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Stochastic building occupancy models are increasingly used to underpin building energy demand models, especially those providing high-resolution electricity demand profiles. This paper describes the development of an established two-state active-occupancy model into a four-state model in which the absent/present state and the active/inactive state are treated separately. This provides a distinction between sleeping and absence and so offers an improved basis for demand modelling, particularly high-resolution thermal modelling. The model uses a first-order Markov chain technique and the paper illustrates the value of this approach in duly representing the naturally occurring correlation of occupancy states in multiply occupied dwellings. The paper also describes how the model has been enhanced to avoid under-representation of dwellings with 24 h occupancy. The model has been implemented in Excel VBA and made available to download for free. The model is constructed from and verified against UK time-use survey data but could readily be adapted to use similar data from elsewhere. [ABSTRACT FROM AUTHOR]

Abstract: The present paper focuses on the development and experimental validation of a model of air-to-air heat exchanger dedicated to domestic mechanical heat recovery ventilation. The proposed model describes dry and partially wet regimes. The first part of the paper presents a semi-empirical model based on the physical characteristics of the heat recovery device and relying on empirical correlations available in the literature for the convective heat transfer coefficients. In the case of partially wet regime, a moving boundary model is applied in order to predict sensible and latent heat transfer rates. A model developed with friction factor coefficients estimated by correlations from the literature is also presented in order to predict the hydraulic performance in dry conditions. The second part of the paper describes the experimental investigation conducted on an off-the-shelf heat exchanger. Experimental data are used to tune correlations for the determination of the convective heat transfer coefficient and validate the proposed simulation model of the ventilation heat recovery exchanger in partially wet conditions. The model developed to determine the hydraulic performance with existing correlations for the friction factor coefficient does not require a calibration. Finally, examples of use of the developed model are presented, which includes coupling the model with a building simulation model, a study of the influence of the humidity on the evolution of the latent and sensible heat transfer rates and strategies to avoid freezing in the heat exchanger. [Copyright &y& Elsevier]

Abstract: This paper computes the thermal delay in multilayer systems. The heat transfer by conduction across multilayer systems under unsteady boundary conditions is simulated using analytical solutions. The solutions, obtained as Green''s functions, are established by imposing temperature and heat flux continuity at the media interfaces of the various layers. The unsteady state conditions are dealt with by first computing the solution in the frequency domain and then applying (fast) inverse Fourier transforms into space-time. After validating the analytical formulation by comparing these results with those obtained experimentally, the thermal delay is computed for different multilayer systems. It is computed as the difference between the time the thermal variation is recorded in one of the system''s surfaces and the time it appears at the opposite surface. The paper calculates the computed thermal delay for construction walls made of cork, mineral wood and extruded polystyrene panels. The thermal properties of these materials have been previously defined experimentally. In the simulations, the systems are subjected to temperature changes that vary according a sine function, with the aim of defining the environmental exterior temperature variation over a period of several days. [Copyright &y& Elsevier]

Abstract: This paper reports on the development, experimental validation and application of a semi-empirical model for the simulation of the phase change process in phase change materials (PCM). PCMs are now increasingly being used in various building materials such as plasterboard, concrete or panels to improve thermal control in buildings and accurate modelling of their behaviour is important to effectively capture the effects of storage on indoor thermal conditions. Unlike many commercial simulation packages that assume very similar melting and freezing behaviour for the PCM and no hysteresis, the methodology employed treats the melting and freezing processes separately and this allows the inclusion of the effect of hysteresis in the modelling. As demonstrated by the results in this paper, this approach provides a more accurate prediction of the temperature and heat flow in the material, which is of particular importance in providing accurate representation of indoor thermal conditions during thermal cycling. The difference in the prediction accuracy of the two methods is a function of the properties of the PCM. The smaller the hysteresis of the PCM, the lower will be the prediction error of the conventional approach, and solution time will become the determining factor in selecting the simulation approach in practical applications. [Copyright &y& Elsevier]

Abstract: Vertical U-tube ground heat exchangers (GHEs) are a key component in geothermal energy utilization systems like ground source heat pumps (GSHPs). This paper presents a new constant heat flux model of its. Different from the existing uniform constant heat flux (UCHF) model, the model proposed in this paper is a cumulative constant heat flux (CCHF) model. The model is developed by reconstructing an experiment-verified three-dimensional unstructured finite-volume model. Applying the model, the borehole resistance with any geometric structure can be found. In addition, it may be used to develop the short time-step temperature response factors (TRFs) for simulating the behavior of the GHE on a short-time-step basis (one hour or less). [Copyright &y& Elsevier]

Abstract: Currently, several whole-building simulation tools (e.g., esp-r, EnergyPlus, TRNSYS, TAS, IES VE, IDA ICE, VA114, BSim, etc.) are used to assess the energy performance of double-skin façade (DSF) buildings. The aforementioned tools are well suited to assess energy performance of conventional building systems or whole buildings; however, it is questionable whether such tools can accurately describe the transient heat and mass transfer phenomena that occur in the complex three-dimensional geometry of DSFs. This paper describes an empirical validation of the EnergyPlus simulation tool for performance simulation of a DSF. A series of experiments were conducted for cavity airflow and thermal behavior of the DSF and then compared with simulation outputs. In this paper, it is shown that there are significant differences in both thermal and airflow behavior of DSFs between the measurements and simulation predictions by EnergyPlus. This study investigates three cases causing the differences and elucidates what should be considered when modeling DSFs using EnergyPlus. [Copyright &y& Elsevier]

This paper reports on a project to construct and test an instrument that, for the first time, enables the accurate measurement of convective heat transfer coefficients (chtcs) in real buildings. Computer simulation models for the prediction of heat and airflow in buildings commonly rely on such empirically derived values. However, there are large uncertainties associated with their evaluation and use.The instrument described in this paper has been tested by measuring the chtcs on a heated plate mounted in a test room. The experimental work reported here was made up of two parts:The results are encouraging. Comparisons of the chtcs determined by the new instrument and the chtcs determined by the ‘traditional’ heated plate method have shown close agreement. It seems that the new instrument has great potential for use in real buildings. [Copyright &y& Elsevier]

The industrial exhaust flue gas contains tremendous waste heat that cannot be efficiently recovered by conventional condensing heat exchanger. This paper proposes a novel full-open absorption heat pump for the total heat recovery of flue gas. The recovered heat is used for district heating. By applying direct-contact heat and mass transfer without solid transfer interfaces, the novel system can save considerable metallic tube or plate materials and therefore the initial investment can be reduced substantially. A prototype full-open absorption heat pump is developed and tested, achieving the COP (coefficient of performance) of 1.621 and the exit flue gas dew point of 36.2   °C at most. A detailed theoretical model in Eulerian–Lagrangian formulation is established, involving in conjugate heat and mass transfer and particle dynamics. The numerical simulation agrees well with the experiment results. On the basis of the validated model, three critical parameters, including excess air coefficient of the burner, moisture content of the objective flue gas and return water temperature of the district heating network, are selected to study their effects on system performances. As a controlled variable, especially, the excess air coefficient plays an important role by influencing the regeneration of the liquid absorbent in the generator. The full-open absorption heat pump outperforms the condensing heat exchanger by 19.7–178.1% in heat recovery capacity as the return water temperature increases from 40 to 55   °C. [ABSTRACT FROM AUTHOR]

Heat losses from a building foundation are affected by both the surrounding conditions and the surrounding soil properties. These include many factors that complicate the analysis of heat loss, such as thermal storage, snow and soil freezing. The effect of snow and soil freezing was studied with a 3D simulation model in a subarctic climate. The heat losses from the most commonly used foundation types in Sweden were studied. This paper shows that it is possible to achieve a good thermal estimation of the air temperatures in a crawl space, with an average difference of 0.4 °C compared with the validation data over a year. Snow and soil freezing reduce the annual heat losses through the different foundation types by 7–10% and the maximum heat loss rate by 13–25%. In order to describe the heat transfer correctly, snow must be included in the calculations, while soil freezing has only a minor impact. The 3D model implemented in this study shows a significant impact on the soil temperatures when these parameters are included. For a subarctic climate, the commonly used calculation methods based on the European standard ISO 13370 are not thorough enough to calculate the heat transfer through a foundation accurately. [ABSTRACT FROM AUTHOR]

Building energy simulations have found widespread use as decision-making tools for determining design and retrofitting actions. Despite their popularity, there exists a well-reported issue regarding the numerical treatment of structural thermal-storage components in these models. The optimal means of discretising multi-layer structures is complicated by the different thermo-physical properties, material configurations and boundary conditions encountered within building energy models. This paper addresses this information gap by proposing a methodology that can be universally applied to all multi-layer structures, ensuring accurate predictions while avoiding excessive computational cost. Governing dimensionless quantities of Biot and Fourier numbers are utilised within the discretisation process, making the methodology equally applicable to all materials. The presented methodology also accounts for the configuration of materials within multi-layer structures when assigning discretisation levels, leading to nodes being distributed in accordance with expected thermal gradients. The proposed discretisation methodology has been examined for a number of boundary conditions and wall types with excellent prediction accuracy achieved throughout. Additionally, the utility of resistance-only layers has been explored as a means of increasing computational efficiency. This highlighted the importance of considering both layer position and local thermal properties when simulating multi-layer structures. [ABSTRACT FROM AUTHOR]

Some highly energy efficient window attachment products are available today, but more rapid market adoption would be facilitated by fair performance metrics. It is important to have validated simulation tools to provide a basis for this analysis. This paper outlines a review and validation of the ISO 15099 center-of-glass zero-solar-load heat transfer correlations for windows with cellular shades. Thermal transmittance was measured experimentally, simulated using computational fluid dynamics (CFD) analysis, and simulated utilizing correlations from ISO 15099 as implemented in Berkeley Lab WINDOW and THERM software. CFD analysis showed ISO 15099 underestimates heat flux of rectangular cavities by up to 60% when aspect ratio (AR) = 1 and overestimates heat flux up to 20% when AR = 0.5. CFD analysis also showed that wave-type surfaces of cellular shades have less than 2% impact on heat flux through the cavities and less than 5% for natural convection of room-side surface. WINDOW was shown to accurately represent heat flux of the measured configurations to a mean relative error of 0.5% and standard deviation of 3.8%. Several shade parameters showed significant influence on correlation accuracy, including distance between shade and glass, inconsistency in cell stretch, size of perimeter gaps, and the mounting hardware. [ABSTRACT FROM AUTHOR]

Radiant cooling systems work fundamentally differently from air systems by taking advantage of both radiant and convective heat transfer to remove space heat. This paper presents an experiment investigating how the dynamic heat transfer in rooms conditioned by a radiant system is different from an air system, and how such differences affect the sensible cooling load and cooling load calculation methods for radiant systems. Four tests with two heat gain profiles were carried out in a standard climatic chamber. For each profile, two separate tests were carried out to maintain a constant operative temperature: one with radiant chilled ceiling panels; and a second with an overhead mixing air distribution system. The experiments show that, during the periods the heat gain was on, the radiant system has on average 18–21% higher instantaneous cooling rates compared to the air system, and 75–82% of total heat gains were removed, while for the air system only 61–63% were removed. Based on the study, we conclude that a new definition must be used for radiant system cooling load. Calibrated dynamic energy simulation based on a fundamental heat balance approach showed good accuracy. Simplified cooling load calculation methods may lead to incorrect results for radiant systems. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the coupled heat transfers in hollow tile with two air cells deep in the vertical direction and three identical cavities in the horizontal one, uniformly heated from below or from above. The end vertical side walls of the structure are assumed to be adiabatic. The Boussinesq approximation is invoked and the flows are considered laminar and two-dimensional for the whole range of parameters considered. Conduction heat transfer in the solid partitions and radiation exchange between gray and diffuse surfaces are accounted for. The governing equations are solved by finite difference technique based on the control volume approach and the SIMPLE algorithm. Based on steady state simulation, the appropriate overall thermal conductances U ′ are derived for the two considered situations (heating from below and from above). The results show that the hollow block with two air cells deep in vertical direction permits a considerable reduction of heat transfer between the inside and the outside of the building roofs. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews and analyzes the compatibility of the simplified empirical method based on the dimensionless parameter of Solar Load Ratio (SLR) and the monthly procedure of the standard ISO 13790 for indirect gains, specifically for unconditioned zones adjacent to a conditioned zone, but separated from it by a partition wall (sunspaces). The main contribution of the work presented here is the new formulation to account SLR correlations in ISO 13790, obtained for sunspaces, but generalizable for other solar systems with known SLR functions. Simulation models are used to perform a sensitivity analysis of internal gains and heat transfer through solar collector surfaces, both issues that distinguishes ISO 13790 from Load Ratio methods. The analysis shows that internal gains can be added to the heat source term or subtracted to heat transfer term without influencing the utilization factor dependence with the gain-to-loss ratio. On the other hand, the SLR assumption that solar collector surfaces are neutral elements and, therefore, not added to the heat transfer term, results in large inconsistencies between SLR and ISO 13790 methods. The detailed monthly methodology of ISO 13790 fairly reproduces results obtained by simulation. However, predictions from the simplified monthly methodology of ISO 13790 fail in mid season months and coldest months. [Copyright &y& Elsevier]

Abstract: Most of the energy expended in buildings is used for heating. Heating insulation of walls has been gaining much more interest in recent years not only because of the hazardous effects energy consumption on the environment, but also the high costs of energy sources. Therefore, the relationship between insulation thickness and orientation was investigated in this paper for in Elazığ (38.4°N), one of the cold regions in Turkey. One dimensional transient heat transfer problem of the walls with and without insulation was solved by using the explicit finite difference method. In the illustration model, hourly values of heat losses of mass and walls were calculated. The annual energy cost was calculated for walls. It was observed that energy consumption will decrease by 19–78%, depending on the insulation thickness. Payback periods based on insulation cost are 1.69–2.89 years. [Copyright &y& Elsevier]

Abstract: This paper proposed a new method based on modified composite model in the thermal response test (TRT) in the variable heat rate case study. The new method considered the unsteady-state heat transfer in the borehole instead of the line-source model assumption. A Matlab program was compiled which can perform inversion calculation to obtain the ground thermal properties. The superposition principle was used to process the variable-rate problem. This new method was applied to two thermal response tests. The simulation value based on the method shows a good agreement with the measurement data of water temperature. The proposed method would save the time and reduce the cost of TRT when power fluctuation or failure occurs. [Copyright &y& Elsevier]

Abstract: This work describes a model developed to simulate a radiant floor system with PCM in simple building types. The building simulation model has been validated by comparing its behavior with Energy Plus. The PCM radiant floor model is based on a one-dimensional finite difference scheme where the effective capacity method is used for PCM simulation. Some adjustments have been made to this one-dimensional scheme so that the thermal effect of two-dimensional heat transfer within the radiant floor slab is taken into account. The results of an analyzed case study are also presented in this paper. Here, the PCM floor heating system is fed by a heat pump which mainly operates during night time, thus reducing the costs of electric energy consumption. [Copyright &y& Elsevier]

Abstract: This paper analyzes the uncertainties propagation of the theoretical model developed to simulate the thermal performance of PCM-air heat exchanger. Numerical results are compared with experimental results obtained with a full-scale heat exchanger prototype. In the model, the energy equation is considered in terms of enthalpy, as the governing equation can be applied at any stage, determining the temperature at each point and therefore assessing the value of the PCM thermophysical properties. Due to the uncertainties of the input variables, this analysis provides a band of uncertainty associated with the solution that is useful and more realistic when comparing the experimental and simulated results. In this sense, for most of the process, there has been observed a high degree of overlapping between the two different heat rate curves. For this type of heat exchangers, the uncertainty propagation analysis also quantifies the consequences that imply making the effort of improving the determination of a parameter or enhancing the measurement of a variable. In this study case, it is not worth to invest efforts in determining the average phase change temperature of a PCM with an uncertainty better than ±0.25°C when the main response is the average heat rate. [Copyright &y& Elsevier]

Abstract: The thermal performance of windows is important for energy efficient buildings. Windows typically account for about 30–50 percent of the transmission losses though the building envelope, even if their area fraction of the envelope is far less. The reason for this can be found by comparing the thermal transmittance (U-factor) of windows to the U-factor of their opaque counterparts (wall, roof and floor constructions). In well insulated buildings the U-factor of walls, roofs and floors can be between 0.1 and 0.2W/(m2 K). The best windows have U-factors of about 0.7–1.0. It is therefore obvious that the U-factor of windows needs to be reduced, even though looking at the whole energy balance for windows (i.e., solar gains minus transmission losses) makes the picture more complex. In high performance windows the frame design and material use are of utmost importance, as the frame performance is usually the limiting factor for reducing the total window U-factor further. This paper describes simulation studies analyzing the effects on frame and edge-of-glass U-factors of different surface emissivities as well as frame material and spacer conductivities. The goal of this work is to define material research targets for window frame components that will result in better frame thermal performance than is exhibited by the best products available on the market today. [Copyright &y& Elsevier]

Abstract: The paper presents a methodology for investigating the influence of three major parameters in the design of two-storey housing units in different neighborhood layouts, on solar energy utilization potential. The parameters are geometric shapes of individual units, density of units and site layouts. Rectangular and L shape with different values of the angle enclosed between the wings of this shape are studied. The density parameter is represented by detached and multiplexed units. The effect of parallel rows of units is also studied. Site layouts include a straight road and south and north facing semi-circular roads. The EnergyPlus simulation package is used to simulate 26 configurations consisting of combinations of the parameter values. Effects are evaluated as the change from reference configurations of the response parameters – incident and transmitted irradiation of facades and integrated PV electricity generation. The results indicate that the total electricity generation is governed by active roof surface area which is affected by both shape and orientation. Up to 50% increase in electricity generation can be achieved in some housing units of certain configurations, compared to the reference. Variation of surface orientation, particularly in curved layouts enables the spread of peak electricity generation over up to 6h. [Copyright &y& Elsevier]

Abstract: Conduction heat transfer through opaque envelope components characterizes the thermal performance of buildings and its consequences in terms of energy consumption and thermal comfort. A building envelope can be thermally described by two parameters: thermal conductivity (λ) and heat capacity (ρ·c). Estimating these thermal properties in situ allows the characterization of real building elements considering different aspects, such as thermal behavior under specific weather conditions, quality variability in materials, local construction technologies and material deterioration. This paper presents a method to estimate the thermal conductivity and volumetric heat capacity of a homogeneous element using a non-destructive test considering natural oscillations. Surface temperature and heat flow are measured in a concrete sample (with known thermal properties) and the data is treated with a signal processing technique. Estimation is carried out with a heat and moisture transfer model. Measurements were performed on six separate days under different sky conditions within a period of one month, to determine the importance of solar radiation as a heat source. Results gave acceptable estimates (average inaccuracy of 10–14%) of both thermophysical properties. [Copyright &y& Elsevier]

Abstract: The heat transfer coefficients between radiant surfaces and room are influenced by several parameters: surfaces temperature distributions, internal gains, air movements. The aim of this paper is to evaluate the heat transfer coefficients between radiant ceiling and room in typical conditions of occupancy of an office or residential building. Internal gains were therefore simulated using heated cylinders and heat losses using cooled surfaces. Evaluations were developed by means of experimental tests in an environmental chamber. Heat transfer coefficient may be expressed separately for radiation and convection or as one total parameter, but this choice may lead to different considerations about thermal performance of the system. In order to perform correct evaluations, it is therefore extremely important to use the proper reference temperature. The obtained values confirm tendencies found in the literature, indicating limitations and possibilities of radiant ceiling systems improvement. [Copyright &y& Elsevier]

Abstract: It is very difficult to calculate and analyze with precision the thermal behavior of the walls of building envelope when coexist various modes of thermal transfer and because of the particularly random climatic phenomena. These problems are very complex in the case of special components such as passive solar wall used in “bio-climatic” architecture. In this paper, the thermal performances of passive solar systems, a classical Trombe wall and a composite Trombe–Michel wall, are studied. The models were developed by our cares with the finite differences method (FDM) [L. Zalewski, S. Lassue, B. Duthoit, M. Butez, Study of solar walls—validating a numerical simulation model, International Review on Building and Environment, 37 (1) (2002) 109–121], and with TRNSYS software [Solar Laboratory of energy (USA), Manuals of TRNSYS, University of Wisconsin-Madison, USA, 1994]. The model for a composite wall developed with FDM was validated by experimentation [1]. The comparisons between the results of simulation with TRNSYS and with FDM, and between the results of simulation a classical Trombe wall and the results of simulation and a composite Trombe wall have been made. They show that the models developed by ourselves are very precise, and the composite wall has better energetic performances than the classical wall in cold and/or cloudy weather. [Copyright &y& Elsevier]

Abstract: In order to cool a room with a cold night air phase change material, PCM, is stored in an air heat exchanger. During night the PCM crystallises, energy is released. During daytime air is circulated in the unit, energy is absorbed and the indoor air is cooled. The characteristic of PCM is that there is an increase of the specific heat over a limited temperature span. This is the principle that is used in the design of the PCM air heat exchanger unit. The action of a PCM storage unit will act differently depending of the thermal properties of the material. In an ideal material the phase transition occurs at a given temperature. On the market, compounds containing PCM are available which, in order to create a suitable melting temperature, are mixtures of different products. In these materials, the transition from liquid to solid takes place over a temperature span, i.e. the specific heat varies with the temperature. This can be represented by a c P(T) curve, specific heat as a function of the temperature. In this paper, the development of a mathematical model of the PCM air heat exchanger is presented. Considerations are taken to different shapes of the c P(T) curve. The mathematical model is verified with measurement on a prototype heat exchanger. The development of the equipment is part of the CRAFT project Changeable Thermal Inertia Dry Enclosures (C-TIDE) the possibility of use of phase change materials integrated into a building is explored. [Copyright &y& Elsevier]

Abstract: In this paper, we develop statistical models of the thermal transmittance of 2D thermal bridges (ψ). We aim to give building designers plain and practical tools for the evaluation of the most common 2D thermal bridges. Three examples are considered: a slab-on-grade floor–wall junction, a floor–wall junction and a roof–wall junction. For each case, we perform computer simulations of the thermal transmittance, ψ, for several values of the most important variables. Then, we fit these numerical results to a nonlinear regression model. The results appear to be good with relative errors less than 5%. [Copyright &y& Elsevier]

This paper deals with the empirical validation of a building thermal model, which includes a roof-mounted radiant barrier. We first present the thermal model, developed with a building simulation code prototype, the objective being to increase understanding of the thermal phenomena that govern the behaviour of the whole building. We then describe the experimental test cell, with emphasis on the details of the roof. A sensitivity analysis technique is applied to the model which shows that convective heat transfer is of great importance for the dry-air temperature of the roof air layer. The origin of the disagreement between measurements and model predictions is then identified as being due to one of the convective heat transfer coefficients. Once this is modified the agreement is found to be acceptable. [Copyright &y& Elsevier]