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.
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.
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.
How does this work?
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. 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.
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.
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.
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.
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, firstname.lastname@example.org
Source: EE plublishers