The important focus of the energy strategy of the European Union relies on the concept of zero energy building (ZEB), which is, by definition, a building that roughly produces yearly as much ...renewable energy as it consumes. This article proposes an enhanced mixed-integer nonlinear programming model for optimal sizing of photovoltaic (PV) and battery energy storage systems to comply with the definition of a ZEB. A salient novel feature of the proposed model is that it factors in the environmental impacts, computed through rigorous life cycle assessment methodology, of buying electricity from the grid and manufacturing battery and PV systems. Furthermore, an adjustable parameter is introduced to make the model adaptive from the perspective of the building owner's willingness-to-pay for environmental impacts. The proposed model is then rigorously reformulated, managing to accumulate its nonlinearity in only one constraint per time interval. Eventually, the reformulated model is linearized to a mixed-integer linear programming model using the McCormick relaxation technique. The case study conducted on archetypal buildings in Luxembourg reveals that the proposed McCormick-based linear model is able to provide high accuracy results with reasonable computational effort.
This paper proposes a new bi-objective optimization model, trading-off cost and environmental impacts, for sizing the key electrical and thermal devices in a zero energy building (ZEB), i.e., a ...building that roughly generates as much renewable energy as it consumes annually. A salient novel feature is the consideration of the environmental impacts, computed through a rigorous life cycle assessment approach, of buying electricity from the grid and manufacturing devices. Furthermore, an enhancement of the proposed model, as compared to the existing models, is to prioritize storing the ZEB excess of energy rather than selling it to the grid. The proposed solution approach of the initial mixed-integer nonlinear programming model relies on McCormick relaxation linearization to obtain a more tractable mixed-integer linear model. An augmented ϵ-constraint method is applied to solve the obtained bi-objective model. Finally, considering the building owners' willingness-to-pay for environmental impacts, a decision-making criterion is proposed to select the optimal size of the devices among all non-dominated solutions of the Pareto front.
Abstract
This study aims to assess the accuracy of a building performance simulation (BPS) model developed in IDA ICE software, focusing on heating energy use and indoor air temperatures in a ...low-energy multi-story residential building located in Northern Denmark. Six apartments were analyzed, and a comparative analysis was conducted between the measured parameters and the results obtained from BPS models with different spatial and temporal resolutions. The findings indicate that while the BPS models can provide reasonably accurate estimates of heating energy use, they may not fully capture the nuanced response to factors such as indoor air temperature This highlights the importance of incorporating qualitative inputs and environmental variables into these BPS models, including heating and/or cooling setpoints, internal gains, and weather conditions. Overall, this study provides insights into the limitations and opportunities of BPS models for accurately estimating heating energy use and indoor air temperatures in low-energy residential buildings.
Applying phase change material (PCM) for latent heat storage in sustainable building systems has gained increasing attention. However, the nonlinear thermal properties of the material and the ...hysteresis between the two-phase change processes make the modelling of PCM challenging. Moreover, the influences of the PCM phase transition and hysteresis on the building thermal and energy performance have not been fully understood. This paper reviews the most commonly used modelling methods for PCM from the literature and discusses their advantages and disadvantages. A case study is carried out to examine the accuracy of those models in building simulation tools, including four methods to model the melting and freezing process of a PCM heat exchanger. These results are compared to experimental data of the heat transfer process in a PCM heat exchanger. That showed that the four modelling methods are all accurate for representing the thermal behavior of the PCM heat exchanger. The model with the DSC Cp method with hysteresis performs the best at predicting the heat transfer process in PCM in this case. The impacts of PCM phase change temperature and hysteresis on the building energy-saving potential and thermal comfort are analyzed in another case study, based on one modelling method from the first case study. The building in question is a three-room apartment with PCM-enhanced ventilated windows in Denmark. The study showed that the PCM hysteresis has a larger influence on the building energy consumption than the phase change temperature for both summer night cooling applications and for winter energy storage. However, it does not have a strong impact on the yearly total energy usage. For both summer and winter transition seasons, the PCM hysteresis has a larger influence on the predicted percentage of dissatisfied (PPD) than the phase change temperature, but not a strong impact on the transition season average PPD. It is therefore advised to choose the PCM hysteresis according to whether it is for a summer night cooling or a winter solar energy storage application, as this has a significant impact on the system’s overall efficiency.
In Hot Summer and Cold Winter Climate Zone, the cooling potential of natural/passive night ventilation is limited during summer due to the insignificant difference between the outdoor and indoor ...temperatures. Therefore, a novel mechanical ventilation strategy, the wall-mounted attached ventilation (WAV) system, is proposed in the present paper to improve ventilation efficiency of night cooling. The idea is that WAV can produce a downward airflow over the internal wall surface that is somewhat similar to a sidewall jet, so as to achieve enhanced heat transfer in the room. This paper starts with a series of experiments in a test chamber, and continues with thermal analysis of the heat transfer characteristics and heat removal performance of WAV. The performance of night ventilation with WAV is further evaluated in terms of ventilation efficiency index and energy performance index. It is shown that the overall average value of the convective heat transfer coefficient at the internal wall surface with WAV is 10.79 W m−2 °C−1. With WAV, the amount of heat removed from the ventilated wall is about five times that in the natural night ventilation case, and the total amount of heat removed from the whole chamber is twice as much. The average value of the surface cooling effectiveness of WAV is 1.48, and the overall coefficient of performance (COP) of WAV turns out to be 26.8. As a night ventilation strategy, WAV is capable to achieve good cooling performance under hot summer conditions.
•A novel wall-mounted attached ventilation (WAV) night cooling system proposed.•Experiments carried out to understand the temperature decreasing effect of WAV.•Transient heat transfer models established to analyse the thermal performance of WAV.•WAV has much better performance on surface cooling and heat removal than natural ventilation.
This paper proposes a ventilated window with a phase change material (PCM) heat exchanger as a new window application. In summer, night ventilation mode is operated to discharge energy stored in PCM ...by the ambient cold air, which can be reloaded again, when ventilation pre-cooled air is provided.
Numerical model is built and verified by full-scale experiment to evaluate the PCM ventilation system. The nonlinear properties and hysteresis of PCM are set in the model. The conclusion is that the configuration optimization should be based on different climates. In the case study in Copenhagen, the heat exchanger with 10 mm plate thickness is optimized. It can cool down the ventilated air 6.5 °C on average in 3.9 h pre-cooling effective time with 3.19 MJ/day energy saving. The material cost saving is 16.87% compared to 20 mm plate thickness which has similar discharged heat amount. Nevertheless, the heat exchanger with 5 mm plate thickness has a faster thermal response and a higher cost saving ability, which is good for the climate when the period of outdoor air temperature suitable for night ventilation in a day is short.
A novel system combining diffuse ceiling ventilation and radiant ceiling was proposed recently, with the aim of providing energy efficient and comfort environment to office buildings. Designing of ...such a system is challenging because of complex interactions between the two subsystems and a large number of design parameters encountered in practice. This study aimed to develop a numerical model that can reliably predict the airflow and thermal performance of the integrated system during the design stage. The model was validated by experiments under different operating conditions. The validated model was further applied to evaluate the effects of different design parameters, including the
U
-value of the diffuse ceiling panel, plenum height, plenum depth, and inlet configuration. In the integrated system, diffuse ceiling separated the radiant ceiling from the rest of the room and consequently changed the energy efficiency of the radiant system. The simulated results demonstrated that using ceiling panel with a higher
U
-value can minimize this impact and make the system to cool down space efficiently. Low plenum height was beneficial to the energy efficiency, but aggravated the non-uniformity air distribution and further led to the draught problem in the occupied zone. This system was recommended to apply in the small offices instead of large, open spaces.
•The integrated systems with radiant heating/cooling and ventilation are reviewed.•Thermal comfort and air quality of various integrated systems are discussed.•Design recommendations are given for ...selecting and designing the integrated systems with radiant heating/cooling and ventilation.
Radiant heating and cooling (RHC) systems typically work together with ventilation systems in order to take care of sensible loads, latent loads and pollutants. There are various combinations according to the location of radiant surfaces and air distribution principles. Even though there are extensive researches on radiant systems and ventilation systems individually, the design and performance of the integrated systems have not been discussed systematically. The objective of this paper is to summarize the integrated system configurations in the building environment from both scientific researches and practical applications, and to identify the system characteristics and suitable application area. The focus of this paper is on thermal comfort and indoor air quality and the critical design parameters that have impacts on these two aspects, such as location and amount of heat sources, contaminant source types, room geometry, and condensation risk. Design recommendation has been given at the end for selecting and designing the integrated systems, which is intended to be used by system designers, engineers, and architects.
In Europe, one of the most sustainable solutions to supply heat to buildings is district heating. It has good acceptance in the Northern countries, a low-carbon footprint, and can easily integrate ...intermittent renewable energy sources when coupled to the electrical grid. Even though district heating is seen as a vital element for a sustainable future, it requires extensive planning and long-term investments. To increase the understanding of the district heating network performance and the demand-side dynamics of the connected buildings, several countries, including Denmark, have installed smart heat meters in different cities. In that context, this paper presents several methodologies to analyze the datasets from the smart heat meters installed in a small Danish town. The first method is concerning data curation to remove the anomalies and missing data points. The second method analyses measured variables (heat consumption, outdoor temperature, wind speed, and global radiation) to acquire new knowledge on the building characteristics. These results were compared with the values given by the energy performance certificates of a smaller sample of 41 households. Finally, to communicate and visualize the analysis outputs in a user-friendly way, an interactive web interface tool has been created.
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•A deeper understanding of the building's energy dynamics can be achieved through smart energy meters data analysis.•The method aims to uncover the influence of the different outdoor conditions on the building's energy consumption.•The method can oversee the transmission and ventilation losses in the analyzed buildings. The solar gains were inconclusive.•This analysis must be applied to other larger building datasets with various outdoor conditions to reach further conclusions.
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