Thermal properties of building materials evaluated by a dynamic simulation of a test cell

A method for the measurement of thermal properties of building components under controllable conditions is presented. It is based on the use of a test cell designed to enable calculation of thermal properties solely from temperature readings, without the need for power measurements. The test cell’s low thermal inertia allows short testing times (about 3 h). Using an appropriate thermal network to simulate the dynamic behavior of the test cell, predicted results were found to have a 0.6°C maximum temperature deviation with measured test cell responses. The thermal transmittance (U-value) of an insulating block, a single glass sheet and a double glazing have been measured with an accuracy of about 5%. A simulation of a scaled-up test cell with dimensions 6.0 m×6.0 m×4.5 m has revealed that the test cell’s response to temperature changes depends strongly on the amount of wall insulation. The scaled-up test cell exhibits a relatively fast response to temperature changes (9 to 18 h) due to its low thermal mass.     

A combined approach for determining the thermal performance of radiant barriers under field conditions

This paper deals with a combined approach for assessing the thermal performance of radiant barriers under field conditions, based both on dynamic simulations and field measurements. The methodology involves the combination of model predictions and experimental results of a complex roof including a radiant barrier installed on a dedicated test cell. During the empirical validation of the building thermal model and more particularly thanks to the results of sensitivity analysis, simplifications of the model were made. These considerations lead to successive simplified versions of the model and finally a very simplified one, which is used to determine the thermal resistance of the complex roof. We first present the detailed thermal model, elaborated with a prototype of building simulation code. We then describe the experimental test cell and put the emphasis on the details of the roof. The simplification of the detailed model is then explained and the results presented. A value of the thermal resistance is finally obtained and confirms the potential of radiant barriers for a tropical climate.     

Improvements on PASSYS test cells

PASSYS test cells are outdoor test facilities for the evaluation of the thermophysical parameters of real scale samples of facades and building components. The most important application is the testing of passive solar facades. While we have the advantage of measurements under real weather conditions (real solar radiation) there is the disadvantage of non steady state boundary conditions. Various strategies are presented to enhance measurement accuracy. A so-called pseudo adiabatic shell (PAS) was introduced to reduce the heat losses through the test cell envelope and the time constant by using a controlled electric heating foil. A similar approach is described here using heat flux sensitive tiles (HFS). A special heat flux sensor was designed and tested at ITW to meet the requirements of an accurate measurement of the overall heat flux passing the test cell envelope. By the application of a movable cold box in front of the tested facade steady state outside conditions can be provided for the evaluation of the U-value according to the requirements proposed by CEN/TC 89/WG7.     

Energy-efficient housing for low-income students in a highly variable environment of central Argentina

Socio-economic, educational and environmental reasons have driven the building of energy-efficient dwellings for low-income students in University of La Pampa. The buildings are located in the central region of Argentina (35° 70′ of South latitude), an area of warm temperate climate. Energy conservation devices, passive solar heating, natural ventilation and solar protection were the main strategies of design. The resulting design comprised three blocks of housing with a useful floor area of 900 m². Two bedrooms, a dining room and essential services make up each house. Solar gains through transparent areas to the North are provided for all main spaces. Northern shading devices and metallic pergolas protect all windows in summer. In spite of high external temperature variability, the simulated performance during the design stage showed a remarkable internal thermal stability. The thermal and energy monitoring started in September 1999 and had two phases: (a) under real conditions of use and (b) during student's summer holidays (when the buildings were not inhabited). The results from the monitoring process suggest that interpretations about the building behaviour cannot be restricted to constructive issues. Useful inferences cannot be done from design and building technology only. The thermal behaviour was the result of construction, non-construction factors like dwellers habits, and their interaction. Energy saving in heating during the winter season was around 50%.     

多工况运行下围护结构动态热响应的评价方法

建筑运行工况会影响围护结构的热响应,为研究自然通风和空调2种居住建筑运行工况下围护结构动态热响应的差异,通过对比2种工况围护结构的边界条件与传热过程,提出围护结构动态热响应的评价指标——墙体温变条件指数WTCI,该指标兼顾2种工况下墙体热性能不同的评价内涵。以夏热冬暖地区为例,选取18种墙体构造来验证WTCI在多工况下对墙体动态热响应评价的有效性,结果表明该指标计算简便、评价有效,能够评价围护结构在多工况动态传热过程中的热响应快慢,可区分墙体在不同工况下的隔热表现。深入分析WTCI在多工况下的适用性,对WTCI指标的应用给出建议。     

Comparison study of two different testing methodologies used to characterize an opaque solar component

The work described in this paper was aimed at comparing two different testing methodologies, set up in order to define performance properties and reliability of passive or hybrid solar components. The former facility is based on the use of outdoor real-size Test Cells, designed to simulate a conventional living environment with a thermal mass distributed approximately in the same way as in a real dwelling. The latter uses an indoor real-size test cell reproducing a common piece of a dwelling; such a cell can assume various spatial arrangements and simulate in a cyclic way any temperature conditions and solar input on the walls under test. Experiments on a same opaque multilayer component were run with both facilities and the comparison of the obtained results are given; the good agreement of the efficiency values and the analysis of the most important working parameters of the tested component points out the effectiveness and the peculiarity of both methodologies.     

Development and application of an actively controlled hybrid proton exchange membrane fuel cell—Lithium-ion battery laboratory test-bed based on off-the-shelf components

The use of commercially available components enables rapid prototyping and assembling of laboratory scale hybrid test-bed systems, which can be used to evaluate new hybrid configurations. The development of such a test-bed using an off-the-shelf PEM fuel cell, lithium-ion battery and DC/DC converter is presented here, and its application to a hybrid configuration appropriate for an unmanned underwater vehicle is explored. A control algorithm was implemented to regulate the power share between the fuel cell and the battery with a graphical interface to control, record and analyze the electrochemical and thermal parameters of the system. The results demonstrate the applicability of the test-bed and control algorithm for this application, and provide data on the dynamic electrical and thermal behaviour of the hybrid system.     

Modeling and investigation start-up procedures of a combined cycle power plant

This study describes the particular development and investigation of a static and dynamic simulation model and its application to improve the start-up process of a combined cycle power plant. Generally, the power plant system and control design mean highly complex interactivities. The dynamic simulation models using powerful computers are effective tools for studying and understanding the operating characteristics of power plants to meet and improve the design, control strategy and operational requirements. The heat recovery steam generator (HRSG) is modeled by using commercial simulation software named advanced process simulation software (APROS). The HRSG model includes an advanced control philosophy and turbine bypass systems to have a high level of accuracy, especially during hard transients. The comparison between the simulation results and measured data is documented. The received results proved and embodied that the simulation is both very reliable to estimate the real HRSG dynamic behaviour and capable to predict the operational processes. Through a parametric study, the start-up time will be reduced while keeping the life-time consumption of critically stressed components under control.     

Effect of magnetic field on the performance of new refrigerant mixtures

Performance test results of new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various magnetic field conditions. Performance tests were conducted according to the ARI/ASHRAE Standards. The test results demonstrated that as magnetic field force increases, compressor head pressure and discharge temperature slightly increase as well as less liquid refrigerant is boiling in the compressor shell. This has a positive effect in protecting the compressor. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point. Furthermore, the use of magnetic field appears to have a positive influence on the system COP as well as thermal capacities of condenser and evaporator. Copyright © 2002 John Wiley & Sons, Ltd.     

Energy efficiency of a dynamic glazing system

The reduction of air-conditioning energy consumptions is one of the main indicators to act on when improving the energy efficiency in buildings.In the case of advanced technological buildings, a meaningful contribution to the thermal loads and the energy consumptions reduction could depend on the correct configuration and management of the envelope systems. In recent years, the architectural trend toward highly transparent all-glass buildings presents a unique challenge and opportunity to advance the market for emerging, smart, dynamic window and dimmable daylighting control technologies (Lee et al., 2004).A prototype dynamic glazing system was developed and tested at ITC-CNR; it is aimed at actively responding to the external environmental loads. Both an experimental campaign and analyses by theoretical models were carried out, aimed at evaluating the possible configurations depending on different weather conditions in several possible places. Therefore, the analytical models of the building-plant system were defined by using a dynamic energy simulation software (EnergyPlus).The variables that determine the system performance, also influenced by the boundary conditions, were analysed, such as U- and g-value; they concern both the morphology of the envelope system, such as dimensions, shading and glazing type, gap airflow thickness, in-gap airflow rate, and management, in terms of control algorithm parameters tuning fan and shading systems, as a function of the weather conditions.The configuration able to provide the best performances was finally identified by also assessing such performances, integrating the dynamic system in several building types and under different weather conditions.The dynamic envelope system prototype has become a commercial product with some applications in façade systems, curtain walls and windows.The paper describes the methodological approach to prototype development and the main results obtained, including simulations of possible applications on real buildings.     

Estimation of building component UA and gA from outdoor tests in warm and moderate weather conditions

Accurate knowledge of the thermal properties of building components is necessary to implement adequate energy saving strategies in buildings. Outdoor experiments using test cells are very useful tools for realistic estimation of these properties. This paper describes the analyses performed, and the procedure followed in identifying and solving some problems found when building components are tested for UA and gA in a test cell under warm and moderate weather conditions. A window component was tested in a PASLINK test cell at the CIEMAT’s ‘Plataforma Solar de Almería (PSA-CIEMAT)’ in Tabernas (Almería, Spain) and several data sets recorded under quite different weather and test conditions were analysed. First the problems identified when applying the usual test and linear analysis procedures are described. Then hypotheses about the cause of these problems are formulated. Afterwards, strategies followed for testing these hypotheses are described. Once the cause of the problems had been identified, they were fine tuned to find a model for accurate UA and gA estimation. This study demonstrated that nonlinear models, in which long wave radiation is considered as nonlinear effect, yield remarkably better performance than the commonly used linear models, for estimating the component UA and gA values.     

Impact of the Relationship between Phase Change Temperature and Boundary Temperature on the Thermal Performance of a PCM Wall and the Presentation of PCM Thermal Performance Indexes

In the composite phase change material (PCM) building envelope, the matching relationship between the phase change temperature of the PCM and the wall's boundary temperature significantly affects the energy storage performance of the PCM building envelope. In this paper, a type of concrete hollow block with a typical structure and a common PCM were adopted to produce multiform composite PCM hollow blocks, and the temperature changing hot chamber method was performed to test the thermal performance of the hollow block walls under different temperature conditions. New indexes were proposed for the thermal performance evaluation of the PCM wall. Meanwhile, combined with experimental data, the effective heat capacity model and the enthalpy model were used to analyze the effect of correlations concerning how the relationship between phase change temperature and wall's boundary temperature influenced the thermal performance of PCM wall. Three main impact factors related to temperature were obtained through the analysis. In addition, approaches for improving the thermal performance of a composite PCM wall were put forward. This paper provides the theoretical basis, data reference and practical instruction for the proper use of a PCM wall and ways for improving the thermal performance of a composite PCM wall.     

Dynamic modelling and simulation of a photovoltaic refrigeration plant

In this paper, we will present the performances, the simulation responses and the dynamic behaviour of a photovoltaic (PV) refrigeration plant using latent storage. This approach uses a new storage strategy of stand alone PV plants which substitutes the battery storage with thermal, eutectic, latent or a hydraulic storage. The measurements and the evaluation of these less battery storage systems at several climatic conditions and under load disturbances allow us to evaluate the PV system reliability and to compare its performances with classic battery storage systems.     

Investigations into the functioning of a supply air window in relation to solar energy as determined by experiment and simulation

‘Supply air windows’ under optimum flow conditions function as an efficient heat reclaim device. Heat escaping from the room, through the inner glass pane, is entrained in the air flow between the inner and outer sashes and returned to the room. A low-E coating to the inner glass acts as a barrier to radiation heat loss across the window so very low U-values can be achieved. These same characteristics enable the window to function as a passive solar component. Its efficiency is inferior to that of a dedicated passive solar device due to its transparency, but even so at modest levels of incident solar gain a worthwhile proportion is entrained into the air flow and supplied to the rooms as pre-heated ventilation air supply. These characteristics have been established by laboratory, test cell investigations, and simulations using computational fluid dynamics and ESP-r, a whole building dynamic thermal modelling tool.     

Evaluation of the environmental quality of buildings towards a more environmentally conscious design

Appropriate design and construction can reduce the environmental impact of buildings over their entire life cycle. Such a prevention strategy can be supported by an evaluation tool. Our approach consists of applying life cycle analysis to the building sector. The use of computers is preferred for an easier comparison of alternative designs and to test possible improvements of a project. We adopted an object oriented approach in order to link models with professional practice. A data structure has been defined, in which a building is decomposed into objects. The corresponding classes include both data (inventories of basic materials and processes) and methods (accounting for fabrication, recycling, etc.). The result of such an evaluation is an environmental profile, constituted from various indicators on natural resources used, environmental effects and waste produced. First sensitivity analysis were performed showing the importance of the utilisation phase with its associated energy, water and waste fluxes. The environmental performance of a building is a result of a sequence of decisions like the choice of the building site, design choices, occupant's behaviour, etc. The potential applications of this research are to inform the various actors about the consequences of their choices, to assess the environmental interest of innovative technologies (e.g. solar components) and to develop new tools for practitioners.     

Design of a hybrid polygeneration system with solar collectors and a Solid Oxide Fuel Cell: Dynamic simulation and economic assessment

Solid Oxide Fuel Cells (SOFC) are very promising energy conversion devices, producing electricity and heat from a fuel directly via electrochemical reactions. The electrical efficiency of SOFCs is particularly high, so that such systems are very attractive for integration in complex polygeneration systems. In this paper, the integration of SOFC systems with solar thermal collector is investigated seeking to design a novel polygeneration system producing: electricity, space heating and cooling and domestic hot water, for a university building located in Naples (Italy), assumed as case study. The polygeneration system is based on the following main components: concentrating parabolic through solar collectors, a double-stage LiBr-H₂O absorption chiller and an ambient pressure SOFC fuel cell. The system also includes a number of additional components required for the balance of plant, such as: storage tanks, heat exchangers, pumps, controllers, cooling tower, etc. The SOFC operates at full load, producing electric energy that is in part self-consumed for powering building lights and equipments, and in part is used for operating the system itself; the electric energy in excess is eventually released to the grid and sold to the public Company that operates the grid itself. The system was designed and then simulated by means of a zero-dimensional transient simulation model, developed using the TRNSYS software; the investigation of the dynamic behavior of the building is also included. The results of the case study were analyzed for different time bases, from both energetic and economic points of view. Finally, a thermoeconomic optimization is also presented aiming at determining the optimal set of system design parameters. The economic results show that the system under investigation may be profitable, provided that it is properly funded. However, the overall energetic and economic results are more encouraging than those claimed for other similar polygeneration systems in the recent literature.     

Effects of thermal control and of passive solar elements on the dynamic behaviour of a building

The design of a building must take into account its dynamic thermal behaviour. In this paper, we model the building as a thermal network and discuss the equivalent passive solar elements. We then discuss a modular computer program able to calculate the dynamic thermal behaviour of the building, the effects of overheating, the saving due to thermal control and the fraction of the load satisfied by passive solar elements.     

无盖板渗透型集热器热性能的对比试验

利用太阳能空气加热系统实验台,对黑、深绿和深蓝3种颜色无盖板渗透型集热器的热性能进行了户外瞬态对比试验。试验结果表明:太阳辐射照度和风量是影响系统热性能的重要因素。在高档和低档两种风量下,黑色集热器的瞬时平均热效率分别为76.04%和67.50%,高于普通平板太阳能空气集热器;集热器表面颜色对其热性能有一定影响,在高档和低档两种风量下,深绿色和深蓝色集热器的瞬时平均热效率比黑色集热器低15%～22%,空气温升低3～4℃,但仍然优于普通平板空气集热器。从保持建筑立面美观考虑,无盖板渗透型集热器的集热板可以采用颜色较深的彩色,不会对系统热性能造成较大影响。     

Modeling and experimental validation of a humidification–dehumidification desalination unit solar part

This paper presents the modeling and the experimental validation of air and water solar collectors used in humidification-dehumidification (HDH) solar desalination unit. The solar desalination process is currently operating under the climatological conditions of Sfax (34 N, 10 E), Tunisia. To numerically simulate the air and water solar collectors, we have developed dynamic mathematical models of the solar collectors. The resulting distributed parametric systems of equations are transformed into a system of ordinary differential equations (ODEs) using the orthogonal collocation method (OCM). A comparison between numerical and experimental data was conducted. It was found that the two-temperature mathematical model describes more precisely the real behaviour of the water solar collector than the one-temperature mathematical model. It was also shown that the developed mathematical models are able to predict accurately the trends of the thermal characteristic of the water and air solar collectors. As a result, the proposed models can be used to size and test the behaviour of such a type of water and air solar collectors.     

Experimental and numerical study of unsteady non-periodic wall heat transfer under step,ramp and cosine temperature perturbations

An experimental and numerical study of the transient non-periodic wall heat transfer problem is presented. A computer-controlled indoor/outdoor environment simulation system produces any desired variation of the air temperature, thus allowing measurement of the dynamic thermal behaviour of any test wall under the desired boundary conditions. Measurements of the temperature field within the wall, of the heat flow and of the convection coefficients at the wall surfaces are performed during step, ramp and cosine perturbations of the outdoor air temperature. The measurements are in very good agreement with the numerical predictions obtained by a developed finite difference solution procedure. The results showed that in building heat transfer applications, for example in air conditioning, the usual assumption of periodic outdoor conditions may lead to considerable errors in case of a significant temporary deviation of the temperature from periodicity.