Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System

Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration System
Author: Ankush Gupta
Publisher:
Total Pages:
Release: 2013
Genre:
ISBN:
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The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148111

Intelligent Building Control Systems

Intelligent Building Control Systems
Author: John T. Wen
Publisher: Springer
Total Pages: 321
Release: 2017-12-04
Genre: Technology & Engineering
ISBN: 3319684620
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Readers of this book will be shown how, with the adoption of ubiquituous sensing, extensive data-gathering and forecasting, and building-embedded advanced actuation, intelligent building systems with the ability to respond to occupant preferences in a safe and energy-efficient manner are becoming a reality. The articles collected present a holistic perspective on the state of the art and current research directions in building automation, advanced sensing and control, including: model-based and model-free control design for temperature control; smart lighting systems; smart sensors and actuators (such as smart thermostats, lighting fixtures and HVAC equipment with embedded intelligence); and energy management, including consideration of grid connectivity and distributed intelligence. These articles are both educational for practitioners and graduate students interested in design and implementation, and foundational for researchers interested in understanding the state of the art and the challenges that must be overcome in realizing the potential benefits of smart building systems. This edited volume also includes case studies from implementation of these algorithms/sensing strategies in to-scale building systems. These demonstrate the benefits and pitfalls of using smart sensing and control for enhanced occupant comfort and energy efficiency.

Cascade and Secondary Coolant Supermarket Refrigeration Systems

Cascade and Secondary Coolant Supermarket Refrigeration Systems
Author: Getu Haile-Michael
Publisher: LAP Lambert Academic Publishing
Total Pages: 260
Release: 2011-08
Genre: Heat exchangers
ISBN: 9783845437163
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Traditional supermarket refrigeration systems have long piping system, fittings and joints causing substantial refrigerant losses. The refrigerant losses bring about high cost and environmental damage. Additionally, defrosting of air-coils is one of the most energy consuming processes in supermarket refrigeration systems to keep display cabinets under the required temperature. Various studies, though limited in scope, have been conducted by several researchers in order to provide efficient and environmentally friendly supermarket refrigeration technologies. The current study, therefore, presents numerical models for cascade and secondary coolant systems and new correlations for frost property. These models showed that energy savings from 17500 to 170000kWh per annum could potentially be achieved from a typical supermarket store. These systems also avoid the use of environmentally damaging refrigerants thereby attracting supermarket owners. Finally, a step-by-step exercise of the application of the secondary coolant model has been presented to completely design, select, evaluate and install such systems or retrofit the existing traditional refrigeration systems in supermarkets.

Superheat Control for Air Conditioning and Refrigeration Systems: Simulation and Experiments

Superheat Control for Air Conditioning and Refrigeration Systems: Simulation and Experiments
Author: Richard J. Otten
Publisher:
Total Pages:
Release: 2010
Genre:
ISBN:
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Ever since the invention of air conditioning and refrigeration in the late nineteenth century, there has been tremendous interest in increasing system efficiency to reduce the impact these systems have on global energy consumption. Efficiency improvements have been accomplished through component design, refrigerant design, and most recently control system design. The emergence of the electronic expansion valve and variable speed drives has made immense impacts on the ability to regulate system parameters, resulting in important strides towards efficiency improvement. This research presents tools and methodologies for model development and controller design for air conditioning and refrigeration systems. In this thesis, control-oriented nonlinear dynamic models are developed and validated with test data collected from a fully instrumented experimental system. These models enable the design of advanced control configurations which supplement the performance of the commonly used proportional-integral-derivative (PID) controller. Evaporator superheat is a key parameter considered in this research since precise control optimizes evaporator efficiency while protecting the system from component damage. The controllers developed in this thesis ultimately provide better transient and steady state performance which increases system efficiency through low superheat set point design. The developed controllers also address the classical performance versus robustness tradeoff through design which preserves transients while prolonging the lifetime of the electronic expansion valve. Another notable contribution of this thesis is the development of hardware-in-the-loop load emulation which provides a method to test component and software control loop performance. This method alleviates the costs associated with the current method of testing using environmental test chambers.