Research

25 pages, 835 KiB

Open AccessArticle

Unlocking the Flexibility of District Heating Pipeline Energy Storage with Reinforcement Learning

by Ksenija Stepanovic, Jichen Wu, Rob Everhardt and Mathijs de Weerdt

Energies 2022, 15(9), 3290; https://doi.org/10.3390/en15093290 - 30 Apr 2022

Cited by 4 | Viewed by 1940

The integration of pipeline energy storage in the control of a district heating system can lead to profit gain, for example by adjusting the electricity production of a combined heat and power (CHP) unit to the fluctuating electricity price. The uncertainty from the [...] Read more.

The integration of pipeline energy storage in the control of a district heating system can lead to profit gain, for example by adjusting the electricity production of a combined heat and power (CHP) unit to the fluctuating electricity price. The uncertainty from the environment, the computational complexity of an accurate model, and the scarcity of placed sensors in a district heating system make the operational use of pipeline energy storage challenging. A vast majority of previous works determined a control strategy by a decomposition of a mixed-integer nonlinear model and significant simplifications. To mitigate consequential stability, feasibility, and computational complexity challenges, we model CHP economic dispatch as a Markov decision process. We use a reinforcement learning (RL) algorithm to estimate the system’s dynamics through interactions with the simulation environment. The RL approach is compared with a detailed nonlinear mathematical optimizer on day-ahead and real-time electricity markets and two district heating grid models. The proposed method achieves moderate profit impacted by environment stochasticity. The advantages of the RL approach are reflected in three aspects: stability, feasibility, and time scale flexibility. From this, it can be concluded that RL is a promising alternative for real-time control of complex, nonlinear industrial systems. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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20 pages, 4674 KiB

Open AccessArticle

Greening of the District Heating Systems—Case Study of Local Systems

by Artur Wyrwa, Maciej Raczyński, Maciej Kulik, Oluwalana Oluwapelumi, Laura Mateusiak, Haoran Zhang and Marek Kempka

Energies 2022, 15(9), 3165; https://doi.org/10.3390/en15093165 - 26 Apr 2022

Viewed by 1663

Abstract

The integration of renewable energy resources into district heating systems is gaining momentum across Europe, as heat producers are expected to work towards the EU Directive of Efficient District Heating and Cooling to achieve carbon neutrality by 2050. This paper studies the techno-economic [...] Read more.

The integration of renewable energy resources into district heating systems is gaining momentum across Europe, as heat producers are expected to work towards the EU Directive of Efficient District Heating and Cooling to achieve carbon neutrality by 2050. This paper studies the techno-economic implications of transforming conventional district heating systems of six locations in Poland, generating 8.5 PJ of heat annually, into sustainable and efficient district heating systems. These new systems consist of flat solar collectors integrated with seasonal pit thermal energy storages and gas heating plants, acting as flexible heat sources, covering residual heat demand and/or increasing the parameters of the working medium in the network. Using the IEA-TIMES software, two scenarios were considered, namely STAT and DYN. The results show that reaching a 20% share of heat production by solar thermal would demand extra construction of seasonal heat storage facilities with a total capacity of 197 TJ, which is approximately 4.5 times bigger than the largest seasonal heat storage located in Vojens, Denmark. The projected increase in the prices of natural gas and CO₂ emission allowances accelerates the transformation of systems towards greater use of solar heating plants. In the period 2025–2050 the heat generation costs increase by ca. 65%. The contribution of the CAPEX and OPEX costs components are presented. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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13 pages, 2075 KiB

Open AccessArticle

Thermal Storage for District Cooling—Implications for Renewable Energy Transition

by Efstathios E. Michaelides

Energies 2021, 14(21), 7317; https://doi.org/10.3390/en14217317 - 04 Nov 2021

Cited by 1 | Viewed by 1428

Abstract

The utilization of air conditioning in public and private buildings is continuously increasing globally and is one of the major factors fueling the growth of the global electricity demand. The higher utilization of renewable energy sources and the transition of the electricity-generating industry [...] Read more.

The utilization of air conditioning in public and private buildings is continuously increasing globally and is one of the major factors fueling the growth of the global electricity demand. The higher utilization of renewable energy sources and the transition of the electricity-generating industry to renewable energy sources requires significant energy storage in order to avoid supply–demand mismatches. This storage-regeneration process entails dissipation, which leads to higher energy generation loads. Both the energy generation and the required storage may be reduced using thermal energy storage to provide domestic comfort in buildings. The development and utilization of thermal storage, achieved by chilled water, in a community of two thousand buildings located in the North Texas region are proven to have profound and beneficial effects on the necessary infrastructure to make this community independent of the grid and self-sufficient with renewable energy. The simulations show that both the necessary photovoltaics rating and the capacity of the electric energy storage system are significantly reduced when thermal storage with a chilled water system is used during the air conditioning season. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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15 pages, 2809 KiB

Open AccessArticle

Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 2: Estimation of Present Thermal Conductivity in Aged Pipe Insulation

by Peter Lidén, Bijan Adl-Zarrabi and Carl-Eric Hagentoft

Energies 2021, 14(17), 5302; https://doi.org/10.3390/en14175302 - 26 Aug 2021

Cited by 7 | Viewed by 1344

Abstract

Buried and operating district heating (DH) pipes are exposed to thermal degradation of their polyurethane (PUR) insulation over time, and their status is hard to assess without excavation. By using DH pipe valves in manholes as measurement points during a shutdown with an [...] Read more.

Buried and operating district heating (DH) pipes are exposed to thermal degradation of their polyurethane (PUR) insulation over time, and their status is hard to assess without excavation. By using DH pipe valves in manholes as measurement points during a shutdown with an ensuing cooling period, non-destructive assessments can be performed. This study compares new improved field measurements with numerical simulations of the temperature decline in drainage valves and shutdown valves. The drainage valve measurements were used to thermally assess part of a buried DH network. Results indicate that by using the drainage valves as measurement points in a cooling method, the thermal conductivity of the buried DH network could be predicted with an accuracy of >95%. In addition, a general diagnostic protocol has been established for assessing the thermal status of a DH network, ready for network owners to use. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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15 pages, 4579 KiB

Open AccessArticle

Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 1: Estimation of Supply Pipe Temperature by Measuring Temperature at Valves after Shutdown

by Peter Lidén, Bijan Adl-Zarrabi and Carl-Eric Hagentoft

Energies 2021, 14(16), 5192; https://doi.org/10.3390/en14165192 - 22 Aug 2021

Cited by 3 | Viewed by 1385

Abstract

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down [...] Read more.

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down and the temperature decline in the valves was analysed in terms of absolute temperature and thermal response time from the DH pipe to the top of the valve. The calculated and measured supply pipe temperatures by the drainage valves were in good agreement, with 1% deviation. The valve measurement analysis from this study shows that the drainage valve has good potential to serve as a measurement point for assessing the thermal status of a DH network. However, the shutdown valve measurements were greatly affected by the manhole environment. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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20 pages, 3811 KiB

Open AccessArticle

Economic Dispatch of CHP Units through District Heating Network’s Demand-Side Management

by Pavel Rušeljuk, Kertu Lepiksaar, Andres Siirde and Anna Volkova

Energies 2021, 14(15), 4553; https://doi.org/10.3390/en14154553 - 28 Jul 2021

Cited by 5 | Viewed by 1516

Abstract

Optimisation of heat and electrical load distribution, where the objective function is the maximum efficiency of the CHP unit for a given load range, can be done considering the limitations of electrical power and the heat load. Simulating a real CHP unit with [...] Read more.

Optimisation of heat and electrical load distribution, where the objective function is the maximum efficiency of the CHP unit for a given load range, can be done considering the limitations of electrical power and the heat load. Simulating a real CHP unit with a district heating network shows that demand-side management can improve the overall economic efficiency of the CHP plant and increase the unit’s operating range in the electricity spot market. Economic dispatch makes it possible to determine a reasonable additional increase in the electric power of the CHP unit, and to optimise the supply temperature and mass flow of the district heating network. The results obtained and the analysis performed indicate that the proposed methodology provides logical results and can be used to calculate the efficiency indicators of the cogeneration of electrical and thermal energy. The problem of optimising the operating mode of the CHP unit was solved, which allows us to determine the optimal additional increase in the unit’s electrical load at a given heat load of consumers, which on average increases the CHP unit’s efficiency up to an additional 1.5%. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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13 pages, 1640 KiB

Open AccessArticle

Optimizing Large-Scale Solar Field Efficiency: Latvia Case Study

by Ilze Polikarpova, Roberts Kakis, Ieva Pakere and Dagnija Blumberga

Energies 2021, 14(14), 4171; https://doi.org/10.3390/en14144171 - 10 Jul 2021

Cited by 7 | Viewed by 1979

Abstract

Solar energy transformation technologies are increasingly being used worldwide in the district heating sector. In the Baltic states, only one district heating company has implemented a large-scale solar collector field into its thermal energy production system, which is analyzed within this research. In [...] Read more.

Solar energy transformation technologies are increasingly being used worldwide in the district heating sector. In the Baltic states, only one district heating company has implemented a large-scale solar collector field into its thermal energy production system, which is analyzed within this research. In this study, we analyzed the first year operation of the solar field, solar collector efficiency, and several influencing factors, i.e., ambient air temperature, heat carrier flow, and the temperature difference between the supply and return heat carrier temperatures. The study includes collecting and compilation of the data, analyzing influencing factors, and data analysis using the statistical analysis method. In addition, the research presents a simplified multi-regression model based on the actual performance of a large-scale solar field, which allows for forecasting the efficiency of solar collectors by taking into account the main operational parameters of the DH system. The results show that solar energy covers around 90% of the summer heat load of a particular district heating system. However, they also show room for improvements in producing all the necessary heat in the summer using solar energy. The regression analyses show that the most significant correlation between all parameters examined was obtained in May, reaching R² = 0.9346 in solar field efficiency evaluation. This is due to several suitable conditions for solar energy production, i.e., placing solar collectors at an angle for them to be the most productive, having enough space in the storage tank, and the demand for thermal energy being still higher than in the summer months. Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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15 pages, 1249 KiB

Open AccessArticle

Supra-Regional District Heating Networks: A Missing Infrastructure for a Sustainable Energy System

by Simon Moser and Stefan Puschnigg

Energies 2021, 14(12), 3380; https://doi.org/10.3390/en14123380 - 08 Jun 2021

Cited by 4 | Viewed by 3114

Abstract

In analogy to electricity transmission networks, this paper analyzes the concept of supra-regional district heating networks (SR-DHN), connecting a large number of actors. Using a back-casting approach, a SR-DHN is assumed to exist and thus, implementation challenges, such as economic feasibility and energy [...] Read more.

In analogy to electricity transmission networks, this paper analyzes the concept of supra-regional district heating networks (SR-DHN), connecting a large number of actors. Using a back-casting approach, a SR-DHN is assumed to exist and thus, implementation challenges, such as economic feasibility and energy losses, are circumvented in the first step (but are analyzed in the discourse). The paper then analyzes, in an interdisciplinary qualitative manner and supported by a case study, what technical, operational, economic and legal issues must have been resolved. Results show that the heat transmission network, being the backbone of the SR-DHN, is an expensive infrastructure, but is likely to become economic in a non-fossil energy system. By decreasing the reliance on single waste heat sources, SR-DHN allows longer payback periods and can thus be an enabler for using industrial waste heat. However, involving many actors requires comprehensive contractual foundations. The derived hypothesis is that SR-DHN, which is predominantly fed by waste heat, shall be operated with lower temperatures in winter (feeding the return while minimizing expensive winter losses) and high temperatures in summer (enabling alternative usages while accepting high but inexpensive summer losses). Full article

(This article belongs to the Special Issue Recent Advances in District Heating)

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