- Email: [email protected]
Decentralized heat supply with seasonal heat storage systems: Comparison of different heating systems
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ScienceDirect ScienceDirect Energy Procedia 00 (2018) 000–000 Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2018) 000–000 320–328 EnergyProcedia Procedia155 00 (2017) www.elsevier.com/locate/procedia
12th International Renewable Energy Storage Conference, IRES 2018 12th International Renewable Energy Storage Conference, IRES 2018
Decentralized heat supply with seasonal heat storage systems: Decentralized heat supply different with seasonal heat storage systems: systems TheComparison 15th Internationalof Symposium on heating District Heating and Cooling Comparison of different heating systems a,b, Prof. Dr.-Ing. Rainer Schacha, of Anna-Elisabeth Wollstein-Lehmkuhl * Assessing the feasibility using the heat demand-outdoor a Prof. Dr.-Ing. Rainer Schach , Anna-Elisabeth Wollstein-Lehmkuhla,b,* Technische Universität Dresden, Institute of construction management, 01062 Dresden, Germany temperature function for a long-term district heat demand forecast Boysen-TU Dresden-Graduiertenkolleg, Strehlener Str. 22/24, 01069 Dresden, Germany Technische Universität Dresden, Institute of construction management, 01062 Dresden, Germany a
b
a
b
Boysen-TU Dresden-Graduiertenkolleg, Strehlener Str. 22/24, 01069 Dresden, Germany
a,b,c
I. Andrić
*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
a Abstract IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Abstract Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c To reach international climate goals, the research about energy consumption to focus more44300 on existing buildings. In the Département Systèmes Énergétiques et Environnement - IMT Atlantique, have 4 rue Alfred Kastler, Nantes, France building the increase of energy efficiency buildings willconsumption not be sufficient consumption fossil resources To reachsector, international climate goals, the researchofabout energy havetotoreduce focus the more on existingofbuildings. In the significantly. Therefore the application of renewable energies have to increase as well. Seasonal storage systems can support building sector, the increase of energy efficiency of buildings will not be sufficient to reduce theheat consumption of fossil resources this process because thethestorage enables heat supply and heat to be time-wise. Nevertheless, innovative significantly. Therefore application of renewable energies havedemand to increase as decoupled well. Seasonal heat storage systems can support Abstract systems, which are using energyheat for heating, in a competition with conventional systems,innovative which are this process because the renewable storage enables supply are andalways heat demand to be decoupled time-wise.heating Nevertheless, using gaswhich or oil.are They must be equally efficient in technical and economic aspects.with For conventional that reason, this studysystems, is focused on the systems, using renewable energy for heating, are always in a competition heating which are District networks commonly addressed insystems the and literature as one of theaFor most solutions decreasing the comparison supply with seasonal heat storage in connection with solar thermal and for system using gasheating orof oil.a heat They must are be equally efficient in technical economic aspects. thateffective reason,system this study isa heating focused on the greenhouse gas emissions building sector. These systems require investments which are returned through the with gas. For this comparison a the technical system and an operating model high was established. This system was aanalyzed by heat his comparison of a heat supplyfrom with seasonal heat storage systems in connection with a solar thermal and heating system sales.gas. Due tothis the comparison changed climate conditions and building renovation policies, heat demand in the future could decrease, economic parameters with complete finance plans. As result, it ismodel shown, sustainable heat supply is analyzed not much with For a technical system and ana operating wasthat established. This system was bymore his prolonging the investment return period. expensive than conventional heat supply. In addition, the social acceptance of different stakeholder is affected by these economic parameters with complete finance plans. As a result, it is shown, that sustainable heat supply is not much more The main scope of this paper is to assess theinvestors ofthe using the heat demand of – outdoor temperature function for heat parameters. Therefor expert interviews with were done. expensive than conventional heat supply. Infeasibility addition, social acceptance different stakeholder is affected bydemand these forecast. The districtexpert of Alvalade, in Lisbon (Portugal), was used as a case study. The district is consisted of 665 parameters. Therefor interviewslocated with investors were done. vary in both construction ©buildings 2018 Thethat Authors. Published by Elsevierperiod Ltd. and typology. Three weather scenarios (low, medium, high) and three district © 2018 The Authors. Published by Elsevier Ltd. renovation scenarios were developed (shallow, deep). To estimate the error, obtained heat demand values were This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) © 2018 The Authors. Published by Elsevier Ltd. intermediate, This is an open access article under the heat CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) compared with resultsarticle from aunder dynamic demand previously developed by theRenewable authors. Energy Storage Selection peer-review under responsibility of themodel, scientific committee of the and 12thvalidated International This is an and open access the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage The results showed that when only weather change isscientific considered, the margin of error could be acceptable for some applications Conference. Selection and peer-review under responsibility of the committee of the 12th International Renewable Energy Storage Conference. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation Conference. scenarios,seasonal the error increased up systems, to 59.5% (depending onmarketability, the weather economic and renovation scenarios combination considered). Keywords: heatvalue storage, heat supply renewable energy, efficiency, energy efficiency The valueseasonal of slope on average within themarketability, range of 3.8% up toefficiency, 8% per energy decade, that corresponds to the Keywords: heatcoefficient storage, heatincreased supply systems, renewable energy, economic efficiency decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +49-351-463-34242; fax:Committee +49-351-463-34680. Cooling. E-mail address: [email protected] * Corresponding author. Tel.: +49-351-463-34242; fax: +49-351-463-34680.
E-mail address: [email protected] Keywords:©Heat Forecast; Climatebychange 1876-6102 2018demand; The Authors. Published Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Selection under responsibility of the scientific of the 12th International Renewable Energy Storage Conference. This is an and openpeer-review access article under the CC BY-NC-ND licensecommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage Conference.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage Conference. 10.1016/j.egypro.2018.11.046
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1. Introduction More than 50% of the total energy consumption in Germany is about heat [1]. The climate protection goals of the German Government can only be reached by a further change of the energy transition into a heat transition. In order to reduce the consumption of fossil energy resources, it is not enough to improve only the energy efficiency of the buildings in the building sector. Therefore the application of renewable energy for the heat production has to increase. The existing building structures in Germany are one of the key factors in this consideration [2]. To supply those building structures with renewable energy is one of the future goals. With the background of a change in the German heat supply, seasonal heat storage systems can support the transforming process because the storage enables heat supply and heat demand to be decoupled time-wise. The advantage of hot water tank storages is, that they can be build independent from geological and hydrogeological soil conditions. Since the construction design of the storage is durable and the storage medium water is not harmful for the environment, the operation is save and the maintenance easy. For heat production a solar thermal system is used, which is theoretically available at all time. The research topic is focused on the marketability of this technical system in comparison with conventional heating systems. Conventional systems are established on the market and optimally designed to meet the needs of users in terms of cost minimisation and security of supply. An innovative system powered by renewable energy is therefore in direct competition for investors and users alike. Despite the volatility, renewable energies are suitable for this purpose. The marketability of a system depends on technical factors such as security of supply and economic parameters, like the heat production price. Furthermore, social acceptance is of crucial importance for a successful implementation of the system [3]. The individual influencing parameters are dependent on each other during the investigation, so that a holistic evaluation must be carried out. Therefore a building model, which is characteristic for urban areas, was designed. The heat supply is ensured by a solar heat system and a seasonal heat storage, build as a hot water tank. The focus of the study is to define in what manner technical, economic and social parameters influence the marketability of seasonal heat storages in comparison with conventional heating systems. 2. Methodology The first step in the research project was to define the framework of the investigation. A differentiation must be made between the building model and the operator model. 1.1 Building model As part of this research model, an existing inner-city building structure was energetically and economically studied. The style of the existing development is characteristic for urban areas in Germany. The existing development involves a trilateral built-up inner courtyard with apartment buildings consisting of over 200 accommodation units. In the future, the heat supply shall be ensured by a solar heat system and seasonal heat storage. The seasonal hot-water storage will be buried within the inner courtyard, with the result that the structure is harmoniously integrated into the properties landscape. The size of the hot-water storage depends on the solar coverage rate of the different scenarios. Therefor different scenarios have been developed. This model makes it possible to reduce potential heat losses arising from the heat grid because of the short distances between storage and buildings. 1.2 Model of the stakeholder The stakeholder model includes the relevant stakeholder, like it is shown in figure 1.
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Fig. 1. Stakeholder model
The research was separated into three parts, which are also shown in figure 1: the technical configuration as well as a carbon footprint investigation (green frame), an economical study (blue frame) and a quantitative social research (red frame). These tests are necessary to determine the data for comparison with a conventional heating system. Since the available data for seasonal heat storages are not sufficient so far and partly based on the pilot projects, these calculations will be implemented as a part of this research. Initially, the technical configuration of the system was realized. Therefore a specific technical solution for the building refurbishment of the existing development was found. The basis of the study was the improvement of energy efficiency of buildings as well as the integration of the solar heat system, the heat storage and the heat grid between the storage and the buildings. Through targeted measures, like the application of composite heat insulation systems or the replacement of external doors and windows, the characteristic energy values of the building shell have been improved within the building refurbishment. An energetic model has been established on the basis of the specific heat load of the building and the heat capacity of the storage as well as the heat balance of the solar heat system. This model contains factors as follows:
primary and end energy consumption of the buildings, heat balance of the solar heat system, the capability of the storage to accumulate heat-energy for the purpose of dimensioning and design, consideration of the required heat grid.
Subsequently a heat supply concept for this structural unit of an urban area was developed. Based on the heat demand of the buildings and the desired solar coverage, the heat storage and the collector surface of the solar thermal system was specified. The building with his related energetic characteristics leads to dimensioning the sizes of the storage tanks and the solar thermal system. Thus it was possible to verify the security of supply. The solar thermal coverage rate for the following calculations was determined on 50 %, 65 % and 80 %. Nevertheless, the back-up heating is covered with a gas condensing boiler in a bivalent mode. Anyhow, the aim of the research is to harmonize the complete system from a structural point of view. With these underlying assumptions, a system with different scenarios is developed as shown in table 1.
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Table 1. Overview of the model scenarios. Solar coverage
Scenario 0:
Scenario 1:
Scenario 2:
Basic scenario
Energetic standard scenario
Energetic optimised scenario
50 %
Scenario 1.1
Scenario 2.1
65 %
Scenario 1.2
Scenario 2.2
80 %
Scenario 1.3
Scenario 2.3
The aim of the technical investigation is to demonstrate the security of supply and to define a harmonized system. For this purpose, the individual system components were coordinated with each other as described above. Afterwards, an economical study was conducted in order to evaluate capital expenditure and operating expenses. Therefor a complete finance plan has been established for the different scenarios and the different stakeholder. By using the complete finance plan, different impacts for financing and taxation can be shown. Unlike classic investment calculations, a modern calculation, like the complete finance plan, is useful for the assessment of longterm investment decisions, because impacts of interest and compound interest are respected [4, 5, 6]. The complete finance plan is based on a spreadsheet analysis. Unfortunately, the required consumptions are risky. For that reason an extended sensitivity analysis was done, which shows the economic and technical chances and complications [7]. The aim of the economic research is an acceptable solution for every stakeholder. In particular for the heat contractor and the owner of the buildings it is required to secure the return on investment. Since the system is in competition with conventional heating systems, the rent has to be on an affordable level. Finally, potentials and recommendations for the operator model and the influence of the different operating costs of the heat storage system have been analyzed. Hereinafter the social acceptance was in the focus of the research. Expert interviews with owners, investors and building contractors estimate chances, risks, marketing options and knowledge about seasonal heat storages. For an integrated investigative approach, the analysis of the social acceptance will be done with potential investors, acting in different building and operator structures. A questionnaire about renovation processes of buildings, decentralized and innovative heat supply systems and the acceptance of the tenants has been established for the interviews. Based on evaluation, fundamental social chances and risks can be identified. As a result, the different investigations can be evaluated by their interdependencies. In addition, there will be an analysis of the carbon footprint. Thus, an integrated ecological and economical assessment is possible. These parameters allow it to compare a conventional system in respect to the marketability of seasonal heat storage units. At the same time, the study enables to achieve climate protection targets. 3. Results and discussion The different research methods allow a holistic assessment approach and reveal multi-causal interrelationships. By determining the relevant parameters, such as technology/ecology, economy and social acceptance, the different heat supply systems can be compared. At the same time, optimisation potential for seasonal heat storage systems can be identified in the further course of the project in order to reduce market entry barriers. In reference to chapter 2, two scenarios have been defined within the system boundaries of the calculation model. Figure 2 shows the reduction of the energy consumptions by the energetic optimisation of the building in relative numbers. The huge reduction of the primary energy consumption and the heating requirement was possible with different restructuring measures, like the insulation of the walls and the roof, the replacement of the windows or a new heating systems such as an underfloor heating system. Additionally, there is a decentralized ventilation system in the energetic optimised scenario. The heating requirement includes the heat transmission losses and heat gains. The primary energy consumption was calculated with the heating requirement, the hot water requirement and the system coefficient.
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Fig. 2. : Results of the building renovation
Thereby, two advantages can be found in an ecological-economical evaluation. Reducing the energy consumption also decrease the consumption of fuels. At the same time, the carbon footprint is reduced, because of the decrease of the heating requirement. If buildings are supplied with regenerative energy, the ecological added value increases again. From an economical point of view, the operating cost will decrease while reducing the energy consumption. Nevertheless, the high investment costs are opposed to these. Based on these results, the solar thermal system and the seasonal heat storage are dimensioned. The collector surface and the storage volume are dependent by the building structure and the solar coverage. The calculation is based on iteration and optimisation processes [8]. The relative results of the energy standard scenario are shown in table 2. The outcome of the energetic optimisation scenario calculation are content-related comparable. If the solar coverage should escalate from 50 % to 65 % (+ 15 %), the collector surface has to increase from 633 m² to 816 m² (+ 30 %) and the storage volume has to increase from 2.737 m³ to 3.926 m³ (+ 45 %). Table 2. Dimensions of the heat storage and the solar thermal system (energetic standard scenario). Solar coverage
Collector surface
Storage volume
50 %
633 m²
2.737 m³
55 %
695 m²
3.130 m³
60 %
756 m²
3.520 m³
65 %
816 m²
3.926 m³
70 %
877 m²
4.290 m³
75 %
937 m²
4.680 m³
80 %
1.060 m²
5.129 m³
The increase in storage volume can be seen depending on the solar coverage and is higher than the increase of the collector surface. This is fundamentally based on the dependency of the calculation and the overall system on the solar coverage ratio. Three different storage sizes are selected for the economic efficiency studies based on the scenarios in table 1. These storage sizes are for the energetic standard scenario (scenario 1): 2.737 m³, 3.926 m³ and 5.129 m³. Previous research has shown that the required surface area of solar thermal collectors increases
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proportionally to the level of solar coverage. At the same time, the increase in the solar coverage ratio is causing disproportionately high growth in the required volume of the seasonal heat storage tank [9]. In the model, the heat storage volume is increased by 30 % to 40 % in relation to the solar coverage ratio. This remarkable difference in the rises illustrates the influence of the solar coverage ratio on the respective parameter. Despite the various interdependencies of all system components, special attention must be paid to this. The relationship between the heat storage volume and the collector surface also has a decisive influence. This has a significant effect on the efficiency of the heat storage tank. If there are large differences between the two sizes, the heat storage tank is not optimally loaded. Heat losses occur and the solar coverage ratio may not be achieved during operation [10]. Figure 3 illustrates these interrelationships, which are depending of the absolute sizes of the storage and the solar thermal system.
Fig. 3. : Connections between different parameters [9]
The construction costs are determined in accordance with German standard DIN 276. For this purpose, the cost groups and types resulting from DIN 276 were considered in the calculation. The derivation of the required cost estimates was based on available information in the literature (e. g. from the specialist book series of the Baukosteninformationszentrum Deutscher Architektenkammern BKI) as well as on doctoral studies and diploma theses at the Institute for Construction Management of the Technische Universität Dresden [11, 12]. The cost trend of the investment and the specific construction costs for the seasonal heat storage are shown in figure 4. Specific construction costs decrease when the specific storage equivalent increases.
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Fig. 4. : Example for the investment and specific construction costs (net) of the seasonal heat storage (energetic standard scenario)
The essential question of the economic marketability of seasonal heat storages is the correlation between the economic advantages for the heat contractor and the building owner, which is a positive return on investment and the stability of the rents or rather the heat price for the tenant. At the end, a win-win-situation must be found for all stakeholder [13]. The complete finance plan is legally based on a contracting agreement between the heat contractor and the building owner. Costs flow from contractor to owner and finally to tenants like it is shown in figure 5.
building owner • target figure: maximum (defined) return on investment • central independent parameter: solar heat price
heat contractor
• target figure: maximum return on investment •central independent parameter: rent (shared costs for the tenants)
• target figure: minimum rent increase •central independent parameter: shared costs
tenants
Fig. 5. : Target figure and cost flow of the economic research
Based on this, complete finance plans for the heat contractor and the building owner were elaborated. Each calculation of investment is an independent calculation. But there are interdependencies between them. Finally, there has to be an affordable result for the tenants. Therefore, all important costs, like operating costs and shared
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costs of the owner, are included in the calculation. In Figure 6 the different return on investment for the building owner are shown. The return on investments is decreasing for the sustainable scenarios. For a higher energetic scenario of the buildings (scenario 2) the return on investments is also decreasing, because the rents are the same in each scenario. At the end, the differences in return on investments in the scenarios are not as high as expected.
Return on investments
4,00% 3,00% 2,00% 1,00% 0,00%
0%
50%
65%
80%
Solar coverage Scenario 1 "energetic standard"
Scenario 2 "energetic optimization"
Fig. 6. : Comparison of return on investments for the building owner
However, there are uncertainties in the calculation due to realization and usage costs and other financial assumptions, such as interest rates or price increases. These are examined by a sensitivity analysis on their influence. During this analysis the deterministic finance plans can be verified. With regard to the current status of the project, the expert surveys made it very clear that pricing plays an important role for tenants. All results for the sustainable and innovative system of seasonal heat storage and solar thermal energy for heat supply are compared with a conventional system. This applies in particular to the ecological impact of the CO2 balance and the economic implementation of the system. One result of this comparison revealed that the boundary conditions must be taken into account when planning and implementing further future developments. 4. Conclusion and outlook The technical and economic studies on the current state of the art have shown that it is possible to implement higher energetic standard for an existing building structure and the heat supply with renewable energies. Additional aspects, such as the uncertain parameters of cost-effectiveness, must be examined in further investigations. A broader perspective on the social aspect of the marketability and market entry barriers of seasonal heat storage systems can be given with expert interviews. Furthermore, the different examination methods have to be combined. The technical and empirical investigation allows a broad perspective on the prospects and obstacles of long-term heat storage technology. In particular, social difficulties such as the investor-user dilemma can also be considered. Further conclusions and possible recommendations for the future implementation of long-term heat storage systems can be drawn for the stakeholder in order to create an optimal cost-benefit-ratio. An effective increase in the use of renewable energies in the heating sector and a reduction of CO2 emissions can be achieved for political objective. In the future, decentralized heat supply in inner-city areas can be a component of sustainable heat supply in Germany. However, it is already evident that the economically advantageous implementation of the heat supply system plays a fundamental role and is one of the main focus for reducing market entry barriers. All results of this investigation can be found in the author's doctoral study, which is being written at the Technical University of Dresden, Faculty of Civil Engineering.
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Acknowledgements The authors thank the Friedrich und Elisabeth Boysen-Stiftung for the financial support given for this work during the second Boysen-TU Dresden-Graduiertenkolleg. References [1] [2] [3] [4]
Bundesministerium für Wirtschaft und Energie: Energiedaten: Gesamtausgabe, Eigenverlag, Berlin, 2015 Bundesministerium für Wirtschaft und Energie: Effizienzstrategie Gebäude, Eigenverlag, Berlin, 2015 Rogers, Everett M.: Diffusion of Innovations, Free Press, New York, 2003 Schach, Rainer; Jehle, Peter; Naumann, René: Transrapid und Rad-Schiene-Hochgeschwindigkeitsbahn. Ein gesamtheitlicher Systemvergleich, Springer-Verlag, Berlin Heidelberg, 2006 [5] Grob, Heinz Lothar: Investitionsrechnung mit vollständigen Finanzplänen, Verlag Franz Vahlen GmbH, München, 1989 [6] Kruschwitz, Lutz: Investitionsrechnung, Oldenburger Wissenschaftsverlag GmbH, München, 2014 [7] Götze, Uwe: Investitionsrechnung - Modelle und Analysen zur Beurteilung von Investitionsvorhaben, Springer Gabler, Berlin, 2014 [8] Calculation by SOLCHIP, Prof. Peter Lund, Aalto University Helsinki, Finland; Lund, Peter: SOLCHIPS - A fast predesign and optimization tool for solar heating with seasonal storage, Solar Energy, Vol. 48, No. 5, 1992 [9] Raab, Stefan: Simulation, Wirtschaftlichkeit und Auslegung solar unterstützter Nahwärme-systeme mit Heißwasser-Wärmespeicher, Dissertation Universität Stuttgart 2006, gedr. Cuvillier Verlag, Göttingen, 2006 [10] Krause, Martin: Technologie und Wirtschaftlichkeit von Langzeit-Wärmespeichern, diploma thesis Technische Univertistät Dresden, 2011 [11]Schmuck, Martin: Wirtschaftliche Umsetzbarkeit saisonaler Wärmespeicher, doctoral study Technische Universität Dresden 2016, Aus Forschung und Praxis, Band 17, expert verlag, Renningen, 2017 [12] BKI - Baukostenindex: Baukosten Positionen Altbau, Eigenverlag, Stuttgart, 2016 [13] Selle, Kati: Wärmecontracting - Fass ohne Boden? Warum Berliner Mieter hohe Heizkosten hinnehmen müssen, Mieterschutz, Berlin, 2014, p. 24 ff.
ScienceDirect ScienceDirect Energy Procedia 00 (2018) 000–000 Energy Procedia 00 (2018) 000–000
Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2018) 000–000 320–328 EnergyProcedia Procedia155 00 (2017) www.elsevier.com/locate/procedia
12th International Renewable Energy Storage Conference, IRES 2018 12th International Renewable Energy Storage Conference, IRES 2018
Decentralized heat supply with seasonal heat storage systems: Decentralized heat supply different with seasonal heat storage systems: systems TheComparison 15th Internationalof Symposium on heating District Heating and Cooling Comparison of different heating systems a,b, Prof. Dr.-Ing. Rainer Schacha, of Anna-Elisabeth Wollstein-Lehmkuhl * Assessing the feasibility using the heat demand-outdoor a Prof. Dr.-Ing. Rainer Schach , Anna-Elisabeth Wollstein-Lehmkuhla,b,* Technische Universität Dresden, Institute of construction management, 01062 Dresden, Germany temperature function for a long-term district heat demand forecast Boysen-TU Dresden-Graduiertenkolleg, Strehlener Str. 22/24, 01069 Dresden, Germany Technische Universität Dresden, Institute of construction management, 01062 Dresden, Germany a
b
a
b
Boysen-TU Dresden-Graduiertenkolleg, Strehlener Str. 22/24, 01069 Dresden, Germany
a,b,c
I. Andrić
*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
a Abstract IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Abstract Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c To reach international climate goals, the research about energy consumption to focus more44300 on existing buildings. In the Département Systèmes Énergétiques et Environnement - IMT Atlantique, have 4 rue Alfred Kastler, Nantes, France building the increase of energy efficiency buildings willconsumption not be sufficient consumption fossil resources To reachsector, international climate goals, the researchofabout energy havetotoreduce focus the more on existingofbuildings. In the significantly. Therefore the application of renewable energies have to increase as well. Seasonal storage systems can support building sector, the increase of energy efficiency of buildings will not be sufficient to reduce theheat consumption of fossil resources this process because thethestorage enables heat supply and heat to be time-wise. Nevertheless, innovative significantly. Therefore application of renewable energies havedemand to increase as decoupled well. Seasonal heat storage systems can support Abstract systems, which are using energyheat for heating, in a competition with conventional systems,innovative which are this process because the renewable storage enables supply are andalways heat demand to be decoupled time-wise.heating Nevertheless, using gaswhich or oil.are They must be equally efficient in technical and economic aspects.with For conventional that reason, this studysystems, is focused on the systems, using renewable energy for heating, are always in a competition heating which are District networks commonly addressed insystems the and literature as one of theaFor most solutions decreasing the comparison supply with seasonal heat storage in connection with solar thermal and for system using gasheating orof oil.a heat They must are be equally efficient in technical economic aspects. thateffective reason,system this study isa heating focused on the greenhouse gas emissions building sector. These systems require investments which are returned through the with gas. For this comparison a the technical system and an operating model high was established. This system was aanalyzed by heat his comparison of a heat supplyfrom with seasonal heat storage systems in connection with a solar thermal and heating system sales.gas. Due tothis the comparison changed climate conditions and building renovation policies, heat demand in the future could decrease, economic parameters with complete finance plans. As result, it ismodel shown, sustainable heat supply is analyzed not much with For a technical system and ana operating wasthat established. This system was bymore his prolonging the investment return period. expensive than conventional heat supply. In addition, the social acceptance of different stakeholder is affected by these economic parameters with complete finance plans. As a result, it is shown, that sustainable heat supply is not much more The main scope of this paper is to assess theinvestors ofthe using the heat demand of – outdoor temperature function for heat parameters. Therefor expert interviews with were done. expensive than conventional heat supply. Infeasibility addition, social acceptance different stakeholder is affected bydemand these forecast. The districtexpert of Alvalade, in Lisbon (Portugal), was used as a case study. The district is consisted of 665 parameters. Therefor interviewslocated with investors were done. vary in both construction ©buildings 2018 Thethat Authors. Published by Elsevierperiod Ltd. and typology. Three weather scenarios (low, medium, high) and three district © 2018 The Authors. Published by Elsevier Ltd. renovation scenarios were developed (shallow, deep). To estimate the error, obtained heat demand values were This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) © 2018 The Authors. Published by Elsevier Ltd. intermediate, This is an open access article under the heat CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) compared with resultsarticle from aunder dynamic demand previously developed by theRenewable authors. Energy Storage Selection peer-review under responsibility of themodel, scientific committee of the and 12thvalidated International This is an and open access the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage The results showed that when only weather change isscientific considered, the margin of error could be acceptable for some applications Conference. Selection and peer-review under responsibility of the committee of the 12th International Renewable Energy Storage Conference. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation Conference. scenarios,seasonal the error increased up systems, to 59.5% (depending onmarketability, the weather economic and renovation scenarios combination considered). Keywords: heatvalue storage, heat supply renewable energy, efficiency, energy efficiency The valueseasonal of slope on average within themarketability, range of 3.8% up toefficiency, 8% per energy decade, that corresponds to the Keywords: heatcoefficient storage, heatincreased supply systems, renewable energy, economic efficiency decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +49-351-463-34242; fax:Committee +49-351-463-34680. Cooling. E-mail address: [email protected] * Corresponding author. Tel.: +49-351-463-34242; fax: +49-351-463-34680.
E-mail address: [email protected] Keywords:©Heat Forecast; Climatebychange 1876-6102 2018demand; The Authors. Published Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Selection under responsibility of the scientific of the 12th International Renewable Energy Storage Conference. This is an and openpeer-review access article under the CC BY-NC-ND licensecommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage Conference.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 12th International Renewable Energy Storage Conference. 10.1016/j.egypro.2018.11.046
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1. Introduction More than 50% of the total energy consumption in Germany is about heat [1]. The climate protection goals of the German Government can only be reached by a further change of the energy transition into a heat transition. In order to reduce the consumption of fossil energy resources, it is not enough to improve only the energy efficiency of the buildings in the building sector. Therefore the application of renewable energy for the heat production has to increase. The existing building structures in Germany are one of the key factors in this consideration [2]. To supply those building structures with renewable energy is one of the future goals. With the background of a change in the German heat supply, seasonal heat storage systems can support the transforming process because the storage enables heat supply and heat demand to be decoupled time-wise. The advantage of hot water tank storages is, that they can be build independent from geological and hydrogeological soil conditions. Since the construction design of the storage is durable and the storage medium water is not harmful for the environment, the operation is save and the maintenance easy. For heat production a solar thermal system is used, which is theoretically available at all time. The research topic is focused on the marketability of this technical system in comparison with conventional heating systems. Conventional systems are established on the market and optimally designed to meet the needs of users in terms of cost minimisation and security of supply. An innovative system powered by renewable energy is therefore in direct competition for investors and users alike. Despite the volatility, renewable energies are suitable for this purpose. The marketability of a system depends on technical factors such as security of supply and economic parameters, like the heat production price. Furthermore, social acceptance is of crucial importance for a successful implementation of the system [3]. The individual influencing parameters are dependent on each other during the investigation, so that a holistic evaluation must be carried out. Therefore a building model, which is characteristic for urban areas, was designed. The heat supply is ensured by a solar heat system and a seasonal heat storage, build as a hot water tank. The focus of the study is to define in what manner technical, economic and social parameters influence the marketability of seasonal heat storages in comparison with conventional heating systems. 2. Methodology The first step in the research project was to define the framework of the investigation. A differentiation must be made between the building model and the operator model. 1.1 Building model As part of this research model, an existing inner-city building structure was energetically and economically studied. The style of the existing development is characteristic for urban areas in Germany. The existing development involves a trilateral built-up inner courtyard with apartment buildings consisting of over 200 accommodation units. In the future, the heat supply shall be ensured by a solar heat system and seasonal heat storage. The seasonal hot-water storage will be buried within the inner courtyard, with the result that the structure is harmoniously integrated into the properties landscape. The size of the hot-water storage depends on the solar coverage rate of the different scenarios. Therefor different scenarios have been developed. This model makes it possible to reduce potential heat losses arising from the heat grid because of the short distances between storage and buildings. 1.2 Model of the stakeholder The stakeholder model includes the relevant stakeholder, like it is shown in figure 1.
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Fig. 1. Stakeholder model
The research was separated into three parts, which are also shown in figure 1: the technical configuration as well as a carbon footprint investigation (green frame), an economical study (blue frame) and a quantitative social research (red frame). These tests are necessary to determine the data for comparison with a conventional heating system. Since the available data for seasonal heat storages are not sufficient so far and partly based on the pilot projects, these calculations will be implemented as a part of this research. Initially, the technical configuration of the system was realized. Therefore a specific technical solution for the building refurbishment of the existing development was found. The basis of the study was the improvement of energy efficiency of buildings as well as the integration of the solar heat system, the heat storage and the heat grid between the storage and the buildings. Through targeted measures, like the application of composite heat insulation systems or the replacement of external doors and windows, the characteristic energy values of the building shell have been improved within the building refurbishment. An energetic model has been established on the basis of the specific heat load of the building and the heat capacity of the storage as well as the heat balance of the solar heat system. This model contains factors as follows:
primary and end energy consumption of the buildings, heat balance of the solar heat system, the capability of the storage to accumulate heat-energy for the purpose of dimensioning and design, consideration of the required heat grid.
Subsequently a heat supply concept for this structural unit of an urban area was developed. Based on the heat demand of the buildings and the desired solar coverage, the heat storage and the collector surface of the solar thermal system was specified. The building with his related energetic characteristics leads to dimensioning the sizes of the storage tanks and the solar thermal system. Thus it was possible to verify the security of supply. The solar thermal coverage rate for the following calculations was determined on 50 %, 65 % and 80 %. Nevertheless, the back-up heating is covered with a gas condensing boiler in a bivalent mode. Anyhow, the aim of the research is to harmonize the complete system from a structural point of view. With these underlying assumptions, a system with different scenarios is developed as shown in table 1.
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Table 1. Overview of the model scenarios. Solar coverage
Scenario 0:
Scenario 1:
Scenario 2:
Basic scenario
Energetic standard scenario
Energetic optimised scenario
50 %
Scenario 1.1
Scenario 2.1
65 %
Scenario 1.2
Scenario 2.2
80 %
Scenario 1.3
Scenario 2.3
The aim of the technical investigation is to demonstrate the security of supply and to define a harmonized system. For this purpose, the individual system components were coordinated with each other as described above. Afterwards, an economical study was conducted in order to evaluate capital expenditure and operating expenses. Therefor a complete finance plan has been established for the different scenarios and the different stakeholder. By using the complete finance plan, different impacts for financing and taxation can be shown. Unlike classic investment calculations, a modern calculation, like the complete finance plan, is useful for the assessment of longterm investment decisions, because impacts of interest and compound interest are respected [4, 5, 6]. The complete finance plan is based on a spreadsheet analysis. Unfortunately, the required consumptions are risky. For that reason an extended sensitivity analysis was done, which shows the economic and technical chances and complications [7]. The aim of the economic research is an acceptable solution for every stakeholder. In particular for the heat contractor and the owner of the buildings it is required to secure the return on investment. Since the system is in competition with conventional heating systems, the rent has to be on an affordable level. Finally, potentials and recommendations for the operator model and the influence of the different operating costs of the heat storage system have been analyzed. Hereinafter the social acceptance was in the focus of the research. Expert interviews with owners, investors and building contractors estimate chances, risks, marketing options and knowledge about seasonal heat storages. For an integrated investigative approach, the analysis of the social acceptance will be done with potential investors, acting in different building and operator structures. A questionnaire about renovation processes of buildings, decentralized and innovative heat supply systems and the acceptance of the tenants has been established for the interviews. Based on evaluation, fundamental social chances and risks can be identified. As a result, the different investigations can be evaluated by their interdependencies. In addition, there will be an analysis of the carbon footprint. Thus, an integrated ecological and economical assessment is possible. These parameters allow it to compare a conventional system in respect to the marketability of seasonal heat storage units. At the same time, the study enables to achieve climate protection targets. 3. Results and discussion The different research methods allow a holistic assessment approach and reveal multi-causal interrelationships. By determining the relevant parameters, such as technology/ecology, economy and social acceptance, the different heat supply systems can be compared. At the same time, optimisation potential for seasonal heat storage systems can be identified in the further course of the project in order to reduce market entry barriers. In reference to chapter 2, two scenarios have been defined within the system boundaries of the calculation model. Figure 2 shows the reduction of the energy consumptions by the energetic optimisation of the building in relative numbers. The huge reduction of the primary energy consumption and the heating requirement was possible with different restructuring measures, like the insulation of the walls and the roof, the replacement of the windows or a new heating systems such as an underfloor heating system. Additionally, there is a decentralized ventilation system in the energetic optimised scenario. The heating requirement includes the heat transmission losses and heat gains. The primary energy consumption was calculated with the heating requirement, the hot water requirement and the system coefficient.
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Fig. 2. : Results of the building renovation
Thereby, two advantages can be found in an ecological-economical evaluation. Reducing the energy consumption also decrease the consumption of fuels. At the same time, the carbon footprint is reduced, because of the decrease of the heating requirement. If buildings are supplied with regenerative energy, the ecological added value increases again. From an economical point of view, the operating cost will decrease while reducing the energy consumption. Nevertheless, the high investment costs are opposed to these. Based on these results, the solar thermal system and the seasonal heat storage are dimensioned. The collector surface and the storage volume are dependent by the building structure and the solar coverage. The calculation is based on iteration and optimisation processes [8]. The relative results of the energy standard scenario are shown in table 2. The outcome of the energetic optimisation scenario calculation are content-related comparable. If the solar coverage should escalate from 50 % to 65 % (+ 15 %), the collector surface has to increase from 633 m² to 816 m² (+ 30 %) and the storage volume has to increase from 2.737 m³ to 3.926 m³ (+ 45 %). Table 2. Dimensions of the heat storage and the solar thermal system (energetic standard scenario). Solar coverage
Collector surface
Storage volume
50 %
633 m²
2.737 m³
55 %
695 m²
3.130 m³
60 %
756 m²
3.520 m³
65 %
816 m²
3.926 m³
70 %
877 m²
4.290 m³
75 %
937 m²
4.680 m³
80 %
1.060 m²
5.129 m³
The increase in storage volume can be seen depending on the solar coverage and is higher than the increase of the collector surface. This is fundamentally based on the dependency of the calculation and the overall system on the solar coverage ratio. Three different storage sizes are selected for the economic efficiency studies based on the scenarios in table 1. These storage sizes are for the energetic standard scenario (scenario 1): 2.737 m³, 3.926 m³ and 5.129 m³. Previous research has shown that the required surface area of solar thermal collectors increases
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proportionally to the level of solar coverage. At the same time, the increase in the solar coverage ratio is causing disproportionately high growth in the required volume of the seasonal heat storage tank [9]. In the model, the heat storage volume is increased by 30 % to 40 % in relation to the solar coverage ratio. This remarkable difference in the rises illustrates the influence of the solar coverage ratio on the respective parameter. Despite the various interdependencies of all system components, special attention must be paid to this. The relationship between the heat storage volume and the collector surface also has a decisive influence. This has a significant effect on the efficiency of the heat storage tank. If there are large differences between the two sizes, the heat storage tank is not optimally loaded. Heat losses occur and the solar coverage ratio may not be achieved during operation [10]. Figure 3 illustrates these interrelationships, which are depending of the absolute sizes of the storage and the solar thermal system.
Fig. 3. : Connections between different parameters [9]
The construction costs are determined in accordance with German standard DIN 276. For this purpose, the cost groups and types resulting from DIN 276 were considered in the calculation. The derivation of the required cost estimates was based on available information in the literature (e. g. from the specialist book series of the Baukosteninformationszentrum Deutscher Architektenkammern BKI) as well as on doctoral studies and diploma theses at the Institute for Construction Management of the Technische Universität Dresden [11, 12]. The cost trend of the investment and the specific construction costs for the seasonal heat storage are shown in figure 4. Specific construction costs decrease when the specific storage equivalent increases.
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Fig. 4. : Example for the investment and specific construction costs (net) of the seasonal heat storage (energetic standard scenario)
The essential question of the economic marketability of seasonal heat storages is the correlation between the economic advantages for the heat contractor and the building owner, which is a positive return on investment and the stability of the rents or rather the heat price for the tenant. At the end, a win-win-situation must be found for all stakeholder [13]. The complete finance plan is legally based on a contracting agreement between the heat contractor and the building owner. Costs flow from contractor to owner and finally to tenants like it is shown in figure 5.
building owner • target figure: maximum (defined) return on investment • central independent parameter: solar heat price
heat contractor
• target figure: maximum return on investment •central independent parameter: rent (shared costs for the tenants)
• target figure: minimum rent increase •central independent parameter: shared costs
tenants
Fig. 5. : Target figure and cost flow of the economic research
Based on this, complete finance plans for the heat contractor and the building owner were elaborated. Each calculation of investment is an independent calculation. But there are interdependencies between them. Finally, there has to be an affordable result for the tenants. Therefore, all important costs, like operating costs and shared
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costs of the owner, are included in the calculation. In Figure 6 the different return on investment for the building owner are shown. The return on investments is decreasing for the sustainable scenarios. For a higher energetic scenario of the buildings (scenario 2) the return on investments is also decreasing, because the rents are the same in each scenario. At the end, the differences in return on investments in the scenarios are not as high as expected.
Return on investments
4,00% 3,00% 2,00% 1,00% 0,00%
0%
50%
65%
80%
Solar coverage Scenario 1 "energetic standard"
Scenario 2 "energetic optimization"
Fig. 6. : Comparison of return on investments for the building owner
However, there are uncertainties in the calculation due to realization and usage costs and other financial assumptions, such as interest rates or price increases. These are examined by a sensitivity analysis on their influence. During this analysis the deterministic finance plans can be verified. With regard to the current status of the project, the expert surveys made it very clear that pricing plays an important role for tenants. All results for the sustainable and innovative system of seasonal heat storage and solar thermal energy for heat supply are compared with a conventional system. This applies in particular to the ecological impact of the CO2 balance and the economic implementation of the system. One result of this comparison revealed that the boundary conditions must be taken into account when planning and implementing further future developments. 4. Conclusion and outlook The technical and economic studies on the current state of the art have shown that it is possible to implement higher energetic standard for an existing building structure and the heat supply with renewable energies. Additional aspects, such as the uncertain parameters of cost-effectiveness, must be examined in further investigations. A broader perspective on the social aspect of the marketability and market entry barriers of seasonal heat storage systems can be given with expert interviews. Furthermore, the different examination methods have to be combined. The technical and empirical investigation allows a broad perspective on the prospects and obstacles of long-term heat storage technology. In particular, social difficulties such as the investor-user dilemma can also be considered. Further conclusions and possible recommendations for the future implementation of long-term heat storage systems can be drawn for the stakeholder in order to create an optimal cost-benefit-ratio. An effective increase in the use of renewable energies in the heating sector and a reduction of CO2 emissions can be achieved for political objective. In the future, decentralized heat supply in inner-city areas can be a component of sustainable heat supply in Germany. However, it is already evident that the economically advantageous implementation of the heat supply system plays a fundamental role and is one of the main focus for reducing market entry barriers. All results of this investigation can be found in the author's doctoral study, which is being written at the Technical University of Dresden, Faculty of Civil Engineering.
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Acknowledgements The authors thank the Friedrich und Elisabeth Boysen-Stiftung for the financial support given for this work during the second Boysen-TU Dresden-Graduiertenkolleg. References [1] [2] [3] [4]
Bundesministerium für Wirtschaft und Energie: Energiedaten: Gesamtausgabe, Eigenverlag, Berlin, 2015 Bundesministerium für Wirtschaft und Energie: Effizienzstrategie Gebäude, Eigenverlag, Berlin, 2015 Rogers, Everett M.: Diffusion of Innovations, Free Press, New York, 2003 Schach, Rainer; Jehle, Peter; Naumann, René: Transrapid und Rad-Schiene-Hochgeschwindigkeitsbahn. Ein gesamtheitlicher Systemvergleich, Springer-Verlag, Berlin Heidelberg, 2006 [5] Grob, Heinz Lothar: Investitionsrechnung mit vollständigen Finanzplänen, Verlag Franz Vahlen GmbH, München, 1989 [6] Kruschwitz, Lutz: Investitionsrechnung, Oldenburger Wissenschaftsverlag GmbH, München, 2014 [7] Götze, Uwe: Investitionsrechnung - Modelle und Analysen zur Beurteilung von Investitionsvorhaben, Springer Gabler, Berlin, 2014 [8] Calculation by SOLCHIP, Prof. Peter Lund, Aalto University Helsinki, Finland; Lund, Peter: SOLCHIPS - A fast predesign and optimization tool for solar heating with seasonal storage, Solar Energy, Vol. 48, No. 5, 1992 [9] Raab, Stefan: Simulation, Wirtschaftlichkeit und Auslegung solar unterstützter Nahwärme-systeme mit Heißwasser-Wärmespeicher, Dissertation Universität Stuttgart 2006, gedr. Cuvillier Verlag, Göttingen, 2006 [10] Krause, Martin: Technologie und Wirtschaftlichkeit von Langzeit-Wärmespeichern, diploma thesis Technische Univertistät Dresden, 2011 [11]Schmuck, Martin: Wirtschaftliche Umsetzbarkeit saisonaler Wärmespeicher, doctoral study Technische Universität Dresden 2016, Aus Forschung und Praxis, Band 17, expert verlag, Renningen, 2017 [12] BKI - Baukostenindex: Baukosten Positionen Altbau, Eigenverlag, Stuttgart, 2016 [13] Selle, Kati: Wärmecontracting - Fass ohne Boden? Warum Berliner Mieter hohe Heizkosten hinnehmen müssen, Mieterschutz, Berlin, 2014, p. 24 ff.