue gas at the boiler outlet. It was also shown that the company is following a traditional technique of lowering the amount of oxygen in the boiler aiming to reduce the NOx emission levels. However, this technique was proven to be limited under certain threshold of boiler load due to other important factors such as the adiabatic flame temperature (AFT) which induces the formation of NOx emissions

Direct solar air heating in linear concentrating collectors assisted by a turbocharger for industrial processes: theoretical analysis and experimental characterization

Mención Internacional en el título de doctorEnergy demand of industry has a relevant share of global energy consumption. The larger portion of industrial demand is heating, mainly provided from fossil fuels. The concerns about pollutant and greenhouse gas emissions, together with the fossil fuels scarcity encourage the research efforts toward environmentally sustainable energy sources and among them, solar energy is widely available. Among solar thermal technologies, linear concentrating collectors represent a suitable solution for providing industrial process heat in the medium temperature range. A heat transfer fluid, as thermal oil, or water, is generally adopted to evacuate heat from the solar receivers and to deliver it to thermal processes, contributing to complexity, cost, and even environmental impact. In this thesis the direct air heating inside concentrating solar collector is investigated as a promising solution for industrial processes requiring hot air in the medium temperature range, aiming at low installation and maintenance costs. Although uncommon, the theoretical analysis carried out revealed the feasibility of direct air heating at atmospheric pressure either in a parabolic trough and linear Fresnel collectors within a limited range of design and operating conditions. The high pumping power required to blow air through the receivers arises as one of the main constraints, becoming unsustainable at medium and large scale. To overcome this limitation, an innovative layout is proposed using an automotive turbocharger to configure an original open-to-atmosphere solar Brayton cycle with null power efficiency. The compressor increases the air pressure before solar heating inside the receivers, minimizing the pumping power consumption. The turbine placed at the receiver outlet recovers the compressing and the pumping power, releasing hot air at between 300 °C and 400 °C for its usage in the thermal process. The maximum allowable temperature of evacuated standard receivers, indicated as 600 °C by most of the manufacturers, limits the inlet turbine temperature. No substantial mechanical excess of power at the common turbine and compressor shaft is expected. Instead, turbocharger freewheeling enables to blow air through the solar receivers without auxiliary energy consumption, eventually delivering the hot air with an overpressure for pumping to the user. To support the proposal, a first small-scale experimental prototype of the turbo-assisted solar air heater is designed and installed, using Linear Fresnel collectors and a low-capacity turbocharger. The experimental results allow the thermal and mechanical characterization of the solar collector and the turbocharger, besides tuning and validating the numerical model implemented. They corroborate the practical viability of the concept and indicates relevant features and critical aspects for scaling up to industrial size. A detailed quasi-steady numerical model is developed, including technical features of commercial linear Fresnel collectors and off-the-shelf turbochargers. Daily and yearly assessments of several medium-scale facilities are obtained considering the typical meteorological year of the selected location. The results allow identifying the relevant design and operating parameters and their effect on the performances of the turbo-assisted solar air heater. By combining theoretical and experimental approaches this thesis establishes the framework for the development, design, optimization, and operation of the innovative technology proposed, opening the possibility to its application to several industrial sectors.La demanda energética de la industria tiene una participación relevante en el consumo energético mundial. La mayor parte de la demanda industrial es calor, principalmente obtenido a partir de combustibles fósiles. Las preocupaciones sobre las emisiones de gases contaminantes y de efecto invernadero, junto con la escasez de combustibles fósiles, fomentan los esfuerzos de investigación hacia fuentes de energía ambientalmente sostenibles, entre las cuales, la energía solar se encuentra ampliamente disponible. Entre las tecnologías solares térmicas, los colectores de concentración lineal representan una solución adecuada para proporcionar calor de proceso industrial en el rango de media temperatura. Generalmente se adopta un fluido caloportador, como aceite térmico o agua, para evacuar el calor de los receptores solares y entregarlo al proceso térmico, contribuyendo a la complejidad, costo, e incluso impacto ambiental. En esta tesis se investiga el calentamiento directo de aire en colectores solares de concentración como una solución prometedora para procesos industriales que requieran aire caliente en el rango de media temperatura, con el objetivo de reducir los costos de instalación y mantenimiento. Aunque poco común, el análisis teórico realizado revela la viabilidad del calentamiento directo del aire a presión atmosférica tanto en colectores cilindro-parabólicos como en colectores Fresnel lineales dentro de un rango limitado de condiciones de diseño y operación. La alta potencia de bombeo necesaria para soplar aire a través de los receptores es una de las principales limitaciones, volviéndose insostenible a mediana y gran escala. Para superar esta limitación, se propone un diseño innovador que utiliza un turbocompresor de automóvil para configurar un ciclo Brayton solar abierto a la atmósfera con una eficiencia energética nula. El compresor aumenta la presión del aire antes del calentamiento solar en los receptores, minimizando el consumo de energía de bombeo. La turbina, colocada en la salida del receptor, recupera la potencia de compresión y bombeo, liberando aire caliente entre 300 °C y 400 °C para su uso en el proceso térmico. La temperatura máxima permitida de los receptores estándar evacuados, indicada como 600 °C por la mayoría de los fabricantes, limita la temperatura de entrada de la turbina, por lo que no se espera un exceso mecánico de potencia sustancial en la turbina común y el eje del compresor. En cambio, el turbocompresor permite soplar aire a través de los receptores solares sin consumo de energía auxiliar de bombeo. Si existiera un exceso, estará disponible para el bombeo hasta el usuario. Para apoyar la propuesta, se diseña e instala un primer prototipo experimental de pequeña escala del calentador de aire solar turbo-asistido, utilizando colectores lineales Fresnel y un turbocompresor de baja capacidad. Los resultados experimentales permiten la caracterización térmica y mecánica del colector solar y el turbocompresor, además de ajustar y validar los modelos numéricos implementados. Los ensayos corroboran la viabilidad práctica del concepto e indican características relevantes y aspectos críticos para escalar al tamaño industrial. Se desarrolla un modelo numérico cuasi-estacionario detallado, que incluye las características técnicas de los colectores Fresnel lineales comerciales y los turbocompresores estándar. Se obtienen evaluaciones diarias y anuales de varias instalaciones de mediana escala considerando el año meteorológico típico de la ubicación seleccionada. Los resultados permiten identificar los parámetros de diseño y funcionamiento relevantes y su efecto sobre el rendimiento del calentador de aire solar turbo-asistido. Combinando enfoques teóricos y experimentales, esta tesis establece el marco para el desarrollo, diseño y operación de la tecnología innovadora propuesta, abriendo la posibilidad de su aplicación a varios sectores industriales, apuntando a la descarbonización y transición industrial sustentable.This research was supported by the Industrial Ph.D. project “Producción directa de aire a alta temperatura y a presión turboalimentada en colectores solares de concentración” (BOCM Reference IND2017/AMB7769) funded by “Comunidad de Madrid”, Spain (Orden 3779/2017 of October 17th 2017, by “Consejero de Educación e Investigación”, pubblished on “BOCM. 252, of October 23th 2017.)Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de MadridPresidente: Eduardo A. Rincón Mejía.- Secretario: José Miguel Cardemil Iglesias.- Vocal: José González Aguilaré Migue

Design and control of mixed-mode cooling and ventilation in low-energy residential buildings in India

Energy security, climate change and economic growth are matters of critical international importance in an effort to achieve a sustainable future. Energy consumption in buildings contributes to higher greenhouse gas emissions than the industrial or transportation sectors combined. In India, the energy in the residential sector accounts for almost 50% of the total energy consumption. The need for comfortable internal environments, healthy indoor air quality and the consequences of global warming are all contributing factors to the high reliance on mechanical cooling and ventilation systems. In recent years, financial growth and increase in disposable income in India, have accelerated purchases of such mechanical systems. In metropolitan cities of India with extreme climates (hot and dry, warm and humid), the use of these systems increases by 30% every year. This upward trend is likely to continue in response to occupants’ higher comfort expectations and the continuous increase of the outside temperature during the summer months due to climate change. This could further impact the climate and the electricity grid. Innovative solutions should establish reliable strategies for cooling purposes by utilizing the use of natural ventilation. Mixed-mode buildings rely on both mechanical and natural systems to maintain comfortable conditions. Although the performance of mixed-mode buildings has already been studied and there is evidence for its positive impact on the reduction of energy demand, there is still a lack of knowledge on the best methods for controlling mixed-mode buildings. Today, the majority of the available algorithms for the control of mixed-mode systems are very simplistic and at a primitive stage of development. Typically, the control algorithms “make the decision” based on a predefined static set-point temperature, disregarding other important parameters, such as relative humidity, the position of windows and activity of occupants. Control algorithms that would account for a variety of parameters are of paramount importance to achieve energy savings whilst maintaining thermal comfort conditions. The aim of this research was to investigate the impact on thermal comfort and energy savings of novel and sophisticated control algorithms in mixed-mode residential buildings in India.Initially, it was important to identify all the control parameters that were important to be included in the control algorithms. Then the control algorithms were designed and presented in flow charts. To analyse the performance of the proposed control algorithms, computer simulations were performed, whilst a validation analysis was conducted to provide evidence of the validity of the control algorithms. Computer modelling comprised of co-simulations, using Dynamic Thermal Modelling (DTM) (EnergyPlus) and equation-based tools (Dymola using the Modelica language). The coupling of these was achieved using the Functional Mock-up Interface (FMI) for model exchange. The co-simulations enabled to examine the energy saving potential that can be achieved by the proposed control algorithms. In order to evaluate the ventilation performance of the proposed control algorithms, the ventilation rates and ventilation effectiveness of the systems were analysed using Computational Fluid Dynamics (CFD). This allowed the final analysis which included the evaluation of the ventilation performance of the control algorithms by calculating the ventilation effectiveness. To provide evidence of the proposed control algorithms and simulation approach, a validation study was done using data from an experimental chamber in India. This research has contributed to the existing body of knowledge by providing four main conclusions concerning the design and control of mixed-mode ventilation and cooling systems: i) to deliver comprehensive guidelines on the design and control of mixed-mode buildings, and the ways in which the co-simulations can be implemented to improve the existing control algorithms that can be found in the literature; ii) the use of the co-simulations showed that the developed control algorithms, when dampers/windows and ceiling fans are used, can improve the predicted hours of thermal comfort by up to 1900h compared to the scenarios when the ceiling fans were turned off, while achieving up to 55% energy reduction depending on the city; iii) the CFD simulations predicted that cross ventilation with the maximum opening areas for windows and dampers in combination with the operation of the ceiling fans can dillute the contaminants and/or heat in the building resulting in comfortable internal environments resulting in heat removal effectiveness of 1.65; and iv) the accurate and validated control algorithms that were developed in this research can be used for any study that requires control of mixed-mode buildings regardless of the geometry of the building. The use of co-simulations provides great flexibility since the same control algorithms can be used in any geometry or building location without the need for any modification of the code.</div