Thermal Load Profiles Research Articles

Optimal Design and Operation of a Low Carbon Community Based Multi-Energy Systems Considering EV Integration

Hybridization of electricity, heat power, and transportation energy combines the advantages of multi-energy sources. This paper proposes the combined use of fuel cell, combined heat and power units (CHP), hot water tank storage, gas boiler and photovoltaic (PV) generators to meet the electrical, thermal and transportation electrification energy demands in an eco-friendly multienergy microgrid. An optimal energy balance methodology is proposed in this paper for sizing the capacity of fuel cell, CHP, gas boiler, and PV. The method is to minimize the total annual cost and emissions of the whole system, based on hourly electrical and thermal load profile. The methodology can be used as a planning tool for multi-energy systems.

Measures to overcome deep cracks of tungsten tiles in the ASDEX Upgrade divertor

A massive tungsten divertor, Div-III, was installed in ASDEX Upgrade (AUG) in 2014. Div-III is an adiabatically loaded component and consists of massive tungsten tiles clamped into their supporting structures. Before installing the new component, extensive studies, including Finite Element Modeling (FEM) and high heat flux tests in the test facility GLADIS, were carried out. After the first experimental campaigns the tile inspection reveals most of the tiles were cracked. The difference between the high heat flux tests and the AUG behavior was attributed to mechanical loads due to disruptions and/or the thermal load profile and history. The actions to understand the cracks comprise tests with the divertor manipulator, DIM-II, and FEM analysis of different target design options. DIM-II was used to test ‘split’ tiles, i.e. the deep crack is avoided by cutting a wide tile into two small tiles. FEM calculations were done to investigate the behavior of castellated targets with reduced tensile stress on top of the target and a clamping with a more elastic material, titanium instead of stainless steel. In addition more ductile tungsten heavy alloy was qualified for use in AUG. Based on this, a new set-up of tungsten tiles was installed in 2016 with different divertor configurations. After about 1000 plasma shots a thorough inspection of the tiles reveals that only 2 configuration out of 4 get rid of deep cracks in the tungsten tiles. Outcome of this inspection are here discussed and the final divertor setup is described.

The influence of thermal load profile of building on the air/water heat pump efficiency simulation

In this paper the authors analysed the impact of the calculation method of the partial load conditions and the accuracy of the energy demand profile on the simulation results of the air/water heat pump operation supplying the heating system. All the analyses results were compared to the results acquired for the real installation of the air/water heat pump located in Poland. The authors assessed the inaccuracy of the unit’s efficiency estimation resulting from the simplified thermal load profile of the air/water heat pump. It has been showed that using the monthly energy demand as the input data gives satisfactory results. Inaccuracy of the monthly simulation results in relation to simulations carried out on the actual hourly energy demand by no more than 7% is acceptable. On average, this deterioration did not exceed 3%.

A dynamic building and aquifer co-simulation method for thermal imbalance investigation

Due to their favorable supply temperature, aquifer thermal energy storage (ATES) systems perform as an efficient heating/cooling energy storage facility for buildings. ATES systems consist of a warm and cold well. They are designed to operate with a temperature difference of at least 8 °C between wells, whereas the existing installations operate in practice with an average temperature difference of 4 °C. The ATES supply temperature is influenced by heat losses to the surroundings and the yearly balance of total heat exchange of heating and cooling between a building and the groundwater. Previous studies mainly focused on the investigation of heat losses to the environment. This paper explored the influence of thermal imbalance of a building load on the temperature of the aquifer and the heating/cooling system performance for the building. Due to the lack of tools capable of simulating the system that connects ATES with the buildings, we develop a co-simulation method that combines COMSOL, MATLAB and TRNSYS. In this method, COMSOL was used to model ATES, TRNSYS to simulate buildings and heating, ventilation and air conditioning (HVAC) systems and MATLAB as a mediator to exchange information between the simulation tools. The developed method was applied to a case study with three different insulation parameters to present different thermal load profiles. The results indicated that a thermally balanced building load achieved a 2.5 °C higher temperature difference between the sources for cooling than a case with a thermal imbalance ratio of 79%, which resulted in a 13.7% and 6% higher system coefficient of performance (COP) higher than the case with 79% thermal imbalance ratio and 51% thermal imbalance ratio, respectively.

Optimization of an HT-PEM fuel cell based residential micro combined heat and power system: A multi-objective approach

Abstract This article presents multi-objective optimization of an HT-PEM fuel cell based micro CHP system under steady-state operation by employing the mathematical model of the plant previously developed by our group. Different optimization procedures have been carried out to find the optimal points while considering two sets of objective functions: I) thermal power generation and net electrical output and II) net electrical efficiency and thermal efficiency. In the first part of the work, optimization has been performed at full load operation with electrical and thermal generation as objectives. The obtained Pareto frontier shows the capability of the system to cater a broad range of electrical demand (21.0 kW-29.4 kW) while offering the maximum achievable thermal generation. In the next step, in order to find the optimal operating conditions of the system while addressing specific thermal and electrical load profiles, a series of Pareto fronts have been acquired at different fuel partialization levels. Finally, using the primary energy saving (PES) index, the best operating points, in terms of electrical and thermal efficiency, have been determined. It was observed that the net electrical efficiency up to 32.3% and thermal efficiency as high as 61.1% can be reached through the optimization.

Feasibility Evaluation of Creep Model for Failure Assessment of Solder Joint Reliability of Wafer-Level Packaging

Among the thermomechanical creep models developed to predict the solder response to progressive inelastic deformation, the Anand model is the most common. However, recent studies have had markedly different formulations of the nine parameters in this model used to describe the stress-strain curve that occurs at nonlinear, temperature-dependent low strain levels under field conditions. Furthermore, this model lacks proper technical specifications compared to the hyperbolic sine model. This has led to the development of multiple user-defined creep models with customized codes that are incompatible with many commercial finite-element tools. Therefore, modifying the current Anand model to improve the reliability of its electronic packages has become an essential task. In this paper, a new creep model was developed based on the assumptions that an instantaneous steady-state creep form eliminates the evolution term, resulting in a creep equation with four parameters. The proposed model had a fundamental statement similar to that of the well-known hyperbolic sine model. The workability of the new model was demonstrated through a simulated solder response that tested the strain rate effect and different thermal cyclic loading profiles. This model greatly broadens the applicability of the hyperbolic model. Furthermore, the modified Anand model has better agreement than the Anand model with the experimental results for different types of electronic packages.

Hidden Markov Models revealing the household thermal profiling from smart meter data

This work describes a methodology based on Hidden Markov Models (HMMs) that are applied for revealing household thermal load profiles which are not available to direct observation. This research is motivated by the necessity of reducing the energy consumption for cooling and heating in residential buildings. Our methodology uses data that is becoming readily available at households – hourly energy consumption records collected from smart electricity meters, as well as hourly outdoor air temperature records. The heat transfer regime, namely the states corresponding to lower or higher building hourly thermal loads related to the outdoor air temperatures, will be considered as the underlying mechanism affecting the generation of observations. We aggregate the observed data to obtain a certain number of clusters. The problem of HMM estimation is addressed and the subsequent HMMs are compared on the basis of information criteria, like Akaike and Bayesian Information Criteria. Our goal is to reveal the dynamic of building thermal load (heating/cooling) under the uncertainties induced by the residents’ behavior. Consequently, we present examples of thermal load profiles generated using our best HMM on a testing facility located in the Polytechnic University of Bucharest campus, namely the UPB's passive building house.

Potential and Optimal Sizing of Combined Heat and Electrical Storage in Private Households

The increase in fluctuating renewable electricity generation requires growing flexibility and balancing capacities in the electric energy grid. Storage systems can provide the necessary balancing capacities. Therefore, it is analyzed which potential for flexible energy consumption can be found in private households. Heat and power in private households are heavily interlinked due to increasing numbers of electrical heating systems (e.g. heat pumps). In addition, installed PV systems on roof tops are making renewable electricity an attractive energy source for space heating and hot water supply. To maximize the consumption of self-generated electricity, battery energy storage systems (BESS) and thermal hot-water based storage systems are used in private households. The challenge is to find economically viable configurations for sizing of combined battery and thermal storage units.The introduced approach simulates a household with a variable size of the relevant components of the thermal and electric system, being the PV system, PV and battery converters (DC linked), the battery (lithium-ion), thermal hot water storage and a heat pump. Profiles for the electrical load are based on empirical analysis of resident behavior coupled with measurements from typical household appliances. The thermal load profiles are derived from representative simulation tools, simulating resident behavior and the resulting heat demand. Based on the simulation results, an optimal sizing of storage units is calculated.

Use of Municipal Solid Waste Landfill as Heat Source of Heat Pump

The heat pump systems are considered today an environmentally friendly technology and, together with other energy production systems from renewable sources, are fundamental for reducing energy consumption and the resulting greenhouse gas emissions due to air conditioning of buildings. The ground source heat pumps use the ground as a heat source able to provide the better energy performance if compared with more common systems which using air as source. The increase of the temperatures inside the controlled landfills of municipal solid waste (MSW), due to the decomposition of waste materials can make the volume of waste a viable alternative in this context, to be used as a heat source for the production of heat. The present work has the objective of analyzing the potential of use of a MSW landfill for space heating through a heat pump.The first part of the work analyzes the main features of a landfill of municipal solid waste starting from system design through to biological degradation processes of organic matter. Subsequently the possible configurations of heat exchangers to be inserted within or covering the landfill is discussed.Based on the findings found in the literature, a dynamic model has been created for a real case study of a MSW landfill located in the north-east of Italy. Boundary conditions (i.e. annual temperature cycles for the soil, heat exchange by convection with the ambient air and radiation, a heat generation function distributed on the rejection of mass) have been imposed to the model in order to carry out annual simulations by means of finite element method, thanks to which the values of temperature reached by the mass of waste have been obtained. By means of the creation of a thermal load profile of a group of users it has been possible to determine the total energy extracted from the landfill and the electricity needed for the operation of the heat pump. The potential energy saving achievable with this type of plant was obtained by comparison with a ground source heat pump using horizontal pipes.

Optimization of the Thermal Load Profile in District Heating Networks through “Virtual Storage” at Building Level

Thermal storage is of extreme importance in modern district heating networks in order to increase the share of waste heat and heat produced through renewable sources and cogeneration. Nevertheless, installation of large storage volumes is not always feasible, especially in dense urban areas. A possible option consists in virtual storage, which is obtained through variation of the thermal request profiles of some of the connected buildings with the goal of producing an effect similar to that obtained using storage. To perform such approach there are three crucial elements: 1) an advanced ICT solution able provide real time information about the thermal request of the buildings and the thermodynamic conditions at the thermal substations; 2) a detailed thermo fluid-dynamic model of the district heating network able to simulate the temperature evolution along the network as the function of time; 3) a compact model of the buildings in the district able to check the acceptability of the internal temperatures following the modified strategies.The model produces changes in the start-up time of the buildings connected with the network as well as possible pauses during the day. These changes in the request profiles usually involve a slightly larger heat load. Nevertheless, peak shaving is accompanied by a reduction in heat generation of boilers and an increase in the thermal production of efficient systems, such as cogeneration units. This results in a significant reduction in the primary energy consumption.An application to the Turin district heating network, which is the largest network in Italy, is presented. In particular, a subnetwork connecting the main transport network to about 100 buildings located in the central area of the town is considered. The analysis if performed in selected days where the optimization was conducted the day before on the basis of weather forecasts and then applied to the network. Despite the changes in the request profiles could be applied only to a limited number of buildings, the analysis show that the peak request can be reduced. Simulations performed considering the application of changes to a larger number of buildings show that reduction in the primary energy consumptions of the order of 5% can be obtained.

Impact of PV and variable prices on optimal system sizing for heat pumps and thermal storage

Heat pump (HP) units coupled to thermal storage offer flexibility in operation and hence the possibility to shift electric load. This can be used to increase PV self-consumption or optimise operation under variable electricity prices. A key question is if new sizing procedures for heat pumps, electric boilers and thermal storages are needed when heat pumps operate in a more dynamic environment, or if sizing is still determined by the thermal demand and thus sizing procedures are already well known. This is answered using structural optimisation based on mixed integer linear programming. The optimal system size of a HP, an electric back-up heater and thermal storage are calculated for 37 scenarios to investigate the impact of on-site PV, variable electricity price, space heat demand and domestic hot water demand. The results are compared to today's established sizing procedures for Germany. Results show that the thermal load profile has the strongest influence on system sizing. In most of the scenarios investigated, the established sizing procedures are sufficient. Only large PV sizes, or highly fluctuating electricity prices, create a need for lager storage. However, allowing the storage to be overheated by 10K, the need for a larger storage only occurs in the extreme scenarios.

Probabilistic behavioural modeling in building performance simulation—The Brescia eLUX lab

Occupant’s behavioural patterns determine a significant level of uncertainty in building energy performance evaluation. It is difficult to account for this uncertainty in the design phase when operational and occupancy profiles are unknown. The relevant “performance gap” usually encountered between simulated and measured energy performance is clearly connected to biased assumptions in modeling, especially in the initial design phase. A probabilistic modeling approach is proposed to improve simulation reliability and robustness with respect to variability in occupancy patterns. The case study presented is the eLUX lab of the “Smart Campus” of Brescia University in Italy. Occupancy dependent input parameters such as air change rates (i.e. mechanically controlled ventilation) and internal heat gains (i.e. due to people, lighting and appliances) are described by means of probability distributions to obtain probabilistic thermal demand and load profiles as output. Probabilistic results enables a more reliable identification of energy saving strategies (operational and environmental settings) with respect to highly variable operating conditions. Further, simulation data are processed to obtain a weather-adjusted energy demand visualization, suitable for establishing a continuity between modeling in design and operation phases, with calibration purpose. Calibrated energy models can be used for several specific tasks in the operation phase, in particular condition monitoring, fault detection and diagnosis, supervisory control and energy management. For the case study presented, a detailed data acquisition scheme has been designed to enable an effective monitoring activity in the operation phase, aimed at experimenting model-based approaches for the tasks reported. The proposed research is the point-of-departure for a general activity aimed at assessing critically the issues of reliability and robustness of simulation results obtained with conventional modeling approaches, in particular with respect to occupants’ behaviour, exploiting at the same time the possibility of using measured data as a direct feedback to promote behavioural change.

Efficient operation of energy hubs in time-of-use and dynamic pricing electricity markets

Natural gas can support the electricity grid through integration of the existing natural gas and electric networks into energy hubs. This paper elaborates on the design of an efficient algorithm for the EMS (energy management system) inside a residential energy hub. We study the strategic operation of the energy hubs in a competitive electricity market. Each energy hub aims to jointly minimize the operating cost and the discomfort cost caused by modifying the electrical and thermal load profiles. We show that there exists a competitive equilibrium for the energy hubs. A linear time EMS scheduling algorithm is proposed to determine that equilibrium. The optimal strategy of the energy hubs are compared for two widely used electricity pricing mechanisms, namely the TOU (time-of-use) and the dynamic pricing schemes. Furthermore, we study the effects of the electrical storage system and renewable resources on the hubs' optimal strategies. Simulations are performed for a group of ten residential energy hubs in a competitive electricity market. It is shown that the energy hubs' daily cost will be reduced by using the proposed scheduling algorithm. It is also shown that the dynamic pricing scheme can better motivate the energy hubs toward modifying their daily operation.

Solar Assisted Ground Source Heat Pump in Cold Climates

The geothermal heat pump (or ground source heat pump) uses the ground as heat source or sink for heating and cooling respectively. The design of the borehole field is the key element of these systems since the wrong evaluation of the boreholes’ length affects the initial costs and/or the energy performance of the heat pump. The geothermal heat pumps are considered as renewable energy technologies, consequently can help the community to reduce the primary energy uses and also the CO2 emissions. However the sustainability and efficiency are ensured in the long period only when the heat balance through the ground is guaranteed.This work evaluates the thermal behavior of ground source heat pumps in cold climates, where the thermal load profile of buildings is not balanced between heating and cooling, especially in residential sector characterized by low internal loads. In these contexts, the heat pump mainly works in heating mode, extracting continuously heat from the ground. As a result, the ground temperature decreases gradually during the years affecting the energy performance of the heat pump. A possible solution to this problem is to use solar thermal collectors to stabilize or gradually increase the mean ground temperature (these systems are called Solar Assisted Ground Source Heat Pump – SAGSHP).In this work a multi floors residential building with 12 flats (88 m2 each) is analyzed in three climate zones, making use of the simulation tool TRNSYS. Different configurations of the plant system have been investigated and the case without the solar thermal collectors has been considered as reference.

Modeling Lighting as Part of the USER Model Based on Stochastic Time Budget Survey Data

Precise forecasts of electrical and thermal load profiles are extremely necessary for the preplanning of home energy management systems. In order to synthesize user behavior and load profiles in high time resolution, User Interaction Model has been developed. By using time budget survey data and stochastic modeling, activity profiles of each inhabitant are created based on statistical input data. Mapping of activities to different categories of appliances allows USER to emulate realistic load curves for both single occupants and the entire residential building. This paper especially deals with modeling of energy demand for lighting and the resulting electrical load profiles.

Fuel partialization and power/heat shifting strategies applied to a 30 kWel high temperature PEM fuel cell based residential micro cogeneration plant

The present study is dedicated to the investigation of applying different strategies on an HT-PEM fuel cell based micro cogeneration plant in order to evaluate the capability of this system to cope with intermittent electrical and thermal load profiles. The performance of the system under fuel partialization strategy is first studied and the thermal and electrical efficiencies of the plant at different partial loads are determined. It was found that due to partialization of the fuel down to 50% of the initial value, the electrical efficiency increases from 29.3% to 33.6% while the thermal efficiency decreases from 53.0% to 47.6%. Power to heat shifting strategy, as a faster approach, is then employed in which, by altering the anodic stoichiometric ratio, the electrical generation is decreased while higher thermal power is produced. The results showed that this partialization method leads to harsh drop, around 13%, in the electrical efficiency of the plant. In the last analysis, the previous strategies are combined and the power to heat shifting approach is implemented on the system operating at partial load. The main advantage of the last strategy is the flexibility of the system in covering a wide range of thermal demand.

Mechanism and kinetics of ultra‐high molecular weight polytetrafluoroethylene sintering

ABSTRACTThe effect of sintering time on the melt evolution of Ultra‐High Molecular Weight Polytetrafluoroethylene was studied in situ by high temperature Wide Angle X‐ray Scattering, and by cyclic thermal loading profiles within a Differential Scanning Calorimeter (DSC) and Thermo‐Mechanical Analyzer (TMA). Results obtained from these techniques support the concept of molecular ordering in the melt state as a function of sintering time well above the melting temperature. TMA, which is not a conventional technique for monitoring thermal transitions, is shown to be sensitive enough for such purposes. Both DSC and TMA exhibit nonequilibrium melt behavior even 30°C above its equilibrium melting temperature for long time periods. A correlation between the DSC and TMA results is established. The cyclic thermal profile leads to a dramatic growth in enthalpy of crystallization/melting. The mechanism for this growth is associated with two independent processes; isothermal annealing at the sintering temperature and lamellar thickening in the solid state. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40967.

Experimental determination of efficiency factors for different Micro-CHP units according to the standard DIN 4709

Since November 2011 the standard DIN 4709 stipulates performance tests for Micro-CHP units in Germany. In contrast to steady state measurements of the CHP unit itself, the test according to DIN 4709 includes the thermal storage tank as well as the internal control unit, and it is based on a 24 h test cycle following a specified thermal load profile. Hence, heat losses from the storage tank are as well taken into account as transient losses of the CHP unit. In addition, the control strategy for loading and unloading the storage tank affects the test results.The DIN 4709 test cycle has been applied at the test stand for Micro-CHP units at Reutlingen University, and results for the Micro-CHP unit WhisperGen and the EC Power units XRGI 15® and XRGI 20® are available. During the analysis a method has been developed to evaluate the results in case the test cycle does not end in a time slot between 24 and 24.5 h after the starting as demanded by DIN 4709. Since this method has been successfully applied to the test of various CHP units of different size and technology so far, it is suggested to incorporate it to DIN 4709 during the next revision of the standard.The performance numbers obtained reveal the differences in efficiencies measured at steady-state on the one hand and following the DIN 4709 test cycle on the other hand. While the deviations in electrical efficiencies are small, thermal efficiencies according to DIN 4709 fall below steady state data by 3–6 percentage points. This is attributed to transient thermal losses and heat losses from the storage tank, which are not included in steady state and separate testing of the CHP unit, only.

Combined cooling, heating and power for small urban districts: An Italian case-study

The paper proposes a methodology and its application developed in order to optimize energy generation and usage in urban areas. The investigation has been applied at the Historical centre of Benevento, a southern Italian city. A geo-referenced energy model of the ancient town is proposed, and it allows – for each individual building – both evaluation and visualization of energy demands for space heating and cooling. In addition, the electric demands of buildings are also available, having quantified these by means of evaluation of all different energy uses and installed appliances. All energy evaluations have been collected through Geographic Information System (GIS) techniques. This procedure permitted the definition of Urban Energy Maps (UEMs), useful for evaluating the present criticalities, and thus suitable for designing possible urban energy retrofits, as – for instance – the installation of combined cooling, heat and power systems (CCHP), in order to satisfy the various energy requests.Finally, the entire method – in terms of combined information regarding thermal, cooling and electric load profiles – may orient towards a rational energy use, cost optimization and reduction of greenhouse emissions. The presented methodology can be easy implemented and repeated, and could be adopted as a new tool for supporting a suitable energy planning.

Economic analysis of hybrid system consists of fuel cell and wind based CHP system for supplying grid-parallel residential load

An evolutionary programming based approach to evaluate the effect of combining fuel cell power plants (FCPP) and wind on the operational and performance cost is presented in this paper. The fluctuating nature of wind energy (WE) has different effects on the system constraints and operational cost. Moreover, FCPPs are able to produce both thermal and electrical energy simultaneously. Results manifest that through combining FCPP and WE in a hybrid structure for CHP systems, causes lower operational cost than that of individual units. In order to consider production cost of energy, electrical power from WE, power trade with the local grid, thermal recovery from the FCPP, start-up cost of FCPP and maintenance cost; an integrated cost model for FCPP and WE is constructed. A six-minute thermal and electrical load profiles for a residential house in Mashhad Province, Iranis engaged along with the wind speed variation to specify the best cost effective strategy. According to electrical and thermal load demand, available wind power and different tariffs for purchasing and selling electricity of local grid the operation of the FCPP system is scheduled to optimize operational cost. Encouraging results indicate feasibility of the proposed technique.