Thermal Performance Of Buildings Research Articles

Thermal effects of dew on cool roofs and conventional roofs in building performance simulations

This paper presents a numerical investigation of dew formation on the roofs of buildings, and its influence on building thermal and energy performance. A new semi-analytical model was developed to evaluate the effects of rooftop dew, including the release/absorption of latent heat due to condensation/evaporation, the variation of apparent thermal emittance of the roof upper surface, and the dew runoff characterised based on laboratory experiments. A set of case study simulations was carried out by implementing the rooftop dew model in the building performance simulation (BPS) software EnergyPlus. Through its impact on roof top surface temperature, dew was found to significantly influence predictions of benefits and penalties of a ‘cool roof’ versus a bare metal roof. When dew effects were neglected in the simulations, the electricity savings attributed to the cool roof were over-predicted by between 39 % and 204 %, however, the gas heating ‘penalty’ of using a cool roof was over-predicted by 266 % to 362 %. Results from this study demonstrate that the thermal effects of dew on roofs can be important in BPS studies, and the model that is presented provides a relatively simple means by which to include such effects in simulations.

A multi-aspect approach to energy retrofitting under global warming: A case of a multi-apartment building in Montenegro

Global warming will seriously affect buildings, and the Montenegrin building stock is no exception. Since the country is one of the most inefficient energy users in Europe, improving the energy efficiency of buildings is essential. Therefore, the study implemented a novel multi-aspect approach to energy retrofitting, linking building thermal performance, occupant interaction and climate change. A representative existing multi-apartment building in Podgorica was selected, and a survey among occupants was conducted to identify their satisfaction with indoor thermal comfort and to evaluate the acceptability of the proposed energy retrofit measures. Next, the thermal performance of the building was simulated under current and future climate conditions. Finally, a comprehensive parametric analysis was performed by applying different retrofit scenarios. The selected retrofit measures were evaluated based on their impact on energy efficiency and occupant acceptability. The results showed that the most impactful retrofit measure would be thermally insulating the building envelope, followed by a lower shading set-point and natural ventilation cooling. Applying the best retrofit combinations would reduce the total energy demand by 75% under the current climate and by 66% and 59% at the end of the 21st century under the RCP4.5 or RCP8.5 scenarios, respectively. However, the occupant survey results disclosed that beyond thermally insulating the building, occupants have limited awareness about the potential of energy retrofit actions, while summer thermal discomfort is the dominant issue. Therefore, building energy retrofit and climate adaptability actions should also address occupant views.

Weather-based operation strategy for a dynamically compartmentalized double-skin façade system

This study proposed a weather-based operation strategy for a dynamically compartmentalized double-skin façade (DSF) system. The system features two separate air cavities, each of which serves as an inlet or an outlet. The cavities are placed at different levels to facilitate the buoyancy-driven ventilation and the preheating effect. To enhance the performance, the compartmentalized DSF needs to be operated in active cooling (AC), passive cooling (PC), and hybrid heating (HH) modes based on the outdoor condition. Therefore, this study proposed the appropriate operation strategy for the system and evaluated the influence of the strategy on building's thermal performance. Various mode-control thresholds for switching between AC–PC and between PC–HH modes were examined. A validated building simulation model was used to evaluate the operation strategy through a case study, and the results were discussed on the basis of the two types of performance indicators (PIs): the cooling and heating energy use intensity (for AC and HH modes) and hot and cold discomfort hours (for PC and HH modes). A lower AC–PC threshold increases the cooling energy while decreasing the hot discomfort. The influence of a PC–HH threshold on discomfort hours is not linear and vary by modes; therefore, PIs in each mode should be prioritized to determine the optimal threshold. The case study indicated that the DSF with the proposed operation strategy saved 28% cooling energy and 98% heating energy in comparison to a single-skin façade system. Significant hot discomfort may occur in the HH mode, emphasizing the importance of adaptive operations.

Empirical Analysis of the Effects of Window Remodeling using the Slim Double-Skin Window on the Thermal Performance of Old Buildings

Building energy consumption accounts for 30% of the total global energy consumption and is increasing every year. Improvement in the heat transfer performance of the building envelope to reduce energy consumption is a current research hotspot. In the present study, we investigated the performance of the slim double-skin window (SDSW) via empirical analysis. The effect of SDSW-based window remodeling on the thermal characteristics of an old building was investigated with a life-size building. Empirical analysis compared the changes in thermal characteristics between the conventional windows in the old building and the remodeled SDSW. Glass and frame temperature, envelope airtightness, indoor heating environment, and cooling energy consumption were measured before and after window remodeling, and the extent of the influence of external environmental factors, such as insolation, outdoor temperature, and wind speed, on these properties was compared and analyzed. The results show that compared with conventional windows, the SDSWs were less affected by external environment-associated factors, such as sunlight and temperature, thereby maintaining a more comfortable indoor heating environment. Furthermore, the annual building energy consumption was reduced by 34.2% with the use of SDSWs, compared with that of conventional windows.

Orientation as a panacea for improving the Thermal Performance of a fully enclosed courtyard in a typical tropical climate

Globalization has resulted in pollution, carbon emissions, climate change, and an insufficient supply of natural resources. As a result, research is required to increase the thermal performance of buildings. In this regard, using a courtyard as a building component is one of the most sustainable ways to improve the building's thermal performance and microclimate. While utilizing the Envi-met program on the configurations chosen for the fully enclosed courtyard, this study investigated the effect of orientation on the fully enclosed courtyard's thermal performance. 1:1:1 and 1:2:1 are examples of this setup. The orientations considered in this example were N-S, E-W, NE-SW, and NW-SE. The air temperature, mean radiant temperature and physiological equivalent temperature were measured during simulations of two configurations of the fully enclosed courtyard. According to the research, the air temperature, mean radiant temperature and physiological equivalent temperature rises as the size of the courtyard grows. As a result, the air temperature in the 1:1:1 courtyard arrangement is lower than in the 1:2:1 courtyard design.

Thermal performance and economy of PCM foamed cement walls for buildings in different climate zones

Using phase change material (PCM) into the building envelope is considered an effective thermal energy storage strategy to improve building thermal performance and reduce space heating/cooling loads. However, different phase transition temperatures and climatic conditions have a huge impact on application effect. This paper investigates the effects of walls containing PCM foamed cement on thermal performance and economy of single-story building in 5 different climate zones in China. The temperature, energy storage, energy consumption and the payback period for PCM foamed cement wall are analyzed by numerical simulation. The results indicate that the PCM foamed cement moderates the indoor and outdoor temperature differences in all 5 climate zones. Among which, Harbin (severe cold region) had the best increase in the south wall inner surface average temperature in January with an increase of 0.378 °C. The optimal phase transition temperature is close to the local annual average temperature except Harbin, and the energy saving rates are 20.17 % (Beijing), 15.87 % (Shenzhen), Shanghai(22.26 %), 37.02 % (Kunming). The shortest payback period is 5.95 years for the application of PCM foamed cement in Harbin, but in Kunming (mild region) at the current price, the investment cannot be recovered.

Simulation of an energy-efficient cool roof with cellulose-based daytime radiative cooling material

Conventional air conditioners are considered the most energy-intensive components in residential and tertiary buildings. Besides high energy consumption, they are also harmful to the environment due to the emissions of hydrofluorocarbons into the atmosphere. Night sky cooling or radiative cooling is a naturally occurring phenomenon that takes advantage of the atmospheric transparency window in the wavelength range of 8–13 µm to effectively dissipate heat from a surface into outer space. However, this can only occur at night, which is incompatible with the cooling demand that peaks during the day. This paper aims to develop a cool roof that relies on a daytime radiative cooling (DRC) material with low solar absorptivity in the wavelength range of 0.3–2.5 µm and high emissivity in the atmospheric window. The used DRC material is derived from cellulose acetate-based films, which are recyclable, sustainable, and bioclimatic. This material is used to improve the energy efficiency of an existing building by reducing the temperature of the roof to improve the thermal comfort of the building in the framework of Moroccan climatic zones. Software simulations are used to assess the needs and the demand of the building and simulate the impact of the smart device on the building's thermal performance and evaluate the thermophysical and optical properties of the DRC material. This latter material will be compared with another DRC material based on titanium dioxide and silicon dioxide mixture coating in terms of cooling performances. Results have shown a drastic sub ambient cooling of more than 3 °C and a great reduction in the indoor temperature of the building and a reduction in the total electricity consumption of up to 60.38 %.

Hygrothermal monitoring of replacement infill panels for historic timber-frame buildings: initial findings.

Energy retrofits aim to improve the thermal performance of buildings' external envelopes. With buildings of traditional construction there exists the risk that these improvements may lead to interstitial condensation and moisture accumulation. For historic timber-framed buildings, this potentially exposes the embedded historic timbers to conditions favouring fungal decay and insect infestation. Hygrothermal digital simulations can assess this risk, but these have limitations, especially regarding the study of historic and traditional materials, due to a lack of accurate material data. The research presented in this paper therefore uses the monitoring of physical test panels to examine the performance of four different infill solutions. These are, traditional wattle and daub, a composite of wood fibre and wood wool boards, expanded cork board, and hempcrete. The article focuses on the design and construction of the test cell and presents initial results from the first year of monitoring, following the initial drying phase. These showed no evidence of interstitial condensation in any of the panel build-ups, with increases in moisture content correlating directly with climatic measurements of wind-driven rain. Infill materials with low moisture permeability were seen to produce higher moisture contents at the interface with the external render due to the concentration of moisture at this point. Those panels finished in the more moisture permeable lime-hemp plaster, overall present lower moisture contents, with reduced drying times. The use of perimeter, non-moisture permeable, sealants would appear to potentially trap moisture at the junction between infill and historic timber-frame. The monitoring work is ongoing.

The Effect of Exterior Wall Color on Thermal Performance of Building

An experimental study of four colors of ordinary dye (white, yellow, tibny, blue) of the external wall of the apartment building was carried out in the current work, to find out the range of its effect on the heating load in the winter season comparing with dark color of cement wall at 24hr. In the southern wall was made two opening, the dimensions of the opening were 1 meter high and 0.3-meter width. Two types of walls are built in the two opening. The first wall was made of bricks and was covered with a layer of cement (Ficus) 1 cm in thickness, while the second wall was also built of bricks covered with cement (Ficus) with a thickness of 1 cm and was painted with different colors. The results showed that the heating load is not affected by the change of the facade color of the buildings where the difference in the external and internal temperatures of the colored wall compared to the black wall was approximately equal during winter season during minimum temperature surface at night.

Building stock characteristics of residential buildings in Salzburg, Austria based on a structured analysis of energy performance certificates

Heating and cooling of residential buildings is accountable for a significant share of the EU’s final energy consumption. In order to determine the current condition of the building stock and to implement appropriate measures and requirements to improve energy efficiency of buildings, a detailed analysis of existing buildings is essential. This paper aims at describing characteristics of the building stock of Salzburg by analysing energy performance certificates. Therefore, the building stock is grouped into archetypes based on the construction period, building condition (not-retrofitted and retrofitted) and building type (single-family house and multi-family house) and then analysed regarding energy need for space heating, energy carrier, heat emission system, share and U-values of building elements and window to wall ratio. The analysis of the data demonstrates that the structure and naming conventions within the EPC-database pose hurdles for a correct investigation of the data. A comprehensible and distinct notation as well as versioning is inevitable for the sake of avoiding a loss of information and enabling international comparability. An analysis of energy carriers of the archetypes reveals, that a significant share of buildings still uses fossil fuels like oil and gas for energy supply, although electricity (heat pumps) and district heating are on the rise for buildings constructed in recent periods as well as for retrofitted buildings, with heat pumps being the most important energy carrier for new single-family houses amounting to a share of 65% and district heating for new multi-family houses amounting to a share of 46%. A detailed observation of the thermal performance of buildings and building elements reveals high potential and practicability not only for energy efficient new buildings, but also retrofitted buildings throughout all construction periods and for both, single-family houses and multi-family houses (e.g. median U-values for retrofitted ceilings/roofs range from 0.17 to 0.26 W/(m2K) compared to a median of 0.14 W/(m2K) for not-retrofitted ceilings/roofs from the most recent construction period). The conducted analysis provides detailed statistical information on the Salzburg building stock and hence a robust basis for further studies regarding the thermal performance of the building stock and future scenarios by means of urban building energy modelling approaches. Furthermore, based on this information, policies for energy efficient buildings can be improved and adapted according to current circumstances.

Comparing the thermal conductivity of three artificial soils under differing moisture and density conditions for use in green infrastructure

AbstractSoil‐based green infrastructure has the potential to improve building thermal performance and contribute to sustainable buildings. This study compares thermal conductivity response to soil moisture of three peat‐free artificial soils to evaluate their potential use within green roofs and living walls. Thermal conductivity was measured with changing soil moisture and density. All soils showed higher thermal conductivity measures with increases in soil moisture. The ‘Biochar‐coconut coir compost’ had the lowest thermal conductivity measures which displayed negligible response to density changes and exhibited the highest water holding capacity. When uncompacted, ‘FabSoil’ had low thermal conductivity measures, but when compacted, its measures were considerably higher. Results show the role of density on thermal performance will be soil type dependent. Overall, findings highlight the importance of considering substrate composition, density and suggest that peat‐free artificial soil substrates that contain biochar, have a higher percentage organic matter content and a finer particle texture are likely to result in lower thermal conductivity and higher soil water holding capacity. The results also showed that ThetaProbe measures (volumetric) had a high equivalence to actual soil moisture content (gravimetric), across different soil types and soil bulk densities. This finding supports the use of ThetaProbe measures as an effective method for monitoring soil moisture; with the potential for integration into irrigation control systems for green infrastructure. The findings of this paper offer the potential to improve building thermal performance by informing soil substrate choice, irrigation control and load bearing requirements in the design of green infrastructure.

Short recent summary review on evolving phase change material encapsulation techniques for building applications

As the world deviates towards sustainability in buildings due to massive increase in energy demand, the effective integration of Phase Change Material (PCM) in buildings gained substantial attention. The capability of PCM in enhancing the thermal performance of buildings relies heavily on the encapsulation technique used as it is in direct link with enhancement techniques required for upgrading thermo-physical, chemical and environmental PCM properties. The current study reviews shortly recent literature involving PCM integration in buildings and highlights different encapsulation techniques used for their proper active and passive incorporation. It also summarizes recent methodologies of properties enhancements prior to encapsulation. Preliminary results reflect the importance of proper encapsulation using the five distinct techniques: direct mixing, imbibing, shape-stabilization, macro-encapsulation and micro-encapsulation. Commercialization of macro-encapsulated PCMs is dominant over other techniques, where micro/nano-encapsulation technique is still limited and requires further study being the most promising.

Integrated assessment of the extreme climatic conditions, thermal performance, vulnerability, and well-being in low-income housing in the subtropical climate of Australia

Social housing stock worldwide can be characterised by poor indoor environmental quality and building thermal performance, which along with the increasing urban overheating put the low-income population at higher health risk. The dwellings’ thermal performance and the indoor environmental quality are often overlooked in the context of social housing compared to the general building stock in Australia. In the present study, the synergies between urban microclimate, indoor air temperature, housing characteristics and quality of life of residents have been investigated by employing subjective and objective assessment of indoor environmental quality in 106 low-income dwellings during the winter and summer of 2018–2019 in New South Wales. It further examines the impact of urban overheating and levels of income on indoor thermal conditions. The subjective method involved assessing the links between the type of housing in which low-income people live, energy bills, self-reported thermal sensation, health and well-being, and occupants’ behaviours. The results show that many dwellings operated outside the health and safety temperature limits for substantial periods. Indoor air temperatures reached 39.8 °C and the minimum temperature was about 5 °C. While the upper acceptability limit for indoor air temperature was 25.6 °C for 80 % satisfaction, periods of up to about 997 and 114 continuous hours above 26 °C and 32 °C were found in overheated buildings, respectively. Indoor overheating hours above 32 °C were recorded up to 238 % higher in Sydney’s western areas compared to eastern and inner suburbs. Similarly, residents in westerns suburbs and regions experience more outdoor overheating hours than those living near the eastern suburbs. This study highlights the interrelationships between ambient temperature, housing design, income, thermal comfort, energy use, and health and well-being in the context of social housing. The evidence of winter underheating and summer overheating suggests that improvements in building quality and urban heat mitigation are required to minimise the impacts of poor-performing housing and local climate.

VPL-based Code Compliance Checking for Building Envelope Design Using OTTV Calculation

Building Envelope plays a vital role in reducing thermal loads, minimizing energy consumption, and ensuring sustainability. The Overall Thermal Transfer Value (OTTV) is a recognized method to evaluate the thermal performance of buildings. Building Information Modelling (BIM) has added great value to the AEC industry as an efficient tool to facilitate the building design process. With the development of BIM, more properties and material characteristics are assigned to the project design and building model that are getting more complex. Meanwhile, performing OTTV assessment and checking compliance with the assigned values involving time-consuming calculations with the possibility of ambiguity. Hence, automation of the code compliance checking process has become on-demand within the BIM environment. The objective is to develop a Visual Programming Language (VPL)-based script for automating the OTTV rule-based code compliance checking process. The applied method is to integrate BIM, VPL, and OTTV requirements; and develop a visual script that is responsible for extracting parameters from the BIM model, performing OTTV calculation, comparing output with assigned standard values of OTTV aiming answering the research question whether automated code compliance checking process can contribute to code compliance facilitation effectively. The results indicate that integrating VPL into the code compliance checking process has promising signs in facilitating the compliance checking process, increasing the accuracy and reliability of outcomes.

Study based on “Heat Flux - Energy Saving Pointer”: Exploring why phase change materials is not energy efficient enough on internal wall in cold region

The combination of phase change materials (PCMs) with internal envelopes is an effective way to enhance the thermal performance of buildings. However, it may be non-energy efficient in some applications. Due to the lack of in-depth exploration, Heat Flux-Energy Saving Pointer (HF-ESP) is proposed to investigate the direction conversion and numerical change of PCM heat flux. In addition, Relative Depth of Activation (RDA) and HF-ESP are combined to evaluate the thermal behavior of PCM. In the whole winter, the energy change caused by PCM in different cases is about 132–233 MJ. However, this change does not necessarily bring benefits, and the energy-saving effect should be evaluated based on the offset of positive and negative returns. RDA of case 2 and case 4 are 98.56% and 33.77% respectively, but they can save almost the same energy. It indicates that the higher latent heat utilization does not necessarily mean the better energy-saving effect. When the phase transition temperature is 17 °C (lower than indoor temperature), PCM will lead to non-energy saving reversals of heat flux. With the increase of phase transition temperature, it will gradually transform into energy-saving reversals. This work can provide some references for balancing initial investment and operating costs.

Effectiveness of phase change material in improving the summer thermal performance of an office building under future climate conditions: An investigation study for the Moroccan Mediterranean climate zone

The rise in global temperature due to the climate change phenomenon would increase the severity of summer season in the future. The integration of phase change materials (PCM) into the building envelope has been considered as one of the most promising measures to improve the thermal performance of buildings. This paper aims at investigating the effectiveness of the PCM in improving summer thermal performance of buildings under the climate conditions of the next three decades. The moderate scenario RCP4.5 of the Intergovernmental Panel on Climate Change was used to simulate future climate conditions. The present study was conducted for two building case studies: free-running and air-conditioned office buildings located in the north of Morocco (Mediterranean climate with hot summer). The findings have disclosed that an appropriate selection of the PCM melting temperature could enhance the thermal performance by 9.87 % for the free-running building and by 20.5 % for the air-conditioned building case over the whole building lifespan (30 years). A decade-by-decade analysis showed that the effectiveness of the optimum selected PCM would slightly decline over time. The research involved an economic analysis of the air-conditioned building case study. The latter led to calculating the maximum allowable cost of the PCM installation to achieve a payback period within the lifespan of the building. The findings of the present work can be used as guidelines to design office buildings integrated with PCM in the Mediterranean region.

An efficient performance assessing index for building climatic zoning methods based on probability density functions

Climatic zoning is the basis of improving thermal performance of buildings, and various methods and parameters have been proposed in previous studies. However, the validity assessment of these climatic zoning methods is rather limited. This study proposes a performance index (PI) for assessing climatic zoning methods by comparing the overlapping probability density functions (PDFs) among different climate zones. The PI was used to assess the performance of the two subjective (i.e., based on the two national standards GB50178 and G50176) and one objective (i.e., cluster analysis) methods of climatic zoning in China with over five different climate zones. The results showed that the cluster analysis method has the smallest mean PI (16.8) compared with those of the subjective methods (17.8 and 19.3). More importantly, the cluster analysis method has less variations in PIs among relevant variables (13.8–23.2), while the PIs largely ranging from 6.4 to 42.7 and 10.4 to 29.9 for the two subjective methods. These results indicate that the PI can accurately assess the validity of climatic zoning methods, and that the objective method may be better for building climatic zoning for the whole China as it can effectively distinguish the relevant climatic variables among different climates. The quantified index may have the potential to assess other zoning methods, particularly when applied in countries with larger areas and more climate zones.

Multiobjective Optimization of Cement-Based Panels Enhanced with Microencapsulated Phase Change Materials for Building Energy Applications

Thermal energy storage using phase change materials (PCMs) is a promising technology for improving the thermal performance of buildings and reducing their energy consumption. However, the effectiveness of passive PCMs in buildings depends on their optimal design regarding the building typology and typical climate conditions. Within this context, the present contribution introduces a novel multiobjective computational method to optimize the thermophysical properties of cementitious building panels enhanced with a microencapsulated PCM (MPCM). To achieve this, a parametric model for PCM-based cementitious composites is developed in EnergyPlus, considering as design variables the melting temperature of PCMs and the thickness and thermal conductivity of the panel. A multiobjective genetic algorithm is dynamically coupled with the building energy model to find the best trade-off between annual heating and cooling loads. The optimization results obtained for a case study building in Sofia (Bulgaria-EU) reveal that the annual heating and cooling loads have contradictory performances regarding the thermophysical properties studied. A thick MPCM-enhanced panel with a melting temperature of 22 °C is needed to reduce the heating loads, while a thin panel with a melting temperature of 27 °C is required to mitigate the cooling loads. Using these designs, the annual heating and cooling loads decrease by 23% and 3%, respectively. Moreover, up to 12.4% cooling load reduction is reached if the thermal conductivity of the panels is increased. Therefore, it is also concluded that the thermal conductivity of the cement-based panels can significantly influence the effectiveness of MPCMs in buildings.

Effects of Climate Responsive Strategies and Adaptive Behavior of Occupants on Thermal Comfort in Indoor Environments of Vernacular Architecture: A Review of Necessities and Goals

This study addresses the goals, reasons, and necessities of analyzing the effects of climate responsive strategies and adaptive behavior on thermal comfort in the indoor environments of vernacular architecture. For this purpose, 86 studies were reviewed, including 71 studies about climate responsive strategies and 15 others about adaptive behavior in vernacular architecture and dwellings that were carried out between 2000 and 2018. The research methodology included a statistical survey and analysis of necessities and goals of the studies reviewed in this paper. To this end, the designated studies were analyzed and reviewed from different aspects, such as the history and process of formation, keywords, goals, reasons, and necessities of research. 
 According to the findings, the most important research goals of climate responsive strategies include (1) analyzing the thermal performance of buildings, and (2) identifying the effects of these strategies on the thermal quality of indoor environments. Moreover, the most prominent research goals of adaptive behaviors in vernacular architecture and residences include (1) evaluating thermal comfort, (2) identifying and analyzing adaptive methods and behaviors, and (3) identifying the existing obstacles. The research necessities of these two areas can also be divided into three sections, i.e. identification of advantages, practical reasons, and addressing research gaps. Another research finding was identification of the concepts pertaining to these two areas.

Assessment of the impact of construction materials on the building’s thermal behaviour and indoor thermal comfort in a hot and semi-arid climate

ABSTRACT This paper aims to identify the most suitable construction materials in terms of building’s energy performance and indoor thermal comfort for a hot and semi-arid climate. An experimental validated TRNSYS-based numerical model was set to carry out dynamic simulations for the energy performance assessment of four similar houses built with different materials, namely Cinder Blocks, Reinforced Concrete, Fired Bricks, or Rammed Earth. The results show that the rammed earth house had the best thermal performance thanks to its high thermal mass, which helped maintain a stable indoor air temperature for optimal thermal comfort. Adding shading and night natural ventilation contributed to the further improvement of the rammed earth house's thermal performance. Indeed, the annual heating/cooling load of the rammed earth house was 23%, 11% and 3% lower than the reinforced concrete, cinder blocks and fired bricks houses, respectively. These thermal load differences were much more reduced to 51%, 24% and 5%, respectively, after adding the shading and night natural ventilation techniques. Furthermore, this study evaluated the use of low embodied energy and weak carbon footprint construction materials to achieve a good building's thermal performance and acceptable indoor thermal comfort.