Circuit Heat Research Articles

Examination and Optimization of a Heating Circuit for Energy‐Efficient Buildings

AbstractThe conference center darmstadtium in Darmstadt is a prominent example of energy efficient buildings. Its heating system consists of different source and consumer circuits connected by a Zortström reservoir. Our goal was to reduce the energy costs of the system as much as possible. Therefore, we analyzed its supply circuits. The first step towards optimization is a complete examination of the system: 1) Compilation of an object list for the system, 2) collection of the characteristic curves of the components, and 3) measurement of the load profiles of the heat and volume‐flow demand. Instead of modifying the system manually and testing the solution by simulation, the second step was the creation of a global optimization program. The objective was to minimize the total energy costs for one year. We compare two different topologies and show opportunities for significant savings.

SYSTEM FOR DIRECT CONVERSION OF THERMAL ENERGY INTO ELECTRICAL ENERGY

The main elements of this unit are the gas boiler and the thermoelectric generator modules (TEGM), heating circuit, electronic three-way valve, the consumer battery and automation components. The housing of the boiler is a hot heat exchanger, and serves for the installation of the heat exchanger and cold TEGM. TEGM is installed between the cold and hot heat exchangers. The cold heat exchanger is cooled heating circuit and the hot heat exchanger is heated by the boiler casing. Thus, during the heating season, individual housing located in urban areas and in rural areas, using the device in their boilers, can receive and use cheap electricity.

Modeling and simulation of the heating circuit of a multi-functional building

In this study, the fossil-fueled heating circuit and the corresponding automation system of a multi-functional building are simulated to lay the foundation for in-depth analysis and optimization of the building energy concept.The considered building is the E.ON Energy Research Center main building which is equipped with a highly integrated energy generation, storage and distribution system. The thermo-hydraulic components and control units are developed in the modeling language MODELICA whereas the relevant part of the global Building Automation System is implemented in MATLAB/SIMULINK. The interaction between the two simulation environments is established using the non-commercial co-simulation platform Building Controls Virtual Test Bed (BCVTB).Data stored in the comprehensive building monitoring system is used for the parametrization of the hydraulic model. Moreover, the data is analyzed to deduct information on the control system such as temperature set-points.Both the single subsystems and the model as a whole are validated by comparing simulation results to monitoring data. The evaluation reveals that the behavior of the hydraulic components and the control system is successfully reproduced and deviations remain in an acceptable range. The reasons for the deviations are identified and mitigation measures are discussed.

Influence of the Operating Regime on the Performances of Thermal Solar Systems Integrated in Heating Networks

The energy performances of the integrated thermal solar systems in the hybrid heating systems are influenced by several aspects like technology used and the way the collectors are placed, the type and technology of the heating storage, the operating temperatures in the hybrid system and last, but not least, the chosen control strategy. The operating regime of the thermal solar system characterized mainly by the thermal solar agent’s temperature and flow rate, as well as the corresponding control strategy, define the parametric framework of the system and impose its energy performances during operation. The optimized systemic variation of the temperatures and flow rates in both, the solar loop and the heating circuit, results in higher annual energy performances of the hybrid heating system. The present paper approaches the premises referring to the different operating regimes that characterize thermal solar systems in order to highlight and quantify their influence over the energy performances of the thermal system. In this respect, a set of computational operating simulations were carried out on the targeted system during one year of operation, in different configurations and operating regimes, for the energy assesment of the thermal system.

Thermal Storage Tanks in High Efficiency Heat Pump Systems – Optimized Installation and Operation Parameters

Abstract Heat pumps have a significant and increasing share in the European heating market. In most applications heat pumps are operated with a storage tank, either for domestic hot water or for the space heating circuit. The design of the storage and its connection to the heat pump has a significant influence on the performance of the heat pump and the whole system. Within a comprehensive investigation, system simulations in TRNSYS are used to identify the optimum design of two typical systems with a heat pump connected to a buffer storage including total storage volume, number and size of heated zones, sensor and in- and outlet positions. As result, a sharp decrease in the energy demand can be reached if the storage is equipped with two heat zones instead of one. This can be explained by the decreased set temperature in the additional heat zone for space heating leading to a higher performance of the heat pump. Other measures with a positive effect on the energy demand are a large space heating volume, the number and place of sensors, low set temperatures and the sensor position in the upper part of the heating zone. The investigation gives important recommendations how to connect a heat pump with a storage tank and may be considered as design rules for all heating systems consisting of heat pump and different types of storage tanks.

Thermal Diffusivity and Thermal Conductivity of Five Different Steel Alloys in the Solid and Liquid Phases

The need for characterization of thermophysical properties of steel and nickel-based alloys was addressed in the FFG-Bridge Project 810999 in cooperation with a partner from industry, Bohler Edelstahl GmbH & Co KG. To optimize numerical simulations of production processes, such as remelting or plastic deformation, additional, and more accurate data were necessary for the alloys under investigation. With a fast ohmic pulse heating circuit system, the temperature-dependent specific electrical resistivity, density, and specific heat capacity for a set of five high alloyed steels were measured. Hence, using the Wiedemann–Franz law with a Lorenz number of $$L =2.45\times 10^{-8}\,\hbox {V}^{2}{\cdot }\hbox {K}^{-2}$$ , the thermal diffusivity and thermal conductivity could be calculated for the solid and liquid phases up to temperatures of 2500 K. This experimental approach is limited by the following requirements for the specimens: they have to be electrically conducting, the melting point has to be high enough for the implemented pyrometric temperature measurement, and one has to be able to draw wires of the material. The latter restriction is technologically challenging with some of the materials being very brittle. For all samples, electrical and temperature signals are recorded and a fast shadowgraph method is used to measure the volume expansion. For each material under investigation, a set of data including the chemical composition, the density at room temperature, solidus and liquidus temperatures, and the change of enthalpy, resistivity, density, thermal conductivity, and thermal diffusivity as a function of temperature is reported.

Development of Miniature Stewart Platform Using TiNiCu Shape-Memory-Alloy Actuators

A Stewart platform is a parallel manipulator robot that is able to perform three linear movements, lateral, longitudinal, and vertical, and three rotations, pitch, yaw, and roll. This paper reports a 30 mm × 30 mm × 34 mm miniscale Stewart platform using TiNiCu shape-memory-alloy (SMA) actuators. The proposed Stewart platform possesses various advantages, such as large actuation force and high robustness with a simple mechanical structure. This Stewart platform uses four SMA actuators and four bias springs and performs a linearz-axis movement and tilting motions. The SMA actuators are activated by passing a current through the SMA wires using a heating circuit that generates a pulse width modulation (PWM) signal. This signal is varied to control the level of the displacement and tilting angle of the platform. The tilting direction depends on the SMA actuator that is activated, while all four SMA actuators are activated to achieve the linearz-axis movement. Each SMA actuator exerts a maximum force of 0.6 N at PWM duty cycle of 100%. The fabricated miniature Stewart platform yields a full actuation of 12 mm in thez-axis at 55°C, with a maximum tilting angle of 30° in 4 s.

Study and verification of the superposition method used for determining the pressure losses of the heat exchangers

This paper deals with study of the pressure losses of the new heat convectors product line. For all devices connected to the heating circuit of the building, it's required to declare a tabulated values of pressure drops. The heat exchangers are manufactured in a lot of different dimensions and atypical shapes. An individual assessment of the pressure losses for each type is very time consuming. Therefore based on the resulting data of the experiments and numerical models, an electronic database was created that can be used for calculating the total values of the pressure losses in the optionally assembled exchanger. The measurements are standardly performed by the manufacturer Licon heat hydrodynamic laboratory and the numerical models are carried out in COMSOL Multiphysics. Different variations of the convectors geometry cause non-linear process of energy losses, which is proportionately about 30% larger for the smaller exchanger than for the larger types. The results of the experiments and the numerical simulations were in a very good conjuncture. Considerable influence of the water temperature onto the total size of incurred energy losses has been proven. This is mainly caused by the different ranges of the Reynolds number depending on the viscosity of the used liquid. Concerning to the tested method of superposition, it is not possible to easily find the characteristic values appropriate for the each individual components of the heat exchanger. Every of the components behaves differently, depend on the complexity of the exchanger. However, the correction coefficient, depended on the matrix of the exchanger, that is suitable for the entire range of the developed product line has been found.

Advanced Measurement, Characterization and Simulation of Thermoplastic Composite Induction Welding

Induction welding is a highly versatile thermoplastic composite (TPC) and hybrid material (metal to composite) fusion bonding process which uses electromagnetic phenomena to generate contact-free heating of the joining partners. Two highly influential sets of parameters in the process are the ‘actual’ applied coil current amplitude and frequency along with the temperature and frequency dependent electrical conductivity behavior of the joining materials. Both sets of data are not easily measurable and may change dynamically during the process. One of these issues can be addressed from an electrical engineering point of view, which focusses on the induction heating equipment itself and accurate measurement of the electrical behavior of the induction heating circuit. Magnetoresistive sensors especially designed for high-frequency current measurement can be used to measure the coil current and its corresponding waveform for any welding setup. The data recorded by the sensor board, together with Fourier Transform analysis techniques, provides accurate values for the coil current and frequency, which can then be used for process and equipment design simulations assisting in the development of suitable control systems and overall process optimization.

Study of Ground – Water Heat Pump Parameters during 3 Years of Operation

The manuscript presents results of a 3 years experiment, concerning in the monitoring of working parameters of a ground – water heat pump with horizontal collectors. The measured working parameters of the refrigerant circuit are: evaporating pressure, condensing pressure, superheating temperature, discharge temperature, sub cooling temperature. There were also measured the flow rate and the temperatures on the heating circuit of water and on the horizontal collectors circuit with antifreeze. The methodology of data processing, described in the manuscript, allowed calculation of evaporating temperature and condensing temperature, based on measured corresponding pressures. The main obtained results consist in a complete set of working and performance parameters and their variation in 3 years of operation. Details are presented for operating conditions characteristic for different cases: middle of heating season, end of heating season, middle of non-heating season, beginning of heating season. Some practical conclusions of the study are also presented in the manuscript. It was indicated how the outside temperature is influencing the values of working and performance parameters, but mainly on the effective number of running periods.

Real-time simulator of agricultural biogas plant

This article presents a real-time simulator of an agricultural biogas plant. The project contains biogas and biomass circuits simulation, as well as heating circuit simulation with a complete control system and visualization interface of the whole process. The software tool used to simulate the plant work is CFD (Computational Fluid Dynamics), which enables a user to create and test simulation objects based on fundamental physical laws related to fluid circuits and flows. The research work was concentrated on building simulation object reflecting real plant dynamics in the most precise way that can be achieved with the provided simulation tools. Presented simulation creates a possibility to minimize dangerous and undesirable situations on a real plant by manipulating of control parameters and observing simulated object reaction. The simulation results enable to optimize biogas production and operation costs. The simulator is intended to be an operator staff training material and can increase the operators’ reliability during plant’s operation. It is an important aspect in biogas plant risk management and it may reduce the requirements for safety instrumented system as well as the cost of their implementation.

Invited Presentation: Li-Ion Battery Safety Considerations during Transportation, Storage, and Disposal

The energy of a Li-ion cell is in average about 3,250 kJ/kg. About ¼ of this energy is related to electrochemical energy (chemical energy convertible into electrical energy via normal use or short circuit) and ¾ to thermal energy (chemical energy convertible only in thermal energy released at suitable stimulation; e.g. short circuit). The main safety related events are overcharge, external heating, external and internal short circuits, and mechanical deformations of the cell/battery case. These unpredictable events may leads to a temperature increase and at T > 120 °C by internal chemical processes (SEI layer breakup, anode-electrolyte reaction) with gas development and internal pressure increase to cell container rupture at predetermined breaking points. Gas and electrolyte will escape through the rupture holes into the environment and, eventually, inflame by an external ignition source. A further temperature increase till about 200 °C triggers high rate chemical reactions (cathode decomposition with oxygen development, oxygen reaction with the electrolyte, electrolyte decomposition) leading to a very rapid temperature rise (thermal runaway) followed by flames caused by reaching the self-ignition temperature of the electrolyte (~ 450 °C) and possibly explosions. The specific occurrence of most of the above described safety related events, that may occur during the Li-ion battery life cycle phases of transportation, storage, and disposal, will be discussed in this presentation. During transportation and storage, external heating, external and internal short circuits, and mechanical deformations, are the events most likely to happen. Measures which can prevent them (e.g. reliable and low flammable packaging, thermal barriers) and transport related standards (e.g. UN 38.3) are described.The safety hazard in the disposal phase of the cell/battery are also associated with external heating, external and internal short circuits, and mechanical deformations. After collections it is to proof whether the battery is defective (not all functions properly) or damaged (loss of physical integrity). Defective batteries with capacity ≤ 80 % of the nominal value (end-of-life by definition) could be still used in lower demanding applications, e.g. stationary storage in PV houses. Damaged batteries and defective batteries with << 80 % capacity and other malfunctions have to be recycled. In order to reduce the safety risk before the recycling process (including transport), it is advisable to de-energize the battery by low current discharge and finally short it permanently.

Air-source heat pump LabView-based model development for NZEB applications

Abstract A net zero-energy building (NZEB) is considered as a resident or commercial building where the energy needs are covered by using locally available renewable energy sources and technologies. Various types of heat pumps are widely used energy conversion systems for NZEB strategies implementation. This paper is focused on the development of a novel LabView-based model for an air-source heat pump system that absorbs heat from outside air and releases it inside the building as domestic hot water supply or room's space heating by using hot water-filled fan-coils. In the first research steps the mathematical background of the considered heat pump system has been developed. Then the LabView-based software implementation of the air-source heat pump and entire heating circuit model is unfolded and presented. The result is a versatile and powerful graphical software toolkit, suitable to simulate the complex heating, ventilation and air-conditioning processes in net-zero energy buildings and to perform energy balance performance evaluations. Beside the elaborated mathematical models, a concrete software implementation example and measurement data is provided in the paper. Last but not least, the proposed original model offers a feasible solution for future developments and research in NZEB applications modeling and simulation purposes.

Research on Information Processing Module in Intelligent Alcohol Tester

Information processing module, which includes fuel cell sensor circuit, pressure sensor circuit, heating and temperature sensor circuit and signal filtering amplifier, is the core of Intelligent Alcohol Tester. Its main task is to complete the collection and pretreatment of alcohol gas signal. In this paper, the hardware module is first simply introduced. And next, test method and the relevant criteria are done to prove that the modules have good accuracy and stability and achieve the requirements of alcohol tester.

Solving hyperbolic heat conduction using electrical simulation

In the present study, the electrical network simulation method is proposed to solve the hyperbolic and parabolic heat conduction problem considering Cattaneo-Vernoute (C.V) constitutive relation. Using this new proposed numerical model and the electrical circuit simulation program HSPICE, transient temperature and heat flux profiles at slab can be obtained easily and quickly. To verify the proposed method, the obtained numerical results for cases of one dimensional two-layer slab under periodic boundary temperature with perfect and imperfect thermal contact are compared with the published results. Comparisons show the proposed technique might be considered as a useful tool in the analysis of parabolic and hyperbolic thermal problems.

MCU based real-time temperature control system for universal microfluidic PCR chip

The analysis of genetic materials in the post-human genome project era has become an ever-expanding branch of research and thus routinely employed in majority of biochemical laboratories. Most of the diagnostic research area emphasizes on polymerase chain reaction for detecting pathogenic organisms. However, the conventional polymerase chain reaction requires expensive and sophisticated thermal cycler and is not handy owing to its large dimensions. Therefore, we fabricated a continuous-flow polymerase chain reaction chip on a PDMS based microfluidic platform to ease the hardship of the conventional system. Temperature being the most crucial factor in polymerase chain reaction, was monitored and regulated by thermostatic action using an on-line computer system. Indium tin oxide coated glass platform was used for heating as it is transparent and has good thermal conductivity under the influence of DC bias. The heating circuit used an ATMega 128 MCU to control the temperature. As a result, a precise and quick heating environment was maintained on the microfluidic chip to amplify the target DNA. We successfully amplified Lambda phage and Escherichia coli DNA on our chip to prove the practicality of the device.

Failure analysis of gas turbine generator cooling fan for 14° and 19° — blades angle of attack

In gas turbine power plants, a fan is used as a cooling system to dissipate generated heat in coils (copper conductors) and generator electric circuits at the end sides of its rotor. In some cases, fracture of blades causes short circuit between rotor and stator and consequently generator explosion and made lot of financial problems. The fracture of cooling fan blades has been occurred five times at the turbine side of the generator in our case of study, just 100 hr after resuming operation after overhaul. Using numerical analysis as well as laboratory investigation — includes visual inspections, metallography and SEM — can help better finding failure problems that cause blade failures. A series of numerical analysis was performed to diagnose the cause of failure possibility. CFD analysis is used to study the airflow distribution in order to observe probable separation phenomenon and pressure forces that they are imposed to fan blades due to operation. A finite element method was utilized to determine the stresses and dynamic characteristics of the fan blade (natural frequencies, stresses and vibrations).

Development of new laminates for high performance interconnection technology in avionics applications

PurposeThe purpose of this paper is to detail various aspects of laminates and their current developments in order to enable the selection and development of appropriate laminate systems for use in high performance avionics interconnection applications.Design/methodology/approachElectronic packaging must provide circuit support, heat dissipation, signal distribution, manufacturability, serviceability, power distribution and data for performance simulation over the required frequency range in avionics applications. Innovations in packaging technology have made a big impact on the types of laminates that can be used in printed circuit boards destined for these applications. The “environments” in which aircraft are required to operate have changed due to global security threats and the laminates traditionally used are not designed for this role. Aircraft systems are expected to withstand disturbances due to unexpected threats. Various factors which determine the performance of laminates are evaluated.FindingsThe safety of aircraft is critically dependent on the interconnection technology in which laminates have a major role. Under global security threats, passenger safety, emergency landing and timely information to the pilot is of paramount importance. Hence, research programs need to be initiated to develop new innovative laminate systems, since traditional laminates have limitations in these applications.Research limitations/implicationsThe availability of data on the performance of laminates used in interconnection technology under various security threats is limited.Originality/valueThe paper describes how new laminates for high performance interconnection technology in avionics applications can be developed.

Failure analysis of a machinable brass connector in a boiler unit installation

Cracking of hexagonal brass connector of a boiler tubing assembly caused leakage and interruption of the function of a water heating circuit. Destructive damage was provoked after two years in service. Visual examination, light and scanning electron microscopy coupled with local elemental energy dispersive X-ray spectroscopy (SEM/EDS) were used as the principal analytical techniques for the present investigation. The collected investigation findings suggest that failure was induced via progressive cracking, attributed probably to fatigue initiated from surface flaws existed on the thread root surface. Recommendations mainly concerned revision of the alloy selection and quality assurance of tubing assembly procedure during installation.

The experimental analysis of the effect of ambient factors on the defrosting of economised vapour injection compressor air source heat pump in marine climates

Air source heat pumps have numerous advantages in many applications over other heating equipment in marine climates with regard to energy efficiency. The main concerns are based around maintaining a sufficiently high seasonal coefficient of performance (COP) when (a) utilising cold air as a heat source and (b) delivering hot water to a residential heating circuit originally designed for water temperatures of 60°C or more with oil heating. The economised vapour injection (EVI) compressor has the capability of overcoming some of the difficulties of high temperature lift operation during cold ambient conditions. However it is not clear except ambient temperature how the other ambient factors may affect the performance of EVI air-source heat pump in marine climates. This paper evaluates operating performance with the defrost effect for a retrofit residential EVI air-source heat pump in Belfast, UK. The ambient factors, which affect the performance of the heat pump defrosting, were studied. The investigation was to optimise the operation of an EVI air source heat pump operating under defrost conditions encountered in maritime climates.