Exterior Thermal Insulation System Research Articles

Towards the use of natural thermal insulation on the exterior of vertical building walls in desert regions: A case study in the city of Bechar, Algeria

The use of natural-based exterior thermal insulation systems constitutes a significant challenge for achieving energy efficiency of construction. The purpose of this article is to propose new exterior thermal insulation solutions based on natural materials such as wood wool, cellulose wadding, expanded cork, hemp fiber, and sheep’s wool, in order to minimize energy consumption, address durability concerns, maintain thermal comfort, and promote the use of natural materials in thermal insulation system designs. The methodology followed consists of presenting a comparative numerical study of different exterior insulation techniques (ETI) using a dynamic thermal simulator for desert regions. The study evaluated ETI systems for vertical walls attached to a concrete block wall, including one EPS system with coating (wet process) and six systems with cladding (dry process). The results show that applying exterior insulation to walls using the two cladding systems based on hemp fiber and sheep wool resulted in a total reduction in building energy consumption of 42.21% and 42.81%, respectively. These results confirm the effectiveness of natural materials in improving the energy performance of buildings, particularly the system based on sheep wool.

Experimental investigation of downward discrete flame spread of the thermoplastic material in exterior insulation walls: melt-flowing and -dripping

Discrete flame spread, accompanied with melt-flowing and -dripping behaviors, significantly increases fire hazards of thermoplastic materials in exterior insulation walls. The movement of melt-burning combustible materials brings rigorous challenges to the current fire protection system but has not been sufficiently studied. Thus, two modes of bench-scale experiments, covering melt-flowing and melt-dripping, have been conducted to explore the basic knowledge and threshold of melting-dominant discrete flame spread. The typical thermoplastic material in the exterior thermal insulation system, expanded polystyrene foam (EPS), was selected as the research objective. For melt-flowing dominant flame propagation, a critical fuel coverage (f = 0.40–0.50) when a barrier prevented molten flows was determined experimentally, and a dimensionless analysis was conducted to clarify the downward flowing stages. For dripping-dominant flame propagation, a threshold diameter for ignition (13.3 mm) was obtained via comparing burning time and ignition time without the impact of dripping height. Then, the influence of dripping height on the critical ignition diameter was investigated by coupling with the established theoretical dripping acceleration. This work attempts to provide a reference for enhancing fire protection in building exterior walls.

Durability Analysis of Building Exterior Thermal Insulation System in Hot Summer and Cold Winter Area Based on ANSYS

External thermal insulation systems often have durability problems, including cracking, hollowing, and falling off, which seriously affect safety and energy-saving effects. Based on finite element theory and using ANSYS software, this paper studies the distribution law of the temperature field and temperature stress of the external thermal insulation system. It was found that, compared with an uninsulated wall, the temperature stress of the substrate in summer was reduced by 52.9%, and the temperature stress of the substrate in winter was reduced by 50.9%. The temperature stress is mainly concentrated in the middle position of the external wall insulation system, and the middle of the wall can appear as a hollow drum and fall off. When the temperature of the external wall surface is 60 °C, the maximum temperature stress of the insulation system is 2.46 MPa, compared with the external wall surface of 70 °C—a decrease of 22.2%; the maximum temperature stress on the substrate is 0.46 MPa—a decrease of 20.7%. When the temperature of the outer wall surface is 50 °C, the maximum temperature stress suffered by the insulation system is 1.75 MPa, compared with the outer wall surface of 70 °C—a decrease of 44.4%. Meanwhile, the maximum temperature stress suffered by the substrate is 0.34 MPa—a decrease of 41.4%. This paper investigates and numerically simulates the durability of external wall insulation systems for buildings in hot summer and cold winter regions, and studies the durability of EPS insulation, which can provide guidance for other insulation material design and durability studies.

Influence of Wind Direction on Fire Spread on the Exposed XPS insulation Wall

Medium-sized wall fire experiments were carried out using extruded polystyrene (XPS) panels to build an insulation layer to simulate the flame spread over the exterior thermal insulation system during the exposed stage. During the experiments, the influences of the wind direction on the lateral and vertical flame spread speed without fire barrier designs under the wind speed of 2.5m/s were studied quantitatively and qualitatively. According to the experimental results, it is found out the averaged peak lateral flame spread rate increases and the averaged peak vertical flame spread rate decreases when the angle between the wind direction and the wall increases from 0° to 60°. It can be seen from the analysis that the largest average lateral flame spread rate and the largest average vertical flame spread rate also show regular changes at same wind direction. This study results can provide valuable references for optimizing the fire safety design of exterior insulation system.

Complex assessment of reconstruction works on an institutional building: A case study

Energy demands of current buildings present an important problem for building designers and engineers. However, the necessity to retrofit building envelopes and achieve a better thermal performance is substantially limited by the economic viability. Despite of the environmental benefits accompanied with enhanced thermal stability, a complex evaluation of the impact of reconstruction works from various perspectives is still needed. In this paper, a quantification of physical, social, economic, and environmental benefits resulting from the application of exterior thermal insulation system to an institutional building is presented. The temperature profiles in the wall cross-section are used for the assessment of the effect of expanded polystyrene boards. The annual energy consumption and carbon emission production is found to decrease by 46% as the result of better thermal performance. The improved social comfort is confirmed by the evaluation of predicted mean vote characterizing the average heat sensation of building occupants. The carbon payback of 3.24 years refers to low initial environmental burden in proportion to obtained energy savings. However, full investments recovery rate varying from 43 to 60 years in dependence on applied economic scenarios reaches almost the lifetime of used materials, which presents a substantial barrier despite of the discounted cost savings of 180,000 Euros during the 60-year lifespan.

Experimental investigation on downward flame spread over rigid polyurethane and extruded polystyrene foams

With the development of social economy and architectural aesthetics, flame spread over exterior thermal insulation system in real high-rise building fire disasters often features inclined downward or upward propagation, however most developed models for flame behavior prediction only assume absolute vertical or horizontal direction. Some researchers have explored the behavior of inclined upward flame spread for its quick development and hazardous characteristics. However, for downward flame spread over plastic polymers, theirs flame spread characteristics can also feature a special hazardous configuration, especially for porous and thermoplastic polymers. In this study, the orientation effects during inclined downward flame spread processes were thoroughly investigated by experimental and theoretical methods. Two kinds of typical thermal insulation materials were selected, rigid polyurethane (RPU) and extruded polystyrene (XPS) foams. The mass flow rate and flame spread rate at different inclination angles were obtained and analyzed. The different flame spread behaviors of RPU and XPS foams were scrutinized. Experimental results show that a linear relationship exists between flame spread rate and cube root of sine of sample inclination angle of RPU and XPS foams when the slope is smaller than a transition angle. The mechanism of orientation effect during the flame spread process was qualitatively analyzed in detail, and simplified expressions of flame spread rate of the two insulation materials with different orientations were deduced. The results of this study have implications concerning the fire safety design of exterior thermal insulation wall.

Effectiveness of vertical barriers in preventing lateral flame spread over exposed EPS insulation wall

Insulation panels made of organic, combustible materials are frequently used in the exterior thermal insulation systems (ETIS) for buildings. Such combustible insulation panels have been involved in several catastrophic building fires in recent years in China. One potential strategy to mitigate this fire hazard is to limit fire spread over the ETIS. The present work evaluates the effectiveness of vertical fire barriers in inhibiting fire spread over exposed insulation walls made of expanded polystyrene (EPS) panels. Reduced-scale experiments were carried out indoors using EPS panels with or without two vertical barriers made of non-combustible mineral wool, the fire started at the bottom center of the middle panel. The interval and width of the barriers were varied systematically, while the temperature distribution on the wall, the radiation heat flux from the fire, and the infra-red (IR) images were recorded. To demonstrate the validity of the concept, an outdoor, full-scale experiment was carried out using a 7-floor building. Our reduced-scale experiments showed that the installation of two vertical fire barriers successfully stopped the lateral flame spread, decreasing the peak temperatures of the two side panels by about 300°C for all barrier configurations tested. When barrier width was fixed at 5cm, an increase of the barrier interval from 30 to 90cm led to increases in the peak temperatures, radiation heat flux, and the maximum rate of upward flame spread. By contrast, when barrier interval was fixed at 90cm, an increase of the barrier width from 2 to 5cm had little influence on the combustion dynamics of the middle panel but the peak temperature on the side panels dropped, consistent with the smaller heat transferred with wider fire barriers. In the regions of the side panels next to the barriers, pyrolysis and deformation could be observed with barrier widths of 2 and 3cm, but not 5cm. Finally, our outdoor, full-scale experiment demonstrated that a 30cm wide vertical barrier made of air-filled cement successfully stopped the lateral flame spread over exposed EPS wall. The study highlights the effectiveness of vertical fire barriers in preventing the lateral flame spread over the exposed EPS insulation wall and provides another option for enhancing the fire safety of the combustible insulation systems.

Experimental study of the out of plane behavior of masonry infill walls with exterior insulation systems

The objective of this study is to evaluate the out of plane behavior of a masonry infill wall provided with an exterior thermal insulation system. For this purpose there were constructed two 1:1 scale specimens of masonry infill walls in order to compare a simple wall with one having already applied an exterior thermal insulation system composed by a polystyrene insulation and a protection layer of plaster and a glass fiber mesh. The load was applied through a horizontal force, acting at the mid height of the wall. Both specimens were tested in displacement control, using alternate force with 3 cycles per loading step. As it was expected, an increased stiffness and out of plane resistance was observed for the wall provided with the insulation system. Various observations were noticed related to the technology and overall behavior of the infill masonry wall.

Fire Spread Caused by Combustible Facades in Japan

With regard to fire safety for exterior walls of a building, fire-resistance performance is considered, according to the current building standard law of Japan. And it was revealed that the fire safety is not specifically regulated from the viewpoint of reaction-to-fire performance, such as fire propagation caused by combustible materials or products which are installed on the exterior side of fire-resistant load-bearing walls. Actual fire issues in the world have shown that massive facade fire could occur at the exterior side of building wall even when the wall itself is fire-resistant. In previous studies of the authors, a test method of facade fire was tentatively proposed for evaluating the vertical fire propagation over an external wall within the same building. Furthermore, especially at the high-density residential areas in Japan, fire spreading would occur mostly from window to window between adjacent buildings, while walls are not burning by facade fire. But in case of combustible facades, such as insulating materials, combustible coating, or even sandwich panel are installed on the wall surface, once they are ignited, facade fire would occur and accelerate both the fire propagation in the same building and the fire spreading to the adjacent building. In this paper, results of fire tests on combustible facades are discussed from the viewpoints of both vertical fire spread along facades and fire spread between adjacent buildings assuming the densely populated residential area in Japan. The tentative criteria were determined based on the time to reach 500°C and duration time exceeding 500°C on facade surface for vertical fire spread along facade. As for intensively burned cases, at 2500 mm height from upper edge of the opening, specimens of exterior thermal insulation system with 200-mm thick expanded polystyrene (EPS), aluminum composite panel with polyethylene core and wooden facade without fire-retardant treatment continued exceeding 500°C for 3.1 min, 5.7 min, and 3.6 min, respectively, that were longer duration compared with specimens of resin painting (approximately 1 min). On the other hand, the another tentative criteria were determined for horizontal fire spread to an adjacent building based on the duration time exceeding the calibration test’s peak incident heat flux on opposite surface 2000 mm from facade surface for horizontal fire spread to an adjacent building. At 500 mm height from upper edge of the opening, specimens of exterior thermal insulation system with high-density 100-mm thick EPS and wooden facade without fire-retardant treatment continued exceeding the peak incident heat flux of calibration test for 13.1 min and 13.6 min, respectively, while one specimen of resin painting and aluminum composite panel with polyethylene core continued for shorter duration of 4.2 min and 5.8 min, respectively, even though they showed relatively high peak facade surface temperatures.

Heat and Water Vapor Transport Properties of Sandwich Composite with Aerogel Insulation

Several thermal insulation systems were developed for improvement of thermal performance of buildings. Exterior thermal insulation systems represent usually natural solution of the problem of low thermal resistance of building envelopes. However, in some cases, there is necessary to realize interior thermal insulation systems, what brings number of possible problems. Their common disadvantage is a limitation of interior space due to the thickness of thermal insulation layer and a possible condensation of water vapor which permeates the thermal insulation system. On this account, new sandwich composite with silica aerogel originally designed for application in interior thermal insulation systems is studied in the paper. Thermal properties are measured by two transient methods using devices ISOMET 2114 and RTB. The water vapor transport parameters are determined on the basis of dry cup and wet cup methods. The obtained data gives information on thermal and water vapor transport properties of the particular layers of sandwich composite and predetermines its behavior at real climatic exposure of building.

Biocides in urban wastewater treatment plant influent at dry and wet weather: Concentrations, mass flows and possible sources

In recent years, exterior thermal insulation systems became more and more important leading to an increasing amount of houses equipped with biocide-containing organic façade coatings or fungicide treated wood. It is known that these biocides, e.g. terbutryn, carbendazim, and diuron, as well as wood preservatives as propiconazole, leach out of the material through contact with wind driven rain. Hence, they are present in combined sewage during rain events in concentrations up to several hundred ng L−1.The present study focused on the occurrence of these biocides in five wastewater treatment plants in Denmark and Sweden during dry and wet weather. It was discovered, that biocides are detectable not only during wet weather but also during dry weather when leaching from façade coatings can be excluded as source. In most cases, the concentrations during dry weather were in the same range as during wet weather (up to 100 ng L−1); however, for propiconazole noteworthy high concentrations were detected in one catchment (4.5 μg L−1). Time resolved sampling (12 × 2 h) enabled assessments about possible sources. The highest mass loads during wet weather were detected when the rain was heaviest (e.g. up to 116 mg h−1 carbendazim or 73 mg h−1 mecoprop) supporting the hypothesis that the biocides were washed off by wind driven rain. Contrary, the biocide emissions during dry weather were rather related to household activities than with emissions from buildings, i.e., emissions were highest during morning and evening hours (up to 50 mg h−1). Emissions during night were significantly lower than during daytime. Only for propiconazole a different emission behaviour during dry weather was observed: the mass load peaked in the late afternoon (3 g h−1) and declined slowly afterwards. Most likely this emission was caused by a point source, possibly from inappropriate cleaning of spray equipment for agriculture or gardening.

Computer aided design of interior thermal insulation system suitable for autoclaved aerated concrete structures

The idea of using interior thermal insulation systems for autoclaved aerated concrete (AAC) structures is introduced. In the computer aided design, the hygric properties of the thermal insulation layer and the connecting layer between the AAC block and the thermal insulation board are investigated. The computational analysis shows that the moisture diffusivity, κ, of the thermal insulation layer should be very high (≈1 × 10−6 m2/s), its water vapor diffusion resistance factor, μ, very low (≈3–5), and hygroscopic moisture content, whyg, moderate (≈0.01 m3/m3). This combination of properties can potentially be met by modifications of some not commonly used thermal insulation materials, such as are hydrophilic mineral wool or calcium silicate. On the other hand, the hygric properties of the connecting layer are not found very restrictive. Common lime–cement or lime–pozzolan mortars can meet the required criteria of κ ≈ 1 × 10−9 m2/s–1 × 10−8 m2/s, μ ≈ 10–20, and whyg ≈ 0.05 m3/m3. The application of an interior thermal insulation system with the properties given above for an AAC envelope can reduce the hygrothermal straining of exterior plaster, which is typical for the exterior thermal insulation systems, in a very significant way, thus increase the service life of the whole envelope.

Exterior thermal insulation systems for AAC building envelopes: Computational analysis aimed at increasing service life

A computational analysis aimed at increasing service life of exterior thermal insulation systems suitable for building envelopes based on autoclaved aerated concrete (AAC) in the climatic conditions of Central Europe is presented. In the first step, a sensitivity analysis of the effect of hygric parameters of materials involved in thermal insulation systems on the hygrothermal performance of AAC envelopes is accomplished, in order to identify appropriate ranges of their values. Computational simulations of temperature and moisture fields in AAC building envelopes are then performed, using proper combinations of properties of exterior layers. The results are evaluated from the point of view of frost resistance of the whole building envelope, and the appropriate values of hygric properties of thermal insulation layer and exterior plaster are identified. Finally, prospective types of materials suitable for the investigated thermal insulation system are proposed.

Analysis on Regional Adaptability of Interior Thermal Insulation System in South China

For seeking out suitable means of thermal insulation system of building envelope in south China, this paper has conducted simulation analysis on respective energy consumption of the typical residential template in cold region and south China, when adopt exterior thermal insulation system or interior thermal insulation system. The study has shown that the exterior thermal insulation system is much better than the interior thermal insulation system in energy efficiency in the cold region, but there isn’t obvious difference between them in south China. And from the aspects of the climate’s influence on the insulation quality, the installation’s influence on the building facades and the construction practices, it is proved that the interior thermal insulation system is more suitable than the exterior thermal insulation system in south China.