Improvement in Energy Self-Sufficiency in Residential Buildings Using Photovoltaic Thermal Plants, Heat Pumps, and Electrical and Thermal Storage

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

1] A typo has been observed at the very end of (Table 2) - Kexcange

2] The current study primarily evaluates the PVT-HP-TES-EES system in a Mdeiterrenean climate, which has specific weather conditions that favour solar PV generation.Would a broader geographical comparison enhance the generalizability of the findings? (include in Discussion section if want to elaborate, or Conclusions/Limitation section if prefer to address this in a more concise manner)

3] "The configuration PVT-HP-TES-EES has achieved better performance reducing the 432 electricity demand by about 25% compared to the other energy system configurations. 433 Also, it attains impressive results for RSC and DSS of 96.2 and 86.9% respectively." In terms of return of investment  - could the economic analysis be expanded to consider return on investment on such combination? (Results section?)

Author Response

First of all we wanted to thank you for your valuable observations and comments. We have revised the article following all your suggestions.

Below are the answers followed by the changes made to the text

1] A typo has been observed at the very end of (Table 2) – Kexcange

Thank you for reporting, it is fixed now.

2] The current study primarily evaluates the PVT-HP-TES-EES system in a Mdeiterrenean climate, which has specific weather conditions that favour solar PV generation.Would a broader geographical comparison enhance the generalizability of the findings? (include in Discussion section if want to elaborate, or Conclusions/Limitation section if prefer to address this in a more concise manner)

Thanks for the observation, we agree that repeating the study for other climates could strengthen the conclusions found. However, in order not to weigh down the paper too much, we have added this limitation in the conclusions that will undoubtedly be investigated in future analyses.

“it is imperative to investigate the performance of the proposed system considering different climate conditions, in particular within cold regions, to confirm the effectiveness of these energy systems in attaining energy self-sufficiency of residential buildings.”

3] "The configuration PVT-HP-TES-EES has achieved better performance reducing the electricity demand by about 25% compared to the other energy system configurations. Also, it attains impressive results for RSC and DSS of 96.2 and 86.9% respectively." In terms of return of investment  - could the economic analysis be expanded to consider return on investment on such combination? (Results section?)

Thanks for the suggestion, we have added the economic treatment, in particular:

in the chapter 2 (materials and method) a paragraph on the economic analyses has been added:

“2.3. Economic analysis

In addition to the comparison of KPIs, it is important to perform an economic comparison based on the possible economic return of the two proposed configurations compared to the baseline. The analysis is based on the comparison between the monetary savings achieved during the life cycle and the increase in costs necessary to realize the proposed plants compared to the baseline configuration, through the estimation of the net present value (NPV).

(11)

where I₀ indicates the investment to be supported, Ry the annual monetary savings, Rn the residual value, which will be considered equal to 0 €, i the discount rate set at 3%, and n is the life cycle assumed to be 20 years.

The investment I₀ to be sustained to modify the "baseline" configuration in the proposed configuration is assumed  to be 1,000 €/kWh for the storage and 400 €/kWp for the PVT plant.

The Ry is calculated considering the difference of annual expenditure incurred for electricity (Cel) between the baseline configuration and the proposed configuration using equation (12).

(12)

with the annual expenditure incurred are the result of the difference between the cost of purchasing energy from the grid and the revenue obtained by selling electricity to the grid

(13)

Pr_purchase is set at 0.39 €/kWh, the result of the average of the tariffs detected in the last year by the Italian regulatory authority for energy, networks and the environment (ARERA), considering both the free and protected market conditions [41], while the Pr_selleing of energy from photovoltaic systems, is set at 0.0464 €/kWh [42].”

in the results the following statements have been added:

“Another important factor concerns the economic sustainability of the investment. In fact, the PV-HP-EES-TES configuration allows a Ry of 1,119 €/y compared to the baseline configuration, while the PVT-HP-TES-EES configuration allows a monetary saving of 1,449 €/y, thanks to the reduced amount of energy drawn from the grid.

As regards the NPV on the entire useful life of the system (20 years) this is €5,895 and €6,127, respectively for the PV-HP-TES-EES and PVT-HP-TES-EES, underlining once again the convenience of the proposed system, which depends above all on the high quantity of energy produced and self-consumed.”

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have developed a Trnsys model to analyze the performance of PV heat pump system with and without energy storage (heat and electricity).

The title does not reflect on the core idea behind the presented research in the manuscript.

The abstract provides the major results but could provide more information about the idea of the research, its goals and applied methods and tools.

The literature review consists of enough references; however, similar to the title and the abstract, the goals of the research are not well defined. The analysis of the state of the art based on the literature review could benefit from including more exact data, instead of just general statements.

The title of 2.1. should be changed; it seems this is a technical mistake.

The authors have applied TRNSYS software to perform modeling and simulations of different configurations of the system, with and without thermal and electrical energy storage, and with PV and PVT systems. The energy system model is coupled to a Type 56 multizone building model, with radiated floor heating. Domestic hot water was also analyzed, heated by an electric heater. The thermal storages accounted for thermal stratification using a library model from Trnsys.

The authors have provided a set of KPIs. The authors should relate the equations for the KPIs to the documentation covering the mathematical models for the TRNSYS library.

In chapter 3, the Case Study, the authors provide some data about the building model. They could consider including a layout of the building or TRNSYS3D model.

The authors should define the abbreviation SHG from Table 1.

The term "Set point temperature" should be better defined so that a reader without prior knowledge could understand what the authors are talking about.

The primary energy needs (or demands) were depicted in Figure 2, using daily values. The authors should provide more information about the model for predicting electricity loads since electrical appliances were also considered. The DHW loads were chosen based on the EN 15316:2007. Furthermore, the weather data used should also be provided.

The results are well presented, including diagrams with daily values and specific daytime diagrams.

The conclusions are based on the data. The authors could try to define the additional pathways that would enable net-zero energy building performance.

 

Author Response

First of all we wanted to thank you for your valuable observations and comments. We have revised the article following all your suggestions.

Below are the answers followed by the changes made to the text.

The authors have developed a Trnsys model to analyze the performance of PV heat pump system with and without energy storage (heat and electricity).

The title does not reflect on the core idea behind the presented research in the manuscript.

Thank you for the observation, we have modified the title by inserting keywords that reflect the study discussed:

“Improvement of energy self-sufficiency in residential buildings using photovoltaic thermal plants, heat pumps, electrical and thermal storage”

The abstract provides the major results but could provide more information about the idea of the research, its goals and applied methods and tools.

Thanks for this comment, we have added more details in the abstract,

“This work proposes a comparison between different energy systems equipped with a Heat Pump (HP), solar plant, (Photovoltaic or Photovoltaic Thermal), and thermal (TES) and electrical (EES) storages. All year-round performances of the different energy system configurations have been simulated using the TRNSYS software.”

The literature review consists of enough references; however, similar to the title and the abstract, the goals of the research are not well defined. The analysis of the state of the art based on the literature review could benefit from including more exact data, instead of just general statements.

The introduction has been revised, adding more detail to the general statements and better emphasizing the objectives.

The title of 2.1. should be changed; it seems this is a technical mistake.

Thank you for reporting, it is fixed now.

“2.1 Energy system’s configuration”

The authors have applied TRNSYS software to perform modeling and simulations of different configurations of the system, with and without thermal and electrical energy storage, and with PV and PVT systems. The energy system model is coupled to a Type 56 multizone building model, with radiated floor heating. Domestic hot water was also analyzed, heated by an electric heater. The thermal storages accounted for thermal stratification using a library model from Trnsys.

The authors have provided a set of KPIs. The authors should relate the equations for the KPIs to the documentation covering the mathematical models for the TRNSYS library.

The different KPIs defined in paragraph 2.2 were analyzed in post-processing. With the TRNSYS software the different quantities that appear in the formulas were simulated and stored (e.g. E_{el. to grid}, E_{el, PV}, etc.), subsequently in post-processing the defined KPIs were calculated. The following statement has been added to the text:

“All KPIs have been calculated in a post-elaboration phase using the results obtained from the TRNSYS simulations.”

In chapter 3, the Case Study, the authors provide some data about the building model. They could consider including a layout of the building or TRNSYS3D model.

The introduction of the building model in TRNSYS was done through "Building wizard", so it is not possible to view the building in 3D.

The authors should define the abbreviation SHG from Table 1.

Thank you for reporting, it is fixed now.

“Solar Heat Gain Coefficient (SHGC)”

The term "Set point temperature" should be better defined so that a reader without prior knowledge could understand what the authors are talking about.

Thanks for the advice, we have added the following clarification to the text:

“based on a set point temperature (i.e. a reference point for controlling the heating/cooling system in the building)”

The primary energy needs (or demands) were depicted in Figure 2, using daily values. The authors should provide more information about the model for predicting electricity loads since electrical appliances were also considered. The DHW loads were chosen based on the EN 15316:2007. Furthermore, the weather data used should also be provided.

The meteorological data used are related to the city of Catania and have been implemented through the Meteonorm application. The following information has been added to the text:

“has been investigated through dynamic simulations considering the weather data of Catania [https://meteonorm.com/en/], which is characterized by 833 degree days and 1632 kWh/m² of annual horizontal solar radiation.”

The electrical loads are defined considering the various devices present in the buildings, as well as the lighting calculated directly in the TRNSYS model. The electrical load related to household appliances is defined starting from a previous study (A. Gagliano, F. Nocera, G.M. Tina. Performances and economic analysis of small photovoltaic–electricity energy storage system for residential applications Energy Environ., 31 (2018), pp. 155-175), therefore the following clarification has been added in the text:

The daily electricity demand refers to common household appliances and the electric consumption due to the air conditioning

The results are well presented, including diagrams with daily values and specific daytime diagrams.

Thank you for the comment

The conclusions are based on the data. The authors could try to define the additional pathways that would enable net-zero energy building performance.

Thank you for the advice, in this regard we added the following sentence in the conclusions:

“The results of this study have evidenced the central contribution of the investigated multi-generation energy systems to achieve the objective of decarbonized net-zero energy buildings as almost the entire energy demand is not only auto-produced but also self-consumed. It is worth underlining as a good thermal insulation of the building envelope and the exploitation of passive heating and cooling strategies are fundamental for reducing as much as possible the building energy demand. Another interesting characteristic of the proposed energy system is its simplicity, indeed all the components, (i.e. heat pump, PVT solar collectors, electrical and thermal storage) are not prototypes but apparatuses available in the market, and they could be also easily installed in both new and existing buildings.”

Reviewer 3 Report

Comments and Suggestions for Authors

The document "Assessment of the performance of renewable air conditioning systems for achieving decarbonized net-zero energy building", is well written and has a relevant contribution to the understanding of the thermal performance of various air conditioning systems for existing and new buildings. I have some suggestions that the authors should consider before publication:

1. Abstract: Avoid unnecessary capitalization in words like photovoltaic plant and heat pump. Please revise the manuscript for such incidences as well.

2. Please state the limitations of the study in detail.

3. Describe how the thermal loads for heating and cooling within type 56 are calculated. Are they left as default with a generic ON/OFF procedure, or is a specific equipment modeled?

4. Briefly explain how the 1221 type works and the associated equations with this calculation.

5. It is recommended that the authors deepen on the conclusions section in order to understand why the proposed systems worked and how it is envisioned that such systems could be incorporated into real-life thermal facilities.

6. Revise missing details on some references, for example: [1], [4], [6]

 

Author Response

First of all we wanted to thank you for your valuable observations and comments. We have revised the article following all your suggestions.

Below are the answers followed by the changes made to the text.

The document "Assessment of the performance of renewable air conditioning systems for achieving decarbonized net-zero energy building", is well written and has a relevant contribution to the understanding of the thermal performance of various air conditioning systems for existing and new buildings. I have some suggestions that the authors should consider before publication:

1. Abstract: Avoid unnecessary capitalization in words like photovoltaic plant and heat pump. Please revise the manuscript for such incidences as well.

Thank you for the valuable advice. Capitalization has been removed, except in words where it is defined immediately after the acronym composed of the initials, e.g. Heat Pump (HP).

2. Please state the limitations of the study in detail.

we have added this limitation in the conclusions that will undoubtedly be investigated in future analyses.

“it is imperative to investigate the performance of the proposed system considering different climate conditions, in particular within cold regions, to confirm the effectiveness of these energy systems in attaining energy self-sufficiency of residential buildings.”

3. Describe how the thermal loads for heating and cooling within type 56 are calculated. Are they left as default with a generic ON/OFF procedure, or is a specific equipment modeled?

Thanks for the observation. The thermal loads are modeled directly using type 56, which allows the building to be simulated in a dynamic regime. As for the supply of thermal energy to the environment, this is modeled considering the circulation of fluid heated/cooled by the heat pump, with a fixed flow rate and temperature dependent on that available in the TES, simulating a radiant floor, with a thermal energy absorption equal to the instantaneous requirement of the building. The following clarification has been added to the text:

“The simulated HVAC system consists of a radiant floor system powered by an air-cooled heat pump…

…The thermal loads for heating and cooling the building have been calculated by type 56, which allows the description of a building with multiple thermal zones having a homogenous temperature (e.g. rooms). This type uses thermos-physical data from walls and windows. Heat Gains from solar direct and diffuse radiation are calculated for each room depending on the window and thermal radiative properties.”

4. Briefly explain how the 1221 type works and the associated equations with this calculation.

Thank you for the comment. The following sentence has been added to the text:

“The HP generator was modelled using the type 1221, which consists of a two-stage HP, capable of tracking thermal performance in terms of coefficient of performance, thermal power supplied and electrical power consumed as a function of operating temperatures, through interpolation of the provided parameters.Furthermore, an enhancement of type 1221 has been implemented in such a way as to model a four-stage heat pump; for each stage of the HP’s thermal power, so that it is possible to associate the correspondent electrical power.”

5. It is recommended that the authors deepen on the conclusions section in order to understand why the proposed systems worked and how it is envisioned that such systems could be incorporated into real-life thermal facilities.

Thanks for the observation. The following sentences have been included in the conclusions.

“The results of this study have evidenced the central contribution of the investigated multi-generation energy systems to achieve the objective of decarbonized net-zero energy buildings as almost the entire energy demand is not only auto-produced but also self-consumed. It is worth underlining as a good thermal insulation of the building enve-lope and the exploitation of passive heating and cooling strategies are fundamental for reducing as much as possible the building energy demand. Another interesting character-istic of the proposed energy system is its simplicity, indeed all the components, (i.e. heat pump, PVT solar collectors, electrical and thermal storage) are not prototypes but apparatuses available in the market, and they could be also easily installed in both new and existing buildings.

However, it is imperative to investigate the performance of the proposed system considering different climate conditions, within cold regions, to confirm the effectiveness of these energy systems in attaining energy self-sufficiency of residential buildings.”

6. Revise missing details on some references, for example: [1], [4], [6]

Thanks for letting us know, the missing details have been added

“[1] Masson-Delmotte, V.; Zhai, P.; Pörtner, H.O.; et. al. Summary for Policymakers. In Global Warming of 1.5°C. An IPCC Special Report on Impacts of Global Warming of 1.5°C above Pre-industrial Levels in Context of Strengthening Response to Climate Change, Sustainable Development, and Efforts to Eradicate Poverty, Cambridge University Press 2024, 3–24, https://doi.org/10.1017/9781009157940.001

[4] European Commission – Department: Energy; In Focus: Energy Efficiency in Buildings. European Commission 2020, https://commission.europa.eu/news/focus-energy-efficiency-buildings-2020-02-17_en

[5] Rousselot, M.; Da Rocha, F.P.; Lapillone, B.; Energy efficiency trends in buildings in the EU. ODYSSE-MURE 2021. https://www.odyssee-mure.eu/publications/policy-brief/buildings-energy-efficiency-trends.pdf

[6] International Energy Agency; Clean Energy Market Monitor: Heat Pumps. IEA Publications 2024. https://www.iea.org/reports/clean-energy-market-monitor-march-2024“

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have made the necessary adjustments to the manuscript. 

Author Response

We would like to thank you for your comments and observations.