Simulation of the Hygrothermal Behavior of a Building Envelope Based on Phase Change Materials and a Bio-Based Concrete

Phase Change Materials(PCMs)have high thermal inertia,and hemp concrete(HC),a bio-based concrete,has strong hygroscopic behavior.In previous studies,PCM has been extensively combined with many materials,however,most of these studies focused on thermal properties while neglecting hygroscopic aspects.In this study,the two materials have been combined into a building envelope and the related hygrothermal properties have been studied.In particular,numerical studies have been performed to investigate the temperature and relative humidity behavior inside the HC,and the effect of adding PCM on the hygrothermal behavior of the HC.The results show that there is a high coupling between temperature and relative humidity inside the HC,since the relative humidity changes on the second and third days are different,with values of 8%and 4%,respectively.Also,the variation of relative humidity with temperature indicates the dominant influence of temperature on relative humidity variation.With the presence of PCM,the temperature variation inside the HC is damped due to the high thermal inertia of the PCM,which also leads to suppression of moisture evaporation and thus damping of relative humidity variation.On the second and third days,the temperature changes at the central position are reduced by 4.6%and 5.1%,compared to the quarter position.For the relative humidity change,the reductions are 5.3%and 5.4%on the second and third days,respectively.Therefore,PCM,with high thermal inertia,acts as a temperature damper and has the potential to increase the moisture buffering capacity inside the HC.This makes it possible for such a combined envelope to have both thermal and hygric inertia.

Performance Assessment of the Overall Building Envelope Thermal Performance-Building Envelope Performance(BEP)Metric

Today,to describe the thermal performance of the building envelope and its components we use a variation of metrics;such as,R-value,ACH(air exchange rate per hour),SHGC(solar heat gain coefficient)of windows,U-factor etc.None of these performance indicators is meant to represent the overall thermal performance.In this paper,such a metric is introduced,the BEP(building envelope performance)value.Unlike the thermal resistance,typically expressed as an R-value,the BEP-value considers additional elements of heat transfer that affect the energy demand of the building because of exterior and interior(solar)thermal loads:conductive and radiant heat transfer,and air infiltration.To demonstrate BEP’s utility,validation studies were carried out by comparing the BEP-value to theoretical results using whole building energy simulation tools such as EnergyPlus and WUFI Plus.Results show that BEP calculations are comparable to calculations made using these simulation tools and that unlike other similar metrics,the BEP-value accounts for all heat transfer mechanisms that are relevant for the overall energy performance of the building envelope.The BEP-value thus allows comparing envelopes of buildings with different use types in a fair and realistic manner.

Preliminary Study to Show the Effect of Building Envelope Materials on Thermal Comfort of Buildings Located in Hot Humid Climate

The main aim of this paper is to study the effect of building envelope constructed with different materials on thermal comfort of buildings located in Jeddah, Saudi Arabia. Four different buildings constructed with brick, glass, stone, and gypsum are taken into account to study the difference in temperature of the indoor and outdoor environments. Also, this paper explores the heat conducted by walls of different materials with different thicknesses. In addition, survey is conducted among the residents of Jeddah to know their perspective about thermal comfort of buildings. From the study, it is found that building envelope constructed with glass is more effective compared to envelope constructed with other materials of with least thickness of wall. Also, it is found that the envelope constructed with brick is more effective in absorbing the heat provided the thickness of the walls remains the same.

Analysis of Thermal Behavior of Materials in the Building Envelope Using Building Information Modeling (BIM)—A Case Study Approach

Building envelope is a fence that controls heat exchange between interior and exterior and plays an essential role in providing thermal comfort conditions of residents. In recent years, due to the necessity of conserving energy and also preventing increased environmental pollution, the importance of sustainable construction has been doubled. Checking the problems of thermal behavior of the building envelope materials, and what influences in the heating and cooling loads exerted and energy consumption of buildings, are the questions that this research seeks to answer. In this regard, building information modelling analysis (BIM) has worthy contribution in the completion process of sustainable design;thus using software Design Builder, it is paid attention to simulation of the thermal behavior of two types of defined materials for the building envelope that was designed as a Research Institute of Renewable Energy of Yazd University. For Type 1 materials, two layers of brick have been selected, and for Type 2 a thermal insulation layer also added it. Results of the analysis showed that the use of materials Type 2 in the cooling load %4.8 and in the thermal load %62.5 reduction can be achieved which means reducing the load on active system and thus reducing the initial cost of building. Also reduction in annual energy consumption by almost %2.4 for cooling and %62.9 for heating buildings have been achieved, which makes saving non-renewable energy consumption, and consequently reducing environmental pollution as well as reducing current costs will be established.

Dynamic thermal performance and energy-saving potential analysis of a modular pipe-embedded building envelope integrated with thermal diffusive materials

In the context of racing to carbon neutrality,the pipe-embedded building system makes the opaque envelopes gradually regarded as the multi-functional element,which also provides an opportunity for thermal insulation solutions to transform from high to zero-carbon attributes.Based on the re-examination of the heat transfer process of conventional pipe-embedded radiant(CPR)walls,the modular pipe-embedded radiant(MPR)wall integrated with thermal diffusive materials is proposed to enhance the heat transfer capacity of CPR walls in the direction parallel to the wall surface,thereby forming a more stable and continuous invisible thermal barrier layer inside the opaque envelopes.A comprehensive thermal and energy-saving analysis study regarding the influence mechanism of several key factors of MPR walls,e.g.,the inclination angle of the filler cavity(θ-value),geometry size of the filler cavity(a:b-value)and thermal conductivity of the filler(λf-value),is conducted based on a validated numerical model.Results show that the dynamic thermal behaviors of MPR walls can be significantly improved due to that the radial thermal resistance in the filler cavity of MPR walls can be reduced by 50%,while the maximum extra exterior surface heat loss caused by the optimization measures is only 2.1%.Besides,a better technical effect can be achieved by setting the major axis of the filler cavity towards the room side,where the interior surface heat load/total injected heat first decreases/increases and then increases/decreases with the increase of theθ-value.In particular,the MPR wall withθL=60°can obtain the best performance when other conditions remain the same.Moreover,the performance indicators of MPR walls can be further improved with the increase of the cavity size(a:b-value),while showing a trend of rapid improvement in theλf-value range of 2–5λC and slow improvement increase in theλf-value range of 5–12λC.In addition,the improvement effect brought by optimizing theθ-value is more obvious as the a:b-value orλf-value increases.

Investigation the Correlation between Thermal Bridging and Geometries in Concrete Buildings

This article focuses on the investigation of the correlation between thermal bridging and various geometric configurations. The article employs QuickField software for conducting three-dimensional steady-state heat transfer simulations to investigate the thermal behaviors of diverse geometric shapes. Significantly, this study involves the simulation of four distinct geometries including concrete circular, square, rectangular, and triangular column through an insulated concrete layer while all geometries maintain the consistent surface areas. The simulations yield findings indicating that circular thermal bridging has the best thermal performance, while rectangular thermal bridging displays comparatively the lowest thermal efficiency. Furthermore, the results indicate that alterations in the perimeter of thermal bridge interfaces, while maintaining a constant area, exert a more pronounced influence on the thermal performance of the geometries compared to proportional changes in area while preserving the perimeter. The study’s findings aid building designers and architects in creating more energy-efficient structural and architectural elements by incorporating thermally efficient geometries and forms. .

A Theory on Increasing the Heat Transfer Performance of Building Wall

The target of traditional thermal conductivity of wall research is the spatial distribution form.In these studies,the change of thermal conductivity with temperature is neglected.Meanwhile,case studies are always used.This method needs large computation and it is hard to obtain the optimal result.In order to overcome the problems,a new approach has been put forward in this paper.Different from the traditional approach,the new approach solves an inverse prob­lem under the concept of passive ideal energy-saving buildings to obtain the optimal distribution of heat ability with temperature on an external wall.The result for a typical summer day shows the heat ability distribution of a wall in summer is a staircase.It is similar to the heat pipe.It is also found that the optimal heat transfer property of the exter­nal wall is closer to the heat pipe when its heat capacity per square meter(ρc_(p)L)is of extreme value.This study can provide guidance to researchers in building materials.

Future of Architecture: Buildings as Power Plants

After the energy crisis in 1970s,buildings began to be used as a platform for the elements which produce energy from renewable energies to return them into energy producing power plants.This is a safe,clean and economic way to produce energy since the energy is produced where it is needed and they use renewable energy resources.So,it promises hope for the future energy production.Therefore,the aim of this study is to examine buildings which produce electricity by using renewable energy resources and to show that this is one of the safest,cleanest and most economic ways to be used to produce energy in the future.This is done by describing power plants and how buildings are used as power producing stations by the use of renewable energy resources or other energy producing materials,then by examining case studies which are constructed and already being used,case studies which are just a design that have not yet been constructed,and by making projections to the future energy producing techniques that are just a proposal in 2021.In the conclusion,buildings are proposed as the future power plants,either here on earth or on another planet like Mars.

Comparative Experimental Study on Heat Transfer Characteristics of Building Exterior Surface at High and Low Altitudes

The external surface heat transfer coefficient of building envelope is one of the important parameters necessary for building energy saving design,but the basic data in high-altitude area are scarce.Therefore,the authors propose a modified measurement method based on the heat balance of a model building,and use the same model building to measure its external surface heat transfer coefficient under outdoor conditions in Chengdu city,China at an altitude of 520 m and Daocheng city at an altitude of 3750 m respectively.The results show that the total heat transfer coefficient(h_(t))of building surface in high-altitude area is reduced by 34.48%.The influence of outdoor wind speed on the convective heat transfer coefficient(h_(c))in high-altitude area is not as significant as that in low-altitude area.The fitting relation between convection heat transfer coefficient and outdoor wind speed is also obtained.Under the same heating power,the average temperature rise of indoor and outdoor air at highaltitude is 41.9%higher than that at low altitude,and the average temperature rise of inner wall is 25.8%higher than that at low altitude.It shows that high-altitude area can create a more comfortable indoor thermal environment than low-altitude area under the same energy consumption condition.It is not appropriate to use the heat transfer characteristics of the exterior surface of buildings in low-altitude area for building energy saving design and related heating equipment selection and system terminal matching design in high-altitude area.

nfluence of envelope insulation materials on building energy consumption

In this paper, the influence of different external wall insulation materials on the energy consumption of a newly built apartment in Germany is investigated. Three types of insulation materials commonly used in Germany including mineral fiber, polyurethane, and vacuum insula- tion panel are chosen for the case studies. An energy analysis model is established to clarify the primary energy use for production of the insulation materials and for building space heating. The calculation results show that the energy consumption for insulation material production increases with the insulation thickness, whereas the energy use for space heating decreases with the insulation thickness. Thus, there exists an optimum thickness to get the lowest total energy consumption for each kind of insulation material. The ascending order of the total energy consumption of the three materials is mineral fiber, polyurethane, and vacuum insulation panel. However, the optimum insulation thicknesses for the three insulation materials show a verse order at a certain heat transfer coefficient of the base envelope. The energy payback time （EPT） is proposed to calculate the payback time of the primary energy use for insulation material production. Mineral fiber has the shortest time, followed by poly- urethane and vacuum insulation panel. The EPTS is 10, 19 and 21 years, respectively when the heat transfer coefficient of the base envelope is 0.2 W/（m2.K）. In addition, the simulated results show that the theoretical value and the simulated value are basically identical.

Microstructure and Characterization of Capric-stearic Acid/Modified Expanded Vermiculite Thermal Storage Composites

In order to improve the thermal storage capacity of expanded vermiculite（EV） based formstable composite PCM（FS-PCM） via organic modification of EV, first, EV was modified with a sodium stearate（Na St） as surface modifier, and organic EV（OEV） with hydrophobicity and higher adsorption capacity for fatty acid was obtained. A novel capric-stearic acid eutectic（CA-SA）/OEV FS-PCM with high thermal storage capacity was then developed. OEV and CA-SA/OEV were characterized by scanning electron microscopy（SEM）, X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, differential scanning calorimetry（DSC）, thermal gravimetry（TG）, and thermal cycling test. Results showed that OEV has obvious hydrophobicity and a higher adsorption capacity for fatty acid. Its adsorption ratio has increased by 48.71% compared with that of EV. CA-SA/OEV possesses high thermal storage density（112.52 J/g）, suitable melting temperature（20.49 ℃）, good chemical compatibility, excellent thermal stability and reliability, indicating great application potential for building energy efficiency. Moreover, organic modification of inorganic matrix may offer novel options for improving its adsorption capacity for organic PCMs and increasing heat storage capacity of corresponding FS-PCMs.

A review and prospect on research progress of adjustable transparent envelope

Considered as the best light source so far,daylight has attracted continuing attention in indoor environment design area.Successful daylighting design could reduce considerable amount of building energy consumption,while retain a satisfactory occupant comfort and working efficiency.Transparent building envelope takes a dominant position in daylighting design as well as solar radiation heat gain,thus attracts attentions from all over the world.Unable to respond to dynamic outdoor environmental parameters,conventional transparent envelope cannot adapt to the continuous development of green building performance requirements,thus the adjustable transparent envelope technologies have become the research focus.In this paper,recent progress on adjustable transparent envelope technologies was collected and analyzed.Their detailed working principle as well as application scope were classified and discussed.Result indicates that existing studies mainly focus on the development of material and equipment.In the aspect of comprehensive application optimization design and control strategy development,the research gap still exists.

Potentials of an Eco-Friendly Composite in Hot-Dry Climate

This study aims to show the aptitude of a locally made composite for providing thermal comfort and mechanical resistance in buildings in hot-dry climates.The thermal characterization reveals that the thermal diffusivity of the studied material is lower than that of commonly used materials such as agglomerated and full cinderblocks and laterite blocks and therefore is a better insulating material.In addition,its thermal inertia is the highest compared to commonly used materials of agglomerated and full cinderblocks,laterite blocks and compressed earth blocks,which implies a longer time lag.On the basis of mechanical resistance,with a compression resistance of 3.61 MPa,the studied material meets the requirement of CRATerre and NBF 02-003(2009)as a material for construction of single-storey buildings.Therefore,this material,containing 1%Hibiscus sabdariffa fibers and compacted by vibration,is a suitable material for the walls of standing buildings and for thermal comfort in hot dry climates.

Simulation Study on the New Average Heat Flux Method to Determine U-Value of a Wall

The U-value is a very important parameter for evaluating the energy efficiency when refurbishing the existing buildings.Traditional in-situ test methods to determine the U-value usually require a very long time to filter weather fluctuations and other boundary condition influences.In this paper,the possibility of a new method to reduce the time necessitated for measuring the accurate U-value of a wall is tested.The proposed method recommends measuring the temperatures and heat flux on both sides of the wall and thereby utilising the average values of the internal and external heat flux to calculate the U-value.Under the idealised sinusoidal internal and external air temperature boundary conditions,four walls with different U-values were simulated according to the admittance procedure(AP).Results show that the proposed method could improve the maximum error level for most of the walls in consideration.It was not sensitive to the measurement start time and it was more stable even in less controlled boundary conditions involving large inner temperature variations or out of phase temperature waves.Besides,the error of the average heat flux method(within 10%)could be estimated earlier than that of traditional method.

A Comparative Study of the Thermal Performance of Plastic Bottle Wall against Traditional Composite Brick Wall Typologies

According to the container recycling institute,nearly a million plastic beverage bottles are sold every minute around the world.Plastic bottles are considered as an urban junk,however,it has shape characteristics which make them usable in construction in lieu of conventional bricks.This research promotes the use of recycled plastic bottles as eco-bricks by substituting it with the typical construction bricks.It evaluates the thermal performance of sand filled plastic bottle-walls in a comparative analysis with traditional composite brick walls.The thermal performance of the plastic bottle walls was evaluated through COMSOL®Multi-physics and the results are noted.

Development of a short duration method to assess the envelope thermal performance of multi-family housings

Building energy efficiency is a key factor in reducing CO_(2) emissions.For this reason,European Union(EU)member states have developed thermal regulations to ensure building thermal performance.These results are often based on results achieved with building simulation software during the design stage.However,the actual thermal performance can deviate significantly from the predicted one,and this difference is known as the energy performance gap.Accurate indicators of the actual thermal performance are a valuable tool to guarantee building quality.These indicators,including the heat transfer coefficient(HTC)and the heat loss coefficient(HLC),can be estimated by the application of in situ methods.As multi-family housing and tertiary sector buildings are an important part of the building stock,mature methods to measure their thermal performance are needed.This paper presents a short-duration method for assessing the HTC in large building typologies using a sampling approach.The method was applied in a four-storey building model under different conditions to study the limits of the method and to improve indicator bias and uncertainty.Indicator quality was strongly influenced by the external weather conditions,the temperature variation during the protocol and the heat exchange with the adjacent apartments.Under winter conditions and with stable indoor temperatures,the method had a high accuracy when the protocol was applied for half a day.It is recommended that the protocol be used over two days to improve indicator quality under less favorable test conditions.

Simulation of thermal and humid environment of rural residence envelope inner surface during the plum rains season in Changsha China

The Plum Rains Season(PRS)has the typical characteristics of outdoor air temperature dramatic changes and high air humidity in the hot summer and cold winter region in China.Even if the indoor heat source and moisture production is constant,when the outdoor air temperature rises rapidly during high air humidity PRS,the build-ing envelope temperature heats up much more slower than the indoor air temperature and therefore the wall surface temperature is lower than the indoor air dewpoint which leads to condensation phenomenon,resulting in deterioration of insulation performance,mouldy walls,deterioration of indoor air quality.At present,there is a lack of research on the factors affecting condensation in rural residence during PRS.This paper evaluates the impact of occupants’habit of window opening modes and building construction parameters on the building envelope surface condensation in Changsha during PRS.Using Designer’Simulation Toolkit(DeST)simulated and analysed the impact of key parameters such as window-to-wall ratio,exterior wall reflectivity,window opening mode(open/close),and external wall insulation on the building indoor thermal and humid environment.The condensation risk X is proposed to evaluate the condensation possibility on the building envelope’s inner sur-face.The results show that from the perspective of anti-condensation:The rural residential building in Changsha should balance the window-wall ratio against better natural lighting;Keeping windows closed during PRS can effectively alleviate the condensation problem while the insulation in the external wall layer could aggravate the condensation.

Comprehensive energy, economic, environmental assessment of a building integrated photovoltaic-thermoelectric system with battery storage for net zero energy building

To realize the goal of net zero energy building(NZEB),the integration of renewable energy and novel design of buildings is needed.The paths of energy demand reduction and additional energy supply with renewables are separated.In this study,those two are merged into one integration.The concept is based on the combination of photovoltaic,thermoelectric modules,energy storage and control algorithms.Five types of building envelope systems,namely PV+TE(S1),Grid+TE(S2),PV+Grid+TE(S3),PV+Battery+TE(S4)and PV+Grid+Battery+TE(S5)are studied,from aspects of energy,economic and environmental(E3)performance.The new envelope systems can achieve thermal load reduction while providing additional cooling/heating supply,which can promote advance of NZEBs.It is found that there is a typical optimum setting of thermal energy load for each one of them with minimum annual power consumption.Except for the S1 system,the rest can realize negative accumulated power consumption in a year-round operation,which means the thermal load of building envelope could be zero.The uniform annual cost for S1 to S5 under interest rate of 0.04 are 19.78,14.77,23.83,60.53,64.94$/m2,respectively.The S5 system has the highest environmental effect with 3.04 t/m2 reduction of CO_(2) over 30 years of operation.

Comparison of space cooling/heating load under non-uniform indoor environment with convective heat gain/loss from envelope

The indoor parameters are generally non-uniform distributed.Consequently,it is important to study the space cooling/heating load oriented to local requirements.Though the influence of indoor set point,heat sources,and ambient temperature of convective thermal boundary on cooling/heating load has been investigated in the uniform environment in previous research,the influence of these factors,particularly the convective heat gain/loss through a building envelope,on cooling/heating load of non-uniform environment has not yet been investigated.Therefore,based on the explicit expression of indoor temperature under the convective boundary condition,the expression of space cooling/heating load with convective heat transfer from the building envelope is derived and compared through case studies.The results can be summarized as follows.(1)The convective heat transferred through the building envelope is significantly related to the airflow patterns:the heating load in the case with ceiling supply air,where the supply air has a smaller contribution to the local zone,is 24%higher than that in the case with bottom supply air.(2)The degree of influence from each thermal boundary to the local zone of space cooling cases is close to that of a uniform environment,while the influence of each factor,particularly that of supply air,is non-uniformly distributed in space heating.(3)It is possible to enhance the influence of supply air and heat source with a reasonable airflow pattern to reduce the space heating load.In general,the findings of this study can be used to guide the energy savings of rooms with non-uniform environments for space cooling/heating.

Multiple regression models for energy consumption of office buildings in different climates in China

The energy consumption of office buildings in China has been growing significantly in recent years. Obviously, there are significant relationships between building envelope and the energy consumption of office buildings. The 8 key building envelope influencing factors were found in this paper to evaluate their effects on the energy consumption of the air-conditioning system. The typical combinations of the key influencing factors were performed in Trnsy simulation. Then on the basis of the simulated results, the multiple regression models were developed respectively for the four climates of China--hot summer and warm winter, hot summer and cold winter, cold, and severely cold. According to the analysis of regression coefficients, the appropriate building envelope design schemes were discussed in different climates. At last, the regression model evaluations consisting of the simulation evaluations and the actual case evaluations were performed to verify the feasibility and accuracy of the regression models. The error rates are within i5% in the simulation evaluations and within ＋ 15% in the actual case evaluations. It is believed that the regression models developed in this paper can be used to estimate the energy consumption of office buildings in different climates when various building envelope designs are considered.