1,720,975 research outputs found
RC building modelling for control purposes: A case study
No full textWhen dealing with models, a key factor to consider when selecting their features is the context in which the models will be used: for example, they could be used for design or for control purposes. If we focus on the second case, the model should be accurate enough to capture the principal dynamics of interest and simple enough to minimize the computational effort. In building modelling for control, a promising paradigm seems to be the use of simplified grey-box models. This paper presents a case study in which the existing temperature control strategy can be improved with the resulting possibility of considerable energy saving. More in detail, we introduce here the first step of the entire process: the choice of the model of the system. We decided to investigate the use of a grey-box model, the parameters of which were estimated using a parametric identification process. Thanks to this approach, full knowledge of the system is not required but this lack of information needs to be balanced with the use of measured data. We decided to use only measured data during the standard operation mode of the system for the parameter identification process. Thus we did not perform targeted experiments on the real system, because of all the restrictions in the specific context. Using this approach, it was still possible to achieve good results in terms of deviation between model simulation and data (indoor air: RMSE = 0.31 and R2 = 0.92)
FREESCOO facade 3.0, a compact DEC thermally driven air-conditioning system for apartments
Full text linkFREESCOO is an innovative Desiccant Evaporative Cooling air conditioning system designed for ventilation, cooling, dehumidification and heating of buildings in residential and tertiary sectors. This paper presents the third generation of the façade version, which will be tested on field in Milan (Italy) within the Merezzate+ project supported by Climate-KIC. The adsorption bed used by the system is a finned heat exchanger packed with silica gel grains, which allows simultaneous dehumidification and cooling of the process air. The direct evaporative cooling process, operated downstream to the dehumidification, is realized using a rotary plate humidifier. The regeneration of the adsorption bed is done through low-grade heat around 60 °C and the only electrical consumption is for the fans and water recirculation. The unit has been designed in order to be integrated in the loggia of small apartments of roughly 47 m2. The result is a Seasonal Energy Efficiency Ratio around 10.7. From the primary energy savings perspective with respect to a conventional air conditioning, they can be up to 36% if the electricity generation is not renewable heavy or the district heating has a renewable energy quota
Building envelope optimization and projected future cooling needs and consumption in residential buildings in Egypt
No full textData driven fault detection and diagnostics for hydronic and monitoring systems in a residential building
Full text linkImprovement to EN ISO 52016-1:2017 hourly heat transfer through a wall assessment: the Italian National Annex
Full text linkEnergy efficiency in buildings is a crucial topic to reduce worldwide energy consumption and fight climate changes. A key aspect is the assessment of the heat transfer through the opaque elements of the building envelope. One way to do it is modeling the element as a resistors and capacitors network (RC), using the thermal-electrical analogy. In the hourly dynamic method introduced by the recently published standard EN ISO 52016-1:2017, each opaque element is modelled with an RC-network. Italy has implemented in the National Annex A of the Standard an alternative methodology for the definition of the number of nodes and position, based on the detailed layers’ characteristics. In this work, the two methods are described and compared with the exact analytical solution for three cases under sinusoidal boundary conditions. In all the test cases, the results obtained applying the Italian Annex provide better results, with a reduction of the error on the internal flux amplitude between 14% and 67%. In addition, it has been verified that the Italian model is actually well-tuned. Indeed, the amplitude of the external flux is overestimated on average of only 3%, and the phase differences are limited (maximum ±1 h). Lastly, also the effect of the change of the number of nodes, and to move the nodes from the layers’ mid-point to the interface, have been analysed, but none of these strategies were demonstrated able to increase significantly the model accuracy, which can be obtained only reducing the calculation timestep
Transformer encoder based self-supervised learning for HVAC fault detection with unlabeled data
Full text linkData driven methods are the most studied fault detection and diagnostics (FDD) type in buildings HVAC systems. However, most studies rely on labeled data for specific faults which are hard to find and collect for real systems. While the fault -free data is easier to collect, it is still time consuming to label for large systems operation. Moreover, most of the studies rely on the usage of supervised learning algorithms which do not generalize well beyond the training data making unseen faults hard to detect. In this paper, we define a methodology to use a self -supervised learning method for HVAC systems ' FDD using a Transformer encoder, moreover, we tested it on a real case study. By strategically masking portions of the multivariate time -series data using Markov chain approach with two states. The model is trained by predicting these concealed segments. This approach, independent of labeled data, offers a scalable solution for practical HVAC applications. Anomalies are labeled using the Peak Over Threshold (POT) method, which dynamically determines thresholds by fitting reconstruction errors to a generalized Pareto distribution. Subsequent fault diagnostics emphasize features with pronounced reconstruction errors, pinpointing potential HVAC malfunctions. This methodology reduces dependence on labeled datasets and augments the model ' s generalization, facilitating detection of unobserved faults. This approach was applied to data from a real building. As a results multiple faults were detected mainly due to the malfunctioning of the monitoring system. The model demonstrates the ability to detect both sequential and individual faults. The period from October 19th to December 23rd was detected as a fault period due to the change in the trend of the data because of the monitoring system
Energy saving potentials of a photovoltaic assisted heat pump for hybrid building heating system via optimal control
Full text linkThe recent rise of renewable energy technologies in the building sector is expected to reduce fossil fuel consumption but leads to a greater complexity in the design and control of Heating, Ventilation, and Air Conditioning (HVAC) systems. As a consequence, the traditional control approach does not fully exploit the potential of the photovoltaic-assisted hybrid HVACs. This paper presents an investigation on the energy cost savings and the optimal control strategies of a photovoltaic-assisted hybrid heating system based on optimal control theory. The considered system consists of a radiant floor heating system, a gas boiler and a photovoltaic-assisted air-source heat pump (AS-HP) as heat sources, with a water tank as thermal energy storage (TES). The building thermal dynamics and all the components of the heating system were modelled in MATLAB environment together with a baseline rule-based controller (RBC). The optimal control problem is formulated such that cost function, constraints, state and control variables are defined. Due to a large number of states and control variables, the optimal control problem is converted to the nonlinear parameter optimization problem, and the solution is obtained by using nonlinear programming (NLP). For simulation settings, model parameters, weather, and energy demand profiles were adopted from historical data from a North Italian case study. The simulation results show that the photovoltaic-assisted hybrid heating system coupled with optimal energy management strategy can potentially save up to 20% of the energy consumption cost when compared to the state-of-art RBC and increase the photovoltaic self-consumption by 30%
Cooling energy use reduction in residential buildings in Egypt accounting for global warming effects
Full text linkResidential and commercial buildings are responsible for almost 50% of the total electricity consumption in Egypt. This percentage is expected to increase due to the global warming effect. This work deals with the cooling energy use reduction strategies for residential buildings compatible with the Egyptian market accounting for the global warming effects. A study in the Egyptian market was done to explore the best available technologies in the Egyptian market. A series of dynamic simulations were executed in each city to optimize the building envelope using the best available technologies to reduce the cooling needs. Financial, energetic and environmental factors were taken into consideration, and comparative analysis was done to assess the best alternatives. The double wall with air gap and insulation on the outside was found to be the best alternative in all the cities. Moreover, simple measures to further reduce the cooling energy need were explored, such as the usage of more efficient lighting and night ventilation. This work led to an average reduction of 40% in the cooling energy needs and CO2 emissions across the three cities, with a maximum discounted payback period down to 6.3 years. Future weather files adapted to climate change were generated, and the selected passive strategies were tested to assess the validity of such strategies in the future. The cooling energy needs are expected to increase by 39%, while the peak cooling loads are also expected to increase by 23% by 2080, rendering the current installed HVAC systems undersized
Performance comparison of quadratic, nonlinear, and mixed integer nonlinear MPC formulations and solvers on an air source heat pump hydronic floor heating system
Full text linkThere is a gap in literature on comparisons between different MPC optimal control formulations and solver choices for the same building HVAC system. Mixed Integer Nonlinear (MINL) formulations are rarely considered, despite being the most physically accurate way to represent HVAC systems. This work compares several MPC formulations, including Quadratic, Nonlinear, and MINL, applied to a case study building and investigates benefits and challenges of MINL MPCs from practical perspectives. Ten different MPC formulations were developed and implemented using Pyomo. Then, a detailed emulator model was developed using open-source Modelica libraries and used with BOPTEST to assess the performance of each MPC. Results show that convergence and control switching behaviours of MINL MPCs are sensitive to formulations, initialization approaches, solver selections, and solver parameters. Thus, they require significant effort for tuning. However, a very well-tuned MINL MPC performed similarly to successful Nonlinear MPC formulations
- …
