Local ventilation for general patient rooms

Numerous studies on ventilation of general patient rooms have been performed, while most of the studies have focused on total volume air distribution (mixing or displacement). This study presents results of local ventilation (LV) aimed to efficiently protect a lying person from cross-infection due to airborne respiratory viruses. Experiments performed in a climate chamber (4.7 m × 4.7 m × 2.6 m) included LV when used alone and when coupled with background mixing ventilation (MV). A thermal manikin and a heated standing dummy were used to simulate respectively a patient lying in bed and an infected doctor or nurse standing beside the bed. The LV was able to reduce substantially the exposure of the patient to the infected air exhaled by the doctor. The results show that the efficiency of the LV depended mostly on its supply airflow rate. An increase of the background ventilation's supply flow rate, i.e. increase of the air change rate in the room, was less important. At 15 L/s supplied by LV the concentration of a contaminant at the patient's mouth decreased by 76%. The findings of the paper give insights for researchers and designers in developing a novel ventilation system to be used during a pandemic in general patient rooms.publishedVersio

District heating load patterns and short-term forecasting for buildings and city level

District heating (DH) load forecasting for buildings and cities is essential for DH production planning and demand-side management. This study analyzes and compares the hourly DH load patterns for a city and five different types of buildings over an entire year. The various operating modes introduce nonlinear dependencies between the DH load and the outdoor temperature. We compare the prediction accuracies of different multiple linear regression (MLR) and artificial neural network (ANN) models. Without nonlinear dependencies, both ANN and MLR provide good, almost identical prediction accuracies. In the case of nonlinear dependencies, ANN is superior to MLR. However, the novel clustering method eliminates nonlinear dependencies and improves the accuracy of MLR on par with the ANN. ANN methods can automatically adapt to various nonlinearities. The advantage of combining MLR with the clustering method is that it is simpler than designing an ANN method, although manual work is required. In addition, MLR methods provide more insight into load patterns and how the load depends on various factors compared with ‘black-box’ ANN models. The developed methodology can be widely applied to building- and city-level load analyses and forecasting in different DH systems combined with or without domestic hot water consumption.Peer reviewe

Discrete event simulation for dynamic thermal modelling of district heating pipe

Funding Information: This study was supported by academy research fellow funding from Research Council of Finland (Funding No. 334205 and 358055 ). Publisher Copyright: © 2023 The AuthorsOptimizing district heating (DH) systems in a holistic manner is often impeded by the computational complexities associated with network modeling. This study introduces a novel, efficient and theoretically accurate method for dynamic thermal modelling of DH pipes. The approach is to track water frontiers traveling along the pipe using discrete event simulation (DES) paradigm. As the DES method is based on variable time steps, the computational effort is significantly reduced compared to earlier methods. The proposed model can compute outlet water temperature, temperature profile along the pipe, and heat loss based on variable inlet temperature and flow rate. The DES model was validated by comparison with real measurements of a long DH pipe. Four variants of the model with different temperature profile assumptions and interpolation methods were compared. Numerical results show that the DES model can accurately predict outlet water temperature with a maximum discrepancy of 0.52 °C. The mean error of simulated outlet temperature was −0.01 ± 0.02 °C. Average computation time for 24-h simulation was 59 μs. Overall, this study shows that the DES method is appropriate for variable time step simulation for DH pipe, potentially, for network simulation. Our study may also inspire variable time step implementation in other energy applications.Peer reviewe

Local ventilation for general patient rooms

Numerous studies on ventilation of general patient rooms have been performed, while most of the studies have focused on total volume air distribution (mixing or displacement). This study presents results of local ventilation (LV) aimed to efficiently protect a lying person from cross-infection due to airborne respiratory viruses. Experiments performed in a climate chamber (4.7 m × 4.7 m × 2.6 m) included LV when used alone and when coupled with background mixing ventilation (MV). A thermal manikin and a heated standing dummy were used to simulate respectively a patient lying in bed and an infected doctor or nurse standing beside the bed. The LV was able to reduce substantially the exposure of the patient to the infected air exhaled by the doctor. The results show that the efficiency of the LV depended mostly on its supply airflow rate. An increase of the background ventilation's supply flow rate, i.e. increase of the air change rate in the room, was less important. At 15 L/s supplied by LV the concentration of a contaminant at the patient's mouth decreased by 76%. The findings of the paper give insights for researchers and designers in developing a novel ventilation system to be used during a pandemic in general patient rooms

Multi-criteria evaluation of novel multi-objective model predictive control method for indoor thermal comfort

We proposed a novel multi-objective model predictive control (MPC) approach based on a straightforward internal prediction model to achieve building energy efficiency and maintain the indoor temperature within a predetermined comfort range. Using the CARNOT Toolbox, we built a detailed room model based on a real room with water-circulated radiator heating. We developed an MPC controller using MATLAB and combined it with the room model in the CARNOT Toolbox to tune the controller parameters and evaluate its performance. Based on the co-simulations, a control step of 15 min and a prediction horizon of 90 min were found to be suitable for room level indoor thermal comfort control. The performance of the controller was evaluated in terms of multiple criteria, including control accuracy, hydrodynamic stability, and energy consumption. Compared with the traditional proportional-integral-derivative (PID) control, the MPC demonstrated a 16.4 % improvement in control accuracy, 2.8 % lower energy consumption, and a 50 % reduction in the hot water flow change rate, improving the system’s hydrodynamic stability. A significant advantage of the MPC is that it is possible to compute different efficient solutions by modifying the parameters, among which the decision-makers can choose their most preferred compromise solution considering multiple criteria.Peer reviewe

A comprehensive review on pit thermal energy storage:Technical elements, numerical approaches and recent applications

Pit thermal energy storage (PTES) is one of the most promising and affordable thermal storage, which is considered essential for large-scale applications of renewable energies. However, as PTES volume increases to satisfy the seasonal storage objectives, PTES design and application are challenged. These difficulties trigged an interest in PTES investigations. This paper aims to identify the success factors and research gaps of PTES by an up-to-date evaluation of 160 recent publications. Existing technical elements that affect PTES thermal properties inclusive geometry design, inlet/outlet design, cover design, and materials, are outlined in depth. Numerical studies are categorized in terms of their mathematical theory and research purposes for a systematic discussion. The current application status of PTES systems worldwide is summarized from four aspects: storage material, geological design, operation strategy, and storage duration. For projects in operation, special attention is given to gathering and comparing operational data on solar fraction, storage efficiency, storage cycle, and PTES tem-perature. This review outlines the progress and potential directions for PTES design and numerical studies by identifying the research gaps that require further effort.Peer reviewe

A zoned group control of indoor temperature based on MPC for a space heating building

Funding Information: This work was supported by the China national key research and development program – China-Finland intergovernmental cooperation in science and technology innovation (Funding No. 2021YFE0116200), academy research fellow funding from Academy of Finland (Funding No. 336268 and 334205), and also supported by the Fundamental Research Funds for the Central Universities of China (DUT21JC32). Publisher Copyright: © 2023 Elsevier LtdThe traditional regulation of district heating (DH) system are mainly based on the central control in heat plants and/or in the substations. But the end-user control is becoming increasingly important in saving DH energy consumption. In view of this, a novel zoned group control method of indoor room temperature based on model predictive control (MPC) for a space heating building is proposed. Firstly, a room temperature simulation model based on IDA Indoor Climate and Energy (IDA-ICE) is developed for the experimental room, where the simulation result is validated by the measurements. But it is still difficult to use this model in the predictive control. Therefore, a resistor capacitor (RC) room temperature simulation model with parameters identified by IDA-ICE is proposed. A room temperature controller based on RC-MPC is developed and tested in the experimental room for model validation. Secondly, a DH building in Dalian, China is chosen for the case study. The IDA-ICE simulation results show that the temperature distribution in different rooms of the building is clearly uneven without end-user control. Corresponding targeted control strategies according to the temperature distribution should be used in different zones (cluster of rooms) to improve indoor thermal environment. Therefore, a zoned group control model based on RC-MPC for DH building room temperature is developed in MATLAB/Simulink, which adopts IDA-ICE for parameter identification in RC simulation model and utilizes RC model to predict the room temperature trajectory in the MPC controller. Results show that the proposed model can achieve active and dynamic room temperature control for different zones more precisely according to the changing heat load distribution. It is not necessary to define every room a group, instead, many rooms with similar conditions can be grouped in the same cluster, and temperature differences between rooms can be controlled within a reasonable range.Peer reviewe

Heat-power peak shaving and wind power accommodation of combined heat and power plant with thermal energy storage and electric heat pump

Funding Information: This work was supported by the China national key research and development program – China-Finland intergovernmental cooperation in science and technology innovation (Funding No. 2021YFE0116200), academy research fellow funding from research council of Finland (Funding No. 336268 and 358055). We also thank Stage Grid Liaoning Electric Power Supply CO. LTD for providing valuable data about wind power. Publisher Copyright: © 2023 Elsevier LtdWind power curtailment becomes a major problem in many countries. The wind accommodation mechanisms and energy saving potentials for the combined heat and power plant with thermal energy storage, electric heat pump and both should be evaluated more systematically and accurately to accommodate more wind power. Heat-power peak shaving capacities for thermal energy storage, electric heat pump and both are analyzed using a graphical method, while the operation strategy is proposed to maximize wind accommodation. A simulation model for wind power accommodation considering the energy balances and constraints of all production units is developed based on EnergyPRO. A regional energy supply system in Jilin Province, China is selected as the case study, where the influences of different peak shaving technologies and their parameters on the wind accommodation and energy saving are studied. The wind curtailment ratio is reduced from 20.31% to 13.04% and 7.51% with thermal energy storage and electric heat pump respectively, and it is further reduced to 4.21% with both. Systems with electric heat pump can save energy from 1.1% to 5.8% with different parameters of the peak shaving devices. It was found that electric heat pump has better accommodation capability than that of thermal energy storage. Wind accommodation can be improved by adding thermal energy storage to electric heat pump, but the effect gradually decreases as the storage size increases. Electric heat pump can increase the system's energy efficiency, but it is not always energy efficient by adding thermal energy storage to electric heat pump. In fact, thermal energy storage should not be too large, otherwise the system's energy efficiency will be reduced.Peer reviewe