Report on a Plus-Energy District with Low-Temperature DHC Network, Novel Agrothermal Heat Source, and Applied Demand Response
Round 1
Reviewer 1 Report
The manuscript deals with a district heating network based on shallow geothermal energy and decentral heat pumps. The key is the low temeprature of the network. PV sources and demand estimation is considered, together with AI techniques for forecasting. The methodology is well described, in depth, and the results are consistent, being well discused.
Only some details should be explained:
Lines 165 to 167. This data are necessary, but can be misleading due to the existence of decental heat pumps. It sounds as if water at 30ºC to 40ºC were taken from the network and it were returned 6 to 10 K below. These values are to do with the healing loop heated up with the condenser of teh heat pump. I suggest authors rewrite this paragraph. In Figure 5 I suggest to add a right-axis with a suitable scale for COP COP appears several times, but the system uses individual heat pumps. How the authors have assessed the heat pump? Are they giving an average value? Do they have real measurements of demand or are they using forecastings from the model? In equation 1, the term SIGMA_i*P_i is duplicated In equation 1 the investment is annualized, which is right. However, nothing is said about the annualization and accumulation of the variable costs. If the current year value is used, authors are assuming a zero scalation nominal rate. In such case, the accumulation factor is the inverse of the capital recovery factor and only the current year value has to be considered. Please, indicate this point. On the other hand, perhaps assuming a zero increase in the cost of electricity is not a good assumptions. If you assume that the discount rate (named "r" in the manuscript) is equal to the scalation factor, the accumulation factor results "n" and authors have only to multiply each variable cost by CRF*N, being CRF the Capital Recovery Factor (used for annualization). In the model of heat pump (lines 404 to 407) and in the control strattegy is suggested that on/off strategy is used. An inverter has been assessed? That is, a speed variator for the compressor, in order to adapt the condenser power of the heat pump to the demand. With an on/off strategy, an oversizing has to be done because no heating backup system is mentioned.Author Response
Point 1: Lines 165 to 167. This data are necessary, but can be misleading due to the existence of decental heat pumps. It sounds as if water at 30ºC to 40ºC were taken from the network and it were returned 6 to 10 K below. These values are to do with the healing loop heated up with the condenser of teh heat pump. I suggest authors rewrite this paragraph.
Response 1: This paragraph has been rewritten to address this point.
Point 2: In Figure 5 I suggest to add a right-axis with a suitable scale for COP COP appears several times, but the system uses individual heat pumps. How the authors have assessed the heat pump? Are they giving an average value? Do they have real measurements of demand or are they using forecastings from the model?
Response 2: A right-axis with a scale for COP has been added to Figure 5. The COP is determined by the monthly average value from of six heat pumps. For those six heat pumps detailed monitoring data exists on the electrical and thermal side (5 s measurement interval for the electrical side and 30 s for the thermal side).
Point 3: In equation 1, the term SIGMA_i*P_i is duplicated In equation 1 the investment is annualized, which is right.
However, nothing is said about the annualization and accumulation of the variable costs. If the current year value is used, authors are assuming a zero scalation nominal rate. In such case, the accumulation factor is the inverse of the capital recovery factor and only the current year value has to be considered. Please, indicate this point.
On the other hand, perhaps assuming a zero increase in the cost of electricity is not a good assumptions. If you assume that the discount rate (named "r" in the manuscript) is equal to the scalation factor, the accumulation factor results "n" and authors have only to multiply each variable cost by CRF*N, being CRF the Capital Recovery Factor (used for annualization).
Response 3: The increase in energy prices and in operation and maintenance costs was already included in the original economical assessment by the “mean value factor of increase in energy prices” and the “mean value of increase of maintenance and upkeep cost” also shown in appendix B1 and B2. Further equations and text now have been added to describe this properly.
Point 4: In the model of heat pump (lines 404 to 407) and in the control strattegy is suggested that on/off strategy is used. An inverter has been assessed? That is, a speed variator for the compressor, in order to adapt the condenser power of the heat pump to the demand. With an on/off strategy, an oversizing has to be done because no heating backup system is mentioned.
Response 4: So far, no inverter has been assessed. The real heat pump also follows an on/off strategy but has an additional electric flow heater if the DHW demand can’t be solely covered by the heat pump. The monitoring so far has shown that the use of this electric flow heater was neglectable in real operations and thus it was not included in the model. It might be interesting to address both, part load operation of the heat pump and the electric flow heater for quick DR activations in future investigations.
Reviewer 2 Report
Lines 13-15: Change syntax of the sentence, to: "Unfortunately, low demand densities render conventional heating and cooling networks inefficient as they occur increasingly through higher building energy standards as well as in rural areas."
Lines 15-18: "At the same time, Power-to-Heat is becoming more and more important to include a larger amount of renewable energy sources on the electrical side by providing more needed flexibility by means of Demand Response and Demand Side Management.". Should rephrase the phrases marked in bold.
Line 19: "...these topics with..."
Lines 26-27: Change sentence to: "On a building level, up to 50 % of cost savings could be achieved under ideal conditions with the optimization of self- consumption of PV electricity.
Line 36: I don't believe that "However" is the proper word to connect the 2 sentences.
Line 41: use different word from "mostly".
Line 43: "...making them less or inapplicable...". "Less" than what? Please correct.
Line 44: Comma (,) not needed.
Line 45: "...which results..." change tense, in order to be consistent. E.g., change it to "...resulting...".
Lines 51-52: "...can feed..." Can feed what? Perhaps rephrase/ change syntax.
Lines 53-55: Please add reference.
Line 59: "in a smaller scale..."
Paragraph, lines 56-67: Please restructure this paragraph, the information provided in it seem a little bit "disconnected", the way the sentences are written and presented.
Table 1: In what order are the projects presented? Alphabetical, time, reference number?
Lines 72-73: "...that as in 2018...". You mean "in 2018", "since 2018"?
Lines 83-85: Please rephrase to: "Advanced prediction, optimization and control algorithms are needed to implement DR and DSM in HVAC (Heating, Ventilation and Air-conditioning) and in specific within heat pump systems and to increase the system efficiency."
Line 94: replace "were" with "where".
Line 118: "...in the final Report of the specific project".
Line 120: "...in 11 out of 23 buildings."
Line 136: You mention that calculated costs were 240.000. Below (line 145), you mention that real projects cost were increased, however you mention again a value of 240.000. What am I missing? Please be more specific in your description, in case the 2 costs don't refer to the exact same thing.
Lines 157-159: Rephrase to "KfW-55 requires the buildings annual demand of primary energy to be equal or less than 55 % of the demand of a new building with the same geometry, according to German energy saving regulation.".
Line 201: "Because there are no thermal losses, no insulation..."
Line 216: I believe that "Despite" is not the appropriate word here.
Line 228: "...estimated at..."
Line 230-232: Correct syntax of the sentence.
Line 242: distant from = far from
Line 243: "The distance... is equidistant.." please rephrase. Perhaps "the distance is equal.." or something like that.
Line 303: Comma (,) not needed.
Line 304: "...0.29 € and the feed in tariff is approx. 0.11 €...". Above you use (.) as a thousand's separator; here you use it as a decimal point. Please correct it here and be consistent throughout the document.
Line 468: You mean "As the..."?
Line 653: Rephrase to "...whole system (e.g. also PV) is equal or better in comparison with other common heating solutions."
Line 695: "...too less.." please rephrase.
Line 698: "...due to the fact, that...". Comma (,) not needed. The same comment applies also in other cases in the document where the phrase "...the fact that..." is used.
Discussion section: Should be improved. Looks more like a summary of the methodology and results section. Should also present the limitations of the study, if any.
General comment: Improvement of English (grammar, syntax, wording), beyond the comments provided above.
Author Response
Point 1: Grammar and syntax corrections.
Response 1: The suggested corrections have been added.
Point 2: Lines 53-55: Please add reference.
Response 2: The reference has been added.
Point 3: Line 136: You mention that calculated costs were 240.000. Below (line 145), you mention that real projects cost were increased, however you mention again a value of 240.000. What am I missing? Please be more specific in your description, in case the 2 costs don't refer to the exact same thing.
Response 3: The preliminary estimated cost for the geothermal field was 240,000 € for an area of 15,000 m2. However, the real costs proved to be much higher, due to machine transporting, additional cost for larger installation chambers for monitoring and other problems related to the fact that the installation was a first prototype of its kind. Hence, 240,000 € were spent for the implementation of the first part of the geothermal field only (4,400 m2). Unfortunately, these numbers coincidentally coincide. Additional text was written to prevent future misunderstandings.
Point 4: Discussion section: Should be improved. Looks more like a summary of the methodology and results section. Should also present the limitations of the study, if any.
Response 4: Additional content was added to address this point.
Reviewer 3 Report
The manuscript reported a systematic investigation on a low temperature district heating and cooling network connected to a novel agrothermal collector supplying residential buildings with decentral heat pumps and PV systems. After the optimization, up to 50% of cost savings can be achieved. The study is technically sound and can be useful for building energy savings. The manuscript is properly organized and could be accepted in the present status.
Author Response
No specific points were adressed.
