A thorough analysis to determine the results of this project is very challenging due to various factors influencing the amount of energy used. The goal is to compare two days with the same meal before and during the project. In some cases, energy consumption and power have been higher during the project, likely because the kitchen staff prepares dishes in advance, one or more days before serving. This also indicates that the staff has significant control over the power need in the kitchens as they can distribute the power load throughout the week.
In order to demonstrate results, various methods will be employed. Firstly, days with the same dishes will be compared. What we hope to observe is a decrease in the maximum power consumption for those meals during the project. Additionally, entire weeks will be studied, focusing on weeks where approximately the same meals were served. A favorable outcome for the weekly graphs would be the emergence of a trend towards a more consistent power usage throughout the week during the project.
Individual days
Potato croquettes
Before the project
After the project
Figure 1: Potato croquettes, Östra Stenhagen school
In the left graph, we can observe a problem that the project aims to solve. Between 8-9 AM in the morning the energy consumption is over 50% higher than during the rest of the day. This time period puts a significant demand on the power grid and will result in a higher electricity bill at the end of the month. On the right, we can see a more even consumption pattern, with no extreme spikes at any particular time. It is interesting to note that the difference in total energy consumption throughout the day is only 3%, which means that the peak we see in the red graph hasn't disappeared but has been spread out over a larger part of the day.
Stew with rice
Before the project
After the project
Figure 2: Tiunda school, stew with rice.
Note that the highest power peak has decreased from 120 kWh to 100 kWh. Once again, the energy consumption hasn't increased but remains at the same level; the peak has been distributed throughout the day. What's the difference? On this day, the stoves were used for the pot, which cannot be influenced significantly. However, the rice cooked in the oven can be prepared using a function that operates the oven at a lower power level. This function makes the oven take longer to cook the food but at a lower power level (same energy usage but distributed over a longer period). This is likely the main reason why we see three lower bars between 8-11 AM instead of the two bars between 8-10 AM as before the project.
Another positive trend is that when cooking starts earlier in the day, it relieves the peak hours that follows shortly after.
Weeks
Week 3 compared with week 35
Before the project
After the project
Figure 3: Energy data from Tiunda school. The difference between week 3 and week 35, 2022. Cooking the same dish.
Note that before the project, the worst power peak occurs on mondays when lentil and chicken stew with rice is prepared. However, during the project, the peaks on challenging mondays have significantly decreased, and it is no longer the worst day. This could be attributed to the kitchen staff having kitchen screens that indicate the power usage on a green, yellow, and red scale. Therefore, they make an effort to limit consumption and strive to stay in the green zone, which leads to better utilization of power-intensive equipment, such as dishwashers or peripheral devices, when the screen is green when cooking non-power-intensive dishes. This is not a problem since the kitchen stays within the "power budget" defined by these kitchen screens.
Sicotronic
This is a smart system that distributes power in a way that prevents power peaks from occurring. It allocates power to different machines in sequences without any control from the staff.
Before Sicotronic
After Sicotronic
On the days displayed below, hamburgers and potato wedges were prepared. The difference between these two days is that in the left graph (before Sicotronic), there is a peak during the most intense part of the day. Sicotronic, on the other hand, takes this peak and spreads it over a longer period, effectively "eliminating" it.
The graph also shows the importance of a balance between behavioral changes and Sicotronic. In the right graph, cooking has started earlier, allowing the peak to be spread over a longer period. Sicotronic can assist in distributing the power over time in the future, but it cannot change the past. Starting cooking earlier and having more time to prepare food at a slightly lower power level is something that the kitchen staff themselves must do. The interaction between technology and humans thus provides us with an opportunity to make a significant difference.
The kitchen's share of the entire school's energy consumption
This image displays the proportion of Tiunda School's total power usage attributed to the kitchen. The powerpeaks that the entire school must handle often originate from the kitchen, as the rest of the school tends to have a more consistent power load throughout the day. Therefore, the power-demanding peaks from the kitchen will be evident in the overall school consumption. This is a clear indication that the kitchens offer the greatest opportunity for change to make a significant difference for the entire school.
For further questions or if you want to learn more:
Information about the project, contact Fredrik Björklund: fredrik.bjorklund@stuns.se.
Questions to Måltidsservice, contact Sandra Harbom: sandra.harbom@uppsala.se.
The project is runned by STUNS Energi in cooperation with Skolfastigheter, Måltidsservice in Uppsala municipality and CIT Energy Management. The project is funded by the Swedish Energy Agency.
