Thermal Response Model Research Articles

Distributed air conditioning control in commercial buildings based on a physical-statistical approach

This paper presents a method to optimally control a commercial building air conditioning operation based on building thermal physics and human behavior. Control plans are developed for zone cooling and according to occupancy patterns at zone levels, and using a novel response model developed in this paper. The thermal response model is a statistical model, which is built on the basis of insights gained from physics-based model of zone thermal behavior. The control model attempts to optimize cooling system scheduling on the basis of occupancy patterns, price signal from utilities and human comfort and productivity. The optimization follows an on-demand routine, such that zone level air conditioning starts at a time epoch that is optimal according to zone thermal response and cooling requirements. We toss the term “pre-occupy” control. We also develop, what we call, “post-occupy” control, where the system shutdown follows thermal inertia and cooling requirements at the time that the zone is expected to become unoccupied. The thermal response modeling of a zone and the two control modes are considered major contributions of this article. EnergyPlus reference models are used to train our models and illustrative examples are presented.

Comparison of simplified and advanced design methods for determining mechanical resistance of timber structures exposed to fire

ABSTRACTEurocode 5, Part 1–2 for the design of timber structures in fire conditions contains two simplified methods and advanced calculation methods, as well. The first method is the reduced cross-section method, which is the recommended procedure in Eurocode 5, Part 1–2. The second method is the reduced properties method. There are differences in results between these two methods. These methods are designated for evaluation of the mechanical resistance of timber members and there is a calculation of the charring depth by means of these simplified rules. Moreover, there are advanced calculation methods. These advanced methods deal with the determination of the charring depth, the thermal response model and the structural response model. They can be used for members, parts of a structure or entire structures. This paper presents differences between these simplified and advanced methods and the comparison of results.

Multiphysics and Thermal Response Models to Improve Accuracy of Local Temperature Estimation in Rat Cortex under Microwave Exposure.

The rapid development of wireless technology has led to widespread concerns regarding adverse human health effects caused by exposure to electromagnetic fields. Temperature elevation in biological bodies is an important factor that can adversely affect health. A thermophysiological model is desired to quantify microwave (MW) induced temperature elevations. In this study, parameters related to thermophysiological responses for MW exposures were estimated using an electromagnetic-thermodynamics simulation technique. To the authors’ knowledge, this is the first study in which parameters related to regional cerebral blood flow in a rat model were extracted at a high degree of accuracy through experimental measurements for localized MW exposure at frequencies exceeding 6 GHz. The findings indicate that the improved modeling parameters yield computed results that match well with the measured quantities during and after exposure in rats. It is expected that the computational model will be helpful in estimating the temperature elevation in the rat brain at multiple observation points (that are difficult to measure simultaneously) and in explaining the physiological changes in the local cortex region.

Thermal Protection System Response Uncertainty of a Hypersonic Inflatable Aerodynamic Decelerator

The objective of this paper is to investigate the uncertainty in the bondline temperature response of a flexible thermal protection system subject to uncertain parameters in the hypersonic flowfield and thermal response modeling of a hypersonic inflatable aerodynamic decelerator configuration for ballistic Mars entry. An inflatable decelerator with a 10 m major diameter is selected for this study based on the forebody dimensions scaled from the 6 m test article that was tested in the NASA Ames Research Center’s National Full-Scale Aerodynamics Complex facility. A global nonlinear sensitivity analysis study for the bondline temperature uncertainty shows that the dimension of uncertain parameters can reduce from 22 to 8. An uncertainty analysis of the bondline temperature in the reduced dimensions indicates that the bondline temperature varies by as much as 125% above the nominal prediction and exceeds the temperature limit of 400°C. The largest uncertainty occurred at 70 s in the trajectory before separation of the inflatable decelerator for transition to a secondary descent technology. The main contributors to the bondline temperature uncertainty are the insulator and outer fabric conductivities, as well as the freestream density. The thickness and initial density of the insulator layer, closest to the gas barrier layer, are also shown to be significant contributors to the bondline temperature uncertainty, especially earlier in the trajectory.

On detailed thermal response modeling of vertical greenery systems as cooling measure for buildings and cities in summer conditions

Vertical greenery systems (VGSs) are becoming a common architectural element in urban environments. In addition to the aesthetics of VGSs, impacts on building's energy demand and heat island mitigation in cities has been identified. In the present study, experimental results of thermal response and properties of VGSs with vertical leaf area index (LAIV) equal to 6.1 and 7.2 are presented. Experimental results show that VGSs can impact up to 34 K lower surface temperatures of a façade, while maintaining air temperatures in the VGSs' canopies close to ambient temperatures. Properties of the VGSs were used as a basis as well as an input for a detailed mathematical model of the thermal response of a building envelope with a VGS. The validated mathematical model was used for parametrical analysis of the impact of thermal resistance of a building envelope on the cooling potential of the VGSs. The results show that the cooling effect is more significant for less insulated façades, and that a VGS can be modeled as an independent urban cooling element. Finally, a parametrical model of the latent heat flux of a VGS was developed and can be used as a boundary condition in urban heat island studies.

A new analytical approach for simplified thermal modelling of buildings: Self-Adjusting RC-network model

A novel method for adjusting the parameters of a lumped parameter model for the transient thermal response of building constructions is presented. Previous analytical adjustment methods can be complex and inaccurate, while optimization algorithms, although more accurate, require prior simulation using a high-order reference model, and so provide no advantages to be integrated into simulation programs. This work presents a methodology for the analytical adjustment of a first-order model based on the hypothesis that the position of the capacitance varies in every time step in response to changes in the excitation value. By comparison with a reference model and using a wide range of constructions (420), the functional form of this dependence was determined in accordance with the value of time step and properties and thickness of the element. Using different typical constructions (41), the method was validated by comparison with the reference model in terms of surface heat fluxes, surface temperatures and indoor air temperature. The results showed an excellent agreement with the reference model for surface temperatures and indoor air temperature, and good agreement for surface heat fluxes. The method can be integrated into simulation programs with a low computational cost, sufficient accuracy, universality and adaptable time step.

Numerical Investigation of Gas-Surface Interactions due to Ablation of High-Speed Vehicles

A conjugate thermal analysis of a typical reentry space capsule is carried out by weakly coupling a particle-based flow solver to a material thermal response solver. Flow solution in the transitional flow regime is obtained by a two-dimensional parallel in-house-developed direct simulation Monte Carlo code capable of solving multispecies gas flows. A material thermal response model is developed for solving a one-dimensional heat conduction equation in the Cartesian coordinates, accounting for the ablative processes taking place in the reaction zone of an ablative material. The pyrolysis reaction results in the formation of char and the release of pyrolysis gases through the porous charred material. In the present work, the one-dimensional thermal response solver is validated against the available data in the literature. The flow solutions with and without the ablation model are then compared and discussed. Through an interesting case study, the interaction of pyrolysis gas blowing off the surface with shock-layer gas and its effect on surface parameters are discussed.

Performance analysis of a solar air heating system with latent heat storage in a lightweight building

In energy-efficient, lightweight buildings, a high solar heating fraction can only be achieved if the solar system contains adequate heat storage. In this paper, the design and thermal response modeling of a solar air heating system, which consists of an air vacuum tube solar collector and latent heat storage, is presented. For the system performance analysis, an experimentally validated numerical model of the solar air heating system was coupled with a building thermal response model. A solar heating fraction and the utilizability of solar heat were used as the main performance indicators. The analysis showed that a solar heating fraction of 63% can be achieved in an energy efficient, lightweight building.

Extended two-temperature model for ultrafast thermal response of band gap materials upon impulsive optical excitation.

Thermal modeling and numerical simulations have been performed to describe the ultrafast thermal response of band gap materials upon optical excitation. A model was established by extending the conventional two-temperature model that is adequate for metals, but not for semiconductors. It considers the time- and space-dependent density of electrons photoexcited to the conduction band and accordingly allows a more accurate description of the transient thermal equilibration between the hot electrons and lattice. Ultrafast thermal behaviors of bismuth, as a model system, were demonstrated using the extended two-temperature model with a view to elucidating the thermal effects of excitation laser pulse fluence, electron diffusivity, electron-hole recombination kinetics, and electron-phonon interactions, focusing on high-density excitation.

Single input-single output identification thermal response model of bridge using nonlinear ARX with wavelet networks

Model identification of a system can be used for a variety of purposes, including model updates, damage assessment, active control and original design evaluation. We used single input-single output (SISO) nonlinear regression with least square solution and nonlinear AutoRegresive with eXogenous inputs (NLARX) with wavelet neural networks models to identify the thermal response of a bridge under hard environmental effects and estimated the nonlinearity model parameters. Fu-Sui Bridge strain structural health monitoring measurements were used as a case study. Nonlinear regression analysis showed that the thermal response is a nonlinear effect with temperature changes; and the NLARX with wavelet network solution is capable of accurately predicting thermal response and can help with interpreting measurements from continuous bridge health monitoring systems.

Experimental study on measurement and calculation of heat flux in supersonic combustor of scramjet

An experimental measurement and calculation method which consist of thermal response model, convergence criteria and control algorithms, is proposed in this paper for the determination of heat flux in a scramjet combustor. Numerical simulations are done to evaluate the effectiveness of the proposed method, and experiments are made in the direct-connect hydrocarbon fueled scramjet combustor of Mach-6 flight for different equivalence ratios. The distribution of heat flux along the axial and circumferential directions can be obtained using the proposed method. The distribution of heat flux is uneven which is caused by the aerodynamic heating, combustion heat release and changes of section area, and the peak heat flux can be more than 2MW/m2 during the experiments. Heat flux increases with the increase in equivalence ratio for the same Mach number. And axial distribution of heat flux is uniform for different equivalence ratios. In addition, the combustion heat release area of the combustion chamber can therefore be concluded which is useful for guiding the structural design of the thermal protection system.

Anatomical-based model for simulation of HIFU-induced lesions in atherosclerotic plaques

Purpose: The aim of this study was to simulate the effect of high intensity focused ultrasound (HIFU) in non-homogenous medium for targeting atherosclerotic plaques in vivo. Materials and methods: A finite-difference time-domain heterogeneous model for acoustic and thermal tissue response in the treatment region was derived from ultrasound images of the treatment region. A 3.5 MHz dual mode ultrasound array suitable for targeting peripheral vessels was used. The array has a lateral and elevation focus at 40 mm with fenestration in its centre through which a 7.5 MHz diagnostic transducer can be placed. Two cases were simulated where seven adjacent HIFU shots (∼5000 W/cm2, 2-s exposure time) were targeted on the plaque tissue within the femoral artery. The transient bioheat equation with a convective term to account for blood flow was used to predict the thermal dose. The results of the simulation model were then validated against the histology data. Results: The simulation model predicted the HIFU-induced damage for both cases, and correlated well with the histology data. For the first case thermal damage was detected within the targeted plaque, while for the second case thermal damage was detected in the pre-focal region. Conclusion: The results suggest that a realistic, image-based acoustic and thermal model of the treatment region is capable of predicting the extent of thermal damage to target plaque tissue. The model considered the effect of the wall thickness of large arteries and the heat-sink effect of flowing blood. The model is used for predicting the size and pattern of HIFU damage in vivo.

Behavioural responses to cold thermal discomfort

Heating energy demand in buildings depends in part on occupants' behavioural responses to thermal discomfort during the heating season. The understanding of this has become one of the priorities in the quest to reduce energy demand. Thermal comfort models have long been associated with occupants' behaviour by predicting their state of thermal comfort or rather discomfort. These assumed that occupants would act upon their level of discomfort through three types of response: mechanisms of thermoregulation, psychological adaptation and behavioural responses. Little research has focused on the behavioural aspect. One of the key challenges is to gather accurate measurements while using discreet, sensor-based, observation methods in order to have minimum impact on occupants' behaviour. To address these issues, a mixed-methods approach is introduced that enables the establishment of a three-part framework for mapping behaviour responses to cold sensations: (1) increasing clothing insulation level; (2) increasing operative temperature by turning the heating system on/up; and (3) increasing the frequency, duration and/or amplitude of localized behaviour responses such as warm drink intake or changing rooms. Drawing on this framework, an extended model of thermal discomfort response is introduced that incorporates a wider range of observed behaviours.

Multi-objective optimal design of lithium-ion battery packs based on evolutionary algorithms

Lithium-battery energy storage systems (LiBESS) are increasingly being used on electric mobility and stationary applications. Despite its increasing use and improvements of the technology there are still challenges associated with cost reduction, increasing lifetime and capacity, and higher safety. A correct battery thermal management system (BTMS) design is critical to achieve these goals. In this paper, a general framework for obtaining optimal BTMS designs is proposed. Due to the trade-off between the BTMS's design goals and the complex modeling of thermal response inside the battery pack, this paper proposes to solve this problem using a novel Multi-Objective Particle Swarm Optimization (MOPSO) approach. A theoretical case of a module with 6 cells and a real case of a pack used in a Solar Race Car are presented. The results show the capabilities of the proposal methodology, in which improved designs for battery packs are obtained.

Thermal decomposition behavior of silica‐phenolic composite exposed to one‐sided radiant heating

When polymer‐matrix composite reaches sufficiently high temperature, pyrolysis reactions of the polymer matrix occur. The thermal decomposition behavior of silica‐phenolic composite was investigated using solar radiant heating experiment with one‐sided heat flux. Thermogravimetric studies and combined thermal analysis techniques were performed to characterize the thermal decomposition kinetics of phenolic resin. Simultaneously a thermal response model was used to calculate the through‐thickness temperature distribution. The calculated time‐dependent temperature profile at different material depths were compared with the experimental results measured at the same location. The silica‐phenolic composite exhibited an excellent thermal insulation during thermal exposure. The postheating specimen was sectioned in millimeter segments to determine the density profile. On the basis of the density profile, the transition from char layer to pyrolysis zone to virgin material was estimated. Finally, the material morphology was analyzed for silica‐phenolic composite after thermal exposure. POLYM. COMPOS., 36:1557–1564, 2015. © 2014 Society of Plastics Engineers

Convergent mortality responses of Caribbean coral species to seawater warming

Species‐specific responses to disturbance are a central consideration for predicting the composition, dynamics, and function of future communities. These responses may be predictable based on species traits that can be analyzed systematically to understand those characteristics important in determining susceptibility and potential for recovery. Scleractinian coral communities of the Western Atlantic are experiencing increased frequency and severity of extreme thermal disturbance, coral bleaching, and mortality. A conceptual thermal bleaching response model developed in this study suggests multiple susceptibility pathways that can lead corals to partial mortality and the loss of biomass, or complete mortality and the loss of genotypes, with implications for species‐specific persistence and recovery. Coral assessments from annual to semi‐annual surveys at 18 sites in the U.S. Virgin Islands, northeastern Caribbean Sea, before, during, and after the catastrophic 2005 coral bleaching event and during the mild 2010 bleaching event were used to evaluate bleaching, disease, and mortality responses. Three convergent groupings of species emerged based predominantly on their responses to the 2005 event: Type I—high bleaching and initial mortality, no subsequent white disease, and severe losses of cover (exhibited by Agaricia agaricites and branching Porites species); Type II—moderate bleaching and initial mortality, high subsequent white disease prevalence, and severe losses of cover (exhibited by Colpophyllia natans, Montastraea annularis species complex, and M. annularis sensu stricto); Type III—moderate to low bleaching and paling, low to no subsequent white disease, and low to no loss of cover (exhibited by Diploria strigosa, Montastraea cavernosa, Porites astreoides, and Siderastrea siderea). Whole colony mortality was uncommon, even in the most susceptible species, suggesting a potential for recovery among the majority (19 of 27) of scleractinian corals studied. Type II species performed worse than predicted by species traits because of their susceptibility to disease, a factor that needs to be incorporated more fully in models of thermal stress response. Responses of all species to the milder 2010 event were less severe, with limited bleaching and no detectible mortality. Future community composition of Caribbean coral reefs under seawater warming will likely be increasingly dominated by resistant Type III species.

Reconstruction of Mars Pathfinder Aeroheating and Heat Shield Response Using Inverse Methods

The Mars Pathfinder probe entered the Martian atmosphere in 1997 and contained instrumentation that provided measurements of the superlight ablator (SLA) heat shield subsurface temperature at different locations during the entry sequence. These measurements represented the first Martian aeroheating flight data since the Viking Lander missions. The objective of this paper is to reconstruct the Pathfinder entry vehicle’s aerothermal heating and heat shield material response using updated modeling tools and approaches in both direct and inverse manners. The direct approach consists of performing updated computational fluid dynamics calculations on a newly reconstructed entry trajectory to characterize the vehicle’s heating environment. From the calculated heating boundary conditions, the heat shield in-depth temperature response is computed using an updated thermal response and ablation model for the SLA material. These predictions are compared directly to the flight data. In addition to the direct comparison approach, inverse methods are used to estimate boundary conditions that result in a closer match between the flight data and subsurface temperature predictions. The unblown surface heat transfer coefficient is reconstructed as a function of time using whole-time domain least-squares methods in conjunction with regularization techniques.

Thermal and Mechanical Modeling of Load-Bearing Cold-Formed Steel Wall Systems in Fire

AbstractAlthough a few fire experiments have been carried out on load-bearing cold-formed steel (CFS) wall systems, the understanding of their fire performance is still limited, and further parametric analysis on the basis of such experiments is expensive and time-consuming. This paper presents a simplified numerical approach to predicting the thermal and mechanical responses of CFS wall systems in fire. Thermal physical property experiments were carried out to measure the essential material properties. With those material properties as inputs, a one-dimensional thermal response model was developed to predict the heat transfer across the cross section of CFS wall systems. Both heat convection and radiation were considered in the thermal boundary conditions. The governing equation was expressed in the form of implicit finite-differential equations and solved using the Gauss-Seidel method. The model predictions of temperature responses of CFS wall systems were in good agreement with the measured temperature...

Thermal Response Modeling of Sheet Metals in Uniaxial Tension During Electrically-Assisted Forming

For the current practice of improving fuel efficiency and reducing emissions in the automotive sector, it is becoming more common to use low density/high strength materials instead of costly engine/drivetrain technologies. With these materials there are normally many manufacturing difficulties that arise during their incorporation to the vehicle. As a result, new processes which improve the manufacturability of these materials are necessary. This work examines the manufacturing technique of electrically-assisted forming (EAF) where an electrical current is applied to the workpiece during deformation to modify the material's formability. In this work, the thermal response of sheet metal for stationary (i.e., no deformation) and deformation tests using this process are explored and modeled. The results of the model show good agreement for the stationary tests while for the deformation tests, the model predicts that all of the applied electrical current does not generate Joule heating. Thus, this work suggests from the observed response that a portion of the applied current may be directly aiding in deformation (i.e., the electroplastic effect). Additionally, the stress/strain response of Mg AZ31 under tensile forming using EAF is presented and compared to prior experimental work for this material.

Robust Modeling of Human Thermal Response to Hand and Forearm cooling for Improved Performance and Energy Efficiency

A modeling approach is used to study the effectiveness of the Active Cooling (AC) method of hand and forearm immersion in cold water to reduce core temperature following heavy physical activity. A transient multi-node segmental bioheat model based on physiology and accurate mathematical modeling of thermoregulatory functions are used to predict human segmental core and skin temperatures, and arterial blood flow for given metabolic rate and environmental conditions. The validity of the model is confirmed by comparison with published experimental data on core temperature during and after immersion of forearms and hands in cold water. The validated model is used in a case study to enhance understanding of associated body thermal changes and arterial blood flow and AVA mechanisms during AC interventions that alleviate thermal stress in hot environment. The time needed for the core temperature to drop from 38.0°C to 37.0°C is found to be 33 minutes when subject is at rest and is exposed to air cooling at 21°C compared to 15 minutes when hands and forearms are immersed in water at 10°C. The average sensible heat loss during the cooling period associated with immersion of forearms and hands in water at 10°C was found to be 106.2 W compared to 75.9 W for passive air cooling at 21°C. The active cooling was found to be an effective method for accelerating reduction on core temperature and can be used with efficient, localized, and portable cooling devices.