Projects / Programmes
Optimisation of energy cost for refrigeration systems in shopping malls
| Code |
Science |
Field |
Subfield |
| 2.06.01 |
Engineering sciences and technologies |
Systems and cybernetics |
Control systems technology |
| Code |
Science |
Field |
| T125 |
Technological sciences |
Automation, robotics, control engineering |
| Code |
Science |
Field |
| 2.02 |
Engineering and Technology |
Electrical engineering, Electronic engineering, Information engineering |
refrigeration systems, shopping centres, energy consumption, energy cost, energy cost reduction, energy cost optimisation, adaptive control system, real-time energy management systems
Researchers (9)
Organisations (2)
Abstract
With increased awareness of the limited energy sources and while coping with consequently constantly growing prices, great attention is being paid to electricity saving. For retail companies, energy is one of the most important parts of the costs; therefore energy efficiency is an important strategic goal. As much as 3% of the total electricity supplied in Sweden is used by large shopping malls, similar results apply to Slovenia. The reason why shopping malls consume more electricity than residential buildings is mainly the use of large refrigeration systems which are huge electricity consumers. The average energy part consumed by refrigeration systems in as high as 38.5 %.
In the scope of the proposed project we intend to perform an analysis for design of automatic control and management of refrigeration systems in shopping malls with the objective of optimizing the expense for electrical energy.
The goal is to design the key elements of the control/management system for shopping mall refrigerating systems. Furthermore, the designed system will enable control of load on the refrigerator generator, depending on the temperature in refrigerating cycle. The proposed control system will not be installed locally; all refrigerating systems will be controlled from a remote operating center. The purpose of the proposed control system is optimization in terms of cost and energy efficiency. To achieve this the following measures will be undertaken:
- Time scheduling of thawing processes for a cluster of refrigerating units
- Optimal control algorithms of each refrigerating unit
A refrigerating system normally runs on constant power, except during the process of thawing of ice from the expansion valve. In that case the generator is turned off until there is no ice on the valve. This process occurs 46 times per day and it lasts approximately an hour.The price of electricity can vary up to 30 % in a day. It would therefore be beneficial to start the thawing process in the time of day, when electricity is expensive. The proposed control system will schedule the thawing processes in above described fashion in order to cut the electricity expenses.
If the starting time of thawing process would be known in advance, the consumer could lease less electricity to cut the electricity expense. Preliminary calculations indicate up to 10 % in financial assets could be conserved. In case of multiple refrigerating units (connected to the control system via the operator) we could achieve overall lower level of energy consumption by thawing processes scheduling. If the thawing processes on different refrigerating units don’t over lapse, the maximum spike in power usage will naturally be smaller. That measure will additionally lower the energy cost in a cluster of shopping malls. Preliminary estimates indicate another 10 % energy expense savings.
To sum up, the goal is to develop an operator based concept of offsite shopping malls refrigerating systems management and control with the objective to optimally control the operation of such machinery, time schedule the thawing processes and reducing the spikes in joint usage.
To additionally optimize the energy consumption of a single refrigerating unit, advanced control algorithms based on simplified models and built in knowledge will be developed. The most critical part is controlling the start of generators right after the thawing process is over. A relatively fast response with a low overshoot (conditions the height of the spike in electricity consumption) is desired. If the start and duration time of the thawing processes is known in advance, an efficient control algorithm could be designed by using predictive control, which takes into account known setpoint demands and technical limitations. The proposed control problem is nontrivial and demands applications of the latest findings from the predictive control research field.
Significance for science
There are several important scientific results of the project in the field of optimization of energy consumption and cooling systems management. The most important result of the project is innovative method for power management in cooling systems while respecting food safety constraints (HACCP). The method is based on controlling the estimated (or measured) internal food temperature while limiting the air temperature in the cooling element. In this way, the power of the cooling equipment can be changed, while considering into account all the relevant temperature limits of the system. When comparing to the existing control methods, the developed method has higher flexibility of the control signals, and thus is faster and more efficient when following the reference power profile. The second result of the project is the new system for reducing current spikes in shopping malls. It is based on the above-mentioned innovative method of managing cooling system power with modifications that allow occasional power control of the cooling elements. We developed the modified control system, which enables quick reduce of current spikes of the entire shopping centre on the basis of changing cooling system power consumption. The third important result of the project, which was crucial for the implementation of the above-mentioned results, is anti-windup protection in cascade control system. Restrictions in the system, wherever they occur, can have negative impact in all control system levels. Applying the anti-windup protection scheme, which continuously extends and sends limited signals from the lowest control level (valve) up to the highest control level (power controller), allows stable operation of the system in all conditions. The fourth result of the project is physical model of the cooling system (including models of food), which has been identified and verified on the real data acquired from the cooling systems. The developed model enables validation and optimization of different control approaches. The fifth result of the project is a prototype cloud platform, which controls refrigeration equipment according to the prescribed scenario (adaptation of power consumption or reducing current spikes). Such a solution enables simultaneous monitoring and management of multiple physically separate cooling systems.
Significance for the country
The importance of the project results for the development of Slovenia can be summarized by the following points: 1. Research and project results indicate commercial interest. The gained experiences, and the developed control approaches for cooling systems are the basis for searching a suitable business model. In this context, the applications for the SME Instrument (H2020) has been submitted, while protection of the intellectual right (patent) is being under preparation for the developed and validated refrigeration control system. 2. The developed solutions will reduce the current spikes, thereby allowing optimal daily power profile for the shopping centres. This will significantly reduce burden on the electrical system. Moreover, the power adaptation and forecasting will facilitate integration of larger share of alternative energy sources (solar, wind, bio-mass, etc.) into the electric grid without adverse effects on Slovenian energy system. 3. New knowledge gained in the project will increase the competitiveness and competence of the companies participated in the project, while enabling research organizations to continue research on the field of refrigeration. The companies as well as research organizations will also improve their competitiveness in the international level. Cloud computing platform for control of refrigeration power is also very suitable for rapid expansion into foreign markets.
Most important scientific results
Annual report
2013,
2014,
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2013,
2014,
2015,
final report
