Dynamic modelling and control of a reciprocating engine

Nowadays energy systems should be considered as integrated energy systems (IESs), where interactions between different energy vectors affect each other. A good performance of the whole system depends on the adequate behaviour of each individual element as undesired dynamics may propagate from one element to another. Due to the system complexity, a common practice is to employ steady-state models. Although such an approach is valuable as it provides significant insight into the system behaviour, it may hide inherent coupling characteristics as the dynamics are not considered. To ensure the satisfactory performance of each component,dynamic models are not only required, but essential. With a truly dynamic model it is possible to clearly understand how the system is affected by different operating conditions, load variations and disturbances over time, which in turn enables an effective control system design. Following this line, this paper presents a mathematical model, based on the mean value approach, of a reciprocating engine, which is used in combined heat and power units – key component of an IES. Although the system is non-linear, it is shown that a single-input single-output linear system can be derived and, thus, a frequency domain representation suitable for control system design can be obtained. The system has been developed in MATLAB/Simulink. Simulation results show that the designed linear controller is capable of ensuring a good performance of the reciprocating engine non-linear model

Dynamic modelling of ice-based thermal energy storage for cooling applications

The development of accurate dynamic models of thermal energy storage (TES) units is important for their effective operation within cooling systems. This paper presents a one-dimensional discretised dynamic model of an ice-based TES tank. Simplicity and portability are key attributes of the presented model as they enable its implementation in any programing language which would, in turn, facilitate the simulation and analysis of complex cooling systems. The model considers three main components: energy balance, definition of the specific heat curve, and calculation of the overall heat transfer coefficient. An advantage of the model is that it can be adapted to other types of TES units employing phase change materials. The modelling approach assumes equal flow and temperature distribution in the tank and considers two internal tubes only to represent the whole tank—significantly reducing the number of equations required and thus the computation time. Thermophysical properties of water during the phase change and of the heat transfer fluid are captured. The ice-based TES tank model has been implemented in MATLAB/Simulink. A good agreement between simulation results and experimental data available in the literature has been achieved—providing confidence in the validity of the mathematical model

Thermal dynamic modelling and temperature controller design for a house

Heat consumption management and effective temperature control strategies to meet heat demand in residential and office buildings have become an important aspect within energy management. A thermal dynamic model of a building is not only necessary to estimate the energy consumption under different operating conditions but also to design effective controllers. This paper presents a classical control approach for the indoor temperature regulation of buildings. State-space and transfer function models of house thermal behaviour are developed. These are obtained from first principles of heat transfer and their analogy with electrical systems. To capture a realistic behaviour of heat transfer, the proposed models consider parametric uncertainties. A frequency response-based approach is used to obtain a reduced order system that facilitates control system design. The models have been implemented in MATLAB/Simulink and a PI controller has been designed to maintain a comfortable indoor temperature in the building. Simulation results show that the controller effectively regulates temperature despite system disturbances. An energy saving of around 8% comparing the proposed controller to a traditional on/off controller is achieved

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Dynamic modeling and control of a plate heat exchanger

Heat exchangers have a predominant role in heat transfer and constitute a key component of integrated energy systems. For instance, heating and cooling of fluids are the cornerstone of district heating systems. Thus, it is fundamental to understand the heat exchanger's dynamic behavior to design controllers which are robust to temperature variations. Following this line, this paper presents a dynamic model of a plate type heat exchanger. The model is obtained from first principles of energy transfer and fluid mechanics and describes the thermal behavior of fluids involved in the heat transfer process. Although the system is non-linear, system linearization is performed to obtain a frequency domain model suitable for control system design. The linear model is implemented in MATLAB to design a controller that regulates the cold stream outlet temperature. To assess its effectiveness, the controller is discretized, programmed in Python and implemented in Apros - an advanced process commercial simulation software. Simulation results show that the controller is capable of tracking reference temperatures while ensuring a good performance of the heat exchanger system

Dynamic modelling and control of counter-flow heat exchangers for heating and cooling systems

A heat exchanger is an essential component in district heating and cooling networks as it transfers thermal energy from energy centers to substations or customers. Thermal loads are typically supplied by regulating the temperature output of one stream of the heat exchanger and by modifying the mass flow rate of the other one. The availability of dynamic models suitable for control design can aid this process to be performed in an efficient way. In this paper, thermal dynamic models of counter-flow heat exchangers are developed. The models encapsulate key heat exchanger characteristics and consider the dynamic calculation of heat transfer coefficients-which includes the hydraulic behavior of the streams. Although heat exchangers are non-linear systems, linearized models are obtained to design simple yet effective and robust controllers in the frequency domain. These are validated in an advanced process simulation software. It is shown that a good temperature control performance in heat exchangers can be achieved for a wide range of operating conditions with a simple PI controller

An experimental facility for latent heat thermal energy storage units

Assessing the performance of thermal energy storage (TES) units beyond software simulation requires testing in a controlled environment, with specific operating modes, and in safe conditions. A test-rig with an energy source and a monitoring system is very helpful to conduct experimental tests to assess the performance of TES systems. To this end, this paper presents an experimental facility for the study of latent heat TES (LH-TES) units. Emphasis is placed on the individual elements of the facility, which includes plumbing components and electric heaters to support the charging process of the TES units. Water is used as the heat transfer fluid (HTF). To demonstrate the capabilities of the test-rig, an LH-TES prototype for heating applications is used. Four different configurations and three operating modes are assessed: charging, discharging and discharging-mixing. The wide range of the experiments possible with the developed facility enables testing of early designs of LH-TES units ahead of deployment in real thermal networks

Numerical modelling of a phase change material-based shell and tube thermal energy storage unit

Numerical modelling analysis is performed to assess the operation of a thermal energy storage unit. The system is comprised by a heat exchanger placed in a cubic case filled with phase change material (PCM). Water is used as the heat transfer fluid. In the charging process, hot water is circulated through the tubes of the heat exchanger and heat transferred to the PCM. The 3-D modelling is performed by solving unsteady Reynolds-averaged Navier-Stokes equations. The modelling approach allows a detailed analysis of the flow and thermal characteristics of the PCM and water in the thermal store