Thermal Response Model Research Articles

Free cooling of a building using PCM heat storage integrated into the ventilation system

This article presents a study of the free cooling of a low-energy building using a latent-heat thermal energy storage (LHTES) device integrated into a mechanical ventilation system. The cylindrical LHTES device was filled with spheres of encapsulated RT20 paraffin, a phase-change material (PCM). A numerical model of the LHTES was developed to identify the parameters that have an influence on the LHTES’s thermal response, to determine the optimum phase-change temperature and to form the LHTES’s temperature-response function. The last of these defines the LHTES’s outlet-air temperature for a periodic variation of the inlet ambient-air temperature and the defined operating conditions. The temperature-response function was then integrated into the TRNSYS building thermal response model. Numerical simulations showed that a PCM with a melting temperature between 20 and 22 °C is the most suitable for free cooling in the case of a continental climate. The analyses of the temperatures in a low-energy building showed that free cooling with an LHTES is an effective cooling technique. Suitable thermal comfort conditions in the presented case-study building could be achieved using an LHTES with 6.4 kg of PCM per square metre of floor area.

Efficiency of free cooling using latent heat storage integrated into the ventilation system of a low energy building

This article presents the results of an investigation into the free cooling efficiency in a heavyweight and lightweight low energy building using a mechanical ventilation system with two latent heat thermal energy storages (LHTESs), one for cooling the fresh supply air and the other for cooling the re-circulated indoor air. Both LHTESs contain sphere encapsulated PCM (paraffin RT20). Using a developed and experimentally verified numerical model of the LHTES, the temperature response functions, based on the heat storage size, the air flow rates and the PCM's thermal properties, are established in the form of a Fourier series and empirical equations and used in the TRNSYS building thermal response model. Several mechanical ventilation, night cooling and free cooling operation modes were analysed and compared. It was found that the free cooling technique enables a reduction in the size of the mechanical ventilation system, provides more favourable temperatures and therefore enables better thermal comfort conditions, and in our studied case also fresh air for the occupants.

Application of microthermometry to measurement of microbial activity and inactivation process by inhibitor

A rapid and simple technique (microthermometry) was developed for the measurement of microbe's metabolic activities and its inactivation process by an inhibitor. To analyze the results and to determine the parameters for the estimation of the activity and inactivation degree, a simple model was proposed. Yeast cells ( Saccharomyces cerevisiae) were used as a microbe. A differential method using two bead-type thermistors as reference and measuring probes was employed for the detection of a temperature change caused by the heat of metabolism of added carbon source (glucose) by the yeast. Experiments were conducted in a 30 °C water bath under non-growth conditions (without nitrogen source). The simple thermal response model was applied to obtain two characteristic parameters for the estimation of the yeast activities, i.e., a metabolic heat production rate, Δ Q, and a metabolic heat inhibition rate, Δ K. The proposed model was well in agreement with the experimental results, and the curve fitting gave Δ Q or Δ K. In the case of the addition of glucose to yeast as a carbon source, Δ Q was proportional to the number of live cell (CFU). The slope of CFU versus Δ Q for yeast in exponential phase was larger by about two-fold than that in the stationary phase. In the case of the addition of gultaraldehyde as an inhibitor to the above system, the logarithmic value of Δ K increased with increasing the concentration of gultaraldehyde within the range of 0.02–6.2 wt.%. It was suggested that the two model parameters, Δ Q and Δ K, can be regarded as characteristics to estimate the activities of bacteria and the degree of their inactivation by the inhibitor.

Influence of accuracy of thermal property data of a phase change material on the result of a numerical model of a packed bed latent heat storage with spheres

With the integration of latent-heat thermal energy storage (LHTES) in building services, solar energy and the coldness of ambient air can be efficiently used to reduce the energy used for heating and cooling and to improve the level of living comfort. For this purpose, a cylindrical LHTES containing spheres filled with paraffin was developed. For the proper modelling of the LHTES thermal response the thermal properties of the phase change material (PCM) must be accurately known. This article presents the influence of the accuracy of thermal property data of the PCM on the result of the prediction of the LHTES's thermal response. A packed bed numerical model was adapted to take into account the non-uniformity of the PCM's porosity and the fluid's velocity. Both are the consequence of a small tube-to-sphere diameter ratio, which is characteristic of the developed LHTES. The numerical model can also take into account the PCM's temperature-dependent thermal properties. The temperature distribution of the latent heat of the paraffin (RT20) used in the experiment in the form of apparent heat capacity was determined using a differential scanning calorimeter (DSC) at different heating and cooling rates. A comparison of the numerical and experimental results confirmed our hypothesis relating to the important role that the PCM's thermal properties play, especially during slow running processes, which are characteristic for our application.

Numerical modeling of thermal response of thermofield electron emission leading to explosive electron emission

This paper gives a numerical model to deal with the thermal effect of field-induced thermal-assisted current passing through the microprotrusion on the cathode surface of a planar high-voltage vacuum diode. The model of protrusion is based on a one-dimensional truncated cone, whose physical and thermal properties have been assumed temperature dependent. The influences of space charge effect and Nottingham effect are included. According to the simulations, the delay times of explosive electron emission of cathodes made of different materials are given and compared with the experimental results, which seems to be in agreement.

A Hybrid Thermal Energy Storage Device, Part 1: Design Methodology

A thermal response model for designing a hybrid thermal energy storage (TES) heat sink is developed. The stabilization time and maximum operating (hot side) temperature-to-transition temperature difference are used to characterize the performance of the heat sink. The thermal properties of the PCM employed in the design are investigated. Integration of a design optimization algorithm into a thermal performance model of the TES-hybrid heat sink results in determination of a best design subject to geometric and heat loading constraints. A prototype based on this best design is build and used to benchmark the performance model. The performance measured is consistent with the simulation model predictions of performance.

Distribution and movement ofCaenorhabditis eleganson a thermal gradient

To analyze thermal responses of Caenorhabditis elegans in detail, distribution of a worm population and movement of individual worms were examined on a linear, reproducible and broad temperature gradient. Assay methods were improved compared with those reported previously to ensure good motility and dispersion of worms. Well-fed, wild-type worms distributed over a wide temperature range of up to 10 degrees C, and, within this range, worms migrated in both directions of the gradient at similar frequencies without any specific response to the growth temperature in most cases. By contrast, worms migrated down the gradient if put in a region warmer than the warm boundary of distribution. The distribution range changed depending on the growth temperature and starvation, but active avoidance of a starvation temperature was not detected. These findings contradict previous hypotheses of taxis or migration to the growth temperature in association with food and instead indicate avoidance of a warm temperature. Our results favor a model for thermal response of C. elegans that postulates a single drive based on warm sensation rather than downward and upward drives in the physiological temperature range. Mutants in ttx-3, tax-2, tax-4 or egl-4 genes showed abnormal thermal responses, suggesting that these genes are involved in warm avoidance. Laser ablation and gene expression studies suggest that AFD neurons are not important, and tax-4 expression in neurons other than AFD is required, for warm avoidance.

Building thermal model reduction using nonlinear constrained optimization

The short-time-horizon modelling of building thermal response is of relevance in situations where HVAC plant and control system analyses are of interest. In this precise area of building thermal modelling issues of model accuracy and computational efficiency become important. In this work a nonlinear constrained optimization method is used for reducing the model order of building elements. The approach involves minimizing the error between the step response of a high-order reference model whilst tuning the parameters of a lower order model in order to obtain an optimized reduced-order model. Results show that a reduced model based on a 2nd-order building element gives minimal loss of accuracy but significant improvements in computational effort when treating both high and low thermal capacity modelling problems.

Modelling of thermal response of oil-heated tools due to different flow rates for the manufacture of composite structures

Aimed at optimising the heat-transfer process during the cure of resin, a series of numerical simulations on thermal responses of an oil-heated tool for the manufacture of composite structures were performed and results of the study were discussed by authors [Compos. Struct. 47 (1999) 491]. There it was found that the temperature response and distribution of the tool was highly dependent on the oil flow rate. Hence, control of thermal response of an oil-heated tool might be achieved by controlling the flow rate of the oil. To verify the numerical simulations, an oil-heating test rig was built at the Department of Mechanical Engineering, Monash University, Australia, and a series of experimental investigations using different flow rates of the thermal oil of BP product – Transcal-N – were conducted. The results of the experimental study presented in this report were found to be in a very good agreement with the results of corresponding numerical simulations. Based on these findings, analytical and empirical models were developed to describe the heat-transfer process using oil-heated tools, including the time period of the transient heat transfer and the maximum temperature of the tools. The results predicted by the alternative models agreed well with those from the experimental and numerical investigations.

Theoretical and experimental FUZZY modelling of building thermal dynamic response

In this paper this main advantages and disadvantages of two different types of modelling: theoretical and experimental are presented and discussed. The theoretical modelling is based on energy balances, which gives the overall model described by differential equations. On the basis of developed theoretical model a complex simulator in the MATLAB-Simulink environment was implemented. The second part is devoted to experimental modelling. In this paper a fuzzy model represented by non-linear relations between input and output variables obtained by least-squares optimisation method is investigated.

Finite element modeling of cyclic thermal response of shape memory alloy wires with variable material properties

This paper considers the influence of variable thermal conductivity and electrical resistivity on the cyclic thermal response of a shape memory alloy (SMA) wire. The specific boundary value problem of an SMA wire under zero-stress conditions is considered, wherein the wire, in an initially martensitic state, is heated by electrical current and cooled by convection. An isothermal boundary condition is considered at the ends of the wire. The heating is continued until the transformation from martensite to austenite has essentially taken place. A Galerkin finite element method (FEM)-based numerical approach is used to solve the boundary value problem. The two key parameters of interest are the maximum possible transformation achievable (i.e. extent of actuation) and the time period for one cycle. It is seen that for short wires, the assumption of constant thermal conductivity underestimates the actuation and overestimates the cycle time significantly. The assumption of a constant electrical resistivity does not affect the actuation but significantly overestimates the cycle time. For long wires, the thermal conductivity effect is diminished whereas the electrical resistivity effect is very similar to that for the short wires.

Analysis of excitation of the 630.0 nm airglow during a heating experiment in Tromsø on February 16, 1999

During an ionospheric heating experiment in Tromsø during February 1999, artificial 630.0 nm airglow enhancements have been observed by the auroral large imaging system (ALIS). The airglow enhancements took place in the F region of the ionosphere near the heating wave reflection point. Two possible mechanisms are proposed for the explanation of this phenomenon. The first is the excitation of the O(1D) state by the energetic electrons from the tail of the artificially heated thermal electron gas, and the second is the excitation of this state by the plasma instability accelerated electrons. The detailed spatial and temporal characteristics of the red line airglow are obtained from the ALIS measurements. An analysis of these characteristics based on the models of thermal response of the ionosphere and the atmospheric optical emissions allows us to draw conclusions about the mechanism of the interaction between the heating radio wave and the ionospheric plasma.

Predicting germination response of four cool-season range grasses to field-variable temperature regimes

Germination of non-dormant seeds under variable-temperature conditions can be predicted from constant-temperature germination data if it is assumed that instantaneous germination rate is independent of thermal history. Thermal-response models of this type have not been validated under simulated field-variable temperature conditions that vary in diurnal pattern, diurnal range and longer-term trends in mean–daily temperature. The purpose of this experiment was to evaluate germination response of thickspike wheatgrass ( Elymus lanceolatus), bluebunch wheatgrass ( Pseudoroegneria spicata), Sandberg bluegrass ( Poa sandbergii) and bottlebrush squirreltail ( Elymus elymoides) under both constant and field-variable temperature regimes in the laboratory. It was hypothesized that the thermal history assumption was valid and that constant-temperature data could be used to accurately estimate field-variable temperature response. Seeds were germinated at seven constant temperatures between 5 and 35°C, and under 18 variable-temperature regimes simulating six planting dates at three field sites. Predictions of germination time under variable-temperature conditions were accurate to within a fraction of 1 day up to a cumulative germination percentage of 70% for thickspike wheatgrass, 60% for bluebunch wheatgrass, 55% for Sandberg bluegrass and 70% for bottlebrush squirreltail. It was concluded that, for the variable-temperature regimes tested in this experiment, the thermal-history assumption was valid for earlier-germinating subpopulations.

Predicting Variable-Temperature Response of Non-Dormant Seeds from Constant-Temperature Germination Data

The objective of many laboratory-germination experiments is to develop insight into the process of field establishment. It is relatively difficult, however, to infer potential field response from laboratory data given the enormous spatial and temporal variability in seedbed microclimate. Previous studies have attempted to survey large numbers of alternating day/night temperature regimes in order to estimate germination response to potential conditions of field microclimate. The objectives of this study were to estimate the errors associated with prediction of variable-temperature germination response from fewer, constant-temperature germination data. Non-dormant seeds of thickspike wheatgrass [Elymus lanceolatus (Scribn. and J.G. Smith) Gould], bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Love], Sandberg bluegrass (Poa sandbergii Vasey), and bottlebrush squirreltail [Elymus elymoides (Raf.) Swezey] were germinated under constant, alternating-constant and sine-wave temperature regimes. Predicted and measured cumulative-germination response generally coincided to within a day for most temperature treatments except for the most slowly germinating subpopulations of seeds. Thermal response models can be parameterized from relatively few experimental data but provide predictive inferences relevant to a wide number of variable-temperature conditions.

Investigation of thermal response of glass bulb sprinklers using plunge and ramp tests

The thermal behaviour of glass bulb sprinklers was investigated in a heated wind tunnel under various test conditions. The response parameters considered were the response time index (RTI), the conduction parameter (C) and the change of phase parameter (CHP). Combinations of one, two and three response parameters were used to predict the response times of various wind-tunnel test conditions, and for slow, medium and fast growth rate fires. These calculations indicate that the wind-tunnel results cannot be fully explained in the framework of the thermal response models applied. Tests with a high precondition temperature of the sprinkler resulted in higher RTI values compared with cases with normal precondition temperatures. A plausible explanation for the higher RTI values could be a time delay caused by temperature gradients within the glass bulb. This indicates that the CHP parameter previously explained in terms of work needed to shatter the glass bulb, more likely reflects an affect of thermal time delay. Calculated heat release rates at sprinkler response under a growing fire condition were used to evaluate the thermal response models. For the fast, medium and slow fire growth rates, the heat release rates at sprinkler response were found to be similar, whether based on calculations with two parameters (RTI and C) or with all three parameters (RTI, C, CHP). When using the RTI value only, however, the predicted rate of heat release at sprinkler response decreased significantly.

Thermal modelling of micropulsed diode laser retinal photocoagulation.

Recent studies have sought to utilize diode laser "micropulsing" in order to preserve therapeutic efficacy of retinal photocoagulation while minimizing pain and subjacent tissue injury. A model for the transient thermal tissue response to continuous and micropulsed diode laser output is presented in order to understand the laser-tissue interactions and to generate optimum parameters for exploiting potential advantages of micropulsed application. The tissue thermal response was calculated by convolving the analytical solution to the three-dimensional, isotropic heat conduction equation with a source term corresponding to the spot size of the laser incident on the absorbing retinal pigment epithelium (RPE) and choroid layers of the ocular fundus. Thermal localization is quantitated by comparing the temperature rise in the RPE (T(RPE) and deep choroid (T(Ch). A 1-watt (average power), 20-microns diameter, 100 ms pulse (continuous or micropulsed) of 810 nm radiation was modelled to be incident on a geometric idealization of the human retina and choroid. A temperature gradient is rapidly established with only modest temperature augmentation between 10 and 100 ms. At 100 ms T(RPE) and T(Ch) are 32 and 23 C, respectively, for continuous application, and 41 and 27 C for 2 ms on/off micropulsed application. For a duty factor (total laser "on" time divided by pulse length) of 50%, T(RPE)/T(Ch) is maximal for a micropulse on/off duration of 2 ms; however, the variation over micropulse durations from 200 microseconds to 50 ms is small. In addition, whereas end-pulse T(RPE)/T(Ch) is greater for 2 ms on/off application when compared with continuous delivery (1.53 vs. 1.39), thermal relaxation during pulse quiescence in the micropulsed mode allows for an early increase in deep choroidal temperature with respect to T(RPE). For ten 200 microseconds pulses equally separated over 100 ms (duty factor = 2%), T(RPE)/T(Ch) = 3.2. With more numerous, lower power micropulses, T(RPE)/T(Ch) decreases monotonically to 1.39 as the duty factor is increased to 100%. These modelling studies provide the first quantitative predictions of thermal localization achieved with diode laser micropulsing and demonstrate that short pulse lengths and low duty factors allow for maximum thermal localization. These studies will potentiate pulse-shape optimization strategies for diode laser retinal photocoagulation applications.

96/05446 Simplified thermal response modelling in building energy management. Paper III — Demonstration of a working controller

96/05446 Simplified thermal response modelling in building energy management. Paper III — Demonstration of a working controller

Simplified thermal response modelling in building energy management. Paper III: Demonstration of a working controller

An optimum start controller utilising parameters extracted in real-time from measured data is described. The five parameters are those characterising the thermal responses of a building in terms of a second-order RC network. After showing that the algorithm is capable of obtaining similar parameter values as procedures reported previously, the performance of the system is demonstrated in a working school, where the boiler firing times were controlled for six weeks.

Free Response of a Thermally Driven, Composite Actuator

A thermally driven force/displacement actuator may be fabricated from a composite consisting of a shape memory alloy (SMA) and an elastomer. A simple onedimensional device is described where a thin layer of SMA overlays an elastomer which is in turn bonded to a heat sink. A thermal response model is developed which includes the martensite fraction of the SMA, in addition to the effects of heat capacity of the composite and conductive resistance of the elastomer. Solutions, in terms of temperature-composition-time trajectories, for free response are obtained using different phase transition models. Calculations for a device consisting of Nitinol overlaying a typical elastomer show that rapid response, coupled with small power consumption, may be achieved if device size is kept small.

Diagnostic Hardware/Software System for Environment Controllers

A system consisting of a commercial environment controller attached to a personal computer programmed to execute a dynamic simulation model for broiler house thermal response was designed. The building model updates interior environment from solution of first order heat and moisture balances. Feedback of predicted interior temperature is provided to the controller; heating and ventilation equipment assigned in the model affect heat and moisture balances and hence the system response. An object oriented design approach was utilized and described. Governing equations for the building and controller temperature circuit dynamic response were solved in real time with a series of simulations to assess the response of the interior environment to different controller settings. Assessments of controller stage differential, building minimum ventilation rate and system sampling time are provided for a simulated broiler house. The combination of an environment controller and a building thermal model such as that presented here can be used to evaluate environment controllers and building heating and ventilating design, as well as for training purposes.