model-based control and renewable energy

model-based control of renewable energy systems in buildings

Professor Dexter assigned me an essay to read the day I arrived, I used 6 days to finish it. first of all, I will summarize the main idea of the essay; then, I will state some of my crazy ideas about it; finally, I will conclude my reading.

What the essay discussed about is the model-based control in a building, but the new trend of the use of renewable energy is also concerned in the essay.

In the first part of the essay, the author discussed about the framework of the HVAC system. The HVAC system is devided into 2 parts----water system and air system. Though it seems to be a traditional way, but what makes it different is the use of SA/VPV. the VPV has four operational modes: preheating, storage(closed circulation), venting(open circuit), and bypass(turned off). This system provides heat and cold to 3 zones.I have some problem at the simulation diagram at first, but after consulting some problems with Zhen, and carefully read them with the equations, I think I can understood most of them, but I don't think I can design it with simulink. After then, the author analized the parameters used in the simulation and explain the contrained evolutionary strategy----repeated runs of evolutionary strategy will reduce the errors.

Then, the arthor presented the building and system model. The system is consist with 4 modules: I/O modules, water system modules, air system module and BEMS control module. information and mass are transfered among those module. These modules are not static models only, they are mixture of dynamic and steady-state component models.
Since the arthor have to compare their own strategy with the default BEMS system to show the advantage of their strategy, he explain both strategies.
BEMS system was based on a set of predefined rules and setpoints devised by setpoints. the difference between average space temperature and occupied set point will determine the suppy air temperature, if they need to use external energy, they will check the availability of VPV first, and then goes to the heat recovery, and if there still have difference, then the AHU will be activated. After the monitoring period, the design engineer remove the air quality control. The temperatures in the storage tank are important parameters, the high-level temperature determines the operation of boiler while the deployment of the evacuated tube collectors are determined by the low-level temperture.
The main approach taken by the Optimal Control Strategy is that using the unoccupied hours to devise a supervisory control trajectory for the next day, and during the runing hours, the control trajectory can be updated using a faster optimization algorithm. The objective of this strategy is to minimize the net external energy consumption within some contraints.

Finally, the author discussed the experimental results, from the charts we can find out that the optimal control can prove the indoor comfort in winter because the temperature is between 20'C to 22'C during 8 a.m. to 8 p.m while the BEMS system can only maintain the temperature within the range from 12 a.m. to 8 p.m. another different is about the water temperature. In BEMS systems, there is only one climax while there are two lacal maxmum temperature when Optimal Control is operated. On control sequence, the difference is that the operation in BEMS systems are mostly happened within occupied hours while the other is not. In the optimal control, components were enabled before the start of occupation. and this give me some idea about control schemes which i will discussed later.

The Optimal Control is proved to save a great amount of extenal energy.



After finished my reading, i am still interested in the idea of "plan first, adjust second". i think it is a bit different from prediction. it acts like human behavior, we make a plan in the night, then we try to finish it, when there is some unexpected things happened, we can adjust our plan but not design it immediately. I think maybe we can use matrix to deal with the problem. we can design matrix A,B,C.. for several typical situation, and everynight we can use the history data and the weather forecast to design another matrix a,b,c. we can calculate them and use the result as a plan. when the plan runs and we can gather the information of parameters and state from the I/O modules, and use them to develop a third matrix, but this one should have a limited range, so the calculation and simulation could be easier...

however, this idea hasn't been examined yet, because i think i need more knowledge about matrix before that. maybe i will lend a book from libaray and take the A4 course.

I think i should develop some reading skills because i find myself hard to get the most important ideas about the essay. recently, i find the only way for me to get a better understanding is to write a report about it. but maybe it will improve my writting as well.