Poor airtightness in buildings can lead to an over-consumption of energy and to many issues such as moisture damage and poor indoor climate. The timber frame constructions are particularly subject to air leakages, and further knowledge in this field is needed to meet the regulation requirements tightened by the development of low-energy and passive houses. This article focuses on a three-scale experimental study carried out in laboratories to quantify the impact of a number of construction details on timber frame wall airtightness. For this purpose, we built two original experimental setups and to complement an existing large-scale facility. Each setup enables to carry out pressurization tests at a different scale. The results put all together give quantitative information for more accurate simulations of building performance. Some specific construction details were investigated. It has been found in particular that the density of the insulation material is significant since a soft glass wool can have an air permeability three times higher than a rigid one with the same thermal performances. Moreover, it has been pointed out that the bond between the gypsum board and the insulation has a significant impact on the resulting pressure–flow law, and to ensure that there is no air gap the whole interface should be glued. The air flow directions also influence the flow values for high-pressure differences. Finally, at wall scale we have found that the sealing of the gypsum boards and the vapor barrier against the bottom wall plate is not very significant as long as the exterior side is sealed correctly. On the other hand, a proper sealing on both sides of a window is required because of the air gaps along it.
This article presents experimental research on the moisture diffusivity in wood within the range of hygroscopic moisture. This research was carried out on samples of three types of trees: Scots pine, small-leaved linden and pedunculate oak. It included measurements of kinetics of moisture adsorption within the range of air relative humidity from 25% to 85%. For each type of wood, the experiment was carried out with unidirectional flow of moisture, in each of the material principal orthotropic directions, by examining the diffusion coefficient along the fibres, in the tangential direction and in the radial direction. Values of moisture diffusion coefficients and mass surface emission coefficient were found with the use of method of minimizing the objective function, that is, by fitting the computational adsorption kinetics curves to the experimental ones. At the same time, three cases of variations of the moisture diffusion coefficient together with moisture content of the material have been analysed each time: in the form of a constant, linear function and a quadratic function, assuming a constant value of mass surface emission coefficient on the absorbing surface of samples. The performed calculations allowed determining whether the moisture diffusion coefficients have extreme values within the analysed range of moisture content and what is the impact of various diffusion mechanisms on the whole process of transferring moisture in the considered cases.
In this article, the comparison of energy performance between a classical and an improved Trombe wall of a model test room has been carried out experimentally. The case study is conducted in Borj Cedria, Tunisia, where there is always heating requirements. Here, we propose an improved Trombe wall whose absorber wall is covered with a thin black copper panel backed rather than simply painted black wall. The proposed idea would offer improved thermal performance, especially in natural convection. The comparison shows that the improved Trombe wall design gives an increase for both conductive and convective flux. The results show that the improved Trombe wall works more effectively than the classical Trombe wall system in utilizing solar energy for the example of test room.
This study investigated the effects of three pore-forming agents on the properties of the fired clay body applied in the production of lightweight bricks for the building envelopes. Test samples were made from clay raw material already containing two combustible pore-forming agents (sawdust and cellulose sludge). A part of this research was focused on studying the influence of adding two combustible pore-forming agents (molasses and cornstarch) and a chemical additive Vuppor to the claw raw material. Testing of the material properties showed that although the three samples had almost the same pore volume, their thermal conductivities varied. These findings led to an important conclusion. The pore size of 1–200 µm (filled with not only air but also biomass ash) reduced the thermal conductivity, and conversely, an increase in the small pore size less than 1 µm increased the thermal conductivity of the fired clay body.
Based on modeling and measurements, the authors investigated the performance of expanded polystyrene and lightweight aerated concrete slabs. The objective of the work was to assess the performance of the brick wall (having various thickness and layering) commonly built in the Silesia Region (Poland) in the 1920s and the changes of water content in layers of the flat wall through the measurement of temperature and relative humidity in the selected layers of the masonry wall.
The main purpose of this study is to evaluate the technical possibilities of incorporating fly ash in clay bricks to produce an industry-acceptable bricks. The effect of fly ash with high replacing ratio from (0% to 50%) of clay on properties of bricks was analyzed. The tests of bulk density, porosity, water absorption, compressive strength, and flexural strength were conducted in accordance with relevant Indian standards in order to estimate the effect of the fly ash content on the performance of the hardened bricks. Novel lightweight bricks have been produced by sintering mixes of fly ash and clay. The results show that fly ash addition up to 50% (in weight) can be beneficial for properties of sintered bricks at temperature 1000°C. Test results revealed that the combined use of clay and fly ash exhibited excellent performance due to efficient micro-filling ability and pozzolanic activity. These bricks give better compressive strength with additional advantage of being lightweight and more environmentally friendly. Effective utilization of fly ash additive is not only for conservation of natural clay resources but also an alternative solution to difficult and expensive waste disposal problems.
The purpose of this study was to investigate how natural convection in air-permeable glass wool insulation affects the thermal transmittance in walls, roofs and floor structures. The results can be used to evaluate the need for a convection barrier in thick mineral wool layers. Natural convection is affected by several parameters. In this study, the angle of inclination, the heat flow direction and the temperature difference across the test section have been studied. Thermal transmittance and temperature distribution measured using thermocouples placed inside the insulation cavity clearly showed convection in the insulation when the test section was in pitched roof and wall positions. An efficient measure to reduce the natural convection is to divide the insulation layer into two thinner layers using a diffusion open convection barrier. A convection barrier is recommended by the authors both in wall and pitched roof structures if the insulation thickness exceeds 200 mm.
Uncertainty and risk analyses are important tools for building designs and performance assessment of renewable energy systems. This task requires to account for the variability of the weather data. In this work, we develop a methodology to characterize and simulate stochastic weather data. The stochastic features of each weather input, such as auto-correlation and hourly cumulative distribution functions, are extracted from the dataset at hand. Then, the procedure of Iman and Conover is used to generate stochastic weather inputs. The approach is applied to a sequence of 1 month extracted from the typical meteorological year of the city of Lyon, France. The simulated stochastic weather data are employed to perform the uncertainty and sensitivity analysis of a real passive, low-energy house. The results show that the uncertainty on the predicted energy needs is roughly 20% and is essential due to the stochastic variability of the outdoor air temperature.
This article analyses the use of dilatometry to assess the durability of load-bearing clay brick masonry in a century home in Toronto (Canada). The building had recently undergone the addition of medium density closed-cell polyurethane spray-applied foam insulation on all interior sides of the exterior clay brick load-bearing walls, increasing the insulating value in areas to RSI 7.9 m2K/W, on average, from the original RSI 0.5 m2K/W, on average. The critical moisture content (saturation degree) of representative samples from the building were compared with values obtained from frost dilatometry testing. The later indicate critical moisture content for freeze–thaw. The frost dilatometry method was furthered by studying three-dimensional testing, rather than the traditional two-dimensional approach. The results showed the brick masonry in the study building are at a relatively low risk of freeze–thaw damage thanks to good resistance of freeze–thaw of the subject brick masonry and low wetting potential of the brick masonry on site. This further strengthens the need for good water shedding characteristics.
Thermal performance discrepancies between theory and practice in buildings is a well known issue. Reducing this gap is crucial for enhancing energy efficient building construction and renovation. To measure the actual transmission heat loss coefficient of a building from in situ testing, an evaluation of time-varying infiltration losses needs to be quantified to improve the result’s precision, especially for short dynamic methods. This study first presents a theoretical analysis to explain why this evaluation is necessary and how to perform it using different technical approaches (simplified aeraulic models and tracer gas). An experimental comparison of four of these solutions on a small shed reveals that blowerdoor and wind speed measurements can be sufficient to evaluate infiltration losses with acceptable accuracy. Results of the identified transmission losses coefficient
A proper generalised decomposition for solving inverse heat conduction problems is proposed in this article as an innovative method offering important numerical savings. It is based on the solution of a parametric problem, considering the unknown parameter as a coordinate of the problem. Then, considering this solution, all sets of cost function can be computed as a function of the unknown parameter of the defined domain, identifying the argument that minimises the cost function. In order to illustrate the applicability, the method is used to solve a non-linear inverse heat conduction problem to determine a temperature-dependent thermal conductivity. Then, a comparison is carried out with the local sensitivity and the genetic algorithm methods. It is shown that the proper generalised decomposition method estimates the unknown parameter with the same accuracy as the other two methods. Due to its advantage in terms of reducing the complexity, the method was then used to solve a transient three-dimensional non-linear heat transfer inverse problem. The results have shown that the method is appropriate to determine the unknown parameter with a low computational cost. Furthermore, the main advantage of the technique is its low capacity for storage, which can be used, as an inverse method, for building energy management and extended to evaluate thermal bridges from on-site measurements.
To diminish peaks of energy power demand in buildings, we need to determine parameters in transmittance models that describe indoor temperature response to changes in heating. This article discusses first- and second-order models as well as an integration model. Calculations deal with indoor temperature drop in the range to –2 K following the heating power reduction for a period of 4–6 h. The second-order model was found to be the most accurate in showing the decrease in temperature. The calculated values of parameters vary within wide ranges, with significant differences occurring even with values obtained in consecutive measurement series. It was shown that the use of averaged values produce large result errors in the predictions of indoor temperature changes. This renders an offline method useless and promotes an online method. The average value of the time constant in the first-order model correlates well with the value of the time constant calculated as a ratio of the heat storage mass to the room heat loss coefficient. This is true if we take into account exclusively this part of the building partition layer that contributes to the heat storage.
There is a need for experimental determination of thermophysical properties to bridge the gap between theoretically prediction and performance of insulating materials in buildings. This investigation concerns the study of hydrothermal performance of glass wool, a widely used insulation on the world market. It has been shown the low sensitivity of glass wool to water vapor, low hygroscopicity, and low permeability. On the other hand, the liquid permeability of glass wool is important. Obviously, the presence of liquid is generally accidental and should be prevented by good workmanship. Thermal characterization (conductivity and diffusivity) by hot disk, a transient technique, has been determined as a function of water. The effect of vapor phase water on thermal properties is not significant. Thermal conductivity increases by a factor 2 when liquid water is present in the insulation. It is shown that the hot disk method is useful to determine thermal characterization of insulation materials. Variations of thermal conductivity with water content have been explained from hydric characterization.
This study seeks to assess the instantaneous deformation of saturated cement-based porous materials induced by supercooling of pore fluid. Thermodynamic equilibria account for the physical behaviors of the confined crystallization of ice for partially frozen porous systems. Pore pressure is built up when ice forms in pores, and this can be intimately related to the pore structure of the porous materials. To overcome the metastability of supercooled water that surpasses a normal poromechanical description, a special program for cooling has been designed. The hydraulic pressure resulting from rapid ice formation and the thermal shock caused by heat release account for an observed dilation peak. The lower the supercooled temperature, the larger the dilation peak becomes. Rapid pore pressure relaxation accounts for significant contraction following the dilation peak. The pore structure also has a significant impact on the freezing deformation of the cement-based porous materials. Results obtained in these examples are comparable with previously published data, which confirms the importance of the detrimental effects of supercooling in porous materials.
This work presents and verifies the model and air transfer in a horizontal, naturally ventilated air cavity that could be under a flat roof or under a building as a crawl space. In this article, this space is represented as a rectangular air channel with a cooled top and heated bottom and walls each either heated or cooled. Temperature of all wall surfaces varies along the attic space length. The model allows estimating temperatures of air and wall surfaces along the channel for a low velocity of airflow in the channel. The results of calculations were compared with a field experiment and agreed within estimated errors of the model, that is, <9%.
Lower limits of measurement are prescribed within all steady-state test methods for thermal insulation. The limit, typically 0.1 m2 K/W, is largely required because of the increasing significance of interface resistance. We have previously proposed the use of a difference method, in conjunction with flexible buffer materials, to minimize the effects of interface resistance and facilitate measurement of rigid materials below these limits. We have now studied this approach at higher thermal resistances and incorporated a refinement to include a known reference specimen in the difference measurement, which largely eliminates the residual resistance terms. Specimens of expanded polystyrene and cast acrylic were measured in a conventional heat flow meter apparatus using two alternative silicone buffer materials: one solid and the other a sponge. Analysis also included earlier measurements of 12 more highly conducting specimens. Across all of these, thermal resistance values obtained by the difference method were lower between 0.008 and 0.016 m2 K/W, attributable to removing the contribution of interface resistance.
The determination of the thermal performance of hybrid insulation assemblies that include an enclosed reflective airspace and a separate layer of insulation is being done using a hot-box test facility operated in accordance with ASTM C1224, the Standard Specification for Reflective Insulation. The thermal resistance determination of the insulated region requires a hot-box test with known thermal insulation to determine heat flow through the framing. Factors that affect the result for the hybrid insulation assembly will be discussed along with results obtained using the ASTM C1224 protocol. The thermal resistance obtained using the hot-box apparatus will be compared with calculated values obtained from published correlations. The uncertainty in the hybrid insulation assembly and the enclosed reflective airspace due to uncertainty in the thermal resistance of the calibration material are of particular interest.
A technique based on the heat flow meter method is proposed for measuring the thermal conductivity of moist earthen and granular loose-fill materials. Although transient methods have become popular, this steady-state approach offers an uncertainty that can be reliably estimated and a test method that is widely accepted for building certification purposes. Variations to the standard method are proposed, including the use of a rigid holding frame with stiff base and silicone sponge buffer sheets, in conjunction with difference measurement to factor out the contributions from base, buffers and contact resistance. Using this approach, results are presented for green-roof substrates based on scoria, terracotta and furnace-ash at different moisture contents. Thermal conductivity ranged from 0.13 to 0.80 W/m K and fitted well to linear regression plots against moisture content. Further comparative measurements of a single specimen showed that direct measurement was less consistent than difference measurement and thus indicated that thermal resistance was higher by 0.023 m2 K/W, attributable to the presence of contact resistance.
This article describes the results of a research project carried out at the University of Reims Champagne-Ardenne. The aim of this article is to develop a new insulating material produced by bonding hemp shives with wheat starch as a binder and to characterize its physical properties such as sorption isotherm, water vapour permeability, thermal conductivity, heat capacity and porosity. The equations of coupled heat and moisture transfer within the panels are introduced. These governing equations are applied on the room level in order to assess the hygrothermal behaviour of the panels and its impact on energy consumption and indoor comfort. Simulations are performed for Nancy (France) winter conditions with the simulation environment Simulation Problem Analysis and Research Kernel (SPARK) suited for complex problems.
The article presents the balance approach of determining the building heat consumption (for heating and ventilation purposes) in the standard heating season based on short-term measurements performed on the real object in actual climatic conditions. The influence of the length of measurements in situ on the accuracy of estimation of the seasonal heat consumption was analysed for the occupied building. The 14-day measurement period was examined as the shortest and it was proved that the accuracy of the heat consumption forecasting was in that case ±20%. The heat consumption for heating and ventilation purposes, determined on the basis of short-term measurements, was recalculated to the reference climatic conditions of the heating season. Such a value is one of the components of the energy performance of a building. According to the Directive of the European Parliament and of the Council on the energy performance of buildings, measurement-based approaches are the alternative for the computational approaches and thus the proposed method can find a practical application in the process of energy certification of buildings. In this article, the results of the application of this method in the multifamily building occupied during the measurements are also presented.
The concentrations of 226Ra, 232Th, and 40K are measured in the material collected from two locations. The collected materials are analyzed using gamma-ray spectrometry. The activity concentration of the naturally occurring radionuclides 226Ra, 232Th, and 40K in building material varies from 12.6 to 121.4, 13.6 to 142, and 69.5 to 620.6 Bq kg–1, respectively. The radium equivalent activity, absorbed dose rate, annual effective dose, and hazard index are also calculated.
Wind discomfort and the dangers that the wind may lead can be harmful in terms of comfort conditions of both indoor and outdoor environment of the building/buildings to be constructed or just completed. The extent of discomfort to pedestrian varies from inducing slightly unpleasant feeling to producing a falling down hazard. Typically, the cause of frequent occurrences of strong wind at pedestrian area is primary related to the configuration of building structures and/or topography in the vicinity of the pedestrian area. Depending on the characteristics of the wind including magnitude, uniformity, ambient temperature, and so on, the level of disturbance to users of pedestrian areas can be different. In this context, the regions where Necmettin Erbakan University temporary education buildings are located have a fairly intensive topography in terms of wind. Therefore, detailed analysis of the inside regions and the surrounding areas of education buildings in particular are performed in terms of microclimatic comfort and indoor energy recovery. Especially, the topography where university campus temporary educational buildings are located has very high wind climate conditions compared to the city of Konya climate conditions.
In this study, pedestrian-level wind conditions around N.E.U. campus buildings and in urban areas and the topography of campus settlements were analyzed through on-site measurement with Delta OHM microclimatic instruments.
The purpose of this study is to investigate the pedestrian-level comfort conditions around the project buildings suggested by concept architects together with microclimatic measurements of comfort conditions, in the light of current topographic and climatic conditions presented by the head architect. However, presentation of these topographic and microclimatic measurements around currently completed temporary classrooms of the university campus have not yet been completed. The topography of the university campus, which is at an altitude higher than that of Konya centrum, is exposed to an extremely high wind velocity. The pedestrian-level comfort conditions are measured using Delta OHM instrument. The study also aims to compare pedestrian-level comfort conditions at locations of various buildings.
In addition, outdoor comfort survey was also conducted in the campus area.
However, measurement results of the microclimatic measurement device, DeltaOHM, are evaluated in this study.
It can be observed from the results that pedestrian-level comfort of current campus settlements around the buildings reach very discomforting levels.
Since the university's topography varies between very high and very low temperature levels and wind velocity values, climatic comfort problems are observed in the area.
Some reasons for the discomfort problems observed in current settlement are; incorrect use of climatic parameters, incorrect directions of buildings, thermal effects due incorrect selection of materials used in constructions of buildings.
In order to achieve thermal comfort, more studies are required on pedestrian-level comfort, use of passive design techniques such as correct direction of buildings and correct selection of materials utilized in the buildings based on their thermal effects.
This would help university campus buildings consume less energy and maximize people's satisfaction.
Thermal energy storage systems incorporated with phase change materials have potential applications to control energy use by building envelopes. However, it is essential to evaluate long-term performance of the phase change materials and cost-effectiveness prior to full-scale implementation. For this reason, we have used the accelerated long-term approach for studying the thermal performance and chemical stability of a commercially available bio-based phase change material during thermal cycling over a simulated period of 20 years. The phase change material was subjected to accelerate thermal aging under controlled environmental conditions. Small samples of the phase change material were periodically removed to measure its latent heat, thermal decomposition, and chemical stability using various analytical methods such as differential scanning calorimetry, thermogravimetry analysis, and infrared spectroscopy. The topographic changes in the phase change material due to the aging process were observed using scanning electron microscopy. The differential scanning calorimetry data indicate a significant reduction of 12% in the latent heat during heating and cooling cycles during the initial 6.2 years remain nearly constant thereafter. The thermogravimetry analysis results showed that the phase change material has excellent thermal stability within the working temperature range and also shows long-term decomposition temperature stability. The Fourier transform infrared spectra of the phase change material indicate absorption of moisture but the phase change material was chemically stable over the duration of accelerated aging cycles. After several aging cycles, the baseline surface morphology appeared to be changed from uniform mix of phase change material with microstructures to segregated microstructures as evidenced by the observation of the scanning electron micrographs.
In this study, effects of built-in balcony on thermal performance in residential buildings were investigated numerically by means of open-ended structure approach. For this purpose, the parametric study has been carried out for various ratios of balcony depth/balcony height (L/H), closed barrier height/balcony height (h/H) and Rayleigh numbers (Ra) using a computer program in case of no wind for laminar flow. Analyses were conducted for Rayleigh numbers ranging from 103 to 106. The calculations were carried out for the ratios of L/H, namely, 0.0, 0.24 and 0.6, and the ratios of h/H, namely, 0.0, 0.18 and 0.35. The working fluid was assumed to be air (Pr = 0.71). According to the findings, for Ra <= 104, Nusselt number (Nu) decreases with the increasing ratio of L/H for the constant h/H = 0.35. However, for Ra ≥ 105, Nu sharply decreases with the increasing ratio of L/H, while Nu again sharply increases after L/H 0.25 and almost remains constant after L/H 0.5. For the constant L/H = 0.54, Nu decreases with the increasing ratio of h/H for the whole Ra. It is suggested that the ratio of L/H should not be over 0.35 and the ratio of h/H should be at least 0.35.
Unvented attics are an energy-efficiency measure to reduce the thermal load of the conditioned space and decrease the space conditioning energy consumption by about 10%. This retrofit is usually done by spraying polyurethane foam underneath the roof sheathing, and on the gables and soffits of an attic to provide an air barrier and a thermal control layer. Unvented attics perform well from this perspective, but from a moisture perspective sometimes homes with unvented attics have high interior humidity or moisture damage to the roof. As homes become more air tight and energy efficient, a better understanding of the hygrothermal dynamics of homes with energy-efficient envelopes becomes more important. One proposed reason for high unvented attic humidity has been that moisture can come through the asphalt shingle roof system and increase the moisture content of the roof sheathing and attic air. This has been called "solar-driven moisture." Oak Ridge National Laboratory investigated this proposed phenomenon by examining the physical properties of a roof and the physics required for the phenomenon. Results showed that there are not favorable conditions for solar-driven moisture to occur. Oak Ridge National Laboratory also conducted an experimental study in a home with an unvented attic and compared the humidity below the roof sheathing before and after a vapor impermeable underlayment was installed. There was no statistically significant difference in absolute humidity before and after the impermeable underlayment was installed. The outcomes of the theoretical and experimental studies suggest that solar-driven moisture does not occur in any significant amount.
The experimental and numerical results of the heat transfer and airflow by turbulent mixed convection in a ventilated cavity are presented. The experimental setup was built to use air as the heat transfer fluid. One vertical wall receives a uniform and constant heat flux, whereas the opposite wall is maintained at constant temperature. The remaining walls are thermally insulated. The experimental temperature profiles were obtained for different heat fluxes and air inlet velocities. Five different turbulence models were used to obtain the numerical results. The comparison between experimental and numerical temperatures indicates that the standard k– turbulence model presents a better agreement, with maximum percentage differences between 2.0% and 3.0%. The heat transfer coefficient had values between 2.2 and 3.4 W/m2 K, and it increases with the Rayleigh number and the Reynolds number. The experimental and numerical convective heat transfer coefficient predictions are closer for the higher Reynolds number (inlet air velocity of 0.5 m/s). The effects of varying the Rayleigh and Reynolds number on flow patterns and temperature fields were analyzed numerically.
Building envelope, such as a roof, is the interface between a building structure and the environment. Understanding of the physics of microbial interactions with the building envelope is limited. In addition to the natural weathering, microorganisms and airborne particulate matter that attach to a cool roof tend to reduce the roof reflectance over time, compromising the energy efficiency advantages of the reflective coating designs. We applied microbial ecology analysis to identify the natural communities present on the exposed coatings and investigated the reduction kinetics of the surface reflectance upon the introduction of a defined mixture of both photoautotrophic and heterotrophic microorganisms representing the natural communities. The findings are (1) reflectance degradation by microbial communities follows a first-order kinetic relationship and (2) more than 50% of degradation from the initial reflectance value can be caused by microbial species alone in much less time than 3 years required by the current standard ENERGY STAR® test methods.
In this study, a copolymer composed of hollow spherical particles with an average particle size of 90 µm was evaluated as a lightweight aggregate in Portland cement–fly ash mortars to improve the thermal conductivity (k) of the composite. Mortars were produced for three different water/binder ratios by mass (w/b), 0.4, 0.5, and 0.6. Optimized proportions were obtained for a minimum target compressive strength of 35 kgf/cm2 (3.4 MPa) according to the requirements of Mexican standards for nonstructural masonry units. Thermal conductivity was determined for dry and saturated samples through the transient plane technique with average results of 0.16 and 0.31 W/(m K), respectively. These values represent an increment of 23% and a reduction of 33% in comparison to an efficient Portland cement–based commercially available thermal insulator.
The main purpose of this research is to assess the impact of four types of energy-saving houses on environment in terms of CO2 emission. In the tropical climate, House 1 is designed as an integration of modified Trombe wall and roof solar collector using concrete block and concrete tiles, House 2 is normally built by concrete blocks and concrete tiles, House 3 is built as usually found in Thailand by red clay bricks and concrete tiles, and House 4 is built with lightweight autoclave concrete blocks and well-insulated roof. All house model dimensions are 1.3 x 1.3 x 2.5 m3. The collection of inventory data is associated with the construction stage, average household electricity consumption, maintenance in the using stage, and energy usage in the demolition stage. Electricity for residential consumption is based on the temperature collected through the experimental data in each house in 1 year. Subsequently, the environmental performance is assessed by Impact 2002+ life cycle impact assessment methods. The result shows that House1 has the highest score in terms of energy and environmental performance which can reduce the amount of CO2 emission contributing to global warming even from the first year of operation.
The project comprises 80 passive solar houses and 20 houses with combined passive and active solar heating in the Qinghai–Tibet Plateau region. The indoor thermal environment and the performance of the solar collection components are discussed through field testing during the coldest part and the transition part of the heating period. Moreover, the fractional energy savings, thermal efficiency, and fraction of the combined passive and active solar heating are analyzed. The results indicate that an auxiliary heat source should be used as a supplement. By comparing the heating of a passive solar house with a vernacular house, the energy savings of the passive solar house in the demonstration project were found to be approximately 62% during the study period. The thermal efficiency of the active solar heating system is 84.5%, and the solar energy utilization is 38.2%. The monthly average heat load index is 15.2 W m–2.
The annual solar gains in public buildings with large percentage of glazing can be shaped by different kinds of shading constructions and by glazing with proper spectral radiative properties. These properties can be obtained by covering panes with special spectral selective coatings or by use of tinted glass. Spectral selective panes enable control of solar gains in summer, reduce heat loss in winter, and reduce electric energy for cooling. These elements, except obvious influence on the annual heat balance of the building, have an impact on thermal and visual comfort parameters. The article presents selected results of the influence of horizontal overhangs and glazing with special spectral radiative properties on the annual thermal balance of analyzed buildings (computer simulations) and on thermal and visual comfort of the users (measurements). The measurements of the microclimate parameters show that it is impossible to maintain thermal comfort conditions during hot summer in natural ventilated buildings with high percentage of glazing without any additional appliances.
Over the last several years, the energy used for air conditioning in buildings increased in most European countries because of the high heat loads during the summer and the occupants’ increased comfort needs. The aim of our research was to determine the incident solar radiation on horizontal and vertical surfaces and to investigate the heat loads of buildings with different orientations of the glazed areas and different thermal masses in the building structures. Using the measured hourly global radiation data for the years 2009–2013, the diffuse and direct incident solar radiation was determined for the horizontal and vertical surfaces. A statistical analysis of the daily energy yield from solar radiation and the daily mean outdoor temperatures was conducted. The number of symmetric and asymmetric days was determined for torrid days. Using the methodology provided by standard EN ISO 13790:2008, the cooling energy demand and daily energy need for cooling was determined and evaluated for representative days of the analyzed years.
Waste ceramic dust originating in the advanced hollow brick production is applied as a supplementary cementing material replacing a part of Portland cement in concrete. The measurements of mechanical and fracture-mechanical properties, water vapor and liquid water transport parameters, thermal conductivity, specific heat capacity, and freeze/thaw resistance show that the ceramic dust application does not affect negatively the properties of the analyzed concretes over the whole studied Portland cement replacement range up to 40% by mass. The achievement of such a high limit for the ceramic dust application can be attributed, besides the pozzolanic reaction being initiated already during the time period of 7 to 28 days, to the positive effect of the excess ceramic dust in the mixes with a high volume of uniformly distributed air voids. The part of the ceramic additive which cannot participate in the hydration and pozzolanic reactions due to the lack of available Ca2+ acts, apparently, as fine aggregate partially filling the voids, thus contributing to the compaction of the hardened mixes and compensating, to a certain extent, the factual decrease of the amount of binder.
A conduction finite difference algorithm developed for EnergyPlus was used to model building walls integrated with phase change materials. The model was validated by comparing it against experimental data in terms of temperatures, wall heat fluxes, and total wall heat transfer. Experimental data, using two identical test houses of conventional residential construction, were collected for the validation and further analyses. The thermal performance of walls without phase change materials (control house) and with phase change materials (retrofit house) was evaluated. The model showed that the differences between experimental and predicted total heat transfer values were under 5%. The total heat transfer reductions produced by phase change materials could be predicted accurately using the conduction finite difference algorithm in EnergyPlus.
The water-permeability, moisture-diffusivity, and sorptivity concepts of modeling liquid water transport in porous building materials are analyzed. An overall assessment of the particular models is performed using the moisture profiles measured for two types of autoclaved aerated concrete. The water-permeability and moisture-diffusivity modeling approaches are found suitable from a point of view of accuracy of moisture-transport simulation but they have certain limitations. While the water-permeability concept is advisable for compact materials, the moisture-diffusivity concept should be preferred for materials with a high water penetration rate. Therefore, a combination of both these approaches in a single laboratory is beneficial. The sorptivity concept, on the other hand, can be recommended for a basic assessment of water transport capabilities of building materials only.
The solution of the simplified thermal and hygric room balance equations and adjacent walls is compared in selected application cases. In this article, the moisture part of the model is first reviewed and then applied to scenarios designed to illustrate the experimental and calculation results. For the common professional use, the user-friendly program CLIMT (Climate–Indoor–Moisture–Temperature) has been developed.
The temperature effect on water vapor transport properties of calcium silicate is studied, together with the influence of sample thickness. For material characterization purposes, the bulk density, matrix density, and total open porosity are measured at first. Sorption and desorption isotherms are measured using dynamic vapor sorption device in order to characterize the water vapor storage in researched material. The sorption process is analyzed for original material samples as well as for finely ground samples in order to evaluate the effect of inner porous space on water vapor storage. The steady state cup method is used for determination of water vapor transport properties, whereas the measurements are performed at several temperatures and for three different sample thicknesses. The obtained data show an important effect of temperature on water vapor transport and storage in studied material. The results also indicate a substantial influence of sample thickness on the calculated water vapor transmission properties.
Flooding events pose a high risk to valuable monumental buildings and their interiors. Due to higher river discharges and sea level rise, flooding events may occur more often in future. Hygrothermal building simulation models can be applied to investigate the impact of a flooding event on the environmental conditions inside a building. The objective of this study is to develop such a model that is able to evaluate the best fitting drying regime for historic buildings. A model is created based on on-site measurements of the indoor climate conditions in one building that had to cope with flooding in the recent past. The result of this study is a hygrothermal building simulation model that can predict the indoor climate conditions inside a room as a result of a flooding event. Different climate control systems can be integrated in this model to evaluate the most suitable drying regime to minimise the risk to the building, its interior and its collection. Furthermore, damage functions can be applied to analyse the risk to the collection caused by the flooding event.
The gas permeability and strength properties of the concrete and cement mortar with three different dosages of polypropylene fibers were tested. The obtained results confirm a significant influence of the fibers on the increase of permeability of cement-based materials heated above 180°C. At the same time, no influence of the polypropylene fibers content on the compressive and flexural strengths, and the fracture energy of the heated cement composites was observed. The measured material parameters were used in the computer simulations of complex physical phenomena in heated concrete, confirming efficiency of the polypropylene fiber admixture in reducing pore pressure in the material exposed to fire conditions.
This article addresses the discrepancies between projected and actual energy performance of thermally retrofitted buildings. Toward this end, we use detailed data and observations pertaining to seven residential buildings in Austria that were thermally retrofitted recently. These include five multifamily residences in Vorarlberg, the upper level of a duplex house in Lower-Austria, and a residential complex for the elderly in Styria. During the heating season 2009–2010 (1st October–30th April), indoor temperature and relative humidity levels were measured and logged in these buildings. For each building, the actual energy use during this period was derived based on bills for gas and electrical power. Additionally, we obtained and examined existing energy calculations (energy certificates) for these buildings. In six cases out of seven, we found a large discrepancy between projected and actual space heating demand. To explore possible reasons for this discrepancy, we generated for each of the buildings an energy certificate and performed detailed thermal simulations. Thereby, we took the main input parameters for energy calculations into consideration (air change rate, indoor air temperature, outside air temperature, and internal gains). If we use standard (default) values as suggested by Austrian standards for these parameters, the above-mentioned discrepancy cannot be explained. Measurements in the buildings, as well as interviews with the building’s inhabitants implied that standard-based input data assumptions were not reliable. A subsequent multi-factor study suggested that specifically the assumptions regarding air change rates might be responsible for the large deviations of the calculated values from the actual heating demand.
Interior thermal insulation is frequently one of the only possible solutions for thermal upgrade of the building envelope where the external appearance cannot be changed. In this study, four insulation materials were used in a case study in a historical school building in in situ test walls. The indoor climate in the test room was controlled to simulate the typical dwelling with high moisture load. The temperatures, relative humidity, and heat flows were monitored over 9 months to analyze the hygrothermal performance of four different insulation materials. The hygrothermal performance of insulation materials during drying and wetting periods are presented. Moisture test reference year was used in working out possible energy-renovation solutions. The results show that timing of the renovation works is a matter of consideration to avoid the hygrothermal risks inside the renovated wall assemblies. The results show that in all the cases, thermal comfort can be improved by increasing the inner surface temperature and decreasing thermal conductivity. However, in some cases, the risks of mold growth and interstitial condensation were present inside the retrofitted wall assemblies. Computer simulations of the wall assemblies with moisture reference years under different humidity loads concluded that all solutions are suitable for future analysis.
This research examines the extent to which drainage and ventilation drying can remove water that has leaked through claddings on walls with no specific drainage cavity. Drainage and drying rates were measured in 18 walls with claddings direct-fixed to the timber frame. The goal was to allocate risk scores to different types of direct-fixed claddings that are consistent with the risk matrix that guides the selection of claddings in the New Zealand Building Code. Drainage performance was measured by introducing a controlled water leak and recording the quantities of water draining back outside or reaching the framing, insulation and cladding. Where a wall underlay was present, it kept the frame and insulation dry, but 40%–80% of the water leak was either absorbed by the cladding or trapped between the underlay and cladding. A subset of walls with no underlay (not uncommon in older houses being retrofitted with insulation) was used to investigate different options for maintaining some drainage when insulation was retrofitted. In these walls, pans of wall underlay and drainage mats were found to keep a drainage path open and protected the insulation but were unable to prevent water reaching the frame. Drying rates from the back of the cladding were also measured and compared with evaporative drying rates calculated from climate information and infiltration behind the cladding. A companion article provides ventilation rate data measured using a tracer gas to calculate ventilation drying rates, which were found to contribute significantly more to water management in weatherboard walls than in walls with barrier-type sheet claddings. In fact, ventilation drying behind weatherboard claddings was found to be of a similar magnitude to previously measured drying rates in vented cavity walls.
This research examines the extent to which drainage and ventilation drying can remove water that has leaked through claddings on walls with no specific drainage cavity. In this study, tracer gas and zonal computer models were used to measure and predict air infiltration in the space between the wall underlay and the cladding and in the insulated spaces in 16 wall specimens. Half of the walls were clad with weatherboards direct fixed to the frame over a synthetic flexible wall underlay, and the remaining eight had ‘barrier’ or sheet claddings. A companion paper describes drainage and drying measurements in the same walls. Tracer gas measurements showed that average infiltration through weatherboard claddings (0.2 L/s) was much higher than behind sheet claddings (0.03 L/s). The range of day-average infiltration measured behind weatherboards (0.02–1 L/s) actually overlapped earlier measurements in bottom-vented cavity walls (0.1–2 L/s), and this is thought to partly explain the successful track record of direct-fixed weatherboard claddings in New Zealand. The airflow characteristics of leakage paths through claddings and at junctions between the timber frame, cladding, lining and underlay were also measured and used in a zonal model to calculate infiltration rates into the insulated spaces and behind the different claddings. There was acceptable agreement between measured and calculated infiltration, and this supports the next step of applying the computer models to whole buildings to better understand the heat and moisture consequences of air infiltration in New Zealand walls.
In this article, the condensation potential for a multiphase moisture sorption system is investigated. The moisture content of a porous material can be imagined as system state, moving through the hill-and-valley landscape of the potential. The condensation potential is determined in linear approximation from the general formula of Part I. Then, the potential is calculated in a unified manner for a broad range of physical moisture sorption mechanisms described in the literature: Van der Waals, capillary condensation, surface sorption, micropore sorption and chemisorption (diffusion–reaction). Non-hysteretic and hysteretic cases are considered. The condensation potentials are illustrated with examples.
A building shall be classified as high performance building if it is energy efficient and durable and at the same time provides comfortable and healthy indoor environment for occupants. To achieve this objective, the hygrothermal performance of alternative building designs should be evaluated based on the simultaneous analysis of these three functional requirements rather than separately. In this article, a Whole-Building Hygrothermal model is used for evaluation of various retrofit design parameters that potentially enhance the overall performance of an existing residential house. The retrofit options considered in this study include changes to the reference house’s ventilation rate and operation, windows, insulation level, and various combinations of these options. Energy efficiency, building envelope and moisture management potential, indoor humidity control, and window condensation potentials are considered to be the four performance indicators in searching for a retrofit option that delivers an optimal performance. The hygrothermal simulation results indicate that changing a design parameter to improve one of the design goals may result in less optimal results in the other one or both goals, or even in some cases result in severe negative consequences.
Infiltration heat recovery is the process that occurs when a building envelope acts as a heat exchanger for infiltrating air. This heat recovery process results in a reduced heat loss compared to predictions that use only flow rate and the total difference in enthalpy between inside and outside air. A series of experiments show the relationship between infiltration flow rate and heat loss in a test cell, with an emphasis on the high flow rate regime. A 3.5-m3 test cell was built with standard light-frame construction and one removable panel, to allow testing of wall sections with different engineered flow path lengths. Experiments were conducted with two different wall sections and at six different infiltration flow rates. Experimentally determined heat recovery factors are compared to computational fluid dynamics and agree to within approximately 15%.
The durability of vacuum insulating panels included in the cavity of insulating glass panels has been studied using a heat flow meter to monitor the thermal conductivity evolution upon accelerated aging. The study highlighted that, thanks to the high degree of protection of the inner cavity against moisture, the vacuum insulation panel maintains its thermal insulation performances even after 25 weeks of cycling from –20°C to 80°C and from 10% to 90% relative humidity. In comparison, unprotected vacuum insulation panels show a steady increase of thermal conductivity, which is setting them close to the end of their theoretical service lifetime. Comparing the slopes of the thermal conductivity evolution over time, the calculated degree of protection provided by such an assembly is superior to 10 in comparison to unprotected panels. This mode of protection could be useful to extend the lifetime of vacuum insulation panels in various building applications.
A method of determining the retro-reflectance of retro-reflective materials used for building coatings is proposed in this article. In addition, the durability of retro-reflective materials over long-term outdoor exposure is also estimated. Retro-reflective materials are currently limited to use in specific purposes, such as road traffic signs in Japan. To consider their application as a building coating, it is also necessary to examine the thermal performance and durability of retro-reflective materials. We proposed a method of determining the retro-reflectance of retro-reflective materials (capsule retro-reflective material and prism retro-reflective material were used in this experiment) by experiment. To explore the durability of retro-reflective materials over long-term outdoor exposure, we measured the changes in solar reflectance and retro-reflectance of retro-reflective materials exposed to the outdoors over about 25 months. The solar reflectance of capsule retro-reflective material decreased from 0.69 to 0.51 and that of prism retro-reflective material decreased from 0.83 to 0.81. The retro-reflectance of capsule retro-reflective material decreased from 0.18 to near 0 (0.0072) and that of prism retro-reflective material decreased from 0.44 to 0.42. At the end of the test period, we cleaned the surface of the retro-reflective materials. Both of the retro-reflective materials recovered about 50% of the lost solar reflectance by cleaning. The retro-reflectance of capsule retro-reflective material increased by about 0.08 (46% recovered) by cleaning and that of prism retro-reflective material increased by only 0.01 (with 50% recovered) by cleaning. We concluded that the durability of prism retro-reflective material is better than that of capsule retro-reflective material for use on building coatings.
Statistical analyses are important for real-world validation of theoretical model predictions. In this article, a statistical analysis of real data shows empirically how thermal resistance, thermal mass, building design, season and external air temperature collectively affect indoor air temperature. A simple, four-point, diurnal, temperature-by-time profile is used to summarise daily thermal performance and is used as the response variable for the analysis of performance. The findings from the statistical analysis imply that, at least for moderate climates, the best performing construction/design will be one in which insulation and thermal mass arrangements can be dynamically altered to suit weather and season.
As a consequence of the reduced transmission heat loss, algal growth on external thermal insulation composite systems has given rise to a serious aesthetical problem over the last decade. Manufacturers of paints and rendering systems are competing to increase the algal resistance of their products. The high time investment of free-weathering tests and the lack of objective measures to quantify the growth, however, prevent a systematic and efficient product advancement. Within a multiannual study, the application of fluorometric and numerical analysis was evaluated for assessing the algal resistance of external thermal insulation composite systems. The efficiency of pulse-amplitude modulation fluorometry for directly quantifying the algal biomass on the facade surface was analysed within three weathering tests which comprised 33 different external thermal insulation composite system specimens. The results show that the IMAGING-PAM (imaging pulse-amplitude modulation) fluorometer of the company Walz allows to measure the algal resistance in the course of the weathering process objectively and efficiently. The measurements confirm the effectiveness of biocides and indicate a higher algal resistance of the mineral rendering systems compared to the organic systems. The options and limitations of using numerical simulation for the assessment of the algal resistance of external thermal insulation composite systems were evaluated using the software WUFI® Pro 5.0 developed by the Fraunhofer Institute of Building Physics. Within selected parameter studies, an appropriate evaluation criterion was identified and the impact of varying material data and exterior boundary conditions was assessed. The integrated results emphasize the need to combine experimental and numerical analysis. The missing correspondence between the calculated and measured algal resistance for selected specimens of the weathering test is attributed to the simplifications inherent to the approximation of the hygric material functions and therefore emphasizes the need for further research.
Field monitorings of thermal performance of residential 2 x 6 wood-frame wall systems that had been retrofitted using vacuum insulation panels (VIPs) and extruded polystyrene foam (XPS) panels were undertaken in May 2011 – May 2012 at the Field Exposure of Walls Facility (FEWF) of NRC-Construction. The main objective of this research was to measure the steady-state and transient thermal performance of three wall assemblies (4 ft x 6 ft), two of which incorporated VIPs within an XPS Tongue and Groove (T&G) configuration and VIPs within an XPS Clip-On (C-O) configuration, and a third assembly incorporating only XPS. The three wall assemblies were installed in the FEWF for 1-year cycle of exposure to outdoor natural weather conditions. The hygIRC-C model was used in this study. The results of the model calculations were in good agreement with the experimental data. Given that the VIPs could be punctured during the installation process or could fail during normal operating conditions, additional model calculations were used to predict the thermal resistance in cases where one or more VIPs failed. The model was also used to predict the yearly cumulative heat losses across these wall systems. It is important to point out that the aging effect and the effect of the thermal bridging due to envelope (i.e. skin) of the VIPs are not accounted for in this study. However, sensitivity analysis of the thickness and thermal conductivity of the VIP envelope was conducted to investigate the effect of these parameters on the effective thermal resistance of VIP.
The moisture transfer effectiveness (or latent effectiveness) of a cross-flow, membrane-based energy recovery ventilator is measured and modeled. Analysis of in situ measurements for a full year shows that energy recovery ventilator latent effectiveness increases with increasing average relative humidity and surprisingly increases with decreasing average temperature. A simple finite difference heat and moisture transfer model is developed, which can explain these results and predict energy recovery ventilator latent effectiveness based on simplified physics and material properties. The model parameters are discussed and, in the case of the membrane’s moisture sorption curve and moisture permeability, compared to direct laboratory measurements.
Dwellings in Israel must include a residential protected room made of thick concrete slabs and walls, with an extremely airtight window and outward opening extremely airtight steel door. An inward opening regular door is applied for everyday usage. Being multipurpose, the residential protected room raised concern regarding long-term radon exposure. This article presents the stage of air change rate investigation (using SF6 as tracer gas) and radon monitoring in a multidisciplinary research performed by two teams. It comprised six residential protected rooms in a tall unoccupied building, including various scenarios of window and door closure. The teams established a common theoretical model and addressed sensitivity to differences in assumptions and methods of analysis. Similar orders of magnitude of air change rates and free surface exhalation rates were obtained, but with nonnegligible discrepancies between specific values. Tracer gas method results were more sensitive to calculation assumptions and radon monitoring results to measurement uncertainties. Measured air change rates were as follows: fully sealed residential protected room: <0.03 ACH (air changes per hour); closed window and regular door: <0.25 ACH; tilted window and closed door: 1–3 ACH; one component open and the other closed: 3–20 ACH; and both components somewhat open: 20–100 ACH. It was shown that expected maximal radon concentrations in a residential protected room under conditions of regular usage or emergency protection would not reach the limit value of 200 Bq/m3.
The need for efficient, sustainable, and planned utilization of resources is ever more critical. Several building energy analysis tools have been developed to assess energy demands and lifecycle energy costs in buildings. Such analyses are essential for an efficient heating, ventilation, and air conditioning design that overcomes the pitfalls of an under/over-designed system. Studies have estimated air infiltration accounts for up to 50% of a building’s energy demand. This stresses the need that energy simulation engines accurately account for air infiltration. An Enhanced Model for air infiltration has been developed.
Many of the current European Member States regulations on energy saving in buildings seem to follow North European trends that call for high insulation of the envelope. However, this kind of set-up overlooks some specific elements that are necessary to build typical buildings in warmer climates. Thermal inertia on the internal surface of the envelope has traditionally been used in such contexts not only to contain solar gains but also to protect against cold winter because of its capacity to store and to slowly release energy. This research investigates how thermal inertia on roof slabs could positively affect the comfort indoors, also in buildings that tend towards being nearly zero-energy buildings, as suggested by last European Directive 2010/31/EU. With this aim, an experiment was conducted on a full-scale building with different roofs, on light and heavy slabs, under hot and moderate climatic conditions (Ancona, Italy). The thermal performance of roofs was monitored during summer and winter seasons. In winter, the building was also subjected to cyclical internal heat gains. The experiment demonstrated that a certain thermal inertia in the slab guarantees better indoor comfort in both summer and winter, and it can also reduce energy consumption from heating.
This work applies a new model that treats solar and longwave radiative transfer, thermal conduction, and sensible heat transport to quantify the flow of energy across single- and double-pane windows. A set of radiometers based in Chicago, Illinois, observed solar and longwave irradiances incident on and emerging from a window on a low-rise building. The incoming radiation fields, averaged over a 10-day period in January, drive the energy budget calculations, while a comparison of measured and computed outgoing irradiances validates the results. The indoor–outdoor temperature contrast creates a gradient in longwave radiative heating across the glass. This drives a heat flux that increases sensible heat flow to the exterior atmosphere by approximately a factor of 3 over what would exist without thermal radiation. Absorption of sunlight by the glass also increases energy lost to the atmosphere. For the conditions analyzed, approximately 40% of the solar energy absorbed by the window-plus-interior system is returned to the exterior as sensible heat and longwave radiation. The remaining absorbed solar energy offsets the demand for heating from the climate-control system.
This article develops a thermodynamic description of hysteretic behaviour of moisture in materials. The moisture sorption is described by a ‘condensation potential’ using a ‘pore interaction energy’ that is considered as an attribute of the condensate. Surface subsystems, (liquid–solid) and (liquid–gaseous), are not needed. In conformity with the classical domain theory, hysteretic effects can be explained as metastable states of the condensation potential (static, time-independent hysteresis) or as unstable states (dynamic, time-dependent hysteresis). The hysteretic extension of the standard heat, air and moisture transport model is derived in an easy and efficient way using a combined-phase thermodynamic approach. This article comprises three parts. First, the general thermodynamic description is given, and later, the condensation potential will be calculated for many different physical sorption mechanisms.
The objective of this study is to examine the reduction in heating and cooling loads that may be attributed to the use of attic radiant barrier and to identify environmental parameters that influence this reduction. To this end, an experimental study was conducted in Zachary, Louisiana for 8 months on two houses built in the same manner and instrumented with thermocouples to measure the temperature in each hour and each layer of the roof. Results showed that an attic radiant barrier can reduce energy loads from 8% to 25% depending on the climatic conditions. Among the evaluated climatic parameters, ambient air temperature had the greatest effect on the ceiling heat flux.
The thermal performance of a modular lightweight steel framed wall was measured and calculated with three-dimensional finite element method model. The focus of this article is on the effect of flanking thermal losses. The calculated heat flux values varied from –22% (external surface) to +50% (internal surface) when flanking loss was set to 0 as a reference case, thermal transmittance equal to 0.30 W/(m2·K). Other critical parameters were the existence of fixing ‘L’-shaped steel elements and the perimeter thermal insulation (10 cm XPS).
A prototype model of modified active greenhouse dryer has been designed, developed, and tested in no-load conditions at the Maulana Azad National Institute of Technology, Bhopal, India. The proposed dryer has been tested under two conditions: (1) with covered inside floor and (2) with uncovered floor. This study revealed that the covered floor condition of the greenhouse is favorable for drying due to higher raise in greenhouse temperature and decrease in its relative humidity.
The incorporation of phase change materials in movable structural cells of shading elements associated with southward-facade windows is evaluated in this article. The proposed phase change material–shutter is a thermal energy storage system designed to take advantage of solar energy for winter nighttime indoor heating. A two-dimensional phase-change heat diffusion model based on the enthalpy formulation was considered. The numerical model follows the finite-volume method with a fully implicit formulation and allows the alternating melting and solidification of a phase change material submitted to cyclical thermal boundary conditions. Parametric investigations were carried out about the effects of thermophysical properties of the phase change material and temperature and convection heat transfer boundary conditions on the charge/discharge rates of energy. Due to the low thermal diffusivity of the phase change material, an aluminum fin arrangement was considered as a heat transfer enhancement technique. The distance between fins is directly proportional to the daily energy storage/release capacity of the system. The solar radiation flux has a strong effect on the charging/melting processes during the day. The indoor temperature and the interior convection heat transfer coefficient have a major influence on the discharging/freezing processes during the night. The design of the phase change material–shutter depends strongly on the thermophysical properties of the phase change material and on the interior and exterior boundary conditions considered.
A new probabilistic model for the assessment of mould growth in buildings has been elaborated within interdisciplinary – building physics/structural engineering – cooperation. Both the occurrences of favourable conditions for the growth of mould fungi and their durations are taken into account. The probabilistic approach can be characterised as time dependent based on the theory of stochastic processes. The resulting probability of occurrence of mould growth cycles having deteriorating potential suggests itself as a measure of the mould growth hazard. By the measure, the management of building performance with respect to mould growth hazard may be conceived. The calculations of an illustrative example show that the variability of the outdoor climate conditions can substantially influence the occurrences and durations of favourable conditions for mould growth.
Reliable methods are needed for classifying the robustness of buildings and building materials for many reasons, including ensuring that constructions can withstand the climate conditions resulting from global warming, which might be more severe than was assumed in an existing building’s design. Evaluating the robustness of buildings is also important for reducing process-induced building defects. We describe and demonstrate a flexible framework for classifying the robustness of building materials, building assemblies, and whole buildings that incorporates climate and service life considerations.
Materials with high moisture exchange capacity may have a strong impact on indoor climate conditions as well as building energy performance. Crop-based materials, characterized by their high porosity and hygroscopicity, belong to this category. Modeling their hygrothermal behavior accurately is thus particularly relevant for appropriate building design. A COMSOL Multiphysics transient heat air and moisture model is developed in this article to simulate moisture exchange between a lime–hemp concrete block and surrounding air during a Moisture Buffer Value evaluation test. Results are then compared with the validated heat air and moisture software using performance criteria showing a slight preference for both moisture exchanges and latent heat effect characterization. It offers yet additional advantages in terms of flexibility and transparency as well as further evolution potential.
In warm climates, internally applied phase change materials may substitute insufficient thermal mass in lightweight constructions. A simplified model was developed for devising initial-design data for phase change material products applied on the inner surface of walls. The model enabled estimating the thickness of the phase change material layer that can be fully discharged via night ventilation and, for a given product thickness, the total area required for storing the internal heat gains occurring during the day. Thermal and energy performance of three building types in the Mediterranean climate was further analysed using the dynamic program EnergyPlus. Results showed that intensive night ventilation is essential for discharging daily stored energy. During the hottest period, only a thin layer of several millimetres can be fully discharged overnight. Minimal thicknesses were very effective in reducing cooling energy demand in lightweight offices but much less effective in semi-lightweight classrooms. Increased phase change material thickness increased energy savings, and by reducing surface temperatures during occupancy periods, improved thermal comfort. In heavyweight construction, phase change material improved thermal comfort but not energy performance.
External thermal insulation composite systems are, nowadays, quite common in European buildings, used both in new constructions and refurbishment. Unfortunately, external thermal insulation composite systems can have serious problems of biological growth causing the cladding defacement. Studies carried out in recent years allowed understanding the hygrothermal behaviour of external thermal insulation composite systems. It is known that biological growth is due to high values of surface moisture content, which depends mostly on exterior surface condensation. Despite this existing knowledge, there is little information available about the influence of obstacles near the façade on condensation and surface moisture content. In this article, the results of a field test campaign to assess the influence of obstacles on surface condensation are presented. They show that nearby obstacles influence exterior surface temperature during the night and, consequently, surface condensation. Different obstacle configurations have different effects, which may lead to stained patterns on the façade due to differential biological growth rates. The effect of nearby obstacles on exterior surface condensation, revealed during the test campaign, addressed the development of a numerical routine to simulate their influence. This routine can be used with any existing hygrothermal model with the ability to simulate explicitly the radiative balance on the exterior surface. It calculates the increase in long-wave radiation due to the obstacle as a function of its geometry and emissivity of its surface. This extra amount of radiation is added to the atmospheric radiation that is an input of the hygrothermal models. The validation of this routine was performed by comparing simulated and experimental results. An example of the practical use of this routine is also presented in this article, with the calculation of the exterior surface condensation on different façades covered with external thermal insulation composite systems, with and without nearby obstacles, and its comparison with the coating defacement that they actually present.
A model has been designed to dynamically analyze and optimize energy consumption in building as integrated in Iran and other countries. This model can cover all characteristics and potentials of different types of building energy models and improve their weaknesses. The first part of this article discusses the capabilities and equations dominating the designed model. It also compares the strengths and weaknesses of the model with those of the existing models considering their historical literature. In this article, the application of the designed model for a XYZ case study building located at north of Tehran has been evaluated. Aiming at verification of the model, the outcomes were compared with the actual data for a 10-story high rise in 2011, and accuracy of the data was then verified by statistical standards. Finally, the typical optimized integrated multienergy systems model for the residential high rise was adopted after fulfilling the energy optimization phases. Using this model, with the initial investment cost of US$751,867 allotted to optimization, payback period of 6.1 years, and adjusted internal rate of return equal to 20.6%, energy consumption saving of nearly 60% can be achieved during 2011.
Deep basements, crawl spaces and slab on grade are typical foundations in residential buildings in North America. The foundation of a house is a somewhat invisible and at sometimes ignored component of the building. Appropriate foundation design and construction practice must not only include thermal performance, but also design for a durable and safe hygrothermal performance.
A hygrothermal simulation tool can be used to evaluate and predict the hygrothermal behavior of an insulated foundation constructions, in cooperation with the surrounding soil. Though, further development of the tool might first be needed and validated to fulfill the prerequisites. Transient hygrothermal simulation tools have existed in Building Science for more than 20 years, but are mainly used for building envelope simulation above ground. A lot of knowledge already exists in Soil Science concerning the variation of the soil material properties in relation to soil texture, moisture content etc. However, Soil Science uses these properties for other purpose and with different modeling approaches, hence a conversion is needed.
This paper studies the existing knowledge of soil pr perties, converted to apply for simulation in Building Science. Further, the soil properties are implemented in a transient hygrothermal simulation tool, studying the applicability for modeling soil temperature and moisture flow. Finally the results are compared with measurement and followed by a discussion of further investigations and development needed.
This study is focused to airflow and heat transfer analyses in an air-cooled room. Three-dimensional numerical results of a rectangular room considering three different inlet configurations are presented. The study was carried out considering turbulent flow and the radiative exchange between the walls. A vertical wall receives a constant heat flux, and the opposite wall is maintained at a uniform and constant temperature; the remaining walls are adiabatic. The air inlet velocity was 0.5 m/s and the emissivity of the walls was considered as 0.8. The mathematical model was solved numerically with Computational Fluid Dynamics software. The temperature fields, flow patterns, heat transfer coefficients, and temperature distribution effectiveness are presented and discussed. It was found that the heat transfer due to the radiative effect is around 50% for the three cases studied; besides, the heat transfer coefficients and temperature distribution effectiveness are highly dependent on the inlet position.
The objective of this study was to evaluate the effectiveness of three different methods to apply closed-cell polyurethane foam to single-wythe concrete masonry wall panels, namely, surface spray-on, filled formwork, and grouting the cores of the concrete blocks. Foams with two densities were applied at three different thicknesses. Two-dimensional heat flow simulations were conducted using THERM to determine the overall thermal resistance of the insulated masonry wall panels. Filled formwork application using normal-density foam yielded the highest thermal resistance. Hygrothermal analysis using WUFI Plus revealed that exterior application of the foam is preferred to avoid durability issues and take advantage of the thermal mass and fire resistance of masonry walls.
There is a strong need to prevent the heat island effect. One of the important countermeasures to the heat island effect is to reduce thermal storage in buildings. The highly reflective material on outer walls and roofs is a significant way to prevent heat from penetrating indoors; such materials have been installed on the surface of buildings in Osaka, Japan. To evaluate the solar reflectance of such highly reflective material, we measured the solar reflectance of reflective roofing sheets installed on the building roofs in Osaka, Japan, over a span of time from February 2010 until September 2011, and examined the change in solar reflectance during this time.
The major purpose of this study is to improve hygrothermal simulation of wood responses to environmental vapor and moisture conditions under high relative humidity conditions. The article first reviews moisture property–related wood microstructures, sorption behavior, the concept of fiber saturation point, the potential for vapor to condense in wood under high relative humidity conditions, the measurement of equilibrium moisture content using traditional sorption methods, and the use of pressure plate test method at relative humidities above 95%. It then summarizes the results of equilibrium moisture content measurements for red pine sapwood at high relative humidity conditions using both sorption and pressure plate methods, with capillary saturation as maximum moisture content. It also discusses a number of wood microstructure and end-use-related factors that could influence the moisture content in service and the measurement of equilibrium moisture content in laboratory. Inconsistencies were found with other equilibrium moisture content data using the pressure plate test method.