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Energy management systems save money



 

Energy management systems (EMSs) reduce energy bills by taking the various tariff times into account and optimising the energy consumption of a plant or building. LBA’s Stellar EMS monitors the energy consumption continuously and regulate outputs according to easily definable rules.

Certain hours of the day have large penalty tariffs for electrical consumption, while other times, lower tariffs are charged. The EMS controls electricity usage based on selected priorities. If the system requires certain processes to run during peak times, this system will allow those processes to operate. Those processes which are not as critical but can run during peak times, will only operate as long as the energy set-point for that particular time period is not exceeded. During standard times, additional processes will be allowed to operate. In the off peak times, the unit’s control software will allow all processes to run.

Fig. 1: Time of day used to determine the various Eskom tariffs charged.

Correct application of energy control software ensures savings

The average user can expect to save in the region of 10 to 20% of their monthly electricity bill. During the high peak months (June to August), savings can be as high as 20% of the total energy bill. Actual case studies have shown this to be the case in all sites where time of use control has been applied.

Fig. 2: Holiday schedule set-up.

To address some users’ concerns regarding how much money the EMS can save, the software licence is offered free of charge for an initial trial period. There is a fixed configuration cost to install the system on site, utilising the user’s existing hardware and software. If the user chooses not to purchase the licence, the software can be returned with no further cost to the user.

An energy meter is required to measure the power used and a programmable logic controller (PLC) is needed to control the operation of the various cold rooms. The EMS is designed to link into any local system via discrete I/O, OPC server or modifications to the client’s own control system.

Fig. 3: The Eskom chart showing the typical time of day tariff over a 24 hour period.

How does this work?

  • Energy control is based on time of day, day of the week (workday or weekend), day of the year (public holiday). If it is a holiday, the system needs to know whether the holiday is regarded as a Saturday or a Sunday in terms of energy control. Holiday schedule files are supplied to the user for download onto the energy management system.
  • An annual fee includes upgrades to the system when these become available.
  • Upgrade and inclusion of new features are added from time to time.
  • Updates to the time of usage tariffs, when they are made available by Eskom, are installed or downloaded at the user’s premises.
  • On-site and remote support of the system.
  • Training on the system for employees.

Fig. 4: Daily energy consumption.

Additional features

  • The system writes SQL commands to a database allowing the user to keep track of the energy consumed. The system makes use of Microsoft Access Runtime which is free of charge to the user. It will also run on a full package of Microsoft Access.
  • The data is used in predicting the expected bill based on historical energy consumption during a particular invoice period.
  • The system determines the expected and actual bills for any given time period. These can be compared to the actual bills received.
  • The system automatically assigns set-points based on historical time of year consumption in order to maximise annual savings. These can be manually changed by the user.
  • The system incorporates a unique “smart control” algorithm which controls priorities based on sets of rules. Smart control modifies the priorities of each sub-system based on these rules. In the case of a typical cold storage facility, these rules included the difference between set-point and actual value, product type in each cold room, protocol times (24 or 72 hour) for commercial or sanitised control settings. Tighter control is applied to the 72 hour protocol in the last 24 hour of use.
  • During the various time periods, certain priorities are allowed to start, but are controlled by the time of day energy set-points.
  • Systems which have been stopped will be inhibited for re-start as some processes require a run down and purge cycle to complete before a re-start is permitted.
  • No two processes are allowed to start simultaneously thereby minimising large inrush currents from multiple simultaneous starts. Shutdown of processes are also performed in an orderly and controlled manner.

Fig. 1 shows when the various tariffs are applied. These are different between the summer and winter months, as well as the day of week, and whether it is a holiday or not.

Fig. 5: Monitoring of the energy usage showing the actual and predictive consumption values.

Fig. 2 identifies each holiday in the year and also how that holiday is to be treated (i.e. will it use a typical Saturday or Sunday tariff structure). If a holiday occurs on a Sunday, the system will automatically assign the next Monday as an additional holiday using a Saturday tariff structure.

Fig. 4 shows the user how much energy is being used daily.

The priority control screen

The priority control screen, shown in Fig. 6, allows the user to set each process’s priority based on importance of operation.

Fig. 6: Set up of the various process priority values.

Priority 1 is selected if the process must run 24 hours a day, 7 days a week.

Priority 2 is selected if the energy consumption has not exceeded the set-point for the peak energy time period. In other words, if all priority 1s are running and the energy consumed in the peak time period is less than the set-point, the priority 2 processes will be allowed to start until such time as the set-point is achieved. All other priority 2 processes will not be allowed to start. However, once a priority 2 process has been running for a period of time, it will be stopped in order to allow other priority 2 processes to run.

Fig. 7: Power trend as a function of time.

During standard time periods, all priority 1, 2 and 3 processes will run. Priority 4 processes will behave in exactly the same way as priority 2 processes in peak times. Priority 4 processes will only run if the energy consumption has not exceeded the standard time set-point. Once again, if not all priority 4 processes are running once the standard time set-point is exceeded, the longest running priority 4 processes will stop to allow other priority 4 processes to run.

Priority 5 processes will only be allowed to operate in the off peak tariff times. During the peak and standard time periods all priority 5 processes will not be allowed to run.

Fig. 8: Reporting system set-up screen.

In Fig. 7, one can clearly see the drop in power usage during the peak and standard times and the subsequent increase in power consumption in the off peak times between 22h00 and 06h00. Peak times are from 06h00 to 09h00 and again from 17h00 to 19h00.

In order to produce meaningfull reports, the user will select the start date for the reporting cycle, see Fig. 8.

Fig. 9: Actual and forecasted bill from ESKOM based on actual and forecasted values.

A typical Eskom bill (Fig. 9), will be produced by the system identifying the actual bill to date as well as the predicted bill to be expected at the end of the monthly billing period. This forecasting tool is invaluable in determining what the forecasted budget would be for the month based on the actual consumption used during the month.

Contact Dave le Roux, LBA, Tel 011 514-0909, dave@lbaa.co.za

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