Building Energy Supply Research Articles

Optimization and simulation of a novel multi-energy complementary heat pump system in cold regions

Solar-assisted ground source heat pump systems(SAGSHPSs) and solar- assisted air source heat pump systems (SAASHPSs) are recognized renewable energy technologies for clean and feasible heating and domestic hot water supply. However, in cold regions, the poor thermal comfort of SAASHPSs and the soil thermal imbalance of SAGSHPSs during heating periods must be resolved urgently. Therefore, to provide an efficient and stable heat source, a multi-energy complementary heat pump system(MECHPS) with seasonal heat storage was designed to meet the needs of building energy consumption. The system comprehensively utilizes solar energy and ambient air for seasonal heat storage during non-heating periods, and then directly provides heat coupled with the ground source heat pump during heating periods. The composition and control strategy of the system were introduced. The system was numerically modeled by the simulation software Transient System Simulation Program (TRNSYS), and the main MECHPS modules were experimentally verified. Additionally, to study the optimal capacity of MECHPS in terms of economy and energy savings, the Hooke-Jeeves algorithm was used for MECHPS capacity optimization with the objectives of minimising the annual cost and maximising the annual savings of standard coal. The results showed that compared with traditional SAASHPSs, the MECHPS exhibited better thermal comfort while maintaining the room temperature above 18 °C. Compared to SAGSHPSs, the MECHPS was able to achieve soil thermal balance, and its soil temperature remained largely constant after 15 years of operation. Finally, compared with the initial scheme, the annual cost reduction rate was 4.98 % under the annual cost optimization scheme and an additional 1310 kg of standard coal could be saved under the annual savings of standard coal optimization scheme. The proposed system provides a way to satisfy the building energy supply for widespread application in cold regions.

Mixed-integer disciplined convex programming approach applied to the optimal energy supply of near-zero energy buildings

Energy needs in the buildings sector accounts for 40 % of global energy demand. Therefore, the implementation of several renewable energy sources is necessary to reduce this demand. The design stage of a decentralized generation project requires quantifying the power to be installed and the energy forecast for each source throughout the useful life of the building. This study develops a novel optimization algorithm for a long-term economic function based on mixed-integer disciplined convex programming (MIDCP) which guarantees the sustainability of the building and its energy systems. The robust algorithm integrates risk management of intermittent sources, technical and economic parameters of selected technologies, and life cycle analysis (LCA) of different energy systems, including storage. Furthermore, the penetration of green hydrogen into the distributed generation mix is evaluated as an important contribution. Meteorological and energy demand variables of two antagonistic scenarios were also used as inputs to the algorithm. As a result, the optimal energy supply sizing for tertiary buildings in the two defined locations was obtained. The results of the simulations have achieved an optimal convergence of 100 % in the proposed scenarios, with a resolution time of 14 s and using a memory of about 183 MB. The simulations suggest a higher penetration of green hydrogen in scenarios where supply and investment costs decrease to gray hydrogen supply levels, reaching up to 81 % coverage of the thermal demand of the building. Hybrid energy systems under favorable conditions show a penetration of about 92 % within the distributed generation mix. The developed tool could enable decision-makers to optimally plan distributed generation projects in buildings based on economic, policy, and geographic conditions.

Pareto navigation for multicriteria building energy supply design

The design of a building’s energy supply is a difficult task, where uncertainty in the requirements has to be taken into account and different conflicting objectives have to be optimized. To date, there exist various studies that consider different objective functions, different concepts of dealing with uncertainty, and different approximation techniques to find efficient solutions. However, there is no approach that gives the decision maker a complete overview of all trade-off solutions with their immediate consequences for the design configuration. This paper addresses the question of how much money and carbon emissions can be saved by allowing a certain amount of undersupply in the heating and cooling of an office building. To explore the trade-offs between the three objectives of minimizing cost, carbon emissions and inconvenience, the Pareto front of the multicriteria linear program is approximated with a Sandwiching algorithm. Then, it is explored using Pareto navigation. This allows to see all (approximate) Pareto points and also to visually observe the behavior of the decision variables by navigating across the front by pulling sliders in a specific software. In a case study, the navigation is demonstrated and ways to overcome modeling limitations that arise from using a fully linear programming approach are shown.

Feasibility study with EnergyPlus simulation for solar chemical heat pump unit introduced into building as next-generation energy supply system

From the viewpoint of rising energy demand and energy costs in buildings, there is an urgent need to develop next generation building energy supply systems characterized by improved resource efficiency and environmental friendliness. The solar chemical heat pump (SCHP) unit can provide heating and cooling in buildings with high efficiency and sustainability, positioning it as a potential candidate. A feasibility study is conducted to introduce the SCHP units into a building in Chiba, Japan, to evaluate the operating characteristics and energy-saving potentials. The building and its HVAC (Heating, Ventilation, and Air Conditioning) system featuring the SCHP unit are introduced into the building energy simulation through EnergyPlus software for the first-step examination. 3E (energy, environment, economy) analysis of the distinctions among conventional, chemical heat pump (CHP), and SCHP systems is conducted to enhance the efficiency of building energy supply systems. Furthermore, the effects of different climate zones and heat and electricity storage equipment on operation characteristics are studied. The study reveals that the SCHP system demonstrates a 75% lower energy consumption, 72% decreased CO2 emissions, and 73% reduced running costs than the conventional system in Chiba City. Moreover, it is shown that integrating the heat storage tank and the electricity storage battery into the SCHP system can reduce reliance on external energy, significantly enhancing the system efficiency.

Preparation and thermal performance study of a novel hydrated salt composite PCM for space heating

In order to effectively address the mismatch between thermal energy supply and demand in buildings, latent heat storage (LHS) based on phase change material (PCM) stands out as a key technology. While hydrated salt has emerged as a promising PCM, it encounters common issues such as substantial supercooling, phase separation, and low thermal conductivity, hindering its development. To mitigate these limitations, this study focused on modifying Ba(OH)2·8H2O by incorporating various nucleating agents and thickening agents to reduce supercooling, enhancing the composite PCM's thermal properties by introducing expanded graphite (EG) to elevate thermal conductivity. Subsequently, the thermal stability of the PCM was evaluated through accelerated thermal cycling tests, encompassing the assessment of critical thermal parameters, including supercooling degree, enthalpy, and thermal conductivity of the composite PCM. Experimental findings unveiled the effectiveness of incorporating 2 wt% BaCl2·2H2O and 1 wt% CMC to Ba(OH)2·8H2O, effectively diminishing the supercooling degree from 14 °C to 1.42 °C. Further integration of 3.5 wt% EG led to a substantial decrease in the supercooling degree to 0.24 °C. Simultaneously, the addition of EG resulted in an improvement in thermal conductivity, elevating it from 0.62 W/(m·K) to 1.03 W/(m·K), while the enthalpy decreased from 283.68 J/g to 252.81 J/g. Notably, the composite PCM exhibited notable thermal reliability with a latent heat drop of 15.9 % following 1000 accelerated cycles of testing. Moreover, the composite PCM demonstrated superior thermal storage density, measuring at 2.36 times that of traditional paraffin wax, yet with a thermal storage cost merely a quarter of paraffin wax, rendering it more favorable for extensive deployment in building energy systems.

Modeling and exergy-economy analysis of residential building energy supply systems combining torrefied biomass gasification and solar energy

A novel hybrid energy system driven by torrefied biomass gasification and solar energy is proposed for the first time, and their complementarity to enhance the system’s energy efficiency is analyzed and shown. The system mainly combines biomass torrefaction, biomass gasification subsystem, solar heat collection and absorption refrigeration technology. The effects of different operating parameters on the gasification products were studied. The economic analysis is carried out based on the theory of exergy economy. The results show that torrefaction pretreatment of biomass can significantly improve its fuel quality and gasification performance. With the increase of torrefied temperature, the volume fraction of CO2 and H2 decreased while the volume fraction of CH4 and CO increased. The economic analysis shows that the expected annual income is $72,735, and the investment recovery period is 2.89 years. Through the calculation of the energy-saving and environmental benefits, it can be concluded that the hybrid energy system can save 1.05 × 106 MJ of heat per year. This equates to about 358.26 tons of standard coal or a CO2 emission reduction of 550.59 tons, the participation of solar energy is conducive to the system emission reduction. By tuning the parameter sensitivity, the influence of biomass price change on the unit exergy cost of system products was more obvious.

Blended finance as a catalyst for accelerating the European heat transition?

Against the background of accelerating climate change, this paper examines to which extent sustainable infrastructure finance can effectively contribute to the European heat transition as a part of a “Great Transformation” towards a climate neutral economy and society. Since the building sector is responsible for approximately 35% of the EU's carbon footprint, district heating and cooling networks can provide an efficient technology for decarbonizing the energy supply of buildings. New district heating and cooling networks technology allows for heat and hot water generation that is combustion free. A large-scale role-out of this infrastructure would require hundreds of billions EUR of investments within the next few years. In view of the high public debt, the public sector will not be able to finance the required investment volumes. Against the background of regulatory changes, such as the EU Action Plan on Financing Sustainable Growth, this paper examines in which way financial markets participants might be able to fill the funding gap. A particular focus lies on blended finance, since related instruments reduce investors' risks, esp. in early stages of the infrastructure lifecycle. Due to an improved risk-return-relationship this makes the investment more attractive to private investors. It is also essential for investors to understand the kind of business model they invest in. Therefore, we discuss the importance of key performance indicators in the four dimensions that are relevant for the investors' decision-making process: return, risk, liquidity and sustainability. With respect to the sustainability dimension, we elaborate on the relevance of EU-Taxonomy-aligned district heating and cooling networks' construction and operation.

Least-cost solutions to household energy supply decarbonisation in temperate and sub-tropical climates

Decarbonisation of building energy supply is key to achieving current targets of greenhouse gas emission reduction. However, the least-cost, net-zero supply of electrical and thermal loads in residential buildings is affected by building type, local climate and grid emissions intensity and is subject to uncertain future energy prices. This work investigated a typical detached house and an apartment in two climates – temperate and sub-tropical – in Australia. Least-cost optimisation of the technology mixes required to serve building energy loads was undertaken, including a range of appliances powered by electricity, natural gas and hydrogen and the use of distributed energy resourced, notably rooftop solar and residential battery energy storage. Solutions were investigated with increasingly stringent greenhouse gas emission abatement constraints and a range of future prices for electricity and hydrogen, demonstrating: i) progressive electrification is the likely cheapest pathway to net-zero emissions for the two building types studied; ii) should grid decarbonisation lag the abatement constraint applied to the homes, a net-zero dwelling is likely unachievable and the deepest achievable abatement is very expensive; and iii) network-delivered hydrogen may be optimal in a subset of buildings with limited distributed energy resources potential and more peaky heating and hot water demands. In such cases, bio-methane or even synthetic methane may also be preferred. Through significant adoption of distributed energy resources, results suggest an affordable route to deep (i.e. > 50 %) abatement for homeowners that relies less on grid emissions and, beyond the Australian case study, can be extended to a significant proportion of dwellings in other countries.

Calculation of the economic and environmental efficiency of introducing advanced technologies in the energy supply of buildings

This article discusses the use of advanced cogeneration technologies at existing combined heat and power plants, regulating the supply of thermal energy in a building using an individual heating point. For Uzbekistan, an urgent problem is the serious study of the use of energysaving technologies, in particular in the heat supply systems, for the efficient use of investments. The achieved effect of reducing specific energy consumption for the production and consumption of thermal energy to the level of world standards will ensure the energy and environmental security of the country, which urgently requires accelerating the implementation of these projects. The search for large and small projects for the technical and technological renewal of production to ensure the competitiveness of products, as well as the means and sources for this should first become the most important task and responsibility of the manager and engineering staff of each heat supply enterprise. The article provides calculations on the basis of which the payback, investment, efficiency of measures in the field of renewable energy sources for electricity and heat supply are determined, as well as the calculation of thermal energy savings when installing an individual heating point.

A collaborative matching method for multi-energy supply systems in office buildings considering the random characteristics of electric vehicles

Multi-energy supply systems for office buildings have been rapidly developed. Although some combinations of distributed energy sources have been applied in office buildings, there is a lack of research on the collaborative matching of office building multi-energy supply systems that integrate random electric vehicles (EVs), stationary battery (STB), photovoltaic (PV), and the power grid (PG). Therefore, in this study, we propose a method for the collaborative matching of supply and demand for multi-energy systems integrated with random EVs, STB, PV, and PG in office buildings to minimize the net operating cost of the system. To this end, we first constructed an objective function, including system operating cost and operating revenue. We then modeled the supply and demand sides of the system. On the supply side, the travel parameters of EVs around the office building were investigated, and the randomness of EVs was quantified using the Monte Carlo algorithm. On this basis, the charging and discharging capacity of EVs was determined. Additionally, an STB charging and discharging model and PV power generation model were established. On the demand side, a prediction model of office building power consumption was constructed using the Random forest (RF) algorithm. Next, the energy supply and demand of office buildings for the following 24 h were matched collaboratively using nonlinear programming. Finally, the proposed collaborative matching method was applied to a real case study. The results showed that the matching method can reduce the net operating cost of the system by up to 92% compared with the Basic scenario.

Environmental Impact Analysis of Residential Energy Solutions in Latvian Single-Family Houses: A Lifecycle Perspective

This study aims to compare the technological solutions that can contribute to more sustainable energy use in the residential sector. Specifically, the goal of the study is to evaluate the environmental impact of different energy (heat and electricity) supply technologies applicable for an average size single-family building in Latvia, a country known for climatic condition characterized by cold winters with frequent snowfall. The study applies the lifecycle assessment methodology of ISO 14040 and the impact assessment method known as ReCiPe 2016 v1.1, which has not been used before for the scope addressed in the study in the context of single-family building energy supply technologies for climatic conditions in Latvia. Thus, the results of the study will provide new information for more sustainable energy solutions in this area of study. The technologies included in the defined scenarios are conventional boiler, electricity from the grid, Stirling engine, and solar photovoltaics (PV). The results of the lifecycle impact assessment for damage categories revealed that all scenarios have a high impact on human health due to fine particulate matter formation followed by global warming. Regarding the damage to the ecosystem, the terrestrial ecotoxicity category has highest impact, followed by global warming. Sensitivity analyses affirmed the model’s validity and also showed that the impacts of conventional systems were most sensitive to changes in electricity consumption, and therefore, the scenarios with electricity supply from a Stirling engine or PV can be considered a more robust solution under changing electricity demands from an environmental perspective.

Performance of energy piles foundation in hot-dominated climate: A case study in Dubai

Energy piles represent an innovative technology that can help provide sustainable geothermal heating or cooling energy for thermal conditioning purposes. In hot-dominated climates, the interest is to inject heat in the ground and extract energy for space-cooling purposes. This study evaluates the feasibility of energy piles in these regions through three-dimensional numerical modelling. The modelling framework is validated against a published experiment and is able to sufficiently capture the development of outlet temperature over time. The numerical analysis is then used to evaluate a case study in Dubai where it is targeted to provide 40 % of the cooling demand of a typical building. The unbalanced energy demand causes an increase in the outlet temperature of the heat carrier fluid and the radial temperature over time. However, observation of long-term behaviour indicates that the temperature increase is most significant in the initial years and gradually stabilizes over time. This stabilization enables to respect the outlet temperature limitation of the heat pump over 50 years. A sensitivity analysis confirms these observations with respect to system dimensioning variables. The obtained results highlight the effectiveness of energy piles to decarbonize energy supply in buildings in hot-dominated climates via the use of renewable energy sources.

A novel operation method for renewable building by combining distributed DC energy system and deep reinforcement learning

Reducing carbon emissions has been a focus problem with the rapidly increasing building energy consumption. One solution is adopting more Renewable Energy Resources (RESs) for building energy supply. To overcome the intermittence of RESs, researchers paid efforts in flexible demand response based on centralized operation and model-based control, however, which get challenges for scalability and uncertain dynamic building systems. Moreover, few works have considered user willingness as an important part of human–machine interaction and user satisfaction. Thus, we propose a novel operation method called DC-RL for renewable building energy systems. DC-RL designs a distributed DC energy system, which is scalable, control-friendly, and provides users the willingness option for flexible operation. For energy control, DC-RL adopts a model-free deep reinforcement learning (DRL) algorithm Soft-Actor-Critic (SAC) to adjust demand to matching renewable supply with maintaining user satisfaction. We evaluate DC-RL on two real-life datasets. Compared to baselines, DC-RL improves energy saving and PV self-consumption by 38% and user satisfaction by 9%. DC-RL achieves near-zero-carbon buildings with 93% self-sufficiency rate and reduces up to 33% of battery dependency.

Towards positive energy islands – a Danish case study

The Danish island of “Ærø” has the ambition of becoming the first Danish island to be self-sufficient in renewable energy and CO2 neutral by 2025, as well as fossil fuel free by 2030. This work investigates the feasibility of re-designing part of the island’s energy system to become the first Danish positive energy island (PEI), evaluating various design scenarios and opportunities for improving and modifying the current energy supply and distribution scheme. The district is modelled considering all building specifications and characteristics and the energy supply systems using the urban scale modelling tool City Energy Analyst (CEA). A simulation of the base-case scenario is performed to calibrate the performance. Different energy improvement strategies targeting building envelopes and energy generation and supply systems are created and implemented in CEA. Six improvement packages are created and simulated. It is demonstrated that a PEI could be built in the district under consideration through a comprehensive energy improvement package of envelope-targeting techniques, energy system upgrades, and the expansion of renewable energy systems. The package includes LED lighting, heat pump installation, and photovoltaic-thermal units. This will enable meeting the annual net need for electricity while producing 20% excess heat.

Game and multi-objective optimization of configurations for multiple distributed energy systems considering building users’ demands and satisfaction degrees

Sustainable building energy supply is crucial to the sustainable development of society, and replacing the separation production energy system with a hybrid renewable energy distributed energy system (DES) can help achieve this goal. However, there are challenges to the application of such building DES, such as collaboration between multiple DESs, conflicts between DESs and users, and user energy management/evaluation. While existing works rarely consider them simultaneously. Therefore, this work presents a two-stage collaborative optimization model to solve these issues. The first-stage optimizes the structures and capacities of DESs and the electricity and heat interchanges between DESs to maximize energy, economic, and emission performances. Based on user energy consumption elasticity, the second-stage evaluates DES revenue and user energy consumption utility/satisfaction to perform a multi-leader and multi-follower game. The interactive game determines energy prices and manages the hourly building user demands. A case study shows the validation of the proposed method. The results indicate that from the initial stage to reaching game equilibrium, the revenue of DESs decreases by approximately 11.2 % due to the declined energy prices, which increase users' hourly loads. Then, users’ utility can be increased by 7.0 % due to satisfaction improvement. Moreover, the renewable energy penetration rate in DESs is increased by 7.1 %, and the relative energy, economic, and emission performances (the baseline is traditional separation production system) of DESs are increased by 5.9 %, 0.5 %, and 4.5 %, respectively. The proposed framework helps to design/manage clean and efficient building energy systems and formulate reasonable energy prices, favoring DES development and carbon neutrality goals.

Thermal performance of energy barrettes in an urban environment

Thermal performance of energy barrettes in an urban environment

Mixed‐integer NMPC for real‐time supervisory energy management control in residential buildings

AbstractIn recent years, building energy supply and distribution systems have become more complex, with an increasing number of energy generators, stores, flows, and possible combinations of operating modes. This poses challenges for supervisory control, especially when balancing the conflicting goals of maximizing comfort while minimizing costs and emissions to contribute to global climate protection objectives. Mixed‐integer nonlinear model predictive control is a promising approach for intelligent real‐time control that is able to properly address the specific characteristics and restrictions of building energy systems. We present a strategy that utilizes a decomposition approach, combining partial outer convexification with the Switch‐Cost Aware Rounding procedure to handle switching behavior and operating time constraints of building components in real‐time. The efficacy is demonstrated through practical applications in a single‐family home with a combined heat and power unit and in a multi‐family apartment complex with 18 residential units. Simulation studies show high correspondence to globally optimal solutions with significant cost savings potential of around 19%.

Performance analysis of the phase-change heat-storage tank based on numerical simulation

Phase-change heat storage system contributes to the smooth operations of building energy supply and demand. In this paper, the numerical model of the heat-storage tank with phase change material blocks is established. The charge and discharge process of the heat-storage tank is analyzed with the numerical model. The performances of the heat-storage tank with and without phase change material blocks are compared by experiment and numerical simulation. The effects of structural parameters of phase change material blocks on the heat storage and release rate are comprehensively discussed, including the number and size of phase change material blocks. The results indicate that under the experimental conditions, the charge capacity and duration of the tank with phase change material blocks are extended by 7.43% and 8.3% respectively under the condition of replacing 6.75% volume of hot water with phase change material. The thermal stratification phenomenon in the heat-storage tank without phase change material blocks is more obvious. For certain volume of the phase change material, the performance analysis of three cases with different amount and size of phase change material blocks is investigated. The results show that the phase change material blocks with number and size of 24 and 0.45 m × 0.1 m × 0.1 m reduces the charge and discharge duration by 2.47% and 3.78% compared with those of 12 and 0.9 m × 0.1 m × 0.1 m.

Optimization of an integrated system including a photovoltaic/thermal system and a ground source heat pump system for building energy supply in cold areas

The photovoltaic (PV) collectors tend to overheat in summer, which reduces the efficiency of power generation. The unbalanced heating and cooling loads cause the ground source heat pump (GSHP) system to operate unstably in severe cold areas. To solve the above two problems simultaneously, an integrated system including a photovoltaic/thermal system and a ground source heat pump system (PVT-GSHP) was proposed, which had an extremely high energy utilization efficiency. However, the complex variation of cooling and heating loads was influenced by meteorological conditions over time. The demand of efficient operation and good economy of the system challenged the optimal configuration and control strategy among multiple energy sources, which was investigated in this study. A dynamic model of the PVT-GSHP system based on TRNSYS was developed and the corresponding control strategy was formulated. The genetic algorithm was used to optimize the matching of buried pipe lengths and PVT collector areas. The effects of different matching on the system parts and the whole performance were analyzed. The results show that increasing the PVT collector area can increase the ground temperature and shorten the buried pipe length, but it is not good for summer cooling, thus there is an optimal match. Compared with two independent systems of the traditional GSHP system and PV generation system, the PVT-GSHP system has excellent advantages and application prospects because it has 48.3% reduction in the total buried pipe length, 68.89% reduction in the footprint area of ground heat exchangers, 10% increase in the heating coefficient of performance (COP) and 72.3% reduction in life circle cost. This study provides theoretical support for the optimal design of the PVT-GSHP systems and similar complementary multi-energy systems.

Factors Affecting the Efficiency of Photovoltaic System

The world's most important source of energy is the sun. The solar heating energy is the main energy source that affects the physical formations in the earth and atmosphere system. Matter and energy flows in the world are possible thanks to solar energy. Wind, sea wave, temperature difference in the ocean and biomass energies are modified forms of solar energy. Solar energy also plays a role in the realization of the water cycle in nature and creates the power of the stream. Solar energy, which is the origin of most of the natural energy sources, is directly used for purposes such as heating and electricity generation. One of the strategic goals of developed and developing countries is expanding the use of energy resources. Solar energy is almost the most widely used of alternative energy sources. In the presented article, the factors influencing the efficiency of the photovoltaic system have been determined in order to achieve effective results in the construction of the photovoltaic system. Based on the obtained indicators, it is aimed to build a photovoltaic system based on a GaAs photocell with 75% efficiency in the educational building. Aims: The goal is to use solar panels to ensure continuity of energy supply in educational buildings. Initially, it was considered to determine the parameters that will affect the efficiency of the solar panel system used.