An Innovative Control Framework for District Heating Systems: Conceptualisation and Preliminary Results
Round 1
Reviewer 1 Report
Dear authors
The manuscript presents an innovative control proposal for District Heating and Cooling (DHC) systems. The subject is highly relevant since in Europe this is an important heating source and its use should be increase according with the actual policies.
However, manuscript development is unclear and must be improved in order make understandable the performed study to the potential readers.
Even if the proposed control complexity is considered, the authors should provide more information about some of the main elements/factors that determinate the control behavior.
Some of these factors could be:
· The reviewer would appreciate more information about the use of weather parameters and how the energy load is calculated (developed in 2.3). Since these weather data and energy use are supposed to be critical in the development of the controller, additional information about these points could be useful for the reader
· The reviewer would also appreciate more information about the evaluation of the stored energy (tool ii, line 93). Since heat transfer depends on the storage and circuit temperatures, among other, this is not a trivial point.
· Point 2.2 - Control time step: The authors should provide the time step scale and horizon used in each control level.
· Point 2.4.
o Line 201: what “The decision problems are solved in near real-time” means? The computational time? Which are the time step and the horizon in this case?
o Line 204: “separating the discrete and continuous parts”. Are these “parts” the optimized variables of the system? This point could be clarified
o Line 204: “Instead of using the standard MPC quadratic criterion we design…” The reviewer thinks that this point is not clear. If the used cost function still maintains the usual quadratic form expanded to the mentioned criteria “total energy production costs, the operational…”, something like: “The cost function is designed based in some economic criteria that reflect…” should be written
If other special form of the cost function has been used it should be explained.
The weight values in the cost function could be discussed at this point.
o The reviewer does not understand the paragraph 231-239. This paragraph describes how an MPC (aka Receding Horizon Control) works. In order soften the inaccuracy of the predicted parameters, some methods are usually used. One of the most commons is the use of a state estimation filter, like the Kalman filter. This point should be discussed or deleted.
· Point 3. Simulation
o As simulation model is based in the DH plant located in Vransko (Slovenia), the plant itself should be referenced to provide the lector information about the system.
o The reviewer is confused about the characteristics of the simulated plant: Table 3 describes a 1Mw biomass boiler while Table 2 indicates an 1100kW Pmax. In the other hand, the information about the plant found in Internet describes a 1 biomass boiler (2MW), 1 biomass boiler (1.5MW) and 1 oil fuel standby boiler (1.5MW) and a 7.2 km heating grid. The authors must reference the plant the study is based on, and describe what part of the Vransko DHS has been used in the simulation. If any change has been done in order to obtain a more representative study, it should also be described (Gas boiler?)
o The simulation shows some results that should be discussed: Although B1 boiler max power is 1MW, the control system in the simulation limits the provided power to 600 kW. When more power is required, it is provided by the boiler B2, a more expensive heat source. The authors must discuss this point. Is it any restriction in the control limiting the provided power?
o The manuscript shows the results for a 2 weeks period. Has been the simulation expanded for a longer period? A small discussion about the results in other seasons, winter or spring, could enrich the manuscript if they are already done.
· Point 4. Discussion
o The authors define a “theoretical optimum reference case” as the one “assuming perfect future forecasts” (line 268). What forecast has been used in the simulations? In the other hand, the authors should discuss if a perfect future forecast is the only parameter that define a “theoretical optimum reference case” or that is the optimum for the used cost functions?
o Line 301: “The applicability of our proposed method was demonstrated in a real-life DH network located in Vransko, Slovenia”. The manuscript does not show any experimental result that supports this. If there are, a comparison between the results of the real plant and the ones obtained in the simulation should highly improve the manuscript.
· Although a multi-layer control is proposed for DHS, the manuscript vaguely describes it. The system simulation is only focused in the in the HiLe of the proposed control and the proposed study shows the benefits that the use of a TES system provides in that case. The reviewer suggests finding a new title for the manuscript in order to provide a better description.
· Table 2A. Reference 7 is from 2013. If available, newer data could be more representative.
There are other aspects of the manuscript that should also be improved or corrected:
· Figure 1 shows the architecture of the proposed control. The reviewer thinks that HiLe, and MiLe nomenclature should appear in that figure.
· Mixed-integer linear programming (MILP) (line 132) should appear in the abbreviation section
· Table 3 (page 7) is placed before Table 2, and it is not referenced!!
· Line 275: the reviewer thinks that the expression “Nh = 24/Δt = 24 (h)” is not correct. If 24 is the step number of the horizon, it should be “Nh = 24*Δt = 24 (h)”
· Cost in figure 7 should show units: €?
The reviewer suggests that the following reference could help improving the manuscript:
Vandermeulen, A. ; van der Heijde, B. ; Helsen, L. Controlling district heating and cooling networks to unlock flexibility: A review. Energy; 2018; Vol. 151; pp. 103 - 115
Comments for author File: 
Comments.pdf
Author Response
Author's responses to Reviewer 1 comments have been uploaded as a PDF file:
author-coverletter-3608483.v1.pdf
Author Response File: Author Response.pdf
Reviewer 2 Report
- The authors are kindly invited to improve the Introduction section, amplifying the text and add further scientific sources. In general, the manuscript does not report a high number of scientific sources. Entire text sections are free of fonts.
Minor issues:
- The use of abbreviations within the manuscript could be improved:
a.) Please abbreviate district heating as DH in line 33, 137, 246 etc.
b.) Please use the abbreviation DHC in line 37 etc.
c.) Please use the abbreviation H&C (heating and cooling) in line 69, 90 etc.
- Please write the terms short-term, long-term always in the same way (in contrast to short term, long term) - lines 24, 25 vs. 157
- Figure 1 entails abbreviations never found before - e.g. HEX, etc.
It's recommended to have a look to the H2020 Hotmaps project https://www.hotmaps-project.eu/
Information entailed in following deliverable might help improving the manuscript: https://www.hotmaps-project.eu/wp-content/uploads/2018/03/D2.3-Hotmaps_for-upload_revised-final_.pdf
Author Response
The Author's response to Reviewer 2 comments have been uploaded as a PDF file:
author-coverletter-3616947.v1.pdf
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The reviewer thanks the authors by their efforts improving the manuscript.
Although the manuscript is ready to be published, the reviewer would like to suggest the authors adding the solar radiation among the weather parameters that influence the power demand (lines 175 and 193). Since it is a main energy source in the system, it should be mentioned.
Comments for author File: Comments.pdf
Author Response
Reviewer 2:
Point 1: "Although the manuscript is ready to be published, the reviewer would like to suggest the authors mentioning the solar radiation among the weather parameters that influence the power demand (lines 175 and 193). Since it is a main energy source in the system, it should be cited."
Author Response 1: According to Reviewer suggestions, the solar radiation has been added to the weather parameters. See lines:175 and 193 (with red).
