As major responsible for CO2 emissions, the energy sector is urgently called to take action against climatechange. The integration of renewable energy resources is a solution that, however, comes with a challenge.In fact, renewables are often variable, unpredictable and distributed. These characteristics add an extremecomplexity to the design and control of energy systems. Sector-coupling is nowadays strongly supported asa promising approach to increase the flexibility of these systems. For example, wind power curtailment canbe reduced by using the power surplus to operate heat pumps. When the wind does not blow, the heat storedin the thermal mass of the buildings and waste heat recovery can be used instead. These solutions are largelyavailable at district-to-city level. However, a suitable framework to design these integrated urban energysystems is missing.This thesis work proposes such a framework, as a set of methodological steps and integrated modellingtools. Among them, the modelling and simulation approach is a fundamental aspect. Given theheterogeneity of integrated energy systems, dedicated technology-specific models are developed and usedto achieve the required level of detail. A co-simulation method is implemented when time step coordinationand data exchange are necessary. Scenarios are developed to compare the techno-economic andenvironmental performance of alternative solutions, based on sector-coupling. Levelized cost of energy andCO2 emissions are used as main performance indicators for this purpose. In order to show the applicabilityof this methodology, Hammarby Sjöstad (Stockholm, Sweden) is selected as a case study. This also allowsto tackle a real local open issue, which is the definition of the best solution between district heating anddomestic heat pumps for multi-apartment buildings.The proposed framework was successfully applied to the case study. Case specific results allowed toformulate more general conclusions applicable to similar multi-apartment residential districts, in a Swedishcontext. It could be shown that co-simulation is a useful approach to capture sector-coupling bottlenecksand opportunities. Respective examples are electricity grid overloadings caused by installations of heatpumps and the control of thermal mass in buildings to replace the use of heat peak boilers. However, cosimulationshould be strictly limited to cases where control feedback loops need to be taken into account,such as in the previous examples. This is because it involves a higher implementation complexity and ahigher computational time. Thus, for example, the models of a heat network and of an electricity grid withno coupling technologies, such as heat pumps and electric boilers, should be preferably analyzedsequentially. The levelized cost of heat was found to be a game-changer parameter when comparing energyinfrastructures, beyond the specific business aspects. For example, the replacement of a district heatingtariff with its levelized cost of heat clearly showed the economic advantage of heat networks againstdomestic heat pumps. The CO2 emissions factors of different energy resources (waste, biomass, electricitymix) were shown to be highly critical for two main reasons. Firstly, different assumptions for these factorsled to opposite findings regarding the carbon footprint of specific technologies. For example, heat pumpscould be estimated as both more and less polluting than district heating, depending on the assumedemission factors. Secondly, control strategies based on the CO2 emission factors of the electricity supplymix (power-to-heat) were found to be a promising sector-coupling solution. By analyzing integrated energysystems, it was possible to assess uncovered bottlenecks and suggest new options. In particular, it wasshown that the installation of a large number of distributed heat pumps can overload the electricitydistribution grid in a district. Demand side management, through the thermal mass in buildings andvehicle-to-grid, could help alleviating this problem. On the other hand, district heating was found to be aneven more promising alternative, by integrating demand side management and heat recovery. Heat pumpswere shown to be a suitable partner technology for supporting heat recovery and enabling power-to-heat.

Då energisektorn ansvarar för huvuddelen av växthusutsläppen finns det behov att omgående vidtaåtgärder för att motverka klimatförändringar. Integrationen av förnybara energiresurser är en lösning, dockkommer den med en del utmaningar. Förnybar energi är ofta variabel, oförutsägbar och distribuerad. Dessaegenskaper medför en ökad komplexitet när det gäller utformning och styrning av energisystemsystemet.Ökad sektorkoppling mellan olika energislag är ett lovande tillvägagångssätt för att öka flexibiliteten i dessasystem. Till exempel kan driftinskränkningar för vindkraft minskas genom att använda kraftöverskottet föratt driva värmepumpar. När vinden inte blåser kan värmen som lagras i byggnaders termiska massa ochåtervinning av spillvärme användas istället. Dessa lösningar finns mestadels på stads- och distriktsnivå. Ettlämpligt modelleringsramverk för att utforma dessa integrerade stadsenergisystem saknas dock.Det föreliggande arbete föreslår ett sådant ramverk som en uppsättning av metodologiska steg ochintegrerade modelleringsverktyg. Tyngdpunkten ligger på modellering och simulering. Med tanke på deintegrerade energisystemens heterogenitet utvecklas dedikerade teknologispecifika modeller för att uppnåönskad detaljnivå. En samsimuleringsmetod implementeras när tidsstegskoordinering och datautbyte ärnödvändiga mellan olika modeller. Scenarier utvecklas för att jämföra den tekno-ekonomiska ochmiljömässiga prestandan hos alternativa lösningar baserat på sektorkoppling. Nivellerade energikostnaderoch koldioxidutsläpp används som huvudindikatorer för detta ändamål. För att visa tillämpbarheten avdenna metod väljs distriktet Hammarby Sjöstad (Stockholm, Sverige) som en fallstudie. Detta gör det ocksåmöjligt att ta itu med en real öppen fråga, nämligen huruvida fjärrvärme eller värmepumpar är den bästalösningen för hushåll för flerbostadshus.Det föreslagna ramverket tillämpades framgångsrikt på fallstudien. Fallspecifika resultat gjorde detmöjligt att formulera mer generella slutsatser som är tillämpbara på liknande flerbostadsområden i ettsvenskt sammanhang. Det visas att samsimulering är ett användbart tillvägagångssätt för att fånga uppflaskhalsar och nya möjligheter i sektorkopplingen. Exempel är överbelastningar av elnät orsakade avinstallationer av värmepumpar och kontroll av termisk massa i byggnader för att ersätta användningen avtoppvärmepannor. Dock bör samsimulering begränsas till fall där regleråterkoppling måste tas i beaktande,såsom i de föregående exemplen. Detta beror på att samsimulering innebär en signifikant högreimplementeringskomplexitet och en längre beräkningstid. Således bör exempelvis modellerna för ettvärmenät och av ett elnät utan kopplingsteknik- såsom värmepumpar och elektriska pannor- företrädesvisanalyseras sekventiellt. När det gäller nyckelprestationsindikatorer visade sig den i detta arbete infördanivellerade värmekostnaden vara en viktig ny parameter när man jämför energiinfrastrukturer utöver despecifika affärsaspekterna. Exempelvis visade byte av fjärrvärmetaxa till nivellerade värmekostnad tydligtden ekonomiska fördelen med värmenät jämfört med lokala värmepumpar. CO2-utsläppsfaktorer för olikaenergiresurser (avfall, biomassa, elmix) visade sig vara mycket viktiga av två huvudskäl. För det första leddeolika antaganden för dessa faktorer till motsatta slutsatser angående koldioxidavtrycket för specifik teknik.Till exempel kan värmepumpar uppskattas vara både mer och mindre förorenande än fjärrvärme beroendepå de antagna utsläppsfaktorerna. För det andra befanns reglerstrategier baserade påkoldioxidutsläppsfaktorerna i elmixen (kraft-till-värme) vara en lovande sektorkopplingslösning. Genomatt analysera integrerade energisystem var det möjligt att fånga upp flaskhalsar i infrastrukturen och föreslånya alternativ. I synnerhet visades att installationen av ett stort antal distribuerade värmepumpar kanöverbelasta elnätet i ett distrikt. Styrning av efterfrågesidan, genom tex användning av den termiskamassan i byggnader och elfordons lagringskapacitet, kan hjälpa till att minska detta problem. På andrasidan visade sig fjärrvärme vara ett ännu mer lovande alternativ genom att integrera både styrning avefterfrågan och värmeåtervinning. Värmepumpar visade sig i detta fall vara en lämplig partnerteknik föratt stödja värmeåtervinning och möjliggöra kraft-till-värme-kopplingen.

Heat recovery from local resources is shown to be a promising solution to reduce the carbon footprint of district heating. Supermarkets equipped with a CO2 refrigeration system and a geothermal storage offer a larger heating capacity, compared to traditional solutions. While district heat could benefit from this higher heat recovery availability, supermarkets could generate an income from a capacity that would be otherwise unused. For the first time, this study applies a detailed modelling approach considering both sides of such a synergy. The objective is to assess the techno-economic and environmental impact of a coordinated control strategy. Since the heat recovery from the supermarket consumes additional electricity, power-to-heat is implemented as a solution to reduce the overall CO2 emissions. This is demonstrated by scenarios simulated for a district in Stockholm. Hourly electricity CO2 intensity and prices are implemented as signals to prioritize either the district heating central supply or heat recovery. By boosting the use of electricity when cleaner, a CO2 intensity-driven control show the potential of reducing the carbon footprint of the district (−9.4%). A control based on prices, instead, is more convenient economically both for the district (−1.4% heat cost) and for the supermarket (−32% operational cost).

During the IntegrCiTy project, a novel urban energy planning approach was successfully tested. The latter combines stakeholder engagement with an innovative multi-energy model using different control strategies, while combining both energy demand and supply dynamics on selected zones. The applied control strategies applied to the energy networks show the potential gains linked to using synergies among networks and technologies, as to foster renewable energy penetration in the system. Thanks to the combined approach of advanced optimization techniques and stakeholder engagement, solutions can be identified much quicker. In addition, unfeasible solutions can be discarded at earlier stages of the planning process, based on the feedback of the stakeholders even though, from a pure mathematical and energy point of view, the solutions might be theoretically interesting to consider.

The planning of energy infrastructures in new districts often follows the practice adopted for the rest of the city. In Stockholm, district heating is a common solution for multi-apartment neighborhoods. Recently, because of an average clean electricity mix, heat pumps have gained interest. However, European studies suggest to limit the reliance on electrification to avoid an extreme demand increase. Thus, an effort is required to improve the environmental impact of alternative options. This study proposes waste heat recovery in low temperature networks as a promising solution. By means of a techno-economic and environmental analysis, this option is compared to domestic heat pumps. A new approach is proposed to combine a district level perspective with simulation tools able to capture sector-coupling interactions. Scenarios, for a real neighborhood, assess waste heat recovery potential and electricity grid loading status. Results show that a waste heat recovery capacity equal to 10% of the peak load can reduce fossil fuel use of 40%. Local grid limitations are shown to be a bottleneck for the feasibility of domestic heat pumps. Their heat generation cost is 28% higher than for district heating. The carbon footprint is strongly dependent on the emission factor of the electricity mix (+11%/-24%).

The energy infrastructure in Stockholm faces an imminent problem caused by the saturation of the electricity distribution grid capacity. Given promising economic savings, a few city neighborhoods have decided to switch from district heating to domestic heat pumps. Thus, technical concerns arise. This study aims at proposing demand side management solutions to unlock the integration of distributed heat pumps. A techno-economic analysis is presented to assess the potential of using the buildings’ thermal mass as energy storage. By means of co-simulation, the electricity grid and the buildings are coupled through a feedback control. The grid capacity is monitored to avoid overloadings. The indoor temperature is controlled in order to serve as thermal energy storage. It is found that, given the grid's capacity limits, the infrastructure should still be partly connected to the district heating (around 7% of the heat demand). This dependency decreases of around 1% when the buildings’ thermal mass is used as thermal storage, with a range of ±0.5 °C. On a heat pump level, the disconnections decrease up to 50%, depending on the buildings’ thermal mass capacity. Thus better techno-economic (about −2% on the levelized cost) and environmental (about −1% on the CO2 emissions) performances are unlocked.

The city of Stockholm is close to hitting the capacity limits of its power grid. As an additional challenge, electricity has been identified as a key resource to help the city to meet its environmental targets. This has pushed citizens to prefer power-based technologies, like heat pumps and electric vehicles, thus endangering the stability of the grid. The focus of this paper is on the district of Hammarby Sjöstad. Here, plans are set to switch from district heating to heat pumps. A previous study verified that this choice will cause overloadings on the electricity distribution grid. The present paper tackles this problem by proposing a new energy storage option. By considering the increasing share of electric vehicles, the potential of using the electricity stored in their batteries to support the grid is explored through technical performance simulations. The objective was to enable a bi-directional flow and use the electric vehicles' (EVs)' discharging to shave the peak demand caused by the heat pumps. It was found that this solution can eliminate overloadings up to 50%, with a 100% EV penetration. To overcome the mismatch between the availability of EVs and the overloadings' occurrence, the minimum state of charge for discharging should be lower than 70%.

The integration of variable renewable resources and decentralized energy technologies generates the need for a larger flexibility of the energy demand. In order to fully deploy a demand side management approach, synergies between interconnected energy systems have to be systematically implemented. By taking this standpoint, this study proposes a new approach to explore the potential of multi-energy integrated energy systems. This approach is constituted by two main steps, which are (1) the performance simulation of selected energy infrastructures and (2) the estimation of related techno-economic performance indicators. Step (1) expands the work presented in previous literature, by including a novel co-simulation feature. In step (2), the levelized cost of energy and location-dependent emission factors are used as key performance indicators. In this paper, the presented approach is demonstrated by implementing two demand side management options for heat peak demand shaving. A Swedish residential neighborhood is considered as a case study. The first option explores the potential of storing heat in the thermal mass of residential buildings. The proposed strategies lead to a decrease of up to 70% of primary energy consumption, depending on the indoor comfort requirements. The second option estimates the techno-economic feasibility of a new set of scenarios based on the integration of geothermal distributed heat pumps within a district heating network. The district heating scenario is found to be the most techno-economical convenient. Nevertheless, a moderate penetration of distributed heat pumps (around 20%) is shown to have a good trade-off with the reduction of CO2 emissions.

Within the Nordic countries, distributed heat and power supply technologies, like domestic scale heat pumps and photovoltaics, are challenging the current centralized district energy infrastructure. An increasing number of customers decide to disconnect from the traditional heating network by comparing the bill to the potential economic savings which can be generated by a residential heat pump system. However, this approach can be considered valid only on a short-term perspective. This paper presents a new approach to compare the techno-economic performance of alternative technologies, based on their lifetime average cost of generation. The proposed analysis is able to determine the optimal energy infrastructure at urban district level. Within this solution, operators, city planners and users will have a solid reference for their decision making process on resources investment. From a first step analysis of a few Swedish case studies, it was found that a district heating based system is more techno-economically efficient compared to the distributed alternative. By comparing the district heating production cost to its final price, a significant profit margin for the utility was qualitatively highlighted. Thus, from a customer perspective, on the medium run, the district heating tariff can be adapted and the estimated savings from switching to a residential heat pump system can be nullified.

Nowadays, direct steam generation concentrated solar tower plants suffer from the absence of a cost-effective thermal energy storage integration. In this study, the prefeasibility of a combined sensible and latent thermal energy storage configuration has been performed from thermodynamic and economic standpoints as a potential storage option. The main advantage of such concept with respect to only sensible or only latent choices is related to the possibility to minimize the thermal losses during system charge and discharge processes by reducing the temperature and pressure drops occurring all along the heat transfer process. Thermodynamic models, heat transfer models, plant integration and control strategies for both a pressurized tank filled with sphere-encapsulated salts and high temperature concrete storage blocks were developed within KTH in-house tool DYESOPT for power plant performance modeling. Once implemented, cross-validated and integrated the new storage model in an existing DYESOPT power plant layout, a sensitivity analysis with regards of storage, solar field and power block sizes was performed to determine the potential impact of integrating the proposed concept. Even for a storage cost figure of 50 USD/kWh, it was found that the integration of the proposed storage configuration can enhance the performance of the power plants by augmenting its availability and reducing its levelized cost of electricity. As expected, it was also found that the benefits are greater for the cases of smaller power block sizes. Specifically, for a power block of 80 MWe a reduction in levelized electricity costs of 8% was estimated together with an increase in capacity factor by 30%, whereas for a power block of 126 MWe the benefits found were a 1.5% cost reduction and 16% availability increase.