Thermal Behaviour Of Buildings Research Articles

Characterising thermal behaviour of buildings and its effect on urban heat island in tropical areas

The heat island phenomenon in major cities is partly due to the excessive use of concrete and brick, which causes many problems regarding thermal comfort and energy expenditure. The thermal behaviour of the envelope wall material depends on its density, heat capacity, and thermal conductivity, and its effect on the heat island intensity (HII) is reported in this paper. Experiments and simulations were carried out on the four most popular building materials: brick, aerated concrete, wood with glass-wool insulation, and glass fibre-reinforced concrete with glass-wool insulation, with each material having a dimension of 1 m × 1 m. Experiments to analyse the thermal behaviour of the wall materials were performed by exposing each material to heat radiation from 2 × 1000 W halogen lamps for 4 h, followed by 4 h of cooling. The HII simulations were carried out in a simple urban kampong in a tropical area using Energy2D software. Heat flow analyses confirmed the thermal behaviour of the four walls, which can be categorised into two types: heat storage of block wall (BW) type and heat flow inhibition of insulated sandwich wall (ISW) type. The BW type showed 0.32 °C higher indoor air temperature than the ISW type, while the HII simulation showed ISW to be 0.74 °C higher than BW; however, both types increase the intensity and need mitigation treatment. The results of this study are important for the technological approach for dealing with local warming to lower the energy expenditure of poor people in an urban area.

Materiales reciclados aligerados y su influencia en el consumo de energía eléctrica en viviendas económicas

Una arquitectura eficiente forma parte integral del desarrollo sustentable y, asimismo, debe contemplar una envolvente que se adapte al clima y a los recursos constructivos de una región. La evaluación del comportamiento térmico de las edificaciones mediante simulación dinámica se utiliza en todo el mundo para evaluar su eficiencia energética. En México existe carencia de datos sobre las propiedades térmicas de los materiales de construcción. En el presente trabajo se obtiene experimentalmente la conductividad térmica, calor específico y densidad volumétrica de materiales de construcción como lo son el ladrillo de barro recocido, el bloque aligerado, el mortero cemento-arena natural y el mortero cemento-arena reciclado, este último fabricado con materiales reciclados de la demolición de concreto. Los resultados de simulación obtenidos muestran disminución en las ganancias de calor en muros y en el consumo de energía eléctrica por enfriamiento. La disminución es superior a 8%, utilizando sistemas constructivos conformados con materiales aligerados y reciclados.

Thermal Behaviour Studies on Building Walls based on Type and Composition of the Materials

Controlling the thermal behaviour of buildings is very important because it affects the energy use in the buildings and impacts the thermal environment of the area. Thermal behaviour of the building is determined by the type and composition of the building material. This paper shows the thermal behaviour of several types and composition of commonly used building wall materials, i.e. brick, aerated concrete, laminated wood with glass wool insulation, and gypsum with glass wool insulation. For the thermal behaviour measurements, we used wall models exposed to halogen lamps of 2000 watts for 4 hours heating and 4 hours for cooling with a measurement interval of 5-15 minutes. Data retrieval using 8 thermocouples mounted on the surface and inserted inside the wall. The observed thermal behaviour phenomena are the heat flow on the walls, the time delay, and the heat capacity. The results show different maps of the thermal behaviour on the walls and indicating the need for additional thermal insulation material to control the heat release to the outside and inside of the building.

Numerical analysis of the thermal behavior of building integrated hybrid solar wall

Abstract Building designers have to think about new strategies to achieve the best sustainable building designs. Well-planned passive solar heating strategies in building design may reduce a building’s energy consumption significantly. In this paper, a proposed design of the south façade of a room by integrating a hybrid solar wall and a window to passively heat a room is studied. The simulations for the three-dimensional model of BIPV Trombe wall system were carried out for December 10th, 2015. The temperature and velocity distribution of indoor air in different positions inside the room are obtained from the simulation results. The obtained results show that the temperature difference between the inlet and the outlet of the solar wall can reach 9°C. The 3D analysis of the proposed model clearly shows that the window’s thermal effect on the passive heating cannot be neglected. Meanwhile, the simulation’s daily electrical efficiency conversion and average indoor air temperature of this system can reach 18% and 28° C, respectively for maximum solar radiation of 470 W/m2.

A procedural technique for thermal simulation and visualization in urban environments

Analysing the thermal behaviour of buildings is an important goal for any and all of the tasks involving energy flow simulation in urban environments. However, the number of variables to be considered, along with the difficulty of implementing some of them, make it difficult to address the problem on an urban scale. In this paper we propose a procedural approach that, from a 3D urban model and a set of parameters, simulates the thermal exchanges that take place inside and outside buildings in an urban environment. We also provide a technique to efficiently visualise thermal variations over time of both the interior and exterior of buildings in an urban environment. We believe this technique will be helpful for performing a rapid analysis when building parameters, such as materials, dimensions, shape or number of floors, are being changed.

Optimizing the evaluation of thermal transmittance with the thermometric method using multilayer perceptrons

The characterization of building thermal behaviour is crucial to achieve the low-carbon objectives of the European Union by 2050. In this way, the knowledge of the thermal transmittance is being developed as a significant factor of the thermophysical properties of the envelope. In the existing building, the theoretical calculation has several limitations with non-destructive techniques typical of the deterioration of the elements. Many experimental methods obtain therefore more representative results. The experimental method developed in ISO 9869–1 is the most standardized, although it presents limitations in the heat flux measurement. However, the thermometric method obtains the thermal transmittance with the surface temperature. This research is focused on the evaluation of the thermal transmittance based on ISO 9869–1 (average method and average method with correction for storage effects), but using variables measured with the thermometric method. For this purpose, multilayer perceptrons were used as post-processing techniques. The models were trained by using a dataset of 22,820 simulated tests of representative walls of the building stock in Spain. The determination coefficient was greater than 98% in both analysis approaches. Individual models were also generated for each building period because they significantly influenced the input variables. The results showed that thermal transmittance values can be obtained without measuring the heat flux, and the error associated with the use of tabulated values for the total internal heat transfer can be removed. This research would guarantee a high assessment tax of buildings establishing adequate energy conservation measures to improve their energy performance.

On the impact of local microclimate on building performance simulation. Part II: Effect of external conditions on the dynamic thermal behavior of buildings

Most of the building energy models are not suited to properly integrate local urban ambient conditions; thus, this study initiates a sensitivity analysis of the heating and cooling needs and operative temperature of buildings to local radiative, thermal and aeraulic external conditions. These conditions were estimated using the possibilities of a building energy model (based on the BuildSysPro Modelica library) or derived from microclimatic simulations (SOLENE microclimat) for generic isolated or urban buildings. The thermal behaviors of both energy-inefficient and energy-efficient buildings in summer and winter are examined. The results show major effects of short- and long-wave radiative heat transfers as well as aeraulics. According to present results, and given current urban growth and climate change challenges as well as the development of energy conservative buildings, this last point may become particularly critical in the future.

Modeling temperature and thermal transmittance of building integrated photovoltaic modules

This study aims at contributing to the progress of the modeling of the thermal behavior of Building Integrated Photovoltaic (BIPV) modules, a progress that runs way behind the pace of development in other areas of characterization of PV modules, such as the electrical one. To this end, a model based on the physics of heat transfer and optics is proposed, allowing the calculation of the temperature of BIPV modules and their thermal transmittance (U-value) in real operating conditions. The main contribution of this model is to include the impact of some parameters not considered so far, like the solar irradiance and the electrical efficiency. After being validated with experimental data, the model has been used to simulate single and double PV glazing, that compared later with common glazing with the same composition and configuration demonstrate the non-equivalent performance between them, showing differences of about 35% in the U-value under high irradiance conditions. This way, a clear disagreement with the current standard testing procedures occurs, something that should be reviewed. The tool proposed allows the complete study of the thermal behavior of BIPV modules and can help in the development of new specific standard procedures for a more realistic characterization of BIPV modules.

Parameter estimation for externally simulated thermal network models

Obtaining accurate dynamic models of building thermal behaviour requires a statistically solid foundation for estimating unknown parameters. This is especially important for thermal network grey-box models, since all their parameters normally need to be estimated from data. One attractive solution is to maximise the likelihood function, under the assumption of Gaussian distributed residuals. This technique was developed previously and implemented in the Continuous Time Stochastic Modelling framework, where an Extended Kalman Filter is used to compute residuals and their covariances. The main result of this paper is a similar method applied to a thermal network grey-box model of a building, simulated as an electric circuit in an external tool. The model is described as a list of interconnected components without deriving explicit equations. Since this model implementation is not differentiable, an alternative Kalman filter formulation is needed. The Unscented and Ensemble Kalman Filters are designed to handle non-linear models without using Jacobians, and can therefore also be used with models in a non-differentiable form. Both Kalman filter implementations are tested and compared with respect to estimation accuracy and computation time. The Profile Likelihood method is used to analyse structural and practical parameter identifiability. This method is extended to compute two-dimensional profiles, which can also be used to analyse parameter interdependence by providing insight into the parameter space topology.

A study of the nonlinearity of a building thermal behavior based on metamodeling

In this work, we present a study of the nonlinearity of building thermal behavior based on a metamodel for cooling energy needs. We studied the nonlinearity of the thermal behavior of an office. The building quadratic behavior and interactions between its components were analyzed based on the metamodel coefficients. The metamodel was fitted with a reduced number of dynamic simulations. The nonlinearity was first assessed as function of the mean outdoor air temperature in fifteen typical European climates and then as function of the internal heat gains for the coldest and hottest climates. The metamodel provided highly accurate results with fast calculation time. However, a higher accuracy was generally obtained for hot climates, high internal heat gains and lightweight thermal mass. Conversely, the nonlinearity of thermal behavior was accentuated in cold climates and with low internal heat gains. Moreover, the interactions between the building components were found to be more influential on cooling energy needs than quadratic behavior. We propose a classification of thermal behavior into three regimes: Highly nonlinear when the energy needs are close to zero; intermediate with decreasing nonlinearities that can be expressed by power functions; and finally, a quasi-linear regime with almost-steady nonlinearities.

Feasibility of Using Wood Chips to Regulate Relative Humidity Inside a Building: A Numerical Study

The use of bio-based materials in buildings has become more and more significant last years. In most of the cases, their health properties and natural provenance have made them a great solution to face global climate warming and the new policies to reduce building energy consumption. In many thermal problems, bio-based materials can allow to optimize the building thermal behavior according to its energy consumption and inside comfort conditions. So it is when they are used as an insulation material in the building. However, it is not the case in this paper. In fact, the bio-based matter is rather used as a desiccant wheel to control air conditioning inside the building. The aim of this paper is to numerically verify if it is possible to use a bed of wood chips as a hygroscopic material (or a desiccant matter) in order to modify the relative humidity inside the building in Reunion Island and so improve thermal comfort. A simple model of heat and mass transfer between a bed of wood chips and building inside air has been set up and implemented into a validated building simulation code named ISOLAB. Numerical simulations were set up for the four climate zones of the island regulations and a focus has been made on the low altitude one (with high, solar irradiation, temperature and relative humidity). Simulation results give the thermal behavior of the building particularly the temperature and relative humidity of inside air temperature, and temperature and moisture content of wood chips. The obtained results lead to determine if the wood chips bed is suitable for the reference building and to verify its technical feasibility (wood species, size of the bed, integration to the building, etc.). The results show that the use of a WCB help to decrease the building inside air temperature and water content up to 10°C less and 11.6 g.kg-1 less. These are the ways to improve inside comfort conditions. Indeed, comfort analysis have shown the possibility to significantly increase building users’ thermal comfort when coupled with a fan and natural ventilation, like the regulation needs for low altitude climate. In this case, a gain of 68% of year time is achieved for a building equipped with WCB system compared to one without it (6308 hours of comfort over a year with the WCB against 350 hours without WCB). So the WCB seems to be able to help reducing cooling loads in tropical climate conditions.

Design of a Ventilation System Coupled with a Horizontal Air-Ground Heat Exchanger (HAGHE) for a Residential Building in a Warm Climate

Energy consumption in new buildings can be reduced at the design stage. This study optimizes the ventilation system design of a new residential building located in a warm climate (Southern Italy). Different system options of horizontal air-ground heat exchangers (HAGHEs), also called earth-to-air heat exchangers (EAHX), have been considered to search for the optimal configuration. The thermal behaviour of the obtained configurations has been modelled by the dynamic simulation software TRNSYS 17. The pipe numbers, the air flow rate, and the soil thermal conductivity are among the simulated building components. For each of them, different design options have been analysed to study how each parameter impacts the building thermal behaviour in winter and summer. The operative air temperature (TOP) has been evaluated inside the building prototype to investigate the indoor comfort. The paper demonstrates that HAGHEs permit to assure a suitable indoor climatization if the building envelope is optimized for a warm area. These conditions require high values of heat storage capacity to keep under control the internal temperature fluctuations, especially in summer. The paper confirms the importance of geothermal systems and design optimization to increase energy savings.

Passive thermal behaviour of buildings: Performance of external multi-layered walls and influence of internal walls

In contemporary architecture, the opaque building envelope is usually realised by multi-layered walls; that is, a sequence of homogeneous layers of different materials. The layer sequence and distribution affect the wall behaviour in terms of its overall thermal inertia, or heat storage capability; hence, analysis of the thermal performance of a multi-layered wall becomes very important under dynamic heat transfer conditions, as usually occurs during summer.In this study, the authors employ analytical models based on the heat transfer matrix method, with the aim of predicting the dynamic thermal behaviour of external and internal building walls. Although numerous studies have been devoted to investigating the dynamic thermal behaviour of walls, the approach followed and results obtained by the authors are original and have significant implications that are of practical interest. By using the analytical models, the effects of continuous variations in the positioning and thickness distribution of the insulation material on the dynamic thermal performance (dynamic thermal transmittance, decrement factor and time lag) are demonstrated with reference to different constructive solutions (from a light-weight wall with a surface mass of 85 kg/m2 to a massive wall with a surface mass of 294 kg/m2). Moreover, a simplified correlation is proposed, which allows for correction of the dynamic thermal transmittance and time lag of external walls to take consider the effect of the internal walls (partition walls and slabs) on the dynamic thermal behaviour of a room. The results presented in the paper can be used during the building envelope design stage as a guideline for the improvement of the dynamic thermal performance of multi-layered walls. Furthermore, the insight provided into the building envelope thermal behaviour could prove useful for understanding how to maximise the effectiveness of possible retrofit interventions.

Predicting the Air Quality, Thermal Comfort and Draught Risk for a Virtual Classroom with Desk-Type Personalized Ventilation Systems

This paper concerns the prediction of indoor air quality (IAQ), thermal comfort (TC) and draught risk (DR) for a virtual classroom with desk-type personalized ventilation system (PVS). This numerical study considers a coupling of the computational fluid dynamics (CFD), human thermal comfort (HTC) and building thermal behavior (BTB) numerical models. The following indexes are used: the predicted percentage of dissatisfied people (PPD) index is used for the evaluation of the TC level; the carbon dioxide (CO2) concentration in the breathing zone is used for the calculation of IAQ; and the DR level around the occupants is used for the evaluation of the discomfort due to draught. The air distribution index (ADI), based in the TC level, the IAQ level, the effectiveness for heat removal and the effectiveness for contaminant removal, is used for evaluating the performance of the personalized air distribution system. The numerical simulation is made for a virtual classroom with six desks. Each desk is equipped with one PVS with two air terminal devices located overhead and two air terminal devices located below the desktop. In one numerical simulation six occupants are used, while in another simulation twelve occupants are considered. For each numerical simulation an air supply temperature of 20 °C and 24 °C is applied. The results obtained show that the ADI value is higher for twelve persons than for six persons in the classroom and it is higher for an inlet air temperature of 20 °C than for an inlet air temperature of 24 °C. In future works, more combinations of upper and lower air terminal devices located around the body area and more combinations of occupants located in the desks will be analyzed.

Hourly simulations of an hospital building for assessing the thermal demand and the best retrofit strategies for consumption reduction

In the framework of energy saving and environmental protection, the role of the energy consumption in buildings is crucial. For existing buildings and especially for public ones, it is mandatory to correctly select and realize suitable retrofitting interventions to reduce costs and increase the efficiency. In fact, innovative solutions for both the envelope and the plants renovation are often very expensive and the correct choice becomes critical for the sustainability from the economic point of view.The aim of the present paper is to propose a methodology to optimize the process of selection for the retrofit interventions, here applied to a case study of the Monoblocco Pavilion at the San Martino Hospital in Genova, Italy. The building thermal behaviour is dynamically simulated by means of an Energy Plus model in order to evaluate the energy needs for both heating and cooling purposes. The base case scenario is evaluated in terms of key performance indicators (KPIs) and compared with benchmark values in order to select the more suitable intervention actions. For the analysed case study, the innovative retrofit solutions are façade void insulated panels, smart rotating windows with different emissivity glass and sunlight carrying optical-fibres coupled with dimmed LED lighting system. The technologies are combined in different intervention packages that are then compared in term of energy saving and economic sustainability by means of the estimation of hourly values of energy consumption and the assessment of the Simply Pay Back Period (SPB) of the investment.

Development of an Optimal/Robust Control Strategy for Electrical Energy Cost Minimization in an Air-Conditioning Plant

This paper focuses on modelling the thermal behaviour of buildings and designing an optimal control algorithm for their HVAC systems. The problem of developing a good model to capture the heat storage and heat transmission properties of building thermal elements such as rooms and walls is addressed by using the lumped capacitance method. The equations governing the system dynamics are derived using the thermal circuit approach, and by defining equivalent thermal masses, thermal resistors and thermal capacitors. In the control design part, we have introduced a control algorithm which is composed in Pontryagin’s Minimum Principle controller. The optimal tracking problem is solved in Pontryagin’s Minimum Principle controller where the interconnection of all walls are taken into consideration. The Pontryagin’s Minimum Principle controller 0minimizes a quadratic cost function which has two quadratic terms. One takes into account the comfort level and the other represents the control effort, i.e. the energy consumed to operate the HVAC system. Simulation results for a single room example show energy savings using this control algorithm over a conventional PI controller.

Application of HVAC Systems with Control Based on PMV Index in University Buildings with Complex Topology

In this work the control of HVAC systems based on PMV index, in university buildings with complex topology, is numerically developed. A numerical software that simulates the building thermal behavior and the occupant thermal comfort, in transient thermal conditions, is applied. This numerical software is based in energy and mass balance integral equations. The numerical simulation is made in a university building, equipped with 344 compartments and with 2072 occupants, in summer and winter conditions. The number of compartments equipped with HVAC system, control physiology system based on PMV index, are 171. The PMV index is calculated as a function of the air temperature, air velocity, air relative humidity, mean radiant temperature, clothing level and activity level. The numerical results show that the application of this type of control allows to guarantee, in an efficient way, good levels of thermal comfort, both in winter and summer conditions, in most of the rooms of the studied building.

Envelope Design Optimization by Thermal Modelling of a Building in a Warm Climate

Finding the most appropriate configuration of building components at the design stage can reduce energy consumption in new buildings. This study aims to optimize the design of the envelope of a new residential building located in a warm climate (southern Italy). The thermal behaviour of the building has been analysed to evaluate the indoor operative air temperature for several configurations. The building prototype has been modelled using the dynamic simulation software TRNSYS 17 (A transient system simulation program, University of Wisconsin, Solar Energy Laboratory, USA, 2010) using a sequential search technique. Starting from the simplest building configuration, the main evaluated components are: walls, slab-on-ground floor, roof, shading, windows and internal heat loads. For each of these components, different design options have been modelled and compared in terms of indoor thermal comfort. Comfort parameters have also been taken into account to evaluate users’ satisfaction with the optimized configurations. The study of the operative air temperature demonstrates that the absence of insulating layers in the ground floor ensures a lower internal temperature in summer. The paper shows how each component impacts the thermal behaviour of the whole building. It highlights the usefulness of the envelope design optimization that is characterized by high values of heat storage capacity, enabling internal temperature fluctuations to be kept under control, especially during summer.

Improvement of the summer cooling induced by an earth-to-air heat exchanger integrated in a residential building under hot and arid climate

This paper aims to investigate the impact of the thermal insulation on the cooling effectiveness of the Earth-to-Air Heat Exchanger systems under hot and arid climate. For that, the dynamic behaviour of two identical buildings submitted to the same exterior solicitations and equipped with an EAHE is presented in detail. To achieve the objective of this study, two transient models are developed; one for modelling the EAHE and the other for describing the thermal behaviour of buildings. The set of differential equations corresponding to different components of the system is solved using the technique of Complex Finite Fourier Transform. The findings indicate that when the insulated building is equipped with an EAHE, the effect of the thermal insulation will be combined with that of EAHE and the resulting effect will be more important, so that the reduction in the indoor air maximal temperature can be greater than 11°C and the reduction rate in the amplitude of the indoor air temperature increases until 91%. In addition, it is found that the thermal performances of the building outer walls represented usually by the decrement factor and the time-lag can be more improved using insulation layers within these components. On the other hand, the investigation conducted on the effect of the building materials showed that in Saharan climate, the light buildings such as those constructed with autoclaved aerated concrete blocks are more performing compared to the heavy buildings in which the outer walls must be judiciously insulated with a material of high thermal resistance. However, it is shown that the insulation with air cavities is an effective and economic solution for the light buildings in hot and arid regions.

Indoor thermal comfort assessment using different constructive solutions incorporating PCM

Sustainable energy and thermal retrofit design of buildings or districts has a strong global impact in the viewpoint of economies and energy-efficiency perspectives. Several aspects such as architectonic design, building materials, construction technology, mechanical systems and outdoor climate determines the thermal behaviour of buildings and their ability to provide indoor thermal comfort to occupants. The use of geothermal energy and phase change materials (PCMs) in the construction systems are an opportunity that may attenuate indoor air temperature fluctuation as well as overheating risk. This paper presents the results of a study on indoor thermal comfort and energy efficiency regarding the PCM’s positive role when applied to new constructive solutions, inside a building with a geothermal system linked to the air conditioning system. The PCM study was based on real and simulated investigations in two rooms of a new university department at the Aveiro campus. Higrothermal monitoring (indoor air temperature) of two rooms in which one of them has PCM panels incorporated into gypsum board partition wall and into a suspended ceiling. The scope was driven to investigate the potential of these solutions for overheating mitigation. The numerical study was conducted by using an evolutionary algorithm coupled with the software EnergyPlus® used in simulations. In the scope of this optimization process, constructive solutions with the incorporation of different types of PCM with different melting temperatures and enthalpy, and different flow rates of natural ventilation were combined to investigate the potential and the payback time of these novel solutions.The results for the room measurements show that the indoor thermal comfort of the rooms, present long periods of discomfort namely in overheating. However, it was proved that the PCM application in one of the rooms lead to an overheating reduction of 7.23% representing a PCM efficiency of 35.49%. After the optimization process an overheating reduction of about 34% was attained by the use of PCM in one of the rooms. Regarding the economic analysis of the use of the PCM for cooling demand reduction, a payback time of 18years was attained.