Investigating Control Strategies in Supermarket Refrigeration Systems
Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
This project aims at investigating the control strategies of the supermarket refrigeration system by differentiating refrigeration system solution and taking field measurement from the web based control and monitoring system of IWmac. In addition, investigations of the control methods have been done on four supermarkets (ICA Maxi Stormarknad Haparanda, ICA Kvantum Hovås, Willys Piteå and ICA Supermarket Weda) in Sweden.
For the sake of investigating, it has been tried to look at each component of the control methods that is implemented within the supermarket refrigeration system. The components include compressors, evaporators, condensers/gas coolers and fans (both evaporator and condenser). Moreover, in this project, the refrigeration system solution is trans-critical CO2 system due the cold climatic conditions and used in Swedish supermarkets.
In compressors, the step control and variable speed control are used inside supermarket refrigeration system. In step control, compressors are start/stop based on the variation of the differential temperature or pressure or on both parameters. However, in variable speed controller, it varies the speed of the compressors by connecting frequency converter on one, two or more compressors. In this case, speed of compressors can be varied based on the suction pressure variation from the set reference suction pressure in order to fulfil the cooling demand of the supermarket refrigeration system. In such controllers, the control zones determine the time response of the controllers whether to increase or decrease the requested capacity.
In evaporators, it has been studied how the injection liquid supply and defrost control controlled the system. For injection liquid supply, due to the fluctuation of the superheat temperature with the reference superheat temperature, the electronic expansion valve starts to supply the refrigerant to the evaporator. This result tends the evaporation temperature to be constant throughout the refrigeration process. Such result also gets the system due to the application of different control means on evaporators such as evaporator fan, rail control and etc. In this project, it has been trying to look the response of fans and rail-heat controller at the time of the defrosting which will advantages to increase the efficiency of the system and reduces the consumption of energy.
In condensers/gas coolers, the main aim of controller in this component is to optimize the gas cooler pressure. It has been trying to look at how the sub cooling, transition zone subcritical and trans-critical sections controls in the Supermarket refrigeration system. Furthermore, the capacity of the gas cooler can be controlled by changing the speed of the fan or step regulation. Here the time response also determines the required capacity of the condenser/gas cooler.
In general, the control of compressor, evaporator, condenser and fan is coordinated at the system in order to optimize the energy, increase the quality of the foods and reduce the failure of the system.
Place, publisher, year, edition, pages
2013. , 80 p.
Control, Compressor, Evaporator, Refrigeration System, Fans
IdentifiersURN: urn:nbn:se:kth:diva-144201OAI: oai:DiVA.org:kth-144201DiVA: diva2:712274
Subject / course
Master of Science - Sustainable Energy Engineering
2013-11-14, Ett Library, Brinellvägen 68, Stockholm, 10:30 (English)
Karampour, Mazyar, Phd Candidate (KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration)
Sawalha, Samer, Phd (Lecturer) (KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration)