Thermal performance impacts of vented EIFS assemblies in the cold climate of Southern Ontario

Nizovtsev M.I., Letushko V.N., Yu. Borodulin V., Sterlyagov A.N.

Laboratory and full-scale experiments were carried out with new facade systems with ventilated channels to remove excess moisture from the insulation material. The aim of the work was to study the effect of ventilated channels of facade panels on the moisture condition of the heat-insulation. In laboratory experiments, the effect of air velocity in ventilated channels on the heat-insulation moisture content at different indoor air humidity was investigated. The results of measurements of temperature and relative humidity of air in the panel and in the ventilated air channels at different humidity of the indoor air in the cold period of the year are given. It was found that even with a high humidity of the indoor air of about 70%, the relative humidity of the air in the material of insulation did not exceed 50%, which provided high heat-protected properties of the panels. Temperature stratification of 8–10 °С on height was recorded in the ventilated channels. It led to the appearance of free convective upward currents in the channels and intensification of the moisture removal from the insulation.

Tariku F., Iffa E.

In the last few decades, rain-screen wall systems have become common in building enclosure designs and construction for the purpose of mitigating moisture damage risk. Existing literature shows an air cavity in rain-screen wall facilitates moisture control performance. However, it is not clear whether it is just the presence of a capillary break created by the air gap or the cavity ventilation. It is a common practice to use a predefined constant cavity ventilation rate while modelling the thermal and hygrothermal performance assessments of rain-screen wall systems. However, cavity ventilation rates in ventilated wall systems vary with driving forces such as, wind and solar radiation. In this paper, three wall types, namely vented, ventilated, and wall system with no air gap, are manufactured and installed in two opposite orientations of a field-experimental test building. The air velocity, relative humidity and temperature in the cavity, and the moisture content and temperature in plywood and wood frame studs are monitored for 15 months. Based on the monitored data and analysis, a cavity ventilation regression model for the combined wind and solar induced flows is developed. The empirical model is presented as a function of hourly wind pressure and the temperature difference between the outdoor and cavity space. The empirical model is tested with the whole measured data and a good fit (R2 value of 0.912) is achieved between the model and measurement. The long-term hygrothermal performance analysis shows that the wall with no air gap accumulates relatively high moisture content and also has high moisture content changes in a year cycle when compared to the vented and ventilated wall systems. The moisture control performance of vented and ventilated wall systems is comparable thus emphasizing the important parameter for enhanced hygrothermal performance is having a cavity vent not the type of ventilation design (vented or ventilated). The temperature readings of the sheathing boards in the vented and ventilated wall systems are somewhat warmer than that of the wall with no air gap for 85.5% and 73% of the experimental measurement time, respectively.

Nardi I., Perilli S., de Rubeis T., Sfarra S., Ambrosini D.

The addition of insulating layers on vertical walls of buildings is a common practice for providing a higher thermal insulation of the envelope. Workmanship defects, however, might influence the effectiveness of such insulation strategy. Damaged materials, incorrect installation, use of aged or weathered materials might alter the capability of reducing heat transfer through the envelope, whether vertical or sloped. In this work, drawbacks caused by the wrong installation of insulating material and by damaged material are assessed. A specimen wall was investigated by experimental and numerical approaches, the latter carried out by using COMSOL Multiphysics®. Results are compared and discussed.

Macias-Melo E., Aguilar-Castro K., Xamán J., Hernández-Pérez I.

This work presents the design, construction, and evaluation of a rectangular ventilated cavity. The cavity has a heated wall, a fixed air inlet port, and an air outlet port that can change in four different configurations: C-1, the outlet gap is on the upper side of the left wall; C-2, the outlet is on left of the top wall; C-3, the outlet is in the middle of the top wall; and C-4, the outlet is on right of the top wall of the cavity. The experimental tests were carried out with a heating power of 200 and 400 W. The measured indoor air temperatures in nine points, the wall surface temperatures, and heat flows are reported for validation of computer codes. Then, the numerical modeling for the ventilated cavity was done with an in-house code based on the finite volume method to show the relevance of the experimental data. From experimental result for a heating power of 400 W, the configuration C-4 presented the smallest air temperature increment of 3.3°C and the lower average indoor air temperature. In addition, configuration C-4 was more efficient to remove heat than the other configurations, with a maximum percentage of heat removed being 4.75%, 4.32%, and 2.11% more than configurations C-1, C-2, and C-3, respectively. From the validation, the maximum error was 9.9% and 11.5% for the test of 400 and 200 W, respectively. In general, most comparison points had an error smaller than 5%. From both comparisons, it can be concluded that numerical results have an acceptable quantitative approximation.

Fantucci S., Marinosci C., Serra V., Carbonaro C.

In recent years, several studies have been performed to evaluate the actual contribute of Opaque Ventilated Facades (OVF) as far as the energy efficiency of buildings in the summer period is concerned. In this framework an experimental real-scale module of an OVF was built and tested. Results demonstrated a reduction of ∼58% of the thermal load obtained by using a OVF with respect to the unventilated facade configuration. In this paper the experimental measurements were used to calibrate dynamic simulations using ESP-r software, in order to identify the input factors and the key issues mainly impacting on the results discrepancy.

Latif E., Ciupala M.A., Wijeyesekera D.C.

An in situ experiment in a full scale timber frame test building was carried out to compare the hygrothermal performance of Hemp and Stone Wool insulations of identical thermal conductivity. Hemp and Stone Wool insulations were installed in timber frame wall panels without vapour barrier. The comparison was made in terms of heat transfer properties, likelihood of mould growth and condensation. Step changes in internal relative humidity were performed to explore the effect of high and normal internal moisture load on the wall panels. No significant difference between the average equivalent thermal transmittance (U-values) of the panels incorporating Hemp and Stone Wool insulations was observed. The average equivalent U-values of the panels were closer to the calculated U-values of the panels based on the manufacturers’ declared thermal conductivity of Hemp and Stone Wool insulations. It was observed that the placement of heat flux sensor along the depth of the insulation had significant influence on the measured equivalent U-value of the panels during high internal moisture load. The frequency and likelihood of condensation was higher in the interface of Stone Wool and Oriented Strand Board (OSB). In terms of the parametric assessment of mould germination potential, relative humidity, temperature and exposure conditions in the insulation-OSB interfaces were found to be favourable to germination of mould spore. However, when the insulations were dismantled, no mould was visually detected.

Guillén I., Gómez-Lozano V., Fran J.M., López-Jiménez P.A.

In this paper, different sorts of facades have been analyzed considering their thermal performance along a 24 h period. A numerical model was developed and compared with experimental measurements considering two different facades for buildings: on one side an opaque multilayer facade; and on the other side, a ventilated facade. The numerical model representing the temperature in every layer of the facades was successfully validated. This model was used for determining the thermal behavior of two new ventilated facades in which the thermal mass had been changed, observing then that the existence of the movements in the air gap affected particularly the air temperature and the thermal transmittance of the facade while the sun hitting the facade, leading to a reduction of transmittance close to 30% along the air chamber. This effect is very important in warm climates and becomes a key-factor for decreasing the cooling needs of buildings in summer with no need of increasing the mass of the facade.

Marinosci C., Semprini G., Morini G.L.

In this paper the thermal behaviour of rainscreen ventilated facades under typical Mediterranean summer weather conditions has been investigated experimentally by using a large-scale test building located at San Mauro Pascoli (Italy). The main goal of this work was to quantify the reduction of the heat flux across the inner wall due to the enthalpy discharge linked to the airflow established within the cavity of the ventilated wall during a typical summer day. The experimental results highlight that the heat flux reduction is strongly correlated to the exterior finish of the rainscreen, to the presence of open joints and ventilation grills and to the air cavity thickness of the facade. In order to study the impact of these different aspects on the thermal performances of the ventilated walls, ten different configurations for the ventilated facade have been investigated. The experimental results highlight that the feature of the ventilated wall to reduce the summer loads depends on the capacity of the system to limit the value of the temperature within the cavity and this can be obtained by reducing the pressure losses along the cavity in order to increase the air flow rate and by minimizing the long-wave radiative contribution within the cavity.

Amaro B., Saraiva D., de Brito J., Flores-Colen I.

This paper describes an expert knowledge-based system for ETICS (External Thermal Insulation Composite System) on walls, which enables facilitating and standardising inspection, diagnosis and repair of ETICS. The system includes specific tools that provide information to aid in the analysis of degraded ETICS and lead to the preparation of solid and reliable reports. Types of anomalies, their related causes, auxiliary tests to be performed in situ and repair techniques applicable to ETICS systems are listed and classified. The relation between these parametres is expressed through correlation matrices, validated and adjusted through data obtained from inspections carried out on a sample of 146 facades with ETICS cladding. The relevant descriptive information is gathered in individual files for every anomaly, plus diagnosis-aiding method, and maintenance and repair techniques. Additional statistical analysis was performed, leading to conclusions on the most sensitive aspects of this system.

Falk J., Sandin K.

To analyse the moisture performance of wall systems with a ventilated rainscreen cladding, the air change rate per hour (ACH) is required. However, the average ACH and its variation depend on many factors. This study focuses on performing field measurements of air velocities and temperatures in south oriented wall cavities characterised by either vertical wooden battens or horizontal vented metal battens. A physical cavity airflow model together with laboratory test of loss factors were used to analyse the data and interpret the results. With vertical battens, findings estimated the average ACH during a measurement period to be 230–310 ACH. In the cavities with horizontal battens, the ACH was 60–70% lower. The daily variations were considerable and hours with solar radiation and clear skies resulted in ACH that exceeded the average values 2–3 times. In contrast to airflow induced by thermal buoyancy, wind-induced airflow was irregular with frequent changes in both velocity and direction. This pattern was observed independent of the angle between the wind and the cladding. The frequent changes in flow direction significantly reduced the efficiency of wind-driven airflow to create air exchange. The wind-induced airflow in wall cavities with a pronounced non-linear relationship between the driving force and the air velocity is suppressed in the presence of buoyancy. For rainscreen claddings exposed to many hours of solar radiation, this effect increases the possibility of accurate estimations of ACH.

Pasztory Z., Peralta P.N., Molnar S., Peszlen I.

In North America, the exterior finish of wood-frame house walls usually consists of a siding, a water resistive barrier, and an oriented strandboard (OSB) sheathing. In Europe, the exterior finish uses the External Thermal Insulation Composite System attached to a gypsum board sheathing. This study was performed to compare the hygrothermal performance of American and European walls by using a finite-element model. Analysis showed that the European wall has better thermal performance mainly because of the heat-insulating ability of the expanded polysterene (EPS) layer. But when the EPS was reduced to the same thickness as the siding used in American construction, the thermal performance of the European wall did not fare any better than the American structure. The resistance of the European wall to moisture damage was also better than the American walls. One reason for this is the high diffusion resistance of the EPS. But this same high diffusion resistance works to the detriment of an Exterior Insulation Finish System (EIFS) wall if water is able to infiltrate the structure. When water leakage is present, the water content of the OSB in the EIFS wall reaches levels that make it vulnerable to mold growth and fungal decay.

Davidovic D., Piñon J., Burnett E.F., Srebric J.

The wetting, storage and drying of moisture is a serious concern in the overall performance of exterior wall systems. Prediction of moisture transport and moisture removal within wall enclosures plays a key role in the design of exterior wall systems. The convective drying potential in ventilated and screened wall systems (VSWS) is directly proportional to the available ventilation flow rate of the air through the vents in the walls. The main goal of this study was to determine the most appropriate analytical equations for predicting ventilation flow rates within VSWS and to provide a solid foundation for estimating convective drying potential. The equations currently available in the ASHRAE literature are primarily intended for mechanical system applications and are not well suited for estimates of convective drying potential in wall systems, mainly due to the extremely low velocities and the unique geometry of VSWS when compared to mechanical systems. Other literature sources were also reviewed for the evaluation of pressure losses in systems with low airflow rates. The pressure losses due to friction at the walls of the ventilated chamber were beyond the scope of this paper. Under most circumstances, the major contribution to pressure losses in VSWS occurs at the inlet and outlet vent openings. A list of the empirical/analytical equations recommended for use in evaluating natural ventilation flow characteristics within VSWS is also provided. The recommended equations provide a solid theoretical background for validation against the laboratory and field results obtained in the ASHRAE Research Project RP-1091.

Desogus G., Mura S., Ricciu R.

This paper introduces a comparison of different measuring methods of buildings fabric thermal resistance, including the test wall measuring points arrangements and measurement results, conducted in a test chamber in Cagliari (Italy) in summer 2009. Two methods and their measurement uncertainties are presented and compared by the compatibility of measurement study. The non-destructive method involves the heat-flow rate measurement through the test wall and its surface temperatures. The reliability of this method depends on the temperatures difference between the two environments separated by the building envelope. Thus two measurement series with different temperatures were carried out on the test wall. The destructive method instead foresees the acquisition of a sample by the use of a hollow drill, the building envelope layers thickness measurement and the thermal properties assignment to each different material. The wall R-value is the sum of each layer thermal resistance. The comparison shows that the R-values measured by the non-destructive method with a temperature difference of 10 °C and 7 °C and the one calculated from the destructive method obey the compatibility of measurement principle.

Bassett M., McNeil S.

New building designs following the New Zealand Building Code Approved Documents complete a 'risk matrix' of climate and building design factors with associated 'risk scores' to guide the selection of wall cladding and cavity design. The risk matrix is briefly described in this paper, along with cavity ventilation results measured with a continuous emission carbon dioxide tracer method. Ventilation rates in a selection of wall cavities are compared with ventilation rates calculated from wind pressures and vent opening sizes. Fan pressurization methods are used to measure the effective leakage areas of infiltration paths because these contribute significantly to ventilation in some cavity types. Acceptable agreement between calculated and measured day average ventilation rates has been achieved in a range of water-managed cavities from drainage planes to drained and ventilated brick veneer cavities with results spanning three orders of magnitude.

Janssens A., Hens H.

This article presents measuring results of the thermal performance of duo-pitched tiled woodframe roof designs. The roofs have been monitored in a test building, exposed to the outside climate. The experiment was part of a programme to study the hygrothermal performance of highly insulated envelope parts in situ, in order to investigate whether a good thermal quality (U = 0.2 W/(m2 K)) is achievable with current residential construction practices in Belgium. The results show the effect of wind on the thermal performance of duo-pitched roofs. The measured thermal properties of the roof components are compared to the design values, and related to the wind speeds and directions registered near the test building. The established thermal effects are explained using tracer gas tests to show the pattern of wind driven air flow in the roofs.

Xu H., Wang H., Huo Q., Qin Y., Zhou H.

External thermal insulation composite systems (ETICS) are widely used all over the world for building envelope insulation. This paper lists the representative standards for ETICS in Chinese, European and ISO technical assessment documents, and it describes the results of a comparative study on standardization, technology and engineering. First, the standards are related to the project organization mode. The Chinese and ISO standards tend to be normative and different from the standards of the European certification system. Second, the problems of leakage and degradation occur frequently in ETICS in China. It is worthwhile to learn from successful experiences in waterproofing, drainage and other measures. Third, China has made some useful technical breakthroughs in wind load resistance design and quality acceptance by means of considerable amounts research, and has an advantage in engineering practice. Lastly, the types of external insulation systems are diversified in development, in order to meet multiple requirements; it is worthwhile to learn from the European certification system. This research and the conclusions can be used as a reference for the technology, engineering and standardization of ETICS, and for understanding the essential national standards to facilitate trade between countries.

Van Linden S., Van Den Bossche N.

Detailed knowledge on expected infiltration percentages through various exterior cladding surfaces is of importance when conducting hygrothermal simulations to evaluate the long-term performance of wall assemblies. Due to the stochastic nature of rainwater infiltration through wall assemblies, it is not possible to precisely predict the amount of rainwater that will infiltrate. However, laboratory and field tests may provide insight into the range of infiltration rates that can be expected for a given cladding and insight into the impact of deficiencies and the parameters affecting infiltration. Therefore, quantitative studies concerning infiltration rates, which were mostly laboratory studies, were reviewed. Based on the reviewed studies, the driving forces for infiltration were determined and the impact of the applied test method, pressure difference and water deposition rate on the infiltration rates was analysed. A methodology to obtain information on infiltration percentages without performing additional laboratory tests was proposed and a categorization of cladding materials was developed.

Wójcik A., Wójcik J., Grymin W., Konca P., Gawin D.

Abstract An EPS ventilated panel, which may be applied as an external insulation to humid walls, is investigated. Dimensions of the air channel sections have been determined using the Ansys software. Afterwards, the drying rate of the walls externally insulated with EPS, mineral wool and EPS ventilated panel has been compared using the WUFI software. The ventilated panel increases the drying rate when compared with the standard polystyrene panel and increases the heat loss through the wall by less than 20%.